A kinetic study is reported for the homologation of methanol to give ethanol. Cobalt carbonyl and iodine or cobalt iodide were used as catalyst systems with tri-n-butylphosphine as ligand. The reaction was investigated in 1,4-dioxane in a batch unit at (CO + H2) pressures between 3 and 15 MPa, with H2/CO ratios in the range of 0.33 to 3. The temperature was varied over the range of 150 to 210°C. The reaction rate was found to be first order with respect to methanol and cobalt concentrations and CO partial pressure. A rate expression is derived. A reaction mechanism is proposed in which the rate-determining step is suggested to be the reaction of methanol with a CO-rich cobalt complex existing in low concentration with regard to cobalt used.

1. 542 Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 542-548
maximum surface area and shows the largest conversion
in this series. The order of the promotion effect (Cs> Rb
> K> Na> Li) observed in this study has been the reverse
tendency against the order in ionization potential of these
cations (Lee et al., 1963). This means that the electron­
donating character of alkali plays an important role in
promoting effect as reported by Dry et al. (1969), Ozaki
et al. (1971), and Aika et al. (1973). On the other hand,
the evidence shown in Table III may be explained by the
hard and soft acids and bases concept. Even though N02-
is a "border line base", nitrobenzene would interacts with
"hard acids". The degree of interaction between nitro­
benzene and hard acid may be inversely proportional to
the hardness of acid. The order of hardness of alkali
cations is Li> Na> K> Rb> Cs which is in reverse order
for the promoting effect found in this work. Therefore,
it is considered that the catalysts having high activity, such
as Fe/Cs/Al and Fe/Rb/Al, strongly interact with nitro­
benzene due to the hard acid character of these cations
(Ho, 1977).
As mentioned above, through our previous work (Tak­
emura et al., 1981), it seemed that the catalyst, available
for hydrogenolysis of C-C bond with Costeam process, is
responsible not only for promoting the WGSR but also for
promoting the subsequent hydrogenolysis, and alumina­
supported molybdenum oxide catalyst was found to be
most effective. However, in the present work, alumina­
supported iron oxide catalyst showed much higher activity
for reduction of nitrobenzene than that of alumina-sup­
ported molybdenum oxide catalyst. Therefore, it is con­
sidered that the catalyst effective for the reduction of nitro
compound with Costeam process is responsible only for
promoting the WGSR. This may be due to the high re-
activity of nitro compounds toward hydrogen.
Acknowledgment
The authors express their gratitude to Dr. A. Nakamura,
Akita University, for helpful discussions and advice.
Registry No. Fe, 7439-88-5; Mo03, 1313-27-5; CoO, 1307-96-6;
W03, 1314-35-8; CO, 630-08-0; Al203, 1344-28-1; K2C03, 584-08-7;
Li+, 17341-24-1; Na+, 17341-25-2; K+, 24203-36-9; Rb+, 22537-38-8;
Cs+, 18459-37-5; H20, 7732-18-5; nitrobenzene, 98-95-3; aniline,
62-53-3.
Literature Cited
Aika, K.; Yamaguchi, J.; Ozaki, A. Chem. Lett. 1973, 161.
Amenomiya, Y.; Pleizier, G. J. Cata/. 1982, 76, 345.
Anderson, R. B. "Catalysis", Emmett, P.H., Ed.; Reinhold: New York, 1956;
pp 29-256.
Appell, H. R.; Wender, I. Am. Chem. Soc.. Div. Fuel Chem.. Prepr. 1968,
12(3), 220.
Appell, H. R.; Wender, !.; Miller, R. D. Chem. Ind. (London) 1969, 1703.
Appell, H. R.; Wender, I.; Miller, R. D. Am. Chem. Soc., Div. Fuel Chem..
Prepr. 1969, 13(4), 39.
Appell, H. R.; Pantages, P. "Thermal Uses and Properties of Carbohydrates
and Lignlns"; Academic Press: San Francisco, 1976; p 127.
Appell, H. R.; Moroni, E. C.; Miller, R. D. Energy Source 1977, 3(2), 163.
Chesnokova, R. V.; Gorbunov, A. I.; Lachinov, S. S.; Maravskaya, G. K. Ki­
net. Kats/. 1970, 11, 1486.
Dry, M. E.; Shingles, T.; Boshoff, L. J.; Oosthuijzen, G. J. J. Cata/. 1989, 15,
190.
Hardy, W. B.; Bennett, R. P. Tetrahedron Lett. 1967, (11), 961.
