This document describes the synthesis and catalytic testing of hierarchical Fe-, Cu-, and Co-beta zeolites for N2O decomposition. Two series of beta zeolites were prepared - a conventional microporous beta zeolite (Beta) and a micro-mesoporous beta zeolite (Beta/meso) prepared using a mesotemplate-free method. Both series were ion exchanged with Fe, Cu, and Co and tested as catalysts for N2O decomposition under various conditions. The Cu-Beta catalyst showed the highest activity for N2O decomposition in inert gas, while the Cu-Beta/meso catalyst had the highest reaction rate under conditions similar to nitric acid plant waste gases.

1. Hierarchical Fe-, Cu- and Co-Beta zeolites obtained
by mesotemplate-free method. Part I: Synthesis
and catalytic activity in N2O decomposition
M. Rutkowska ⇑
, Z. Piwowarska, E. Micek, L. Chmielarz
Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland
a r t i c l e i n f o
Article history:
Received 31 May 2014
Accepted 6 October 2014
Available online xxxx
Keywords:
Zeolite b
Hierarchical zeolites
N2O decomposition
a b s t r a c t
Two series of BEA zeolites (Beta and Beta/meso) have been prepared. A first series of the samples was
obtained by a conventional aging of parent zeolite gel, while the second series (Beta/meso) was prepared
by mesotemplate-free method. In this method Beta nanoparticles are aggregated under acidic conditions
with the formation of micro-mesoporous material. Both series (Beta and Beta/meso) were doped with Fe,
Cu and Co by ion-exchange method and tested as catalysts of N2O decomposition. The Cu-Beta catalyst
was found to be the most active in the process of N2O decomposition conducted in inert gas atmosphere.
However, in the process performed under conditions similar to those prevailing in waste gases emitted
from nitric acid plants (one of the main sources of N2O emission) higher reaction rate was found for
the Cu-Beta/meso catalyst.
Ó 2014 Elsevier Inc. All rights reserved.
1. Introduction
The emission of nitrous oxide (N2O) to the atmosphere is one of
the main environmental problem, contributing to the greenhouse
effect and destruction of the ozone layer. The regulations drafted
by European Council in 2009 assumed a decrease of greenhouse
gases emission, in the most developed countries, by 30% (with
regard to emission levels from 1990) till 2020 [1]. Therefore, there
is a need of intensive studies focused on optimization of the exist-
ing processes and the development of new technologies of N2O
emission abatement.
Nitrous oxide is one among six substances (CO2, CH4, N2O, HFCs,
PFCs, SF6) approved in the Kyoto Protocol as the most dangerous
greenhouse gases [2]. Moreover, N2O contributes to the ozone layer
depletion [3]. One of the most important anthropogenic source of
N2O emission is industrial production of nitric acid (about 1% of
all greenhouse gases emission). Among several options of N2O
emission abatement its direct catalytic decomposition in the tail
gas (about 523–773 K) is preferable from both application and
operation costs [4].
The concept of zeolites with the hierarchical pore structure
(containing both micro- and mesopores) was proposed to over-
come diffusion limitations characteristic for classical microporous
zeolites, which hinder the accessibility of active centers for bulky
molecules [5]. Development of a new type of materials combining
both advantages of zeolites (e.g. strong acidity, ion-exchange prop-
erties, hydrothermal stability) and mesoporous silica materials
(favorable diffusion rates) is important due to possible optimiza-
tion of a large number of catalytic processes [6].
The origin of mesoporosity in zeolites can be fundamentally dif-
ferent, what greatly extends the areas of the synthesis methods.
The most common methods are: (i) desilication [7], (ii) dealumina-
tion [8], (iii) recrystallization of amorphous material [9,10], (iv)
solid templating [11], (v) pillaring and delamination of layered
zeolites [12,13]. In the presented studies the novel way of the mes-
oporosity generation in zeolites, called ‘‘mesotemplate-free
method’’, was applied [14–17]. This method is based on the prep-
aration of zeolite nanoparticles, followed by their controlled aggre-
gation in acidic media, resulting in the formation of the
mesoporous interparticle structure. This method does not need
any templates for the generation of mesopores, making it very
attractive from the economic and environmental issues.
Zeolites exchanged with transition metals are known as active
catalysts of various chemical processes. MFI, BEA, and FAU zeolites
were widely studied in N2O decomposition e.g. [14,15,18]. Espe-
cially interesting catalytic properties were reported for the sam-
ples doped with Fe, Cu and Co. Liu et al. [19] studied the
catalytic performance of (Fe, Co, Cu)-BEA zeolites in N2O decompo-
sition. Moreover, (Fe, Cu)-BEA zeolites were reported to be active
http://dx.doi.org/10.1016/j.micromeso.2014.10.011
1387-1811/Ó 2014 Elsevier Inc. All rights reserved.
⇑ Corresponding author. Tel.: +48 126632096; fax: +48 126340515.
E-mail address: rutkowsm@chemia.uj.edu.pl (M. Rutkowska).
