Organic catalysis over zeolites

MICROPOROUS
MATERIALS
Microporous Materials 2 (1994) 297411
Review
Organic catalysis over zeolites: a perspective on reaction paths
within micropores
Paul B. Venuto*
Central Research Laboratory, Mobil Research and Development Corporation, P. 0. Box 1025, Princeton,
NJ 08543-1025, USA
(Received 13 September 1993; accepted 18 December 1993)
Dedication
This paper is dedicated to my father, L.J. Venuto, a pioneer in the field of carbon black chemistry and its application
in the paint and ink industry; to Dr. S.L. Meisel, an inspiring leader of Mobil’s research effort, who initiated the
organic catalysis effort at Mobil in the early 1960s; to Dr. C.D. Prater of Mobil, an outstanding scientist and research
manager, for his guidance over the years; to Professor J. Wei of Princeton University for many stimulating discussions
and penetrating insights into catalytic phenomena; and to Professor A.G. Oblad of the University of Utah, a
pathbreaker in catalytic science, for his longstanding friendship and support.
Abstract
Since the early 196Os, the field of organic catalysis over zeolites and related microporous materials has shown
enormous international expansion. Not only has a multiplicity of new reactions been explored over a continually
increasing assemblage of zeolite structures, but also the depth of understanding of the catalytic chemistry and
structure-reactivity relationships has shown dramatic growth. Further, the utilization of ZSM-5 and related medium-
pore zeolites has truly enabled a revolution in shape-selective control of reaction selectivity. In the present review, we
first conduct a broad classification and survey of organic chemistry over zeolites. This reflects, for the most part, a
mechanistic rather than a process or applications frame of reference. We then examine selected examples of underlying
physicochemical phenomena and structure-reactivity patterns that are peculiar to heterogeneous catalytic reactions
within zeolite micropores. These include diffusion/adsorption effects, shape-selective principles, mechanistic disguises,
catalyst deactivation pathways and related considerations.
Key words: Organic catalysis; Zeolite chemistry; Reaction mechanisms
Contents
1. Introduction and scope ................................................................................ ...... ....... ....... ............... ..... ... ... ......
2. ClassifiMtion and survey of organic reactions over zeolites and related molecular sieves ....................................................
2.1. Nucleophilic substitution (S, type) at aliphatic carbon ..................................................................,............................
2.2. Carbocationic rearrangements and isomerizations ........................................ ...... . .... .... .... .... . ......... .. ..
2.3. Rearrangements involving electron-deficient nitrogen as terminus and other complex rearrangements of nitrogen
compounds ........................................................ .............. .....................,.................................... .... .... ...... .......
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l Present address: 1073 Princeton Drive, Yardley, PA 19067, USA.
0927-6513/94/%26.000 1994 Elsevier Science B.V. All rights reserved
SSDI 0927-65 13 (94)00002-D

298 P. B. VenutoJMicroporous Materials 2 (1994) 297-411
2.4. Simple additions to olefinic double bonds ....................................................................................................................
2.5. Electrophilic addition to olefinic double bonds in complex reaction systems ..............................................................
Olefln generation ...........................................................................................................................................................
Olefm interconversion ...................................................................................................................................................
Hydrogen-transfer processes .........................................................................................................................................
2.6. Cycloaddition-type reactions of olefins .........................................................................................................................
2.7. Olefin-forming B-elimination reactions .........................................................................................................................
2.8. Olefin-forming dehydrocondensation reactions: substrates without /3-hydrogens ........................................................
2.9. Reactions involving possible carbanion-type species ....................................................................................................
2.10. Reactions of carbonyl compounds. I. Simple addition-elimination reactions .............................................................
2.11. Reactions of carbonyl compounds. II. Additions involving carbon or hydride nucleophiles ......................................
2.12. Reactions of carbonyl compounds. III. Cyclocondensations with ammonia and related reactions ............................
2.13. Reactions involving carboxylic acids and esters ...........................................................................................................
2.14. Electrophilic substitution of aromatic ring systems ......................................................................................................
General mechanism .......................................................................................................................................................
The alkylating agents ....................................................................................................................................................
The aromatic nuclei ......................................................................................................................................................
General discussion of ring-orientation patterns in substituted benzenes ......................................................................
Orientation patterns in other rings ...............................................................................................................................
The ortholpara ratio ......................................................................................................................................................
The issue of kinetic versus thermodynamic control ......................................................................................................
Reaction patterns observed in molecular sieve-catalyzed electrophilic aromatic substitutions ....................................
Alkylation of aromatic hydrocarbons ...........................................................................................................................
Ring-positional orientation and aromatic substrate reactivity effects ..........................................................................
Alkylation of other aromatic hydrocarbons .................................................................................................................
Dealkylation ..................................................................................................................................................................
Alkylation of aromatic rings with polar substituents ...................................................................................................
Alkylation of aromatics with carbonyl compounds .....................................................................................................
Alkylation of heterocyclics with olehns and alcohols ...................................................................................................
Acylation of aromatic hydrocarbons, phenolics, and heterocyclics and the Fries rearrangement ...............................
Nitration of aromatics ..................................................................................................................................................
Halogenation of aromatics ...........................................................................................................................................
2.15. Nucleophilic substitution in aromatic rings ..................................................................................................................
2.16. Redox- and radical-type reactions ................................................................................................................................
Hydrogenations and other reductions ..........................................................................................................................
Dehydrocyclization reactions ........................................................................................................................................
Dehydrogenation-type reactions ...................................................................................................................................
Oxidation reactions .......................................................................................................................................................
Oxidations with hydrogen peroxide over titanium ZSM-5 (TS-1) and related catalysts .............................................
Oxidations with hydrogen peroxide over vanadium ZSM-11 (VS-2) and related catalysts .........................................
Reactions involving alkyl hydroperoxides ....................................................................................................................
Photochemical-type reactions .......................................................................................................................................
Miscellaneous reactions ................................................................................................................................................
3. Structure-reactivity phenomena in organic catalysis over molecular sieves ..........................................................................
3.1. Some structural features of molecular sieves ................................................................................................................
Small-pore zeolites ........................................................................................................................................................
Medium-pore zeolites ....................................................................................................................................................
Large-pore zeolites ........................................................................................................................................................
Mordenite ......................................................................................................................................................................
Synthetic faujasite (zeolites X and Y) ..........................................................................................................................
AlPOd-, SAPO-, MeAPO-, MeAPSO-type molecular sieves ........................................................................................
Some contrasts to carbon molecular sieves, ion-exchange resins and enzymes ............................................................
3.2. Activity and acidity in molecular sieve catalysts ..........................................................................................................
Generation of acid sites in large-pore zeolites: early work ...........................................................................................
Structure-activity correlations in ZSM-5 .....................................................................................................................
Activity in AIPO,, SAPO, and related molecular sieves ...............................................................................................
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P.B. Venuto/Microporous Materials2 (1994) 297-411
3.3. Factors relating to selectivity in zeolite catalysts ..........................................................................................................
Some aspects of zeolite surfaces ...................................................................................................................................
Nature of intra-zeolitic fluid .........................................................................................................................................
Diffusion, adsorption and mass transfer-related aspects. The general mass-transfer issue ..........................................
Molecular diiusion aspects ...........................................................................................................................................
Some aspects relating to adsorption phenomena .........................................................................................................
Adsorption inhibition and disguise ...............................................................................................................................
Aspects related to shape-selective phenomena ..............................................................................................................
Shape selectivity by mass-transport discrimination .................................................................................................... .:
Restrictive transition-state selectivity (spatioselectivity) ............................................................................................ .:.
Some examples of shape-selective organic reactions ....................................................................................................
Para-selective alkylation of aromatic hydrocarbons .....................................................................................................
Selective alkylation of aromatics with polar substituents .............................................................................................
Selective toluene disproportionation (transalkylation) .................................................................................................
Selective xylene isomerization .......................................................................................................................................
Shape selectivity in methanol dehydrocondensation and related reactions ..................................................................
Formation of low-molecular-weight olefins ..................................................................................................................
Influence of shape selectivity on aromatics product distribution .................................................................................
Shape-selective olefin oligomerization ..........................................................................................................................
The window effect .........................................................................................................................................................
Reactions on the external surface .................................................................................................................................
4. Aging/deactivation pathways .................................................................................................................................................
General factors .......................................................................................................................................................................
Coke formation in zeolites and the importance of structure-reactivity factors ....................................................................
Small-pore zeolites ..................................................................................................................................................................
Medium-pore zeolites .............................................................................................................................................................
Large-pore zeolites .................................................................................................................................................................
Aging patterns in benzene-ethylene alkylation over a rare-earth faujasite catalyst ..............................................................
5. Future perspectives and conclusion .......................................................................................................................................
Acknowledgements ......................................................................................................................................................................
References ....................................................................................................................................................................................
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1. Introduction and scope
Since the appearance of the early Advances in
Catalysis, Vol. 18 in 1968 [l], the field of organic
catalysis over zeolites and related microporous
materials has shown enormous international
expansion. Not only have a multiplicity of new
reactions been explored over a continually increas-
ing assemblage of zeolitic structures [2], but also
the depth of understanding of both the catalytic
chemistry and structure-reactivity relationships
has shown dramatic growth. This has been
accelerated by the rapid evolution of a variety of
techniques for the post-synthetic modification of
zeolites [31. The extension in breadth of organic
reaction chemistry is reflected in a number of
excellent recent reviews, e.g. by Ono [4], Chang
et al. [5], Van Bekkum and Kouwenhoven [6],
Hoelderich and co-workers [7-121, Parton et al.
[ 131, Dartt and Davis [ 141, and others.
Applications using small-pore (g-ring) zeolites
have continued but at a rather modest pace, while
those employing large-pore molecular sieves
(12~ring and larger) have greatly expanded, ampli-
fied by a steady proliferation of new synthetic
materials - including the emergence of the
AlPO,-, SAPO-, MeAPO-, and MeAPSO-type
molecular sieves [15-181 in the early 1980s.
Clearly, however, it is the discovery and utilization
of the medium-pore zeolites, notably the ZSM-5
family [ 19-221 and other lo-ring zeolites [2,23,24],
that have had the greatest impact. The use of
ZSM-5 and related materials has enabled a revo-
lution in shape-selective control of reaction selec-
tivity [5,25-311, a revolution that has led to
impressive commercial applications in petroleum
refining [27,32], petrochemicals and aromatics pro-
cessing [27,33,34], and synthetic fuels (methanol-
to-hydrocarbons reaction) [35-371. Further, via
the techniques of isomorphous substitution
[38-411 a variety of exciting new chemistries has
been enabled, most notably the remarkable shape-

300 P.B. Venuto/Microporous Materials 2 (1994) 297-411
selective oxidations with hydrogen peroxide using 2. Classification and survey of organic reactions
TS-1 [42] and related titanium zeolites. over zeolites and related molecular sieves
In this review, we have surveyed and classified
organic chemistry over zeolites and attempted to
integrate earlier and recent work into a new per-
spective. While reasonably comprehensive and
broad, the survey is not necessarily exhaustive.
Where possible, we have inserted the zeolite cata-
lytic chemistry into a “matrix” of classical or
conventional organic chemistry as a frame of refer-
ence, with the objective of better highlighting the
similarities and interfaces, as well as the diver-
gences arising from the zeolitic environment. Our
orientation is mainly that of organic reaction
mechanism rather than process or application. We
then focus on selected examples of underlying
physicochemical phenomena and structure-reac-
tivity patterns that are peculiar to heterogeneous
catalytic organic reactions within zeolite micro-
pores. This includes diffusion/adsorption effects,
shape-selective principles, mechanistic disguises,
catalyst deactivation pathways, and related
considerations.
Using as guidance the reaction categories listed
in Carey and Sundberg [43], Gould [44], March
[45] and Sykes [46], we have attempted to con-
struct a generic, best-guess, mechanism-based clas-
sification. This can, of course, be done in many
different ways, and involves the obvious pitfall
that the actual mechanisms may not be those
assumed by the classifier. It is further complicated
by the fact that in zeolite catalysis, multiple
steps - and types of mechanism - frequently
occur in the trajectory between initial reactants
and final products. Table 1 shows selected data on
the molecular sieves referred to most frequently in
Tables 2-25. These 24 tables comprise our organic
reaction classification and survey, and contain the
primary citations for most of the literature refer-
ences. Fig. 1 summarizes the advantages of zeolite-
type materials for potential industrial processing
of organic chemicals. In Fig. 2, we highlight some
catalyst structural aspects and reaction-related
Catalytic Versatility
+Uniform micropores (L active sites
-Variety of discrete pore sizes 8 shapes (‘keyholes”)
* Diversity of microchannel connectlvtties
-Broad spectrum ofacidities
* Cation exchange options
* Ability to sorb 8 concentrate organics
* Potential control of selectivity
* Capacity for post-synthetic modiftcation
-Support / carrier for metals I metal complexes
-Dual- I multi-functional catalytic applications
l Convenience in handltng
* Acceptably low cost
Process Englneerlng Flexibility
-Wide selection of reactor deatgna
-Fixed-. fluid-, moving-bed
- Batch, semi-batch
- CSTR. continuous slurry
* Easy separation from RUMS
* Higher weratfng temperatures than H,SO, ,
ien-exchange resins
* =;&8r multf-step conversion in single
* Use of bfnders for attrition-restatanca
l High internal surface araa for economic
throughputs 8 reasonable reactor size
Environmental Advantages
* Catalytic rather than stoichiometrlc like some Lewts actds
l Regenerable I reusable
* Safer handling than liquid mineral or solid Lewis acids
l Non-toxic
* No inorganic salt waste disposal
. Non-corrosive
Fig. 1. Zeolites and molecular sieves meet the requirements for industrial processing of organic chemicals. They also offer significant
opportunities for “molecular engineering” or “tailor-making” of desired products.