Ho, T-L. "Hard and Soft Acids and Bases Principles in Organic Chemistry";
Academic Press: New York, 1977; pp 5-6.
Krupay, B. W.; Amenomiya, Y. J. Cata/. 1981, 76, 345.
Lee, E. H.; Holmes, L. H.J. Phys. Chem. 1963, 67, 947.
Morikawa, Y.; Ozaki, A. Nippon Kagaku Kaishi 1972, (6), 1023.
Ozaki, A.; Aika, K.; Hori, H. Bull. Chem. Soc. Jpn. 1971, 44, 3216.
Royen, P.; Erhard, F. Erdoef Kohle 1953, 6, 195.
Takemura, Y.; Itoh, H.; Ouchi, K. Ind. Eng. Chem. Fundam. 1981, 20, 94.
Umemura, S. Shokubai 1982, 4, 223.
Received for review March 31, 1983
Accepted August 9, 1983
Methanol to Ethanol by Homologatlon: Kinetic Approach
Patrick B. Fran9olsse and Fernand C. Thyrlon*
Jnstitut de Genie Chimique, Universite Catholique de Louvain, Voie Minckefers, 1, B-1348 Louvain-la-Neuve, Belgium
A kinetic study is reported for the homologation of methanol to give ethanol. Cobalt carbonyl and iodine or cobalt
iodide were used as catalyst systems with tri-n-butylphosphine as ligand. The reaction was investigated in
1,4-dioxane in a batch unit at (CO+ H2) pressures between 3 and 15 MPa, with H2/CO ratios in the range of 0.33
to 3. The temperature was varied over the range of 150 to 210 °C. The reaction rate was found to be first order
with respect to methanol and cobalt concentrations and CO partial pressure. A rate expression is derived. A
reaction mechanism is proposed in which the rate-determining step is suggested to be the reaction of methanol
with a CO-rich cobalt complex existing in low concentration with regard to cobalt used.
Introduction
The cobalt-catalyzed homologation of methanol to eth­
anol has been the subject of many recent papers and
patents (Bahrmann and Cornils, 1980, 1982; Ball and
Stewart, 1981; Barlow, 1981; Cornils et al., 1982a,b; De­
luzarche et al., 1978, 1979; Doyle, 1981a,b,c; Dumas et al.,
1980; Fiato, 1980, 198la,b; Gane and Stewart, 1979a,b,
1980a,b; Gauthier-Lafaye and Perron, 1981; Isogai et al.,
1980, 1982; Koermer and Slinkard, 1978; Pretzer and
Kobylinski, 1980; Pretzer et al., 1979, 1980a,b,c; Slinkard
and Baylis, 1979; Sugi et al., 1981; Taylor, 1978; Walker,
1981). However, very few authors have dealt with sys­
tematic kinetic measurements.
0196-432118311222-0542$01.50/0
The purpose of this paper is to investigate the influence
of the main reaction parameters, to derive reaction orders,
rate constants, and activation energy, and to postulate a
mechanism for the methanol homologation.
Though the overall equation is quite simple
catalyst
CH30H+CO+2H2 C2H50H+H20 (1)
the mechanism of this reaction appears to be much more
complex (Slocum, 1980). This is particularly true if iodides
are used as promoters and phosphines as ligands to sta­
bilize the cobalt catalytic species (Berty et al., 1956; Mi­
zoroki and Nakayama, 1964; Slaugh, 1976; Pretzer and
Kobylinski, 1980; Bahrmann and Cornils, 1982).
© 1983 American Chemical Society

2. Nevertheless, the three-component catalyst, cobalt­
iodine-phosphine, first described in a Shell patent (Slaugh,
1976) seemed quite appropriate for kinetic study. This was
undertaken under homogeneous liquid phase conditions
with 1,4-dioxane as solvent, since it has been reported that
it favors the selective conversion of methanol toward
ethanol (Koermer and Slinkard, 1978; Gane and Stewart,
1979b).
The interest in the methanol homologation to produce
ethanol is based on the large difference in carbon value
between carbon monoxide and carbon in ethylene which
can be derived from ethanol by dehydration. The value
of the carbon contained in ethylene is currently assumed
to be 2-3 times that of the carbon contained in CO.
Experimental Section
Materials. Anhydrous Col2 (Ventron Co), dicobalt
octacarbonyl (Strem Chemicals), iodine (resublimed,
Aldrich Europe), tri-n-butylphosphine (98%, Aldrich Eu­
rope), carbon monoxide (99.7 %), hydrogen (99.99 %),
methanol (99.9 %), and 1,4-dioxane (99.5 %) were pur­
chased from commercial sources and used without further
purification.