Microporous and Mesoporous Materials xxx (2014) xxx–xxx
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2. and selective catalysts of N2O reduction by CO [20]. The results of
catalytic tests over Fe-, Cu- and Co-exchanged Beta zeolites in the
processes of N2O decomposition are very promising and therefore,
in the presented work, were extended for Beta zeolites with the
hierarchical porous structure.
2. Experimental methods
2.1. Catalysts preparation
The synthesis gel of zeolite Beta was prepared using the proce-
dure described earlier [14]. Tetraethylammonium hydroxide (TEA-
OH, 35%, Sigma–Aldrich) was used as a structure-directing agent,
while fumed silica (Aerosil 200, Evonic) and NaAlO2 (Sigma–
Aldrich) as silica and aluminium sources, respectively. The result-
ing solution with the molar composition: SiO2: 0.024; Al2O3:
0.612; TEAOH: 0.200; HCl: 21 H2O was divided into two parts
which where hydrothermally treated in autoclaves at 423 K for
24 h and 8 days, respectively. The slurry after 24 h of aging (con-
taining nanoseeds of Beta zeolite) was acidified in a proportion
of 5 mL of concentrated HCl per 18 mL of the nanoseeds slurry.
Subsequently, the acidified slurry was hydrothermally treated at
423 K for 72 h, yielding micro-mesoporous Beta zeolite denoted
as Beta/meso. Conventional microporous Beta zeolite, denoted as
Beta, was obtained from the slurry aged for 8 days. After aging peri-
ods the autoclaves were quenched and the samples were filtered,
washed with distilled water, dried in ambient conditions and cal-
cined at 823 K for 6 h.
The negative charge of the zeolite framework, in the samples
prepared by this method, was compensated by sodium cations
which were replaced by protons in the next step of the catalysts
synthesis (exchange details presented in [14]).
The H-forms of the obtained samples were modified with Fe, Cu
and Co by ion-exchange method. Transition metals were intro-
duced to the zeolite samples by stirring with 0.06 M solutions of
FeSO4Á7H2O, Cu(CH3COO)2Á4H2O or Co(CH3COO)2Á4H2O (Sigma–
Aldrich) for 6 h at 358 K (in case of iron salt) and at 353 K (in case
of copper and cobalt salts). In each ion-exchange procedure 250 mL
of a solution of transition metal per 2 g of the sample was used.
Iron was deposited in anaerobic atmosphere to avoid oxidation
of Fe2+
to Fe3+
. Then the samples were filtered, washed with dis-
tilled water, dried in ambient conditions and finally calcined at
823 K for 6 h. The codes of the catalysts are given in Table 1.
2.2. Catalysts characterization
The specific surface area (SBET) area of the samples was deter-
mined by N2 sorption at 77 K using a 3Flex v1.00 (Micromeritics)
automated gas adsorption system. Prior to the analysis, the samples
were degassed under vacuum at 623 K for 24 h. The specific surface
area (SBET) of the samples was determined using BET (Braunauer–
Emmett–Teller) model according to Rouquerol recommendations
[21]. The micropore volume (at p/p0 = 0.98) and specific surface area
of micropores were calculated using the Harkins and Jura model (t-
plot analysis). The pore size distributions were determined from the
adsorption branch of nitrogen isotherm by applying density func-
tional theory (DFT). For calculations the method assuming nitrogen
adsorption in cylindrical pores was used.
The X-ray diffraction (XRD) patterns of the samples were
recorded using a Bruker D2 Phaser diffractometer. The measure-
ments were performed in the 2 theta range of 5–50° with a step
of 0.02°.
Thermogravimetric measurements were performed using a
TGA/SDTA851e
Mettler Toledo instrument. The samples were
heated in a flow of synthetic air (80 mL/min) with the ramping of
10 K/min, in the temperature range of 303–1073 K.
IR measurements were performed using a Nicolet 6700 FT-IR
spectrometer (Thermo Scientific) equipped with DRIFT (diffuse
reflectance infrared Fourier transform) accessory and DTGS detec-
tor. The dried samples were grounded with dried potassium bro-
mide powder (4 wt.%). The measurements were carried out in the
wavenumber range of 400–4000 cmÀ1
with a resolution of 2 cmÀ1
.
The transition metals content, as well as the Si/Al ratio in the
samples, were analyzed using a mass spectrometer with induc-
tively coupled plasma (ICP-MS, ELAN 6100 Perkin Elmer).
Coordination and aggregation of transition metal species intro-
duced into the obtained zeolitic materials were studied by UV–vis-
DR spectroscopy. The measurements were performed using an
Evolution 600 (Thermo) spectrophotometer in the range of 200–
900 nm with a resolution of 2 nm.
Surface acidity (concentration and strength of acid sites) of the
samples was studied by temperature-programmed desorption of
ammonia (NH3-TPD). The measurements were performed in a flow
microreactor system equipped with QMS detector (VG Quartz).
Prior to ammonia sorption, a sample was outgassed in a flow of
pure helium at 688 K for 30 min. Subsequently, microreactor was
cooled to 343 K and the sample was saturated in a flow of gas
Table 1
Textural properties of the samples determined from N2-sorption measurements at 77 K and the crystal sizes obtained using Schererr’s equation.