P. B. VenutofMicroporous Materials 2 (1994) 297-411 301
Table 1
Key properties of molecular sieves referred to in Tables 2-25’
Molecular
sieve type
Structure type
code
(ref. 2)
Abbreviationb
(if used) in
Tables 2-25
Ring size’
of channels
Pore size
largest
channeld (A)
Channel system
dimensionality’
Small pore
Linde type A
Erionite
Chabaxite
SAPO-34
ZK-5
Rho
Medium pore
ZSM-5’
ZSM-11
Ferrierite
ZSM-48
ZSM-23
ZSM-22/Theta-1
AlPO,-11
!&APO-l1
Clinoptilolite
SAPO-31
Large pore
Faujasite/X/y
SAPO-37
Beta
Mordenite
Offretite/Ts
Maxxite/Omega/ZSM-4
Linde Type L
ZSM-12
AlPo,-5
SAPO-5
LTA
ERI
CHA
CHA
KFI
RHO
MFI
MEL
FER
-
MI-l-
TON
AEL
AEL
HEU
AT0
FAU
FAU
BEA
MOR
OFF
MAZ
LTL
MTW
AFI
AFI
A
Erio
Chab
-
-
P
-
-
Ferr
-
-
-
Clin
-
FaWD’
i-
Mord
Offr
52
L
8-8-8 4.1
8-8-8 3.6 x 5.1
8-8-8 3.8 x 3.8
8-8-8 3.8 x 3.8
8-8-8 3.9
8-8-8 3.6
10-10-10 5.3 x 5.6
10-10-10 5.3 x 5.4
10-8 4.2 x 5.4
10 5.3 x 5.6
10 4.5 x 5.2
10 4.4 x 5.5
10 3.9 x 6.3
10 3.9 x 6.3
1O-8-8 3.0 x 7.6
12 6.5
12-12-12 7.4
12-12-12 7.4
12-12 7.6 x 6.4
12-8 6.5 x 7.0
12-8-8 6.7
12-8 1.4
12 7.1
12 5.5 x 5.9
12 7.3
12 1.3
1
‘Mainly assembled from ref. 2; some data from refs. 9, 16,27,32 and 47. Table 1 does not include data for members of the MeAPO,
MeAPSO families of compositions, a few of which are listed in Tables 2-25; for information on these, the reader is referred to refs.
15-18 and references therein.
bAbbreviations are for convenience only, i.e. they are not structural codes as used in ref. 2. Ion-exchanged (or cationic) forms are
represented as NaX, CaFauj, HMord, etc.; RE=rare earth; forms moditied by other elements (e.g. isomorphously substituted or
not necessarily cationic) are shown as Ti-ZSM-5, P-ZSM-5, B-ZSM-5, etc., TS-1 refers to Ti-ZSM-5; presence of (zero valent)
metals, metal complexes (e.g. in dual-functional systems) is represented as Pt/ZSM-5, W/y, etc.; USY represents ultrastable Y,
Deal refers to dealumiked forms; Zeol is used for non-specitic reference to zeolites as catalysts.
‘Number of T or 0 atoms comprising smallest rings in channel.
dMainly crystallographic diameters as given in ref. 2.
“Based on criteria given in ref. 2, pp. 8-l 1;infers interconnecting channel systems, but not necessarily accessibility to organic molecules.
fThe “silicalite” nomenclature is not used because this composition is a member of the ZSMJ substitutional series (see ref. 48).
SLinde T is an erionite-offretite intergrowth [2].
considerations that can significantly impact the
level of conversion and type of selectivity observed
in organic transformations over zeolites. Fig. 3,
from the classic paper of Chang and Silvestri [2071,
shows the product distribution wsus space/time
for the conversion of methanol to hydrocarbons
over ZSM-5, a fine example of an A+B+C!-t...
sequential reaction scheme.

302 P.B. VenutolMicroporous Materials 2 (1994) 297-411
Catalyst Structure
*SVAI ratio:
- Cation composition
-Thermal I hydrothermal I acid stabiltty
-Acid site density I strength
- Hydrophilic I hydrophobic balance
* lsomorphous substitution (e.g., Al. 6. Si, Ga. Cr. Fe,
-Added metal functtonaiiiies
-Trace impurities (e.g., Fe)
-Micropore size 8.shape
* Microchannel connectiity
* Thermochemical I activation history
* Crystallite size I morphology
* External surface activity
* Binder effects
Reactants
L-r’
o”o
oto
00
- oo +
00
00°
000
vL
Reaction System
* Thermodynamics
-Reactants8theirratios
l Reactor design I fluid I catatyst contacttng
* Reactton vartables / severtty (e.g.. temp., pressure /
cont.,spacevelocilyI contactttme)
* Sotvent effects
* fluid flow 81mass transfer
* Molecular diision
* Heat transfer
-Adsorption I deaorptlon phenomena
* Catalyst agtng I daacttvation
* Presence of poisons & lnhlbttors
1 Products 1
Fig. 2. Some factors affecting conversion and selectivity in organic catalysis over zeolites. Both microscopic and macroscopic aspects
must be kept in mind; because of the complex interplay among thermodynamics, kinetics, and adsorption/diffusion, mechanistic
“disguises” frequently occur.
8 __-------------_b-#- Water
. _._.....”
(and C,+ Oleihs)
Space/Time (j-j-&)
Fig. 3. Reaction path for methanol conversion to hydrocarbons over HZSM-5 (371°C); product distributions at points A, B, C,
and D along the space/time (extent of conversion) coordinate show dramatic differences; “blind” comparisons could be misleading.
Modiied after Chang and Silvestri [207].

P. B. Venutolhficroporous Materials 2 (I 994) 297-411 303
In Tables 2-25, we have listed major reaction
classes and examples of reactions, together with
catalyst type used, temperature, and reference
citations.
In this survey, we have not attempted to include
data on the level of conversion, side-reactions,
thermochemical history, whether internal or exter-
nal surface was involved, or on any of the multi-
plicity of catalyst structure and reaction system
factors outlined in Figs. 1 and 2; nor have we
addressed whether selectivity comparisons were
made at comparable conversion levels (examining
product distributions at various points on the
space/time axis in Fig. 3 will remove any doubts
as to the importance of this issue). Finally, we
have not considered whether appropriate control
or blank runs were employed, or whether other
heterogeneous catalysts (e.g. macroreticular ion-
exchange resins, clays, silica-alumina, alumina, pil-
lared layered materials) or even mineral or Lewis
acids would also be as effective as or even better
catalysts for the same reactions. What we have
done in Tables 2-25, however, is documented the
extraordinary range of chemistries possible when
organic reactants are contacted with the surfaces
of zeolites and molecular sieves under a wide range
of conditions.
2.I. Nucleophilic substitution (S, type) at aliphatic
carbon (Table 2)
There are two limiting cases for &-type substitu-
tion, the SN2and the Snl pathways. The former is
a one-step displacement process via a transition
state (Eq. l), while the latter is a two-step (ioniza-
tion) process via a carbocation intermediate
(Eq. 2). Many other variations are, of course,
possible.
R3

e
R3

.c-Y - Nu C-Nu + Ye
4I’ ;, (2)
In systems unconfined by zeolitic pore channel
systems, the course of SN reactions is strongly
influenced by the nature of the nucleophile (Nu),
the leaving group (Y), and the substituents (R,,
Rz, and R3) on the saturated carbon under attack.
This not only includes electronic, steric, strain and
neighboring group effects, but also the effect of
organic solvents, water and dissolved acids and
salts. Further, since polar or even cationic species
are involved, p-elimination to form oleflns can be
a significant side-reaction: Clearly, when these
reactions occur within 4-8 A zeolite micropores -
a size range closely mapping that of simple organic
molecules - constraints on the size of the reactants
that can enter, the transition states and intermedi-
ates that can be formed, and the size and shape of
products that can exit, must be expected. The
already complex organic molecular structure-
reactivity effects combined with the potential com-
plexities inherent in a heterogeneous catalytic
system (see Fig. 2) can sometimes lead to mech-
anistic disguises and apparent distortions
from “expected” reaction patterns.
The majority of the &-type reactions listed in
Table 2 involve alcohol functions, with -OH as
the leaving group, Y (C-O bond breakage),
and formation of new C-O-C, C-N, C-S,
C-Cl, and C-C bonds, when Nu=R-OH,
NH,(RNH2,R,NH), H,S(RSH), HCl, or active
methylene species, respectively. Detailed studies in
the methanol-NH,-methylamines system have
been reported [58,59,61]. If the proper multiple
functionality is present in the reactants, 5- and
6-ring cyclics - as well as bridged bicyclics [70]
(Eq. 3) - can be formed by intramolecular
substitution.
A wide variety of zeolites have been employed in
these reactions, and it is not difficult to visualize
catalytic assistance in C-OH bond scission by
zeolitic protons, cation electrostatic fields, or the
polar external surface of small-pore zeolites such
as chabazite or Linde A. A Rideal-type etherifica-

304
Table 2
P.B. Venuto/MicroporousMaterials 2 (1994) 297-411
Nucleophilic substitution (S, type) at aliphatic carbon
Conversion of alcohols to ethers
Simple etherifcation
Methanol-rdimethyl ether
Alcohols+ethers
Phenol + methanol+anisole
Etherification with ring closure
1,4-Butanediol +tetrahydrofitran
1,CButenediol +dihydrofuran
1,2,5-Pentanetriol-r2,3-dihydropyran+2-hydroxymethyltetraydrofuran
Diglycolamines+morpholines
trans-l,4-Cyclohexanediol+7-oxabicyclo[2.2.1]heptane
Phenol + ally1 alcohol -+3-methylbenxofuranb
2,5-Dihydroxyhexane+2,5-dimethylfuran
1,5-Dihydroxypentane+tetrahydropyran
Conversionof alcohols to aminefunctions
Formation of simple amines
Methanol +NH,+methyl-, dimethyl- and trimethylamines
Ethanol + NHs+ethylamine
Ethanolamine + NHs *ethylene diamine
Ethanolamine + ethylene diamine+polyethylene polyamines
Butanol + NH3 + butylamines
Aniline + methanol+N-methyl + N,N-dimethylanilinesd
Aniline +isobutylene+N-fert.-butylaniline
o-Tolmdine + isobutylene+N-tert.-butyl-o-tolmdine
2,4-Diaminotoluene + isobutene+2-N-tert. -butyl-4-aminotoluene + 4-N-tert,
butyl-2aminotoluene
Amineformation with ring closure
4-(g-Hydroxyethyl)piperidine+azabicyclo[2.2.2]octane
N-(g-Hydroxyethyl)piperazine (or N-(/I-
aminoethyl)piperaxine)wdiazabicyclo[2.2.2]octane
Ethanolamine+diazabicyclo[2.2.2]octane
Conversion of alcohols to surfurspecies
Formation of simple thiols
Methanol + H2S+methanethiol
Alcohols + H,S-+thiols
Formation of thioethers (sulfides)
Methanol + H,S+dimethyl sulfide
Formation of disu&&s
Alcohols + H,S + S”+disu16des (RSSR)
NaX: 260°C [l]; Zeol: 390°C [49]; HZSM-5:
250-500°C [36,37]; ZSM-5, T: 320-45O”C [50]
Zeol (ref. 8, p. 230)
HZSMJ: 350-45O”C [51]
B-, Fe-ZSM-5: 200-300°C [521
B-ZSM-5 [52]
B-Zeal: 350°C [53]
Zeal [54]
NaA’: 215°C (ref. 9, p. 697)
CaY [56]
HY: 300°C [57]
HY: 300°C [57]
HZSM-5, Ca-, RE-X, HY: 250°C; Na Mord’:
325-370°C [58]; HMord, NaY: 290-340°C [59];
HZSM-5: 454°C [60]; ZSM-5, T: 320-48O”C [50];
H-Y, -Mord, -Clin, -Ferr, -Erie, -Rho, -ZK-5,
-Chab; CaAz 250-4OOC [61]; H-ZSM-5, -B,
-Mord, -Y; Na-, Mg-, La-, Cu*+-Mord: 300450°C
1621
Zeal: 550°C [63]; HY, REY [64]
RE-, H-Mord: 300°C [65]
Zeol[66]
NaX, NaY [67]
H-, NaH-, CsH-, KH-, MgH-, Fe-, Na-, FeNa-,
MgNa-, CsNa-ZSM-5: 300-42O”C [68]
HY: 120-150°C [69]
Hy: 120-150°C [69]
HY: 180°C [69]
HZSM-5: 400°C [70]
HZSM-5: 400°C [70]
ZSM-5: 400°C [71]
Li, K-, Cs-, H-Y: 250-350°C [72]; H-, Na-Y:
210-300°C [73]
L: <3OOC [74]
H-, Na-Y: 300-4OOC [73]; Li-, K-, Cs-, H-Y:
25s350°C [72]
Zeol[75]