Apparatus and Procedure. Batch reaction studies
were carried out in a 600-mL 316 stainless steel Parr re­
actor. Cobalt iodide or carbonyl and tributylphosphine
were weighed under nitrogen and introduced in the reactor
containing the solvent and methanol. When Co2(CO)s was
used as cobalt source, the promotor was introduced as
iodine.
The autoclave was purged of air, and finally CO and H2
were introduced up to the desired pressure. The reaction
mixture was heated to 195 °C over a period of about 20
min, then the stirring (565 rpm) was started.
In most experiments, regular additions of gas were made
during the course of the reaction to allow a maximum
pressure drop of 1 MPa. The extent of the reaction was
determined either by cumulative pressure decrease or by
liquid sample analysis.
Analysis. Liquid and gaseous organic products were
analyzed by gas chromatography using an Intersmat 112
GC equipped with flame ionization detector; a column, 7
ft x 1/8 in. Chromosorb 101, heated from 60 to 150 °C at
20 °C/min, was used.
The concentrations of reactant or products were de­
termined by using the internal standard method with 2-
propanol.
Permanent gas analysis (H2, CO, CH4) was performed
on an Intersmat 120 equipped with a thermal conductivity
detector and a 6 ft X 1/8 in. column of 13X molecular sieve
(carrier gas: H2) or 5A molecular sieve (carrier gas: argon).
The output signal was fed to a recording data Shimadzu
ICR-1 microprocessor.
All concentrations reported in this work are given at
reaction conditions. The determination of these concen­
trations required the knowledge of the liquid and gas phase
volumes inside the autoclave. The liquid volumes of the
mixtures were determined by the Amagat rule using the
Rackett equation (Rackett, 1970) and the Chueh-Prausnitz
relation (Chueh and Prausnitz, 1967) to predict the in­
fluences of temperature and pressure on the volume of
pure components. Average derivations are reported to be
1.5% for alcohols and 0.7% for other organic compounds
(Pan and Maddox, 1981).
The amounts of reactants and products distributed
between the gaseous and the liquid phases at reaction
temperature were derived from chromatographic analysis.
Results
The reaction conditions are listed in Table I.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 543
Table I. Reaction Conditions
run 1,4-dioxane, T, P, H,/ MeOH, Col,,a
no. mL oc MPa co mol mmol
1 225 195 var. 2 2.224 36
2 75 195 13.8 var. 1.854 18.5 b
3 var. 195 12.5 2 var. 11.8
4 65-82 195 12.5 2 0.742 var.
5 75 var. 12.5 2 0.742 12
a This catalyst as well as Co,(C0)8 (run 2) was used in
conjunction with tribut
[
lphosphine (�u3�) in a molar
ratio Bu3P/Co of 3.6. Co,(C0)8 + 10dme (I/Co= 2).
8
•
6 "
4 -
2 "
o L
17 15 JO
press3re (MP, J
Figure 1. Effect ofpressure on gas consumption rate (Table I, run
no. 1).
Effect of Pressure. The effect of pressure on the rate
of gas consumption was studied by using an initial pressure
of synthesis gas (1:2 CO/H2) of 17 MPa: the pressure was
then allowed to decrease by the reaction of gas with
methanol. The free space in the reactor was kept to a
minimum in order to enhance the effect of gas consump­
tion on pressure and to reduce methanol conversion to a
maximum value of 15% at the end of the run.
The rate of gaseous reactants consumption in a run
carried out at 195 °C is plotted vs. total pressure in Figure
1. It shows a maximum which could be explained in this
manner. The left part of this curve represents the active
complex formation, during which the homologation already
proceeds with catalyst formed.
.
This induction period of about 10 to 20 mm was ob­
served in all the experiments using Col2 and appeared also
when the temperature was raised at 195 °C after cooling
the reaction medium to room temperature. This cycle did
not influence the catalyst performances. The induction
period was absent when Co2(C0)8 was chose� as �tarting
material. All the subsequent results reported m this paper
were recorded after this preliminary stage.
The right side of the curve corresponds to methanol
conversion and shows a first-order dependence in pressure.
The slope allowed us to calculate a rate constant kP = 1.39
x 10-3 mol of gas/(L min MPa) under the caption con-
ditions. .
At 3 MPa synthesis gas partial pressure, the reaction did
not seem to proceed further. This could be explain�d by
a possible catalyst dissociation at low pressures while re­
generation of catalyst occurs at higher CO/H2 partial
pressures.