Sample code SBET
(m2
gÀ1
)
External surface area
(m2
gÀ1
)
Micropore area
(m2
gÀ1
)
Total pore volume
(p/p0 = 0.98) (cm3
gÀ1
)
Micropore volume
(cm3
gÀ1
)
Meso + macropore volume
(cm3
gÀ1
)
dhkl
(nm)
H-Beta 710 89 622 0.433 0.242 0.191 19
H-Beta/meso 745 368 377 1.437 0.159 1.278 25
Fe-Beta 720 95 625 0.446 0.244 0.202 18
Fe-Beta/meso 551 273 278 1.013 0.116 0.897 26
Cu-Beta 566 78 488 0.340 0.189 0.151 16
Cu-Beta/meso 460 237 223 0.906 0.093 0.813 24
Co-Beta 748 106 642 0.480 0.253 0.227 20
Co-Beta/meso 512 261 251 1.064 0.105 0.959 24
Table 2
Conditions of N2O decomposition.
Inlet composition Total flow (ml minÀ1
) w= _nN2 O (g h molÀ1
) CN2O (ppm) CO2
(ppm) CNO (ppm) CH2O (ppm)
N2O 50 746 1000 – – –
N2O + O2 50 746 1000 40,000 – –
N2O + NO 50 746 1000 – 200 –
N2O + H2O 50 746 1000 – – 30,000
N2O + H2O + O2 + NO 50 746 1000 40,000 200 30,000
2 M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx
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3. mixture containing 1 vol.% of NH3 in helium for about 120 min.
Then, the catalyst was purged in a helium flow until a constant
base line level was attained. Desorption was carried out with a lin-
ear heating rate (10 K/min) in a flow of He (20 ml/min). Calibration
of QMS with commercial mixtures allowed recalculating detector
signal into the rate of NH3 evolution.
2.3. Catalytic tests
Catalytic studies of N2O decomposition were performed in a
fixed-bed quartz microreactor. The experiments were done at
atmospheric pressure and in the temperature range from 473 to
823 K in intervals of 25 K. The composition of outlet gases was
Fig. 1. Nitrogen adsorption–desorption isotherms (a) and pore size distributions calculated by DFT method (b) for the samples of Beta and Beta/meso series.
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4. analyzed using a gas chromatograph (SRI 8610C) equipped with
TCD detector. For each experiment 0.1 g of catalyst (particles sizes
in the range of 0.160–0.315 mm) was placed on quartz wool plug
in microreactor and outgassed in a flow of pure helium at 823 K
for 1 h. Then the appropriate gas mixture (total flow rate of
50 ml/min) passed over the catalyst and the reaction proceeded
Fig. 2. XRD patterns of the samples of Beta and Beta/meso series.
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5. for about 1 h to stabilize the catalyst. The compositions of the reac-
tion mixtures are summarized in Table 2. The space time (s) of N2O
in these conditions, defined as s ¼ W= _nN2O (where: W is a catalyst
mass, and _nN2O is a molar flow of N2O in the inlet mixture), was
equal to 746 g h molÀ1
. The analysis of the outlet gases was per-
formed 20 min after temperature stabilization and a steady state
regime was achieved.
3. Results and discussion
Textural parameters of the H-, Fe-, Cu- and Co-forms of Beta and
Beta/meso series of the samples, determined by nitrogen sorption
measurements, are presented in Table 1.
The properties of H-Beta and H-Beta/meso (parent samples for
ion-exchanges) are significantly different. Both samples are charac-
terized by relatively high BET surface area (about 700 m2
/g), how-
ever external surface area and volume of macro and mesopores are
considerably greater in case of H-Beta/meso. Moreover, both vol-
ume and surface area of micropores are lower in comparison to
the H-Beta sample. These effect could be explained by various crys-
tallization conditions (which, in case of H-Beta/meso, were affected
by acidification). On the other hand, an increase in external surface
area and volume of meso and macropores proves the successful
generation of mesopores in the H-Beta/meso sample.
Introduction of iron and cobalt into Beta zeolite by ion-
exchange method resulted in slight increase in surface area, while
an opposite effect was observed for deposition of cobalt. An
increase in surface areas of the samples could be related to the sec-
ondary recrystallization of zeolites under hydrothermal conditions.
A decrease of surface area observed in case of Cu-Beta, but also for
all the ion-exchanged samples based on Beta/meso series, can be
related to a partial blocking of pores by metal oxide aggregates.
The nitrogen adsorption–desorption isotherms recorded for the
samples of Beta and Beta/meso series are shown in Fig. 1a. The iso-
therm of type I (according to the IUPAC classification), characteris-
tic of microporous structure, was obtained for the samples of Beta
series. While in case of Beta/meso series the adsorption–
desorption isotherms form hysteresis loop of type H4, characteristic
for micro-mesoporous materials [22]. An increase in nitrogen
adsorbed volume, observed in the range of low partial pressures,
is smaller for the Beta-meso samples than for the Beta samples,
what proves lower microporosity of this series. The shape of the
isotherms reminded unchanged after deposition of transition
metals, although adsorbed volume of N2 decreased (especially in
case of Beta