P. B. VenutoJMicroporous Materials 2 (1994) 297-41 I 305
Table 2 (continued)
Conversion of alcohols to haloalkanes
Ethanol + HCl+ethyl chloride
Nucleophilic attack by active carbon species
Phenylacetonitrile+methanol or diiethylcarbonate+a-methylphenyl-
acetonitrile
Nucleophilic additions on epoxides
Ethylene oxide + H,O+ethylene glycol
Cyclohexene oxide + H,O +cyclohexane- 1,2-diol
Ethylene oxide +NH,+mono-, di-, and triethanolamines
Ethylene oxide+NH,+piperazine, morpholine, p-dioxane
1,2-Epoxyoctane + aniline +N-2-hydroxyoctyl-
+ N-l -hydroxymethylheptylaniline
Styrene oxide + aniline+ 1-hydroxy-1-phenyl-2-anilinoethane + 1-phenyl-l-
anilino-2-hydroxyethane
2,3-Epoxydecanol-l + NaN,+3-azidodecane-1,2-diol
Ethylene oxide + H+p-dithiane +p-thioxane +p-dioxane
Polymer hydrolysis
Amylose (starch) + HrO+sorbitol”
Oxygen-nitrogen or oxygen-sulfur interchange in cyclic etherfi
Tetrahydrofuran +NH,+pyrrolidme
Tetrahydrofuran + propylamine+N-propylpyrrolidine
Tetrahydropyran+NH,-piperidine
1,4_Dimethoxytetrahydrofuran + NH,+pyrroleP
2-Methoxy-2,3dihydro4pyran + NH,+pyridineh
Tetrahydrofuran + H+tetrahydrothiophene
H-, RE-Y; RE-, Ca-, Na-X, SA: 170°C [76]
CsX, Na-, K-Y: 350-375°C [77]
Na-, Ca-X, 4A, 5A: 90-240°C (ref.1, p. 152);
HZSM-5: 25°C [78]
HZSM-5: 25°C [78]
NaX, 4A, Chab: 55-140°C [79]
NaX: 340°C (ref. 1, p. 152)
Na-Y, -X: 80°C [SO]
Na-, K-, H-Y: SO-100°C [SO]
CaY: 50°C [Sl]
NaX: 200°C [1]
Ru/HUSY: 180°C (ref. 9, p. 715)
H-, Mg-, Ce-L, HY, HMord: 326350°C [55,82,83]
AlHY: 360°C (ref. 9, p. 699)
H-Y, -L, -Mord: 350°C [82,84]
AlZeol: 400°C (ref. 7, p. 87)
HZSM-5, B-ZSM-5, FeZSM-5, Lay, AlPO,-9,
AlPO,-5, SAPO-5: 400°C [85]
NaK 350°C (ref. 11, p. 14)
*Probably reaction on external surface.
‘Perhaps alkylation via olefin function followed by !&-type etherification.
“Strong selectivity for methyl- and dimethylamines, but very little trimethylamines formed with Na Mordenite.
dNuclear alkylation products (toluidines, N-methyltolmdmes and N,Ndimethyltoluidines) also formed.
*Probably dual-functional; acetal hydrolysis + mild hydrogenation.
‘Classified as S, type: sequence probably involves oxygen protonation, SN attack by NH,, hydroxyl protonation, intramolecular
SNattack.
‘Also involves elimination of methanol to form double bonds.
hAlso involves elimination of methanol to form double bond, with dehydrogenation step.
tion mechanism might be favored in medium- and
large-pore zeolites:
v, G-Zeal y//
‘
H 6+
h+‘C-CH2 R
H’ t*- 0- CH2 R
H’
Epoxide additions require specific comment.
tion. Unsymmetrical epoxides are ambident sub-
strates, i.e. they can be attacked at two different
positions, with substituents exhibiting steric (or
stabilizing) effects depending on the mechanism.
For example, zeolite-specific regiospecifrcity has
been demonstrated by Onaka and co-workers
[80,81] in the reaction of styrene oxide with aniline
(Eq. 4), where isomer la was favored with KY
and isomer lb with HY.
Epoxides can react by SN2- or &l-type pathways
depending on conditions, and isomerization and
condensation reactions can accompany substitu-
Ph-4 + Ph-NH2 -_) PhaH_/NH--Ph + phxOH (4)
I* lb

306 P. B. VenutofMicroporous Materials 2 (1994) 297411
2.2. Carbocationic rearrangements and
isomerizations (Table 3)
The operation of carbocation-type mechanisms
in acidic zeolite catalyst systems has been well
documented [ 1,95,361,415-4191. Table 3 com-
prises a broad and diverse assembly of rearrange-
ments, including both aliphatic and aromatic
hydrocarbons and reactants having oxygen,
nitrogen, and halogen functionalities. These
transformations range from the very mild (e.g.
hydrogen-deuterium exchange in olefins at - 80°C
[1,95]) to the very severe (e.g. methylaromatic
disproportionations at 700°C [ 113,134] or the
very profound endo-tricyclo[ 5.2.1.02*6]decane-
adamantane conversion [92] shown in Eq. 5).
4% Q
(5)
H
H -Yiis-+
The gas phase rearrangement of norbornene to
nortricyclene also proceeds over faujasite-type cat-
alysts with high selectivity (Eq. 5a)
(5‘4)
with minimal polymer formation and consequent
catalyst aging (ref. 532, p. 176). Also the zeolite-
catalyzed isomerization of cis-decahydronaphtha-
lene to the trans isomer (conformational isomeriza-
tion) (Eq. 5B) has recently been reported by Song
and Moffatt [533].
J+ z’-+ (5B)
Rearrangements and dual-functional metal-zeolite
conversions of cyclooctane and other naphthenes
have been described earlier in an excellent review
by Jacobs et al. [532].
Depending on conditions, carbocation reactions
can proceed via a number of different pathways
as shown schematically in Fig. 4. A proton can be
eliminated from the /?-carbon atom (C,) or /?-
Fig. 4. Carbocations can react via a multiplicity of pathways.
scission (cracking of bond between C2 and C,)
can occur to form olefins; intramolecular
1,2-migrations of hydride or alkyl or aromatic
groups are common, and 1,3-hydride migration
has been observed [ 1411. The positive charge on
the carbocation can also be satisfied by intermolec-
ular hydride transfer, attack of a nucleophile (Nu),
or by addition to an unsaturated linkage (oligo-
merization). The oligomerization route leads to
formation of a new carbocation, as does /Lscission
and intramolecular migration. The opportunities
for continued structural transformations are thus
apparent. Allylic rearrangement, ring-contraction
and ring-expansion can also occur, and shape-
selective constraints can greatly impact reaction
pathways. Olefin cis-trans and double-bond iso-
merization can occur under relatively mild condi-
tions, while paraffins may require more severe
conditions, or preferably dual-functional metal
acid catalysis for reasonable catalyst lifetimes.
In addition to various hydrocarbon rearrange-
ments, Table 3 shows a large number of oxygenate
rearrangements, including isomerization of alde-
hydes to ketones, isomerization of epoxides to
carbonyl compounds, pinacol-type diol rearrange-
ments, aldehyde dehydrations, etc. Hoelderich’s
recent innovative exploratory studies with
ZSM-5-type zeolites (e.g. refs. 8-10, 53, 137, and
142) are noteworthy in this area. As shown in
Eq. 5C, using ZSM-5, olefin double-bond iso-
merization can be effected without skeletal
isomerization
CH2
4
CH2-CH2-C

cm ZSM-5 H ,%
3oo’c
c=c
CH,’ ‘CHO
c5c)
while simultaneously retaining an aldehyde group
[ 1021. Also, allylic rearrangement of 1,4- (or 1,2-)

P. B. Venuto/Microporous Materials 2 (1994) 29741 I 307
Table 3
Carbocationic rearrangements and isomerizations
Saturate skeletal isomerization
n-Butane+isobutane
n-Pentane+isopentanes
n-Hexanedmixed Ce isomers
n-Octane+mixed Cs isomers + gas
HY, Lay, HOffr: 200°C [86]
Pt/ZSM-5: 232-260°C [87]
Pt/SAPO-5, -11, -34, 41, Pt/ZSM-5: 482°C [88];
Pt/HZSM-5, HZSM-12: 260°C [87]
Pt-, Pd-, Ni-/SAPO-11; Pd/SAPO-5; Pt/HZSM-5,
-Nab, -HY: 257-396°C [531]
Pt/ZSM-5, Pt/ZSM-11: 257-297°C [89]
Pt/HZSM-5: 250°C [90]
Pt/H-ZSM-5, -ZSM-11, -Y: 1lo-300°C [891
Pt/CeY: 275°C [91]
Pt/HY, -HZSM-5, -SAPO-11: 246-368°C [531]
H-, RE-Y: 150-270°C [92]; REY, PtRe/CoLaY’:
250°C [1071
2,2,4-Trimethylpentane+Cs isomers + gas
n-Nonane-+methyloctanesb
n-Decane+2-, 3-, 4-, 5-methyhronanes
n-Undecane+mixed CI1 isomers
n-Hexadecane-mixed C16isomers + gas
endo-Tricyclo[ 5.2.1.02~6]decane+adamantane
exo-Tricyclo[6.2.1 .02~7]undecane-+1-methyladamantane
Electrophilic hydrogen-deuterium exchange in olefins
Ethyleneddeuterated ethylene
Propylene+deuterated propylene
1-Hexene-+deuterated hexene isomers’
2,3-Dimethylbutene-1 +deuterated hexene isomers
H-, RE-Y: 150-270°C [92]
DHY: < 150°C [93]
DHY: 25°C [93]
REX-D20: 64°C [94]
DHY: - 8O”C-20°C [1,951
Olefin cis-trans isomerizationd
tram-2-Butene+ 1-butene + cis-2-butene
cis-2-Butene+ trans-2-butene
NaB-ZSM-5: 450°C (ref. 8, p. 231)
SO,/Na-, Li-, K-X; NaMord, KL: 25°C” [96,97]
Olefin double-bond isomerization
I-Butene+2-butene
1-Hexene+hexene isomers
Na-, Co-, Ni-, Cr-X: lOO-350°C [98]; Na-, Co-,
Ni-, Cr-Y: 50-200°C [99]; HZSM-5: 454°C [loo];
HB-ZSM-5: 175-200°C (ref. 8, p. 231); Mg-, Ca-,
Zn-, La-, Ce-, Mn-X: 150°C [1011
SAPOS, -11, -31; MnAPO-11, MnAPSO-31: 343°C
WI
2,3-Dimethylbutene-1+2,3dimethylbutene-2 DHY: -SO-20°C [1,951
2-Ethylacrolein-*tiglaldehyde(trans-2-methyl-2-butenal)’ CeB-ZSM-5: 300°C [1021
3,4-Diacetoxybutene-+ 1,4diacetoxybutene* B-, Al-ZSM-5: 300°C [1021
Skeletal isomerization of olejns
Cyclopropane+propyleneh
Methylcyclopropane+butenes
1,1-Dimethylcyclopropane+Cs alkenes
1,2-Dimethylcyclopropane+C5 alkenes
n-Butenehisobutene
1-Pentene+2-methyl-2-butene + 2-methyl-1-butene
1-Hexene + hexene isomers
Norbomene+nortricyclene[tricyclo(2.2.1.02*6)heptane]
Conformational isomerization of bicyclic naphthenes
cis-Decahydronaphthalene+ trans-decahydronaphthalene
Ring positional isomerization of aromatics
o-xylene+m-,p-xylene
NaY: 200400°C [103]; H-, Deal-Y; Co-, Mn-X
WI
NaHB: 22-62°C [1051
NaHSZ: -4420°C [1051
NaHSZ: - 60-7°C [1051
ZSM-5: 300°C (ref. 8, p. 232)
SAPO-11; MeAPO-11: 300-400°C [1061
SAPO-5, -11, -31; MnAPO-11, MnAPSO-31,
ZSM-5: 343°C [88]
CaNaX: 357°C; Pt/MgY: 297°C [532]
H-, FeH-, NiH-, LaH-Y; HMord: 250-300°C [533]
HMord: 200-600°C [108,109]; REX: 177-204°C
[1lo]; Y-type [1111;“large-pore”: 150-320°C
[1121;HZSM-5: 300°C P-ZSM-5: 410-5OO”C,
Mg-ZSM-5: 500°C [1131;HZSM-5: 316°C [341;
Ferr [FU-91: 4Ot-450°C [1141
(Continued on p. 308)