The first-order dependence in pressure agrees well with
formerly recorded results (Beuther et al., 1980) where a
first-order dependence was reported with respect to total
pressure during the first 20% methanol conversion with
a 1:1 CO/H2 synthesis gas.

3. 544 Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
::;
�
l
100
1
----,---------- 15
I
I
.,;,, 50f-----++--+-<�·
I
��-�+-·--------
I /
,:'
"
'
3
Pea IHPa)
Figure 2. Dependence ofgas consumption and methanol conversion
rates on CO partial pressure (Table I, no. 2).
Although mass transfer between gas and the liquid so­
lution was surely not rate limiting due to low gaseous
absorption rate, an experiment was planned in order to
check this assumption. Modifying the stirring rate from
565 to 910 and back to 565 rpm during the same experi­
ment did not alter the normal course of gaseous absorption,
so we concluded that the first order in total pressure was
truly representative of the chemical reaction.
Dependence of the Rate on H2:CO Ratios. The first
order observed with respect to the total pressure should
reflect a rate proportional to Pco or PH or to a linear
combination of both. Experiments were
2
therefore con­
ducted at various initial H2:CO ratios, over the range of
0.33 to 3.
In that range, CO partial pressures were revealed to be
high enough to stabilize the catalytic complex, whereas H2
partial pressure allowed ethanol yields of at least 35% in
4 h.
During the course of the reactions, a stoichiometric 2:1
H2/CO synthesis gas was fed to the reactor, to keep total
pressure constant, while regular analysis of gas samples
from the autoclave allowed us to compensate any devia­
tions of the initial H2/CO ratio.
Figure 2 shows the effect of H2:CO ratio on reaction rate.
The graph clearly shows a linear dependence between the
initial rate of methanol conversion and the CO partial
pressure. Increasing Pco not only increases methanol
conversion rate but also leads to higher selectivities in
acetaldehyde, 1,1-dimethoxyethane, and methyl acetate,
at the expense of ethanol.
CH30H + CO + H2 - CH3CHO + H20 (2)
CH3CHO + 2 CH30H ;=0 CH3CH(OCH3)2 + H20 (3)
2CH30H +CO - CH3COOCH3 + H20 (4)
However, as far as acetaldehyde is concerned, it is gen­
erally considered as an intermediate, leading to ethanol
through a further hydrogenation step (Ziesecke, 1952;
Albanesi, 1973; Koermer and Slinkard, 1978).
The initial rates of synthesis gas consumption have also
been plotted in Figure 2. They depart from the linear law
at high Pc0, where yields in methyl acetate and 1,1-di­
methoxyethane are quite substantial. As the conversion
of methanol to these products requires much fewer moles
of H2 and CO per mole of methanol (respectively 1/2 and
2
/3) than its conversion to ethanol, this can account for the
discrepancy between the two graphs of Figure 2 at high
CO partial pressures.
40i-
-----�---�
10
cHeDH . mo/ IL
Figure 3. Dependence of gas consumption rate on initial methanol
concentration (Table I, no. 3).
Methanol conversion rates determined under running
conditions departed also from the linear law at high Pc0,
though this phenomenon was less important than with gas
consumption rate. Consequently, the first order observed
with respect to total pressure can be explained by a first
order with respect to CO partial pressure, so far as the
H2/CO ratio is not much lower than 1.
Though the H2 partial pressure does not affect the rate
of methanol conversion, it clearly favored the selectivity
toward ethanol. The hydrogenation steps therefore occur
after the rate-limiting step.
Dependence of Rate on Methanol Concentration.
Experiments conducted with methanol initial concentra­
tions, C°MeOH• ranging from 1.5 to 10 mol/L gave the results
displayed in Figure 3. Even if methanol concentrations
were quite high in some experiments to derive kinetic
results, the data suggest a linear dependence of gas con­
sumption rate with methanol concentration.
As emphasized in the preceding point, the product
distribution should remain fairly the same for the whole
set of experiments, so that neither the gas consumption
rate nor the methanol conversion rate would be affected
during the course of the reaction. This was effectively the
case. A typical product distribution is shown in Table II.
In these experiments, 2.6 mol of gas were consumed in
a H2:CO molar ratio of 2.0 to convert one mole of methanol.
An initial rate of methanol conversion can thus be deduced
as
0 _ _!_Q _ Q Qr MeOH -
2.6
r g - k 1C MeOH (5)
with k01 equal to 1.46 X 10-
3
min-1• Chromatographic
analysis of methanol concentrations during the course of
the reactions allowed us to confirm this result.
Figure 4 shows a kinetic treatment derived from the
expression
rMeOH =
k1CMeOH (6)
and based on methanol conversion with time. The rate
constant, k1, was found to be 1.41 x 10-3 min-1• The fact
that initial and running rate constants are similar is an
indication that the reaction products do not disturb the
course of the reaction.
Dependence of Rate on Catalyst Concentration. In
order to derive the effects of catalyst concentration, the
rate of methanol conversion as well as the rate of gas
consumption were determined under conditions where
cobalt to methanol molar ratio extended over the range
of 0.0047 to 0.032, while the catalyst composition in cobalt,
iodine, and tri-n-butylphosphine was kept constant (molar
ratios Co:I:P = 1:2:3.6).

4. I --------------- -·-
.:: 0,8 --- - ,_
----- - -�--
0,6 ---- -----
O/, - --
time(h)
Figure 4. Dependence of methanol conversion with time(Table I,
no. 3). Values of CoMeOH(at 195 °C) and slope(= k
1
). respectively:
(&) 9.97 mol/L, 1.23 X 10-3 min-1; (e) 3.79 mol/L, 1.39 X 10-3 min-1;
(*) 1.50 mol/L, 1.54 x 10-3 min-1•
��
'
�
Q
Jo----
"'
c;
S I
�20 r--------1----1-------1
I
10 f-------+--- _ ,________J
o �----�----�
0 50 100 150 200
catalyst concentration,mmol/L
Figure 5. Dependence of gas consumption rate on cobalt concen­
tration(Table I, no. 4).
As expected, increasing the cobalt concentration in­
creased the reaction rate, but it slightly decreased the
ethanol selectivity. Figure 5 shows a linear relationship
between initial gas consumption rates and catalyst con­
centration. Initial methanol conversion rates can be de­
rived from
0 _ __!_0 - 0 0
r MeOH -
2.6
r g - k 2C MeOHCcat. (7)
k0
2 was found to be 1.64 X 10-2 L mo1-1 min-1.
The kinetic treatment of methanol conversion with time
is presented in Figure 6, from which a value of k1 can be
derived for every catalyst concentration. Assuming that
k1 =
k2Ccat. (8)
a 0.99 slope was found between log k1 and log Ccat. and
confirmed the first-order dependence with respect to
catalyst concentration, whereas k2 was found to be equal
to 1.53 X 10-2 L mo1-1, in good agreement with the initial
rate determination, k0
2•
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 545
0 -----·-----
0 2 3 5 6 8
ti me (h)
. '
Figure 6. Dependence of methanol conversion with time(Table I,
no. 4). Values of Ccat. (195 °C) and slope(= k
1
), respectively: (&)
168 mmol/L, 2.58 x 10-3 min-1; (e) 85 mmol/L, 1.38 x 10-3 min-1;
(*) 24.9 mmol/L, 0.397 X 10-3 min-1•
- 2,8 ----------- ------:
- 3,0 .
.:: - 3,2 -----'.--.-------,
-J.4 I
_
§i.=-4807R __L
- 3,6 f---------+-----___J
,.
- 38 i
. II
i
-4,0'
I
-4,2 1
•
I •
- 44 ' 17x10'
' 2 2,1 2,2 2.3 2,1. IK-1!
Figure 7. Arrhenius plot(Table I, no. 5).
The linear dependence between the methanol conversion
rate and the catalyst concentration confirmed the absence
of mass transfer limitation between gaseous and liquid
phases.
The Influence of Temperature. Experiments were
conducted at five different temperatures ranging from 150
to 210 °C. This temperature interval was chosen to fulfil
the conditions of catalytic complex formation (Pino et al.,
1977), as well as a high hydrogenating activity (Beuther
et al., 1980) and low yields in byproducts resulting from
hydrogenation and cracking of methanol. These reactions
become important at temperatures above 215-220 °C
(Mizoroki and Nakayama, 1964; Bahrmann and Cornils,
1980). An activation energy of 40 kJ mo1-1 was calculated
from the Arrhenius graph (Figure 7).
Rate Expression and Products Distribution. The
following rate expression can be derived from the above
results
dCMeOH
rMeOH = -
dt
= k3PcoCMeOHCcat. (9)
with k3 = 4.2 :I: 0.5 X 10-3 L mo1-1 MPa-1 at 195 °C (95%
confidence interval).