308
Table 3 (continued)
P.B. VenutofMicroporous Materials 2 (1994) 297-411
m-Xylene+o-,p-xylene
Diethylbenzenes+iiethylbenxene isomers
I-Methyl-2-ethylbenzene+methylethylbenzene isomers
Trimethylbenzenes-rtrimethylbenzene isomers
I-Methylnaphthalene-+2-methylnaphthalenei
2,6-Dimethyhtaphthalene+methyhraphtbalene isomersl
1,2,3,4,5,6,7,8-Octahydrophenanthrene+ 1,2,3,4,5,6,7,8octahydroanthracene
o-Cresol+m-,p-cresols
Dimethylbenzonitriles+dimethylbenzonitrile isomers’
Tohmitriles --*tohmitrile isomers
o-, m- or p-Toluidine-+toluidine isomers
p-Toluidine-wn- + o-toluidine
2,4- or 2,5- or 3,4-Dimethylaniline+dimethylaniline isomers
o- or p-Ethylaniline+ethylaniline isomers
o-Chlorotoluene-wn-,p-chlorotoluenes
o-Bromotoluene-wrr-,p-bromotoluenes
Dichlorotoluenes-dichlorotoluene isomers
2- or 4Chlorophenol+chlorophenol isomers
2,4-Dichlorophenol+2,5-dichlorophenol
2-Methylthiophene-*3-methylthiophene
2-Chlorothiophene+3chlorothiophene”
2-Bromothiophene+3-bromothiophene
2-Iodothiophene-,3Godothiophene
5-Bromo-2chlorothiophene~4-bromo-2-chlorothiophenen
Transalkylation (disproportionation) of alkylaromatics”
Toluene + benzene + xylenes
o-Xylene+benxene + trimethylbenzenes
m-Xylene-tbenzene + trimethylbenzenes
1,2,4-Trimethylbenzene+xylenes + tetramethylbenzenes
1-Methyl-2-ethylbenzene+ toluene + ethylbenzene + trialkylbenzenes
Diethylbenxenes+ethylbenzene + triethylbenzenes
Diethylbenzene + benzene-+ethylbenzene
sec.-Butylbenxene~benxene+dibutylbenzenes
1-Methyl- or 2_Methyhaaphthalene+naphthalene + dimethylnaphthalenes
[113,134]; SiO,-ZSM-5: 5WC [135]
REX 177-204°C [94]
SAPO-5, -31; MAPO-5, -36: 538°C [88]
H-, NaH-, CsH-, BaH-, LaH-Mord: 350°C
Y: 20~400°C [1161;Y, Mord: 200400°C
CeHY: 170°C [115]
REX: 232°C [1lo]
REX: 200°C [94]
HY: 300°C [120]; HNa-62, -Y: 210-330°C
Side-chain isomerization in alkylaromatics
sec.-Butylbe.nzene+isobutylbenzene REX: 200°C [94]
Isomerization of aldehydes to ketones
Isobutyraldehyde+methylethyl ketone
Pivalaldehyde+3-methylbutan-f-one
2-Phenylpropanal+phenylacetone
3-Phenyl-2-methylpropanal-+4-phenylbutan-2-one
HZSM-5: 375-500°C [1361
B-ZSM-5: 360°C (ref. 137, p. 1385)
B-, Fe-ZSM-5: 400°C (ref. 8, p. 232)
B-ZSM-5: 400°C (ref. 137, p. 1385)
Isomerization of epoxides to aldehydes and ketones
Ethylene oxide -+acetaldehyde (+ dioxane + crotonaldehyde)
Propylene oxide+propionaldehyde (+ acetone + ally1 alcohol)
Na-, RE-X: lOf-200°C (ref. 1, p. 351)
Na-, RE-X: lOO-200°C (ref. 1, p. 351); alk. metal X
(ref. 8, p. 234)
Butene-1 oxide+butyraldehyde (+other products) Zn-, Cd, Ag-A (ref. 8, p. 234)
1-Methylcyclopentene-1 oxide +2-methylcyclopentanone (+ other products) Fauj (ref. 8, p. 234)
SAPO-5, -11, -31, -41; MAPO-5, -11, -36: 538°C
WI
CeHY: 170°C [115]; REX: 232°C [llO]
Y: 206400°C [116]; Y, Mord: 2OG4OO”C[117,118]
ZSM-5, ZSM-11: 350°C [108]
HNaY: 270°C [119]; H-ZSM-5, -ZSM-12, -Y:
100&400”c [1201
HZSM-5, FeZSM-5, ZSM-11: 350-45O”C [1211
HMord, H-, FeH-, NiH-, LaH-Y: 250-300°C [533]
ZSM-5, -11, -12: 380-42O”C [1221
HZSM-5: 500°C [1231’
HZSM-5: 5OOC [123,124]
HZSM5: 350-500°C [124,125]; ZrZSM-5:
340430°C [1261
NaZSM-5, HZSM-11, -34, -35, -12; H-B, -L, -Mord,
-0ffr: 300-500°C [1251
HZSM-5: 350-500°C [124,125]
HZSM-5: 295-420°C [124,125]
ZrZeok 250-340°C [1261
Zeol [1271
/I, 62,Mord: 300-350°C [128,129]
HZSM-5: 400°C [1301
ZSM-5, Mord, Fauj: 400°C [1301
ZSM-5: 330°C [131,132]
ZSM-5: 300-45o”C [131,132]
ZSM-5: 150°C [1321
ZSM-5: 100°C [1321
ZSM-5: 180-190°C [1321
REX: 264°C [llO]; ZSM-5: 300-316°C [34,133];
HZSM-5: 450-600°C; P-ZSM-5: 550-700°C;
B-ZSM-5: 500-700°C; Mg-ZSM-5: 500-600°C
: [108]
[117,118]
u191

P. B. VenutojMicroporous Materials 2 (1994) 297-411 309
Table 3 (continued)
Styrene oxide-+phenylacetaldehyde
Styrene glycol-+phenylacetaldehydeP
Limonene-1,2-epoxide+carvenones
2-Pinene oxide-+camphorene aldehyde’
2-Methyl-2,3-epoxybutane +methyl isopropyl ketone + pivalaldehyde +
isoprene
Phenylglycidic acid methyl ester+2-oxo-3-phenylmethyl propionate
p-tert.-Butylphenylglycidic acid methyl ester-,2-oxo-3-(p-ret?.-butylphenyl)
methylpropionate
Pinacol-type rearrangement of diols
2,3-Dihydroxy-2,3-diethylbutane-tmethyl-?er?.-butyl ketone
1,2-Dihydroxypropane-,propionaldehyde (+acetone)
2,3-Dihydroxybutane+2-butanone (+ 1,3-butadiene)
2-Hydroxy-2-phenylethanol+phenylacetaldehyde
Other rearrangements
Cyclic acetals of neopentyl glycol+highly-branched alkanals’
1,2,5-Pentanetriol+2,3-diiydropyran’
Tetrahydrofurfuryl alcohol+2,3-dihydro-2H-pyran”
3,5,5-Trimethylcyclohex-2-ene-1,4-dione~trimethylhydroquinonev
Dihydro-5-(hydroxymethyl)-2-furanones~3,4-dihydro-2-pyronesW
2-Methylbutanal+isoprene”
2-Methylpentanal-+2-methylpenta-1,3-diene
Pivaldehyde+isoprene
Isovaleraldehyde+isoprene
Cyclohexanecarbaldehyde+methylcyclohexadiene +methylenecyclohexane
a-Nitrotoluene +phenyl isocyanate + benzaldehyde + stilbeney
Ti-ZSM-5: 30-100°C (ref. 7, p. 78; ref. 138);
HZSM-5: 200-250°C [1391
HZSM-5: 200-250°C [1391
CaA: 150-210°C (ref. 7, p. 78)
NaMordjHCOOH: 35°C (ref. 7, p. 78)
B-ZSM-5: 150°C (ref. 10, p. 39)
B-, Fe-ZSM-5: 200°C (ref. 10, p. 40)
B-, FeZSM-5: 180°C (ref. 10, p. 40)
HY: 230-350°C [57]
HY: 350°C [57]
HY: 350°C [57]
Al-, B-ZSM-5: 250-300°C [I401
ZSM-5: 250400°C [141]
B-ZSM-5: 350°C [11,53]
B-ZSM-5: 350°C [53]
HY: 450°C (ref. 8, p. 233)
Zeol (ref. 8, p. 233)
B-ZSM-5: 400°C [1421
B-ZSM-5: 350°C [1421
B-ZSM-5: 450°C [1421
B-ZSM-5: 500°C 11421
B-ZSM-5: 350-450°C [1421
5A, NaX: 220-250°C [143]
“Hydroisomerization (dual-functional).
?hape selective; no dimethylheptanes or ethylheptanes were formed.
“Accompanied by isomerization and oligomerization.
dGenerally accompanies double-bond isomerization.
“No double-bond isomerization observed at 25°C.
‘Note that carbonyl group remains intact.
gAllylic rearrangement; reverse reaction also can be effected with somewhat different reaction system.
“Viewing cyclopropane reactivity as more olehnic than paraffinic.
‘Profound rearrangement, preferably in presence of H,.
‘In an infrared cell.
kWith dealkylation.
‘1,2-Shift mechanism.
“Minor dechlorination.
“At > 300°C in gas phase, the less reactive chlorine begins to migrate, and appreciable amounts of 4-bromo-3-chlorothiophene and
5-bromo-3-chlorothiophene are formed.
“This could conceivably be classified under electrophilic aromatic substitutions.
PIncluded here because glycol is precursor to epoxide.
qProbably occurs on external surface.
‘With ring contraction.
“With 1,3-hydride shifts.
‘Rearrangement accompanied by dehydration.
“Ring expansion; alternative route is via 1,2,5pentanetriol.
“With methyl and hydride shifts.
“Retro-pinacolone rearrangement.
““Dehydration” of aldehyde; a proposed mechanism (for aldehydes with a, j?- and y-hydrogens) involves enoliiation followed by
1,Celimination of water (ref. 8, p. 235).
YMechanism uncertain; may involve aromatic nitrile oxide intermediates.

310 P. B. VenutofMicroporous Materials 2 (1994) 297-411
diacetoxybutene has been demonstrated without
loss of functional group [ 1021(Eq. 5D).
CHZ-CH=CH-CCH2
zstJ-5
I I 3oo’c
CH2=CH-CH-CH2
0 0 b :,
I I
Y=O Y=O
;=o A=o (5D)
C% C”B AH3 kis
Using highly siliceous, hydrophobic medium-pore
zeolites seems to favor preservation of potentially
sensitive oxygen-containing functional groups.
There are also several cases obviously involving
surface reaction, e.g. the limonene- 1,Zepoxide
conversion to carvenone [71.
As shown in Table 3, alkyl- or halo-substituted
aromatic hydrocarbons, phenols, anilines, benzo-
nitriles, and thiophenes undergo ring positional
isomerization over a variety of medium- and large-
pore zeolites. Data on transalkylation of alkyl-
benzenes and naphthalenes are also included.
Compared to simple alkylations, somewhat greater
severity (i e. higher temperatures, longer contact
times) is generally required for reactions of alkyl-
aromatics, and there is a complex, temperature-
dependent interplay of thermodynamics and kinet-
ics. Early work with acidic faujasite catalysts
[ 115,116] showed that at temperatures below
N 250°C ring-positional isomerization and trans-
alkylation were linked and related mechanistically
via benzylic carbenium ions and bulky diphenyl-
methane intermediates (Fig. 5). Above -3OO”C,
however, isomerization becomes unimolecular and
proceeds via 1,2-shifts [1161 with transalkylation
occurring in parallel. Recent work by Song and
Moffat [533] has shown that acidic zeolites
can catalyze the ring-shift isomerization of
sym-1,2,3,4,5,6,7,8-octahydrophenanthrene to sym-
1,2,3,4,5,6,7,8-octahydroanthracene (Eq. 5E), with
minimal ring contraction reactions to substituted
indanes.
In 1970-1971, Csicsery [ 117,118] reported shape
selectivity in mordenite (pore size 6.5 x 7.0 A),
namely that transalkylation to form symmetrical
trialkylbenzenes was inhibited because there was
not enough space to form the large
Fig. 5. Coupled isomerization-transalkylation mechanism for
low-temperature (170°C) reaction of diethylbenzene over CeY;
scheme is based on findings of Bolton et al. [115]. Note that
there is no direct communication between the ortho, meta, and
para isomers.
1,l -diphenylalkane intermediate leading to it; in
contrast, transition states leading to the other
trialkylbenzene isomers were relatively less bulky
and hence were not inhibited. Moreover, in
HZSM-5, which has an even more restrictive pore
size (5.3 x 5.6 A) than mordenite, Haag and Olson
[341 have shown that a consecutive 1,2-methyl
shift mechanism (transition-state selectivity) is
dominant in xylene isomerization. Likewise,
Weigert has shown that alkyl migration by intra-
molecular 1,2-shifts occurs in isomerization of
methylbenzonitriles [1231 and alkylanilines
[124,125] over HZSM-5. Shape selectivity in
ZSM-5 will be discussed in more detail in Part 3
of this paper.
2.3. Rearrangements involving electron-dejicient
nitrogen as terminus and other complex
rearrangements of nitrogen compounds (Table 4)
Included here are data on the Beckmann
rearrangement, the Fischer indole synthesis (Eq.
6), and the benzamine rearrangement of anilines
to pyridines (Eq. 7). The mechanism of the Fischer
indole synthesis over conventional protonic and
Lewis acids is complex, with a [3,3] sigmatropic

Table 4
P.B. VenutojMicroporous Materials2 (1994) 297-411 311
Rearrangements involving electron-deficient nitrogen as terminus and other complex rearrangements of nitrogen compounds
Beckmann rearrangement
Acetone oxime+N-methylacetamide
Acetophenone oxime+acetanilide+N-methylbenzamide
Cyclohexanone oxime-+caprolactam+ S-cyano-1-pentene
Fischer indole synthesis
Acetone phenylhydrazone-+2-methylindole
Cyclohexanone phenylhydrazone+tetrahydrocarbazole
I-Phenyl-2-butanone phenylhydrazone-+2ethyl-3-phenylindole + 2-benzyl-3-
methylindole
Benzamine rearrangement
Aniline + NH, +Zmethylpyridine
1,3-Diaminobenzene+NH,-+2-amino-6-methylpyridine +4-amino-2-
methylpyridine
HY: 325450°C [1441
HY: 300°C [144]
HY, RE-, Co-, Zn-, Ni-X, HMord: 250400°C
[1441;TS-1, ZSM-5: 340°C [1451;B-ZSM-5 [1461;
ZSM-5: 350°C [1471;HZSM-5, MgZSM-5,
LiZSM-5: 350°C [1481;SAPO-11, -41: 350°C [149];
NaHY: 335°C [1501;H-,Ni-ZSM-5, HZSM-11, -23;
REY: 350°C [1511;ZSM-5, SiOr-ZSM-5: 350°C [1521
RE-, Ca-X: 150°C (ref. 1, p. 345)
RE-, Ca-X: 150°C (ref. 1, p. 345)
H-Y, -Mord (ref. 9, p. 701)
HZSM-5: 510°C [153,154]; HZSM-5: 380°C [155]
HZSM-5: 350-4OOC [1551
rearrangement as the key step (ref. 45, p. 1032).
This may be applicable over acidic zeolites. Chang
and Perkins [ 1531 have proposed two possible
mechanisms for the benzamine rearrangement over
ZSM-5, one involving ring-opening and nitrile
intermediates, and the other featuring ring-
expansion and a 7-membered, nitrogen-containing,
tropylium ion-like intermediate.
REX, tax (@
HY. Mord
Y
ZSMB (7)
CHs
The Beckmann rearrangement features migration
of an R group from carbon to nitrogen, and is
known to be catalyzed by a wide variety of acidic
reagents [46,144]. Stereochemical factors generally
determine which group migrates in the Beckmann
rearrangement, and in the reaction of acetophenone
oxime over HY (Eq. S), the anti-migration product
2a was the dominant product [ 1441.
Ph 0 0
‘C--N, 5 CH3-8-NH--Ph
CHj OH
+ Ph-A-NH-CH, (8)
a W%) m 6%)
Isomerization of the reactant oxime prior to
rearrangement may explain the presence of the
benzamide.
The cyclohexanone ox&e-caprolactam trans-
formation is also catalyzed by both large- and
medium-pore molecular sieves (see Table 4). The
reaction scheme in Fig. 6 is an attempt to rational-
ize mechanistically the various major and side
products that have been observed [ 144,145,150] in
this reaction. The key role of the zeolitic acid sites
Fig. 6. Reaction scheme for conversion of cyclohexanone
oxime (A) to c-caprolactam. Products B-D are most frequently
reported; E-I have been found in traces only. Formation of
products G and H from F or D might conceivably be effected
by the chemistry described by Chang and Perkins in ref. 153,
since minor hydrogenation-dehydrogenation processes seem to
operate in this system.

312
Table 5
P.B. VenutolMicroporous Materials 2 (1994) 297-41 I
Simple addition to olefinic double bonds”
Hydration: addition of water
Ethylene + H,O-tethanol H-Ferr, -ZSM-5: 200-300°C [1561;HZSM-5:
325°C [1571
Propylene + HzO+isopropanol
C2-C, olefins + H,O +C,-C, alcohols
HZSM-5: 150-254°C [1571
ZSM-5, Ferr, Mord: 120-300°C [158,159]; ZSM-5:
<24O”C [I571
I-Butene + H,0+2-butanol
Bicyclo[2.2. l] hepta-2,5-diene + H,O+nortricyclan-3-ol+ norbomen-5-
ol+ (3-tricyclo[2.2. 1.0t*6]-3’-heptyloxy)bicyclo[2.2.1]hept-5-
ene + 3,3’-oxydinortricyclane
a-Pinene + H,O+bomeolb
H-Clin: 120-140°C [160]
H-ZSM-5, -Mord; NdY: 130°C [1611
Acetylene + H,O+acetaldehyde
Addition ofalcohols, ROH
Zeol: 50-70°C (ref. 7, p. 85)
CdX: 120-240°C [1601
Isobutene+ CH,OH+methyl tert.-butyl ether H-ZSM-5, -ZSM-11, -Mord, -8, -ZSM-35, REHY:
66-121°C [162]; NW2, /?, ZSM-5, ZSM-35: 90°C
(ref. 10, p. 32)
Addition ojcarboxylic acids, RCOOH
Ethylene facetic acid-ethyl acetate
Propylene + acetic acid+isopropyl acetate
l-, 2- or 4-Octene+acetic acid-+C,H,, acetate isomers
4-Octene +propionic acid-C,H,, propionate isomers
4-Octene+isobutyric acid+C,H,, isobutyrate isomers
2-, 3-, and 4-Pentenoic acid esters+5-methyl-y-butyrolactone”
Cyclohexene + acrylic acid+cyclohexyl acrylate
Cyclohexene + acetic acid-+cyclohexyl acetate
Norbomene + acetic acid+norbomyl acetate
Addition of ammonia and amines
Ethylene + NH,+ethyl- and diethylamines
HZSM-5, LaY: 200°C [163]; HZSM-12: 200-250°C
11641
B-, Cr-, H-ZSM-5: 160°C [1631;HZSM-12: 200°C
[164,165]
HZSM-5, HZSM-12: 150-250°C [164,165]
HZSM-12: 150-200°C [164,165]
HZSM-12: 200-250°C [164,165]
HY: 180°C (ref. 9, p. 709)
Zeol: 120°C (ref. 10, p. 37)
HZSM-5: 120°C (ref. 10, p. 37)
HZSM-12: 100°C [164]
Propylene + NH,+isopropyl- and diisopropylaminesd
1-Butene+NH,+isobutylamine
Isobutene +NH,+tert.-butylamine
Isobutene + methylamine+isopentylaminee
Ethylene diamine +isobutene+N-terr.-butylethylene diamine
2,5-Dimethyl-1,5-hexadiene+NH,+2,5-dimethyl-5-
aminohexene-1+2,2,5,5-tetramethylpyrrolidine
4-Vinyl-1-cyclohexene+NH,-,l-amine-4-( I-aminoethyl)cyclohexane
Addition ojphosphine and mono- and dialkylphosphines
Isobutene + PHa+tert. -butylphosphine
Isobutene+methylphosphine-*methyl-tert.-butylphosphine
Cyclohexene + PH, +cyclohexylphosphine
2,3-Dimethyl-hexa-l,5-diene + PH, + 1,1,4-trimethyl+hexenylphosphine
Addition of hydrogen suede
Ethylene + H,S+ethylmercaptan + diethyl &tide
Propylene + H,S+propyhnercaptan + propyl sulfide
Vinyl chloride +H,S-+di( 1-chloroethyl) sulfide
Addition of mercaptans, RSH
H-Y,- Mord, -Offr, -Erie, -Clin: 360-370°C [1661;
H-, Zn-ZSM-5: 350-380°C [1671
HY: 300°C (ref. 9, p. 704); H-, Zn-ZSM-5:
330-350°C [1671
HZSM-5: 300°C [1671
REY, H-Y, -Mord: 220-300°C [168]; H-, Fe-,
Zn-ZSM-5: 320-330°C [81; H-, Zn-ZSM-5:
320-330°C [1671
HZSM-5: 330°C [1671
B-ZSM-5: 300°C (ref. 9, p. 705)
CeB-Zeal: 300°C (ref. 9, p. 705)
HZSM-5: 330°C [1671
B-ZSM-5: 100°C [1691
B-ZSM-5: 100°C [1691
B-ZSM-5: 100°C [1691
B-ZSM-5: 100°C [1691
CdX: 220-310°C [1701
CdX: 220-310°C [170]
Cd-, Zn-Fauj [1701
Thiophenol+ I-decene-tdecylphenyl sulfides (+decyldecylphenyl sulphides)’ HY: 182°C [llO]

Table 5 (continued)
P.B. VenutolMicroporour Materials 2 (1994) 297-411 313
Addition of halogens
Ethylene + Cl, +chloroethyleness
Addition of silanes
REX: 288°C [76]
Isobutene + trimethylsilane-tterr.-butyltrimethylsilaneh
“Largely electrophilic or polar in nature.
bHydration followed by skeletal isomerization.
Rh-ZSM-5: 100°C [1691
“Intramolecular addition of carboxylic group; presence of water required.
dComplicated by acid-catalyzed side-reactions of ole6n.
‘Suggests initial alkylation of isobutene by methylamine, with subsequent reaction of Cs olefin with released NHs; this type of
reaction also occurs on borosilicates and borogermanates.
fS-Alkylation accounted for 92% of 1-decene; n-decylphenyl sulfide, probably arising from a competing free radical addition,
comprised 21% of the decylphenyl sulfide fraction; remaining isomers showed CiO residue attachment to sulfur at secondary
carbon atoms.
*Sequence of chlorine additions followed by dehydrohalogenations leading to a range of highly chlorinated products; although
electrophilic chlorine addition is inferred, it is diicult to prove, and the operation of radical-type chemistry can by no means be
eliminated.
“Mechanism other than simple electrophilic addition probably operates here.
is probably to convert the OH of the oxime into
a better leaving group by protonation, although
there are different opinions on this issue [ 148,152].
Sato and co-workers [ 148,152] also conclude that
the Beckmann rearrangement occurs on the exter-
nal surface of ZSM-5-type zeolites. Polar solvents
with high dielectric constant usually enhance this
rearrangement in homogeneous systems. The
opposite effect was observed in conversion of
cyclohexanone oxime over REX at 250°C [144],
suggesting that the polar solvents (e.g. acetic acid,
methanol) blocked contact of reactant with the
zeolite acid sites by competitive adsorption.
2.4. Simple additions to olejinic double bonds
(Table 5)
Olefin chemistry plays a critical and all pervasive
role in zeolite catalysis, and their transformations
(Tables 5-7) and formation (Tables 8 and 9)
comprise a significant fraction of this survey.
Table 5 includes addition to alkenes of HOH,
ROH, RCOOH, NH3, NH,R, PH3, RPH,, H,S,
Clz, and R&H, for the most part over acidic
medium- and large-pore zeolites. In cases where
reactants were gaseous and/or low-molecular-
weight compounds, e.g. CzH4 + NH3 [ 1671,imposi-
tion of pressure was helpful in conversion. The
“reverse” of many of these reactions (i.e. /?-
elimination) is shown below in Table 8.
It is worthwhile to recall that a carbon-carbon
double bond contains a strong c bond and a
weaker n bond:
The electrons in the R orbital are less strongly held
by the carbon nuclei, hence they are more polariz-
able and accessible, leading to the known reactivity
of alkenes. Although radicals can initiate addition
to unsaturates, for many addenda (HNu), such as
HOH, ROH, RCOOH, or NH3(NH2R), electro-
philic or polar addition - with acid catalysis -
is a reasonable model.
Electrophilic additions are sometimes stereo-
selective, and in uncomplicated systems the
Markownikov rule is followed. These points are
illustrated in simplified form in Eq. 9:
a+b-
HNu +

314 P.B. VenutojMicroporous Materials 2 (1994) 297-411
Here, (probably) rate-limiting proton addition
from the top to form a ?I complex, followed by
rapid attack of the nucleophile from the bottom
of the planar alkene can occur (anti addition, path
A), or protonation to form a planar carbocation,
followed by attack of Nu from either side (seenor
anti addition, path B). In either case, the
Markownikov rule is obeyed, since the negative
moiety (Nu) has become attached to the more
highly substituted of the two alkene carbons.
Although more data would be desirable, the
products in Table 5 from additions to C, and
C4 olefins are generally consistent with the
Markownikov pattern. In the case of additions
within the micropores of zeolites, where the olefin
might be adsorbed at a protonic acid site, attack
of the nucleophile (Nu) on a near-planar n complex
might be expected to show anti addition:
,: ..*
Rl _ c”_ “c 0 R2
4 q
H
Also, the addition reactions of NH3(RNH2) seem
to require higher temperatures than most of the
other additions, reflecting in part energy require-
ments to maintain some fraction of the intra-
crystalline active sites free from adsorbed (i.e.
protonated) nitrogenous base. Finally, in the reac-
tion of isobutene and methylamine to form iso-
pentylamine [ 1671, initial alkylation of isobutene
by methylamine to form isopentene seems likely.
2.5. Electrophilic addition to olejinic double bonds
in complex reaction systems (Table 6)
Many of the reactions in Table 6 involve at some
stage addition of electrophiles more complex than
protons to unsaturated linkages, or conversely
expressed, involve attack of olefins on adsorbed
carbocations. This was one of the intermolecular
routes to satisfy the positive charge on a carbo-
cation shown earlier in Fig. 4. This kind of mecha-
nism is shown in Fig. 7 for three of the reaction
types in Table 6.
For isoparaffin-olefin alkylation (Fig. 7A), the
cycle involves attack of an olefin, say
Fig. 7. Elementary catalytic cycles for (A) simple isoparaflin
-olefin alkylation, (B) simple olefin oligomerization, and (C)
methanol-olefin alkylation. These reactions probably involve
Rideal-type attack of olefin on adsorbed carbocation.
trans-Zbutene, on an adsorbed tert.-butyl cation
to form a new iso-C,H,,@ cation, which, after
transfer of hydride from isobutane, is desorbed as
a branched paraffin, iso-C,H,,. For this mechanism
to operate with any efficiency, it is necessary to
have a high ratio of isobutane to butene, otherwise
hydrogen transfer will not be able to compete with
olefin oligomerization (see Fig. 7B), and catalyst
deactivation will occur. A likely initiation path
involves protonation of butene to form a linear C,
cation with hydrogen transfer from isobutane to
form a tert.-butyl cation and n-butane. An excel-
lent mechanistic discussion on alkylation is given
by Weitkamp [ 1791.
In polymerization/oligomerization (Fig. 7B),
initiation is via proton attack on propylene to
form adsorbed carbocation Rre, with the cycle
repeating until desorption of a product olefin,
CnHzn, by eliminating a proton to the zeolite
lattice. Of course, carbocation stabilization can
occur at lower degrees of polymerization, i.e. with
desorption of dimers, trimers, etc. The alkylation
of C,-C4 olefins by methanol or dimethyl ether
[ 184,185] over HZSM-5 as represented in Fig. 7C,
features initiation via proton-assisted formation of
an electron-deficient adsorbed C, species (repre-
sented as CH,6@), with attack by C3H, to form a
GH,@ carbocation. Stabilization of this carbo-
cation by proton elimination then generates C4H8.