5. 546 Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table II. Comparison ofMethanol Homologation Results
reference
pressure,MPa
temperature, °C
H./CO molar ratio
P�0,MPa
solvent
a
34
190
0.9
15 .9
none
b c this work
20 31 - 18 13.5
190 200 195
2 2 2
5.4 9.5 - 5.2 3.6
none benzened 1,4-dioxane e
cobalt source Co(acac)2 Co(OAc),·4H,O Col, Co,(CO),
cobalt amount, Atg/L
promotor
I/Co molar ratio
ligand
P/Co molar ratio
reaction time, h
MeOH conversion, %
molar selectivities, %
carbon dioxide
methane
dimethyl ether
methyl ethyl ether
acetaldehy de
1,1-dimethoxyethane
methyl acetate
ethyl acetate
ethanol
l·propanol
1-butanol
0.051
none
none
2
31
4.3
6.9
3.1
1.5
22.4
12.1
37.7
2.8
0.4
0.3 0.11 0.185
L J-(Col,) I,
1 2 2.1
Ph,P PC6P n-Bu3P
1.7 5 3 3.6
2 2 4.33
45 27.8 52.2
} 15.5
? 1.0
4.5 6.8
? ? 0.7
? ? 0.8
4.4
} 8.9
1.3
19.7 3.7
}14.6
0.6 3.4
0.7
39.5 80.7 74.4
}4.0
1.3 2.5
0.2
rate constant, k, l 4.26 x 10-3 3.44 x 10"3 3.36 x 10"3 3.87 x 10·3
a Koermer and Slinkard (1978). b Gane and Stewart (1980) (comparison test; by use of diphosphines, these authors
c!aim ethanol selectivity of 65%). csugi et al. (1981). d 2 vol/vo!MeOH. "0.33 vol/volMeOH. fLmo1·1 min-1
MPa·1•
In a typical experiment, where 30 mL of methanol was
diluted in 75 mL of dioxane, the volume increase, at re­
action temperature, was estimated to be about 12% at a
methanol conversion degree of 50%. When neglecting this
liquid volume variation during the course of the reaction,
eq 9 can be integrated into eq 10
XMeOH = 1 - exp(-k3PcoCcat.e) (10)
This relation was used to compare some literature results
with ours, though the volume increase amounts to about
25% after 50% methanol conversion, when the reaction
is conducted without the addition of an auxiliary solvent
(Table II).
As publications and patents commonly report the
methanol conversion degree achieved after a given reaction
time, the rate constants k3 were calculated from eq 10
taking into account the temperature influence, whereas Pco
and Ccat. values were determined by estimating solution
partial pressures and solution volumes under reported
reaction conditions.
The rate constants k3 were found to be close to one
another whatever the ethanol selectivity and the nature
of the catalytic system. The ethanol selectivity (75%)
realized in this work is among the best ones in the field
even if it was performed at lower pressures than the other
homologation reports.
Yields in ethanol and byproducts, along with methanol
conversion, are presented vs. reaction time in Figure 8.
Methanol conversion can be achieved up to completion
(97.6% at the end of the experiment). When ethanol
concentration increases in the reaction medium, its con­
version in 1-propanol becomes significant in agreement
with free energy calculations, though this reaction was
slower than the methanol homologation (Berty et al., 1956).
Yields in acetaldehyde, acetals, acetates, and methane
remain fairly constant after an initial build-up period.
However, methyl acetate is gradually converted into ethyl
acetate.
-t;
100
� 75
----- - - -�-------
.. ,--- -
time (hours)
Figure 8. Evolution of methanol and product yields with time
(Table II, 4th column): (0) methanol;(*) ethanol; (.6.) acetaldehyde
and 1,1-dimethoxyethane; (D) methyl and ethyl acetates; (•) 1-
propanol; (e) methane.
Discussion
The homologation mechanism has recently been exam­
ined by several authors (Slocum, 1980; Pretzer and Ko­
bylinski, 1980; Bahrmann and Cornils, 1982). Although
the presentation appeared to be somewhat different, all
the authors agree with this general reaction scheme: (step
1) formation of the methylcobalt bond; (step 2) migration
of the methyl group to a carbonyl group followed by a CO
addition on catalyst; (step 3) reduction of the acylcobalt
intermediate to acetaldehyde; (step 4) reduction of acet­
aldehyde to ethanol.
The experimental rate law described in the preceding
section implies the intervention of methanol and cobalt

6. concentrations and CO partial pressure; this is consistent
with step 2 being the rate-limiting step. However, in the
hydroformylation reaction, which proceeds through steps
similar to steps 2 and 3, the alkyl to acyl cobalt conversion
is known to be very fast (Whyman, 1974; Van Boven et al.,
1975; Alemdaroglu et al., 1976). Moreover, the hydro­
formylation reaction rate can be estimated to be more than
20 times higher than the homologation rate under similar
operating conditions: this prompted us to reject step 2 as
being the rate-limiting step.
Some authors have postulated that the formation of the
alkyl cobalt bond in hydroformylation was rate deter­
mining when less reactive olefins were used (Whyman,
1974). Alcohols which are certainly less reactive than
olefins in the presence of homogeneous catalysts can be
suspected to react more slowly with cobalt complex to form
an alkyl metal bond.
This was demonstrated in a comparison of synthesis gas
consumption rates in the case of propene hydroformylation
and 2-propanol homologation where step 1 was proposed
to be rate limiting in the homologation of higher alcohols
(Hunf, 1978).
In the case of methanol, the nature of step 1 could be
somewhat different (Slocum, 1980). This step is the least
understood one: as many as nine different routes were
recently considered (Bahrmann and Cornils, 1982).
Whatever the kind of methanol reaction with cobalt com­
plex, we have assumed it to be the slowest step in the
reaction scheme.
This is in agreement with an order of one with respect
to methanol and catalyst concentrations. With regard to
this last concentration, it is thought that all the cobalt
present does not appear under active form; the relative
proportion of this latter could be very low (Pregaglia et
al., 1973; Forster, 1982). Taking into account the presence
of promotors and ligands, a considerable number of cobalt
complexes could be formed (Bahrmann and Cornils, 1982).
However, the first order with respect to cobalt concen­
tration ensures the existence of an equilibrium in which
the active species concentration is proportional to that of
the cobalt used.
The influence of CO partial pressure would intervene
in this equilibrium step and should favor the formation
of active catalyst. This leads us to assume that the active
form is a CO rich complex.
Some additional evidence about this positive influence
of carbon monoxide could be found in the absence of in­
duction period when starting with the CO-rich Co2(C0)8
catalyst as well as in the vanishing of the reaction rate
when lowering CO partial pressure down to 1 MPa (Figure
1).
Methanol, iodides, and phosphines are known dispro­
portionation catalysts for cobalt carbonyl: this reaction,
which results in the formation of Co(C0)4- anion, produces
carbon monoxide (Bortinger et al., 1978; Pretzer and Ko­
bylinski, 1980; Bahrmann et al., 1982).
In this respect, higher carbon monoxide pressures would
reduce these disproportionation reactions and favor co­
valent cobalt species. We suggest therefore that the first
order with respect to carbon monoxide is the result of
higher concentration of active catalyst, which is assumed
to be under covalent form.
Thus anionic derivatives of cobalt carbonyl such as
Co(C0)4- would not be active for homologation, although
this latter species has been detected in the reaction me­
dium by some authors (Pretzer and Kobylinski, 1980).
Nomenclature
MeOH =methanol
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 547
Co(acac)2 =cobalt(II) acetylacetonate
Co(0Ac)2·4H20 =cobalt(II) acetate tetrahydrate
Ph3P =triphenylphosphine
n-Bu3P =tri-n-butylphosphine
PC6P =1,6-bis(diphenylphosphino)hexane
Pco =carbon monoxide partial pressure, MPa
P/j-2 =hydrogen partial pressure, MPa
C MeOH =initial methanol concentration, mol/L
CMeOH =current methanol concentration, mol/L
Ccat. =catalyst concentration, Atg Co/L
k
8
=rate constant, �ol L-1 �in-1 MPa-1
k 1 =rate constant m (5), mm-1
k
b
=rate constant in (6), min-1
k 2 =rate constant in (7), L moi-1 min-1
k2 =rate constant in (8), L mo1-1 min-1
k3 =rate constant in (9), L moi-1 min-1 MPa-1
r0g =initial gas consumption rate, mol L-1 min-1
r0MeOH = initial methanol conversion rate, mol L-1 min-1
rMeOH =current methanol conversion rate, mol L-1 min-1
X, XMeOH =methanol conversion (%) =(mol of methanol
converted)/(mol of methanol fed)
selectivity to product i (%) =(mol of methanol converted into
product i)/(total mol of methanol converted)
yield of product i (%) =(mol of methanol converted into
product i)/(total mol of methanol fed)
Greek Letters
6 =reaction time, min
Registry No. Methanol, 67-56-1; ethanol, 64-17-5; Col2,
15238-00-3; 12, 7553-56-2; Co2(C0)8, 10210-68-1; n-Bu3P, 998-40-3.