Table 6
P. B. VenutojMicroporous Materials 2 ( 1994) 297-411 315
Electrophilic addition to olefinic double bonds in complex reaction systems
Hydroformylation (hydroformyl addition)
Ethylene + CO + Hr-tpropionaldehyde (+ n-propanol)
Ethylene + CO + H,+propionaldehyde (+n-
propanol+ methylbutyraldehyde)
Propylene + CO + H, -rmethacrolein
Propylene + CO + H,+4-heptanone + 2-methyl-3-hexanone
1-Hexene or 2-hexene + CO + Hs+ 1-heptanal + 2-methylhexanal +
2-ethylpentanal
1,5-Hexadiene + CO + H,+dialdehydes + monoaldehydes
Isoparafin-ole$n alkylation
Ethylene + isobutane-+2,3diiethylbutane + other isomers
n-Butene + isobutane+isooctane isomers
1-Butene + isobutane jalkylate
Olefins + isobutane+alkylate
Methanol-olejin alkylation
Ethylene + methanol+propylene + butenes
Propylene + methanol-*butenes + Cs aliphatics
Propylene + methyl ether+ butene + pentene
1-Butene + methanoldpentenes + hexenes
2-Butene + methyl ether +pentenes + other compounds
Olefin oligomerizationJpolymerizationd
Ethylene-+oligomers
Propylene-rtrimer + tetramer + pentamer
Propylene-dimer + trimer + tetramer
1-Hexene+oligomers
C,-C, olefhrs+oligomers
C2-C,, olefins-+oligomers
Cz-CzO olefins+ohgomersf
Olejin interconversionldisproportionation
Propylene, mixed pentenes, 1-hexene, or 1-decene+similar Cg-Cg olefin
mix
Cs-C, olefins-+olefin oligomers
Intermolecular hydrogen transfer/redistribwtionh
Carbon monoxide + Hz-C,-C,,+aromatics + saturates’
Ethylene +complex mixture of aromatics + C3-Cs paraffins
Propylene+C,-C, aromatics+hght saturates
C,-C, oletins +cyclooleSns + aromatics + saturates
1-Hexene-taromatics + saturates
Methane+benzene+light products
Ethane+aromatics + light saturates
Propane++C, aromatics + light saturates
(Continued on p. 316)
Ru/‘X: 200°C [171]; Rh/Y: 115-140°C [172]
Ru/Zeol: 200°C (ref. 8, p. 237)
H-Mord, -Y; REX: 25-150°Cb (ref. 1, p. 356)
Rh”‘/Na-X, -Y: 150°C [173]
Rh/X, -Y: 50-130°C (ref. 174, p. 189); Rh/Na-X,
-Y; Rh/CaA: 50°C’ [175,176]; Rh/NaY: 50-130°C
11771
Rh/NaY: 50-130°C [1771
REX: 40-150°C [178]
Ce-X, -Y: 80°C [179,180]; Lay: SO-314°C [1811
REHY, USY: RE-, Deal-USY: 88-97°C [182]
REHY [183]
P-ZSM-5: 350°C [1841
P-ZSM-5: 30%350°C [1841
P-ZSM-5: 250-400°C [1841
HZSM-5: 450°C [1851
P-ZSM-5: 300-400°C [1841
HZSM-5: 27-600°C [1861
HZSM-5: 200°C [1871;HZSM-5: 150-288°C [188]
NiH-, ZnH-ZSM-5: 49-54°C [1891
SAPO-5, -11, -31, -34; ZSM-5: 343°C [88]; REX
64°C [94]
Fauj: 25-300°C (ref. 1, p. 315)e; HZSM-5:
250-300°C [1901
HZSM-5: 200-260°C [1871
Ni-, Ni/Zn-ZSM-5, ZSM-11 (ref. 8, p. 240)
HZSM-5: 275°C [1871
HZSM-5: 200-300°C [1911s;HZSM-5: 150-350°C
[30,188]
Fe-ZSM-5, Zr-HMord, Zr-ZSM-5, ZnCr-ZSM-5:
371427°C [192,193]
REX: 90-213°C [94]; HZSM-5: 350°C [184];
HZSM-5: 500°C [1941
HZSM-5: 538°C [195]; HZSM-5: 500°C [194]
HZSM-5: > -250°C [191]
HY: 2Of-260°C [1961
Ga-, Zn-/HZSM-5: 500°C [534]
Ga-, ZnCu-ZSM-5: 570-620°C (ref. 8, p. 237);
Ga-ZSM-5: 530°C [1971
Zn-, Cu-ZSM-5: 570-620°C (ref. 8, p. 237);
Ga-ZSM-5: 530°C [197,198]; /?, Ga-fi: 450°C [1991;
Ga-ZSM-5: 600°C [200]; Ga-, Pt/HZSM-5: 500°C
[201]; Ga-, Zn-/HZSM-5: 500°C [534]

316
Table 6 (continued)
P.B. VenutolMicroporous Materials 2 (1994) 297-411
Isobutane+C,-C, aromatics + light saturates
n-Pentane-+C,-C, aromatics+light saturates’
n-Hexane+C-Cs aromatics+light saturates
Cyclohexane or methylcyclohexane-C,-C, aromatics + light saturates
n-Heptane+C,-C, aromatics +light saturates
Biomass-type compounds [hevea braziliensis latex, dipentene, corn oil
(C,,H,,,Os), castor oil (CJ7H1,,.,09), Jojoba oil (C,,HsoOz)-‘Cs-C, aro-
matics (+light gas saturates)7
Xylose, glucose, starch, sucrose-+hydrocarbons + CO + COz
Methanol+C~-CIO aromatics+light saturatesm
Methyl formate+Cs-CIO aromatics + other products + CO”
Ethanol-+C,-C,, aromatics + aliphatics”
tert.-Butanol+C,-C,, aromatics+aliphatics”
Mixed pentanols+C,-C,, aromatics + aliphatics”
1-Heptanol+C,-C,, aromatics +aliphatics”
2-Ethylhexanol-tC6-C10 aromatics+aliphatics”
Mixed oxo-alcohols-K,-C,, aromatics +aliphaticsm
Tri-n-butylarnine+C,-C,, aromatics + aliphatics”
Acetic acid-C&& aromatics + CO2+ other productsm
Propionaldehyde+C,-C,, aromatics + aliphatics”
Acetone-C,&,, aromatics+light aliphatics”’
n-Propyl acetate +C6C10 aromatics + aliphatics”
Cyclopentanone+C&r,, aromatics + aliphatics”
n-Butyl formate++CIO aromatics + aliphatics”
Hexanoic acid-&,-C,, aromatics + aliphatics”
Ga-ZSM-5: 530°C [1971
HZSM-5: 575°C [195]; H-, Ga-ZSM-5: 400-550°C
PO21
HZSM-5: 538°C [195]; ZnUSY: 470°C [203];
Ga-ZSM-5: 530°C [1981
Ga-ZSM-5: 530°C [1981
Ga-ZSM-5: 530°C [1981
ZSM-5: 450-500°C [204,205]
HZSM-5: 510°C [206]
HZSM-5: -330-460°C [37,207,208]; H-, Zn-, Cd-,
Mg-, Ca-, Al-, Co-, Pt-, Ru-, Pd-, Sn-, Cu-ZSM-5:
400°C [209]
HZSM-5: 371°C [210]
HZSM-5: 307-370°C [208,211,212]
HZSM-5: 371°C [207]
HZSM-5: 427°C [208]
HZSM-5: 371°C [207]
HZSM-5: 371°C [208]
HZSM-5: 427°C [208]
HZSM-5: 260°C [208]
HZSM-5: 371°C [207,210,213]
HZSM-5: 371°C [207,210]
CeHZSM-5: 315-371°C [207,210]
HZSM-5: 371°C [207,210]
HZSM-5: 371°C [210]
HZSM-5: 371°C [207,210]
HZSM-5: 371°C [210]
Pyrrole + H2S+ thiophene
Furan+ H,S-+thiophene
2-Methylfuran + H,S -+2-methylthiophene
2-Phenylfuran + H,S+2_phenylthiophene
Benzofuran + H,S+benzothiophene
Furfural+ H,S +2-formylthiophene + 2-thioformylfuran +
2-thiofonnylthiopheneO
Oxygen-nitrogen, nitrogen-suljicr and oxygen-sulfur interchange in jive-ring heterocyclics”
Furan + NH,~pyrrole NaX: 300°C (ref. 1, p. 355); Bay: 330°C (ref. 11, p.
14; ref. 55)
NaX: 400°C (ref. 1, p. 355)
NaX: 340°C (ref. 1, p. 353)
NaX: 300°C (ref. 1, p. 353)
NaX: 300°C (ref. 1, p. 353)
NaX: 500°C (ref. 1, p. 353)
NaX: 300°C (ref. 1, p. 353)
Acetylene condensation to aromatics
Acetylene-+benzeneP Cry: 160-200°C [214]
“Ethane rather than n-propanol was also formed.
bPressure of 74-400 atm.
‘Pressure of 300 p.s.i.g.
*A much studied reaction; only a few examples will be given; frequently accompanies olefin isomerization.
‘Summarizes data for a range of catalysts and conditions.
‘Mainly open-chain and cyclic aliphatic products, i.e. uncomplicated by hydrogen transfer.
sAt higher temperatures, cyclics, aromatics and saturates are obtained from hydrogen transfer.
hHas also been termed “conjunct polymerization”.
‘Dual-functional polystep reaction combining a metal function (Fischer-Tropsch catalyst) and acid (hydrogen-transfer) function
(HZSM-5).
Whe generic name “M2-Forming” has been given to this type of high-temperature reaction.
‘Since all these reactants either have olefinic double bonds, or could generate them upon pyrolysis or catalytic reaction, these
reactions are classified as “hydrogen transfer”.

Table 6 (continued)
P. B. Venutolkficroporous Materials 2 (1994) 297-411 317
‘Reactants are in 50-70% aqueous solution.
“All these reactions almost certainly proceed via olefin intermediates.
“Classified here because, in contrast to thiophene, furan and pyrrole rings have more “olelinic” character; a possible multi-step
mechanism might involve initial 1,2- or 1,4 addition of H$, with subsequent intramolecular SNattack by S-H, elimination of HZ0
or NH,, etc.
OOxygen of aldehyde group as well as that of furan ring replaced by sulfur.
Wp to 2OO”C,acetylene undergoes mainly Cr ion-catalyzed cycliition into benzene; at higher temperatures (2OC-35O”C), benzene
condenses with acetylene to form styrene, which is thought to be the precursor of C, + aromatics found at these higher temperatures.
This alkylation might also be termed electrophilic
olefin substitution. Methylation by methanol can
be limited if reaction conditions permit significant
competitive adsorption by olefin or known
[ 37,184,185,246,420] alternative conversion path-
ways for the C1 reactant. Finally, although an
acid-catalyzed mechanism for olefin carbonylation
over acid zeolites such as H-mordenite was pro-
posed earlier [l], most recent hydroformylation
work utilizes zeolites containing Rh or Ru com-
plexes (see Table 6). The chemistry of the transition
metal is probably dominant in these cases, and
mechanisms featuring Rh- or Ru-carbonyl species
may be likely.
A perspective on the thirty or so diverse reac-
tions listed under the category of “intermolecular
hydrogen transfer” in Table 6 is provided by Fig. 8.
Most of these reactions are ZSM-5-catalyzed and
reflect at least these three aspects: (1) generation
of olefins; (2) olefin interconversion; and (3)
hydrogen transfer (largely intermolecular) to form
aromatics and lower-molecular-weight paraffins.
Fig. 8. Convergence of diverse reactants towards oleiins -
and ultimately towards aromatics and parathns - in multi-
step reaction paths over HZSM-5. Modified after Haag [29].
Olefin generation
Although the seven reactant groups shown in
Fig. 8 comprise strikingly different chemical struc-
tures, their reaction paths tend to converge toward
olet?ns (although other products are also formed)
under the conditions listed in Table 6. While high-
molecular-weight biomass-type species such as
latex rubber undergo initial thermal conversion to
smaller intermediates [204], the majority of reac-
tion chemistry is acid-catalyzed [27,29,195] and
involves complex multi-step, consecutive reactions
within ZSM-5 pores. Paraffins, naphthenes and
olefins with a wide range of sizes are cracked and
restructured towards small olefins [195]; with
methanol [2071, dehydrocondensation reactions
build up towards Cz--C5 olefins (i.e., see product
distribution between points A and B in Fig. 3);
Cl oxygenates, etc. can undergo a variety of
dehydration, isomerization, dehydrocondensation,
and related reshullling reactions to generate ole-
tins; syngas (CO+H,) can be converted via
Fischer-Tropsch chemistry to liquid products,
which are in turn subjected to cracking and struc-
tural rearrangement [ 192,193].
In all these transformations, much of the chemis-
try reflected in Tables 3, 6, 8, and 9 can occur,
and in a sense (depending on reaction conditions),
all of the reactants in Fig. 8 can be considered
“olefin precursors”, but by no means exclusively
so. Interesting insights into the mechanism of C-H
activation and the effects of molecular stoichiomet-
ric hydride acceptors on aromatization of light
alkanes (C,H,, CH.,) over Ga- and Zn-/I-IZSM-5
have been provided in a recent paper by Iglesia
and Baumgartner [5341.
Olejin interconversion
This very characteristic ZSM-5 acid-catalyzed
process has been well described by many authors