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Received for review January 21, 1982
Revised manuscript received May 6, 1983
Accepted June 10, 1983
The authors wish to thank SOLVAY S.A. for financial support.
PBF was granted a loan from the I.R.S.I.A. fund. Part of this
paper was presented at the "International Symposium on Catalytic
Reactions of one Carbon Molecules� held in Bruges, Belgium, June
1982.
Effect of Pretreatment on Dispersion and Structure of Silica- and
Alumina-Supported Pt Catalysts
Janos Sarkanyt and Richard D. Gonzalez•
Department of Chem istry, University of Rhode Island, Kingston, Rhode Island 02881
The dispersion and structure of silica- and alumina-supported Pt catalysts have been studied as a function of
pretreatment. Initial pretreatment In He resulted in Pt/Al203 catalysts having dispersions which were considerably
larger than those obtained when H2 was used. This is explained by considering the enhanced mobility of the Pt
surface complex in the presence of the He carrier gas. The choice of pretreatment was found to be less important
tor Pt/Al203 catalysts with lower Pt loadings. Pt dispersions for the Pt/Si02 catalysts did not depend on the choice
of pretreatment. When Pt/Si02 or Pt/Al203 catalysts were diluted with either pure alumina or silica prior to
pretreatment, extensive interparticle diffusion of Pt occurred. The lnterparticle transfer of Pt from silica to alumina
during pretreatment for a series of Pt/Si02:Al203 mixtures was studied by both selective chemisorption and infrared
spectroscopy. The extent to which CO was bridge-bonded to Pt on a series of Pt/Al203 catalysts was found to
depend on crystallite size only when the catalysts were pretreated in H2• This is explained in terms of possible
preferential crystallographic orientations. Surface water and the extent to which the catalysts are dried prior to
pretreatment play a prominent role in the surface diffusion of the resulting surface complexes.
Introduction
The start of the reduction process is a particularly
sensitive stage in the preparation of supported metal
catalysts. In particular, the dispersion of supported metal
catalysts prepared by the incipient wetness technique
appears to be particularly sensitive to variations in the
initial pretreatment. Because of the enormous industrial
importance associated with supported Pt catalysts in
catalytic reforming, these preparative variables have been
the subject of considerable study and a coherent picture
regarding the reduction process is beginning to emerge.
The preparative variables which have received the most
attention are: (1) the choice of Pt salts to be used in
connection with a particular support {Dorling et al., 1971;
Brunell et al., 1976); (2) the acidity of the support (An­
derson, 1975); (3) the extent to which the catalyst has been
dried prior to reduction (Dorling et al., 1971; Dorling and
Moss, 1967); (4) the decomposition of the surface complex
(Shchukarev et al., 1956; Dorling et al., 1971; Lieske et al.,
1983; Lietz, et al., 1983); (5) the interaction between the
surface complex and the support during the initial pre­
treatment (Sarkany and Gonzalez, 1982a; Lieske et al.,
t On leave from the Department of Organic Chemistry, Jozsef
Attila University, Szeged, Hungary.
0196-4321/83/1222-0548$01.50/0
1983, Lietz et al., 1983); (6) calcination and reduction
temperature (Jenkins, 1979); (7) the role played by anions
added to the catalyst during pretreatment (Aboul-Gheit,
1979); (8) porosity of the support (Dorling et al., 1971); (9)
the role played by H20 during the initial pretreatment
(Dorling et al., 1971); and (10) the role played by chloride
in the redispersion of Pt following high temperature
treatment in 02 (Lieske et al., 1983; Leitz et al., 1983).
In a previous paper (Sarkany and Gonzalez, 1982a), we
reported on the rather extensive differences in migration
of the surface complex formed as a result of the decom­
position of H2PtCl6 that occurred when the catalyst was
pretreated in He rather than H2 prior to reduction. In
particular, a new synthetic technique enabling the prep­
aration of highly dispersed supported Pt catalysts having
relatively high metal loadings was suggested. In this paper,
we report further on the aspects of this surface migration.
Experimental Section
The flow system which enables use of the reactor as
either a pulse microreactor or a single-pass reactor has been
described in detail elsewhere (Miura and Gonzalez, 1982).
In several experiments, an infrared cell also capable of
operating either as a pulse microreactor or a single-pass
differential reactor was used in place of the Pyrex micro­
reactor. Details regarding the design of this infrared cell
© 1983 American Chemical Society