318 P. B. Venuto/Mcroporous Materials 2 (1994) 297-411
[27,29,33,187,418,419,421]. For a wide variety of
olefinic feeds, e.g. C,-Cl0 [187], there is con-
vergence toward the same mixture of C,-C, ole-
fins, i.e. toward a thermodynamic equilibrium
composition that is dependent on the temperature
and pressure of the reaction system. Reaction
mechanisms include true oligomerization (gen-
erally observed at lower temperatures) (Eq. 10)
and, at temperatures higher than 150°C a more
complex random oligomerization (reaction
sequences shown in Eq. 11) that includes /I-scission
and intramolecular rearrangement of carbocations,
that might loosely be termed disproportionation
[27,29]. Highly branched olefins are generally not
found because of shape-selective factors [33].
Hydrogen-transfer processes
The last aspect depicted
(10)
(11)
in Fig. 8 comprises
hydrogen-transfer processes - dominated by
intermolecular redistribution of structural
hydrogen towards aromatics and co-produced low-
molecular-weight paraffins. The convergence of
olefins toward similar mixtures of Cz-Cg olelins
by olefin interconversion is typically complimented
by a corresponding channeling toward similar mix-
tures of C,&lO/C1l aromatics and Cz-C5 aliphat-
its, at least when the experimental conditions are
similar [27,421] (see, for instance, the product
distributions from methanol and biomass mole-
cules conversion over ZSM-5 from ref. 204 as
shown in Fig. 59 below). It is also reflected in the
product distribution at point D in Fig. 3, the
methanol-to-hydrocarbon reaction path.
The importance of such hydrogen transfer-type
reactions in zeolite organic chemistry cannot be
underestimated. Not only are they critically impor-
tant in the ZSM-5-catalyzed reactions shown in
Fig. 8, but also they occur almost universally in
transformations over acidic faujasites and other
large-pore zeolites, whenever olefins are either
reactants or products [ 1,94,95,415,416]. Their role
in catalytic cracking and coke formation has been
described in detail [2251. They include highly com-
plex polymerization, isomerization, cyclization, /I-
scission, and hydrogen-transfer reactions that have
collectively been termed “conjunct polymeriza-
tion” [94,95,191,418]. These are well known in
“conventional” acid catalyst systems, e.g. HzS04,
H3P0,, silica-alumina, etc. Profound hydrogen
redistribution occurs with the result that some
molecules are essentially “dehydrogenated” to aro-
matics, although little transfer of molecular
hydrogen is observed. At higher temperatures,
cyclization and hydrogen-transfer processes
become more extensive, and a complex assembly
of molecular classes is generated [191].
Redistribution of hydrogen to light (e.g. C3-C5)
paraffins counterbalances the formation of aro-
matics, cycloolefins, and other hydrogen-deficient
species. The stoichiometry of a few typical such
reactions is shown in Eqs. 12-14 [225,418].
3C,H,, + C,HB,,+ 3C,Hz, +2 + GJ32, - 6
olefins + naphthene *paraffins + aromatic
(12)
4C,H2,+ 3C,H2, +2 + GH2, - 6 (13)
olefins or naphthenes -+paraffins + aromatic
3C,H2,-2~2C,H,,+C,H,,-,
cycloolefins+naphthenes + aromatic
(14)
Despite the modest channel dimensions
(5.3 x 5.6 A) of ZSM-5, adequate space for the
transition states of bimolecular hydrogen-transfer
reactions probably exists in the large, roughly
spherical space at the channel intersections, as
proposed by Derouane and Vedrine [4221.
The hetero-atom interchange reactions in furan
and pyrrole ring systems probably involve 1,2- or
1,Caddition of H2S or NH3 as an initial step,
hence their inclusion in Table 6. A speculative
multi-step mechanistic scheme is shown in Fig. 9.
The chemistry of the transition metal is probably
the dominant factor in the acetylene-benzene con-
version over CrY [214] cited at the end of Table 6.

P.B. Venuto/Microporous Materials 2 ( 1994) 297-411 319
Fig. 9. Possible mechanistic scheme for oxygen-sulfur inter-
change over NaX for the furan-H,S system. 1,4-Addition of
H,S, intramolecular S, attack by SH, and l+elimination of
H,O are proposed. These steps might be assisted by the polar
NaX surface at the high temperatures involved. Modified after
Venuto and Landis [11.
2.6. Cycloaddition-type reactions of olefins
(Table 7)
A good example of this type of reaction is the
Diels-Alder reaction, which involves the 1,4-
addition of substituted alkenes to conjugated
dienes. This is shown in Eq. 15 for the cyclodimeri-
zation of 1,3-cyclohexadiene (3a), where a con-
certed, cyclic, six-membered ring transition state
(3~) with syn orientation of diene (3a) and die-
nophile (3b) molecules is visualized.
Table 7
Cycloaddition-type reactions of olefms
Stereochemically, both endo (3d) and exo (3e)
adducts are possible, but the endo adduct is fre-
quently the major or sole product [46]. Generally,
Diels-Alder reactions appear to be relatively unin-
fluenced by solvent polarity, catalysts and radical
inhibitors, etc., i.e. do not follow polar or radical
reaction pathways. They can, however, be influ-
enced thermally or photochemically, and the
electronic or steric effects of substituents may be
significant (ref. 46, p. 341).
The list of reported cycloaddition-type reactions
over zeolites is short (Table 7). In his study of
the cyclodimerization of 1,3-butadiene (4a) to
4-vinylcyclohexene (4b) over the sodium forms of
large-pore zeolites (Eq. 16), Dessau [215] con-
cluded that the major role of the zeolite was to
concentrate the hydrocarbon reactants within their
cavities, an effect commensurate with high
pressure.
g I- - CT= (16)
4a 4b
A 13-a pore size carbon molecular sieve was also
an effective catalyst. In the same study [215],
Dessau also observed that in the large-pore zeo-
lites, there was adequate space within their cavities
for proper alignment of the reactants; in medium-
pore zeolites like ZSM-5, little catalysis was
Die&Alder-type reactiona
1,3-Butadiene+ 1,3-butadiene-+4+inylcyclohexene
Cyclopentadiene + methylvinylketone+2-acetyl-5-norbomene
Furan+methylvinylketone-,2-acetyl-(7-oxa)-S-norbomene
1,3-Cyclohexadiene + 1,3cyclohexadiene+endo- and exodimers
2,4-Dimethyl-1,3-pentadiene + 2,4-dimethyl-1,3-pentadiene+
1,1,3,3,5-pentamethyl-2-isopropenyl-5-cyclohexene
Myrcene+methylvinylketone~l-acetyl-4-(4-methyl-3-pentenyl)cyclohex
Cycloadditions toform small-ring systems
trans-Anethole + trans-anethole+[2 + 21 diier
Cyclopropene+cyclopropene~tricyclo[3.l.O.O*.4]hexane([2+2] dime#’
Ethyl diazoacetate + olefins-t 1-carboethoxycyclopropanes
Na-ZSM-20, -8, -Y: 250°C [215]; Cu’-, Cu”-Y:
90°C [216,217]
HY, Deal-Lay, C$‘Y: 0°C [218]
Cu’Y: 0°C [219]; NiX, CuNa-, NiNa-Y: 20°C [220]
NaXz 40°C [221]
NaX: 40°C [221]
-3-eneiNiiP&[%?@thyl-3-pentenyl)cyclohex-3-ene
NaX: 40°C [221]
Na-, K-A: -35°C [222]
NaCuX: 80°C [223]
“In many of these cases, actual catalysis is minimal if existent.
b1-Methylcyclopropene and 3-methylcyclopropene also form [2 + 21 dimers; this reaction probably occurs on external surface

320
Table 8
P. B. Venuto/iUicroporous Materials 2 (1994) 297-41 I
Olefin-forming /&elimination reactions
Catalytic cracking ( /T-scission)a
n-Hexane +propaneb
Cs-Cl0 n-Paraffins, C,-C,, n-olefins+cracked + restructured products
n-Decane+n-pentane + I-pentene
n-Dane+ 1-pentene + I-pentene
Gas oil+propylene + butenes + higher-molecular-weight products
Dehydration of alcoholf
Ethanol-ethylene f H,O
iso-, n-Propanol+propylene + H,O
n-Butanol+ butenes + Hz0
sec.-Butanol+butenes + Hz0
terr.-Butanol+isobutene + H,O
n-Pentanol +pentenes + Hz0
2,4_Dihydroxypentane+Cs dienes’
n-Hexanol-thexenes + H,O
Cyclohexanol+cyclohexene + Hz0
3-Hydroxy-3-methylbutan-2-one + H,+methyl isopropyl ketone + HzOf
Mg-, Ca-, Na-, Li-A: 310°C; Mg-, Ca-, Na-,
Li-Mord: 310°C; Mg-, Ca-, Na-, Li-X: 270-350°C
[229]; AgY: 187°C [230]; Na-X, -Mord; 4A:
200-350°C [231]
Cay: 250-275°C [232]; H-, Na-X, CaA: 210°C
[233]; NaX/C02: 235°C [234]; ZSM-5: 177°C
[208]; AgY: 150-182°C [230]; Na-X, -Mord; 4A:
200-350°C [231]
Ca-X, -Y: 220-275°C [67]; &A: 220-260°C [235Jd;
Li-, Na-, K-, Rb-X: 350°C [236]; Na-X, -Mord;
4A: 200-350°C [231]
CaX: 109-130°C [235]
HMord: lOO-200°C [237]; Ca-X, -Y: 168-228°C
[2381
NaX: 275-325°C [239]
NaX, -Y; HY: 250-300°C [57]
CaY: 150-170°C [232]
H-, Be-, Mg-, Ca-, La-Mord; Be-, Mg-, Ca-Clin;
Be-, Mg-, Ca-, Sr-Y: 120°C [240]
Pd/CeB-ZSM-5: 375°C [241]
Dehydration of ethers
NaXz 350°C (ref. 11, p. 6)
Alcohol elimination from simple ethers
Methyl tert.-butyl ether+isobutene + CH,OH B-ZSM-5: 200°C [40]
Alcohol elimination from acerals to form enol ethers
Acetaldehyde dimethylace.tal+vinyl methyl ether+CH,OH
1,1,3,3-Tetramethoxypropane+3-methoxyacrolein+ CH,OH
3,3-Dimethoxymethylbutyrate+3-methoxycrotonic acid methyl
ester + CH,OH
Na-ZSM-5, -Mord: 300°C (ref. 7, p. 76); SAPO-5:
300°C (ref. 10, p. 35)
ZSM-5, CsB-ZSM-5: 300°C [242]
B-ZSM-5: 220°C [242]
2,2,4,4-Tetramethoxypentane+4-methoxybut-3-ene-2-one + CH,OH B-ZSM-5: 220°C [242]
2,5-Dimethoxytetrahydrofuran-r4-methoxybut-3-en-alh + CH,OH B-ZSM-5: 300°C (ref. 10, p. 42)
Carboxylic acid elimination from esters
n- or sec.Butyl acetate+ isomeric n-butenes+acetic acid
1,4-Butane diformate-r butene formate + formic acid’
1,CButane diacetatedbutene acetate + acetic acid’
Fauj, Mord, A: 190-290°C (ref. 95, p. 261)
ZSM-5: 300°C (ref. 10, p. 38)
FeZSM-5: 400°C (ref. 10, p. 38)
Dehydrosulfurization
Ethanethiol-tethylene + H,S
trans-4-~ert.-butyl-cis-2-methylcyclohexanethiol~isomeric I-methyl-3-tert.-
butylcyclohexenes
NaX: 200-600°C (ref. 1, p. 314)
NaX: 200°C (ref. 1, p. 314)
Dehydrohalogenarion
Ethyl chloride+ethylene+ HCl RE-, Na-, Ni-, Ag-X; HY: 260°C [76]; ZSM-5:
265°C [243]
NiHErio: 370°C [224]
ZSM-5, USY, REY: 316-538°C [535]
X-, Y-type Zeal: 200-550°C [225,226]
X-, Y-type Zeol: 200-550°C [225,226]
ZSM-5: -5oO-550°C [227,228]

P.B. VenutolMicroporous Materials 2 (1994) 297-411 321
Table 8 (continued)
Ethyl bromide -+ethylene + HBr
1,2-Dichloroethane-rvinyl chloride + HCl
1,1-Dichloroethane +vinyl chloride + HCl
1,l ,1-Trichloroethane +vinylidene chloride + HCl
1,1,2-Trichloroethane -dichloroethylene + vinylidine chloride + HCl
REX: 66°C [76]
REX: 288°C [76]; ZSM-5: 325-350°C [243]
REX: 240°C [76]
REX: 163°C [76]
HY, Mg-, K-, Na-X: 300°C [244]; ZSM-5:
225-350°C [243]
tert.-Butyl chloride+isobutylene + HCl CaA: 260°C [245]
Ethylene + Clr +chloroethylenes’ + HCl REX: 288°C [76]
‘Not strictly /I-elimination but included here because of genetic similarity; when conducted in presence. of hydrogen with a dual-
functional acid-metal catalyst, hydrocracking occurs.
bAnother classical example of reactant shape selectivity: selective conversion of n-hexane but not 2-methylpentane in competitive
hydrocracking over 8-ring zeolite; olefinic products are generally hydrogenated under these conditions.
‘Frequently concurrent with etherification.
*A classical example of reactant shape selectivity: selective conversion of n-butanol but not sec.-butanol in competitive experiment
over I-ring zeolite.
‘Dehydration to dienes (major pathway) accompanied by some fragmentation and isomerization.
Dehydration followed by hydrogenation of ole6nic bond.
BMechanism may involve cleavage of cyclic ether with /3_elimination followed by dehydration of remaining carbinol.
hMechanism presumably involves cleavage of cyclic a&al with /%imination; elimination of methanol from remaining
-CHOH(OCH,) group forms the aldehyde.
‘Note selective elimination of only one of the two functional groups; the other is preserved.
Chlorine addition to ethylene followed by dehydrohalogenation.
observed, probably due to steric inhibition of the
transition state required for this bimolecular reac-
tion. In regard to Ct.?-promoted catalysis of the
butadiene-4-vinylcyclohexene reaction in X- and
Y-zeolites [216,217], Dessau [215] suggested coor-
dination of butadiene with the Cu’ ion. This makes
sense, particularly if such coordination rendered
an adsorbed butadiene a better dienophile:
Zeol - 0
The small-ring cycloadditions over NaX [221] and
Linde A [2221 depicted in Eqs. 17 and 18 presuma-
bly occur on the zeolite external surface.
4 + /D Na-. K-A_ /& (18)
2.7. Olejin-forming ~-elimination reactions
(Table 8)
/?- or 1,2_elimination involves formation of a
double bond when atoms are lost from adjacent
carbon atoms, usually a nucleophile, Nu from
the a-carbon, and a proton from the fi position
(Eq. 19).
H -‘C:- i(- Nu
- cd + HNu
(19)
/ /
It is stoichiometrically the reverse of simple addi-
tion of HNu to an olefin. A number of mechani-
stic options exists, and the El (Eq. 20) and E2
(Eq. 21) mechanisms represent good working
base cases.
H R3 H
/
R,--C--C=Nu
‘7 /
R3 R1
/
R3
- R,-C-C@ __) c=c + HN,,

‘i R4
/
Rz N,? FL
(20)
4 R.
Rl
/
%
c=c
/
+ BH” + Nu” c21j
R2 R4

322 P. B. Venuto/Microporous Materials 2 (1994) 297-411
In the El case, formation of a carbocation is
usually the rate-limiting step, and is comparable
to that formed in the SN1 reaction (Eq. 2). The
E2 pathway is typically a concerted base-catalyzed
reaction in which (in simple acyclic systems), anti-
periplunar elimination is much preferred, although
there are numerous factors which can influence
the degree of stereoselectivity [45,46].
Olefin-forming j&eliminations occur frequently
in organic catalysis over zeolites, and are com-
monly encountered in single-stage conversion
processes involving multiple steps. For the elimin-
ations in Table 8, the leaving groups, Nu, include
-OH, -OCH,, -0-CO-CH3, -O-CO-H, -SH,
-Cl, and -Br. In catalytic cracking (Eq. 22), which
is not strictly speaking a B-elimination (but which
has analogy relevance), the positive charge on the
carbocation 5a is satisfied by scission of the C,C,
bond, generating a neutral olefin and a new carbo-
cation, 5b (see refs. 225 and 226 for details on the
mechanism of catalytic cracking).
nz
cs-“l
n3’ q P
n2
/R1
H

H-C-Cc - cm + c =c’
4
/
(22)
/ /
R4 Rs R3 R4 %
so 5b
It is evident from Table 8, that zeolites with a
wide range of pore size and acidity-basicity charac-
teristics catalyze B-eliminations. Clearly zeolite
structural features such as protons in hydrogen
forms, metal cation fields (either unscreened or
mediated by proton donors), lattice defects or
other electron-deficient sites could convert
hydroxyl, alkoxyl, halide, etc. to better leaving
groups, thereby facilitating C-Nu heterolysis.
Clearly, strong acidity, i.e. of the type required for
paraffin alkylation, is not universally required.
Even the anionic lattice oxygens might assist to
some extent by polarizing C-H bonds, as would
residual traces of base in alkali forms. Assistance
to elimination could also be provided by the polar
landscape of the external surface. It is also possible
that radical pathways may come into play with
sulfur-containing species [11. Further, side-
reactions can be multiple and complex as demon-
strated for vinyl chloride in Fig. 10. Substrate
CH2 = CHCI
-HCI
I H-C=C-H
I
I CH3-T-Cl 5
1 CH, -CHCI,
POLYMER
COKE
/ CH,-CH2CI
1
-HCI
POLYMER c--- CH2 =CH2
+
C3H8, C,H,, , etc.
Fig. 10. Reactions of vinyl chloride over REX catalyst at
260°C. Reproduced from ref. 76 (Venuto et al.), copyright
1966, Academic Press.
reactivity [ 1] and kinetic effects [23 1] in alcohol
dehydration have also been discussed.
Attention is also called to the ZSM-5-catalyzed
diester systems (ref. 10, p. 35), where even at
300-400°C selective elimination of RCOOH from
only one of the two functional groups occurred
(Eq. 22A).
CH-CH,-CH,-CH
ZSM-5
I 2 I* 3oo’c-
CH,=CH-CH,-CH
I2
+ HCOOH
0 0 0
I I
Y=O
Lo
I:
Y=O
WA)
H H
Also, shape-selective effects are obviously possible,
and the classic early work of Weisz et al. [235] in
the butanol-CaA system is still worthy of note.
Finally, the eliminated HNu (water, for instance)
can have important effects within the catalytic
system, e.g. by “self-promotion” of catalyst acidity
via metal cation hydrolytic mechanisms (ref. 1,
pp. 282-283) or by sometimes significant effects
on diffusion coefficients (ref. 1, p. 270).
2.8. Olefin-forming dehydrocondensation reactions:
substrates without /?-hydrogens (Table 9)
We have used the term dehydrocondensation to
describe the olefin-forming reactions assembled in
Table 9, since it seems to be a better description
than dehydration, dehydrosulfurization or even
a-elimination. In contrast to structures that can
undergo P-elimination, the reactants in Table 9
have one common feature, namely, the absence of

P.B. VenutolMicroporous Materials 2 (1994) 297-411 323
Table 9
Olefin-forming dehydrocondensation reactions: substrates without b-hydrogen
Dehydrocondensation of simple methyl derivatives, CH,X
Methanol +ethylene + propylene + butenes (+ other products)
Dimethyl ether+ethylene + propylene + butenes (+ other products)
Methylal+light olelins + other products
Methyl formate+light olefins (+other products)
Methyhnercaptan+C, + C, olelk + methane (major)
ZSM-5: 370°C [5,37,207,208,246,247]; ZSM-5P:
300~600°C [1841;Erio, ZSM-11,ZSM-4, Mord:
370°C [S]; T, Chab, ZK-5: 340-538°C [248]; REX:
360-38O”C, ZnX: 360-390°C (ref. 1, p. 309); NaX:
260°C [2491”;SAPO-17, -34: 375450°C [250]
P-ZSM-5: 300-700°C [1841
HZSM-5: 371°C [207]
HZSM-5: 371°C [210]
NaX: 200-600°C (ref. 1, p. 314); HZSM-5: 288°C
[2081b;HZSM-5: 482°C [207]
Acetic acid-light olefins + CO2+ other products HZSM-5: 371°C [207,210]
Dehydrocondensation accompanying intra-zeolitic terramethyl ammonium cation decomposition
Tetramethyl ammonium cation (TMA)-+C,-C, olefins (+other products) TMA-NaY: 150-45O”C [2511;TMA-Offr:
85-425”C [252]
Dehydrocondensation involving more complex reactants without B-hydrogens
Benzyhnercaptan-ttrans-stilbene
Benzyhnercaptan + methyhnercaptan + trans-stilbene + styrene
a-Nitrotoluene+stilbene (+other products)
p-Methoxybenzylmercaptan+ trans-4,4’-dimethoxystilbene
Cinnamyhnercaptan+1,6-diphenylhexatriene
a-Mercaptomethylnaphthalene+ 1,2-di-a-naphthylethylene
p-Methoxybenzyhuercaptan + benzylmercaptan+ trans-stilbene + rrans-4,4’-
dimethoxystilbene + trans-4-methoxystilbene
NaX, 4A: 250°C [253]
NaX: 260°C [253]
5A, NaX: 220-250°C [1431
NaX: 250°C [253]
5A: 300°C [2531d
CaX: 300°C [253]
NaX: 250-300°C [253]
“1.6 mol-% of product was a mixture of C,-C, olefins, with butene the predominant product.
bSome CSz and Cs-Cl0 aromatics also formed.
“May involve Stevens rearrangement or ylide-type mechanism.
dAlmost certainly surface-catalyzed.
a hydrogen in the position b to the carbon atom
with the leaving group, Y. These reactants are
represented by structures 6a-6c below.
I/
H H H C H
la la
H-C-Y
Ig la
Ar- C-Y CH=CH-k-Y
Ii
I
H Pll’ Ii
->-p-p-Y
C H
/I
6a (w, 6c 66
For the methyl systems (6a), Y is -OH, -OCH,,
-SH, -COOH, and -N(CH,),@; for the benzyl
systems (6b), Y is -SH and also -NO,; for the
ally1 (cinnamyl) system (6c), Y is -SH. The neo-
pentyl configuration (6d) might also be expected
to show this reactivity pattern, provided that
1,Zmigration of an alkyl substituent does not
accompany or follow leaving of group Y. Although
a number of a-eliminations are well known in
classic organic chemistry [46], these usually require
strong base and the presence of a powerful
electron-withdrawing group, Y; the absence of a
0-H atom is not a strict requirement, and carbene
mechanisms are usually operative.
In discussing mechanism, the question must be
asked as to how the C=C bond is formed in these
dehydrocondensation reactions. Further, it should
not be presumed a priori, that the chemistry is
necessarily the same in systems where the leaving
group is -N(CH,),@, -SH, or -OH(-0-CH3).
However, even today, it is safe to say that this
issue has not yet been conclusively resolved [420].
For the intracrystalline tetramethylammonium
cation systems, an ylide-Stevens rearrangement
has been proposed [251,252,416]; for the benzyl
and cinnamyl mercaptan reactions, a carbene inser-
tion reaction was postulated [253], but the concur-
rent operation of radical processes in these sulfur-

324 P. B. Venutolkficroporous Materials 2 (1994) 297-411
containing systems renders final interpretation
uncertain. In these latter systems, e.g., the reaction
over a small-pore zeolite shown in Eq. 23, dehydro-
condensation must surely have occurred on the
external surface because of the bulkiness of both
reactants and products. However, the polar zeolite
surface must play some role in this reaction, since
a relatively inert alumina showed only a fraction
of the conversion of the zeolites in these systems.
CH2SH
4A
250-c -
“,_-,a
@ ,, (23
Most interest and effort, of course, have centered
on the commercially important [37] methanol-to-
hydrocarbons reaction. Much controversy has cen-
tered on the mechanism of the initial formation of
a C-C bond from two single carbon species
[37,420]. Referring once again to Fig. 3, these
initiation events might be occurring in and around
point A on the methanol-to-hydrocarbons reaction
path. As noted by Chang in a 1988 review on
mechanism [4201, “Virtually every possible
reactive Ci intermediate has been invoked to
explain the crucial step of initial C-C bond forma-
tion from methanol/DME”. Most of these species,
which include carbenes, carbeniurn ions, ylides and
free radicals, are concisely summarized in Fig. 11.
Still another aspect is whether ethylene itself is the
Fig. 11. Relationship of a variety of intermediates proposed
for the reactive one-carbon intermediate in methanol conversion
to hydrocarbons. Reproduced from ref. 420 (Char@, copyright
1988, ACS.
primary olefin produced from methanol
[29,36,37,185,420,421,423]. While recognizing that
this issue may still remain moot, we will argue
(perhaps simplistically) that in a reaction where
C1 species are combining, the combination of two
of them (to form ethylene) seems more likely than
the combination of three or more of them to form
C3 and higher olefins.
However, once ethylene is formed in a presuma-
bly slow step, much faster, well known reactions
take over, including repeated olefin methylations
to form higher olefins [29,36,185,421,423], olefin
oligomerization and cracking (i.e. the olefin
interconversion process described in Section 2.5
and Fig. 8) in what has been described as an
“autocatalytic” reaction pattern [36,37,185,424].
Of course, once substantial olefin concentrations
are established, the intermolecular hydrogen-
transfer processes discussed in detail earlier come
into play, particularly at higher conversions (see
Fig. 3) leading to generation of aromatics and
paraffins. Recent mechanistic studies [ 1851provide
evidence that most of the ethylene ultimately
formed (under most reaction conditions) derives
from the reequilibration (interconversion) of
higher olefins. Perhaps the fate of the primary
ethylene product may be masked by later sequen-
tial products because of a sorption or diffusion
disguise [37,421].
2.9. Reactions involvingpossible carbanion-type
species (Table 10)
In classic organic chemistry, any organic species
containing a C-H bond (7a) can function as an
acid, provided a suitable base proton acceptor (B:)
is available (Eq. 24).
R&--H + s: Z= RIG
e + BH
c
(24)
70 7b
In simple alkyl-substituted aliphatic systems, the
observed stability of the carbanion (7h) is the
reverse of the sequence for carbocations, i.e. :
CHF > RCHF > R&He > R,Ce
In hydrocarbons, pK, values for CH,, &H,CH,,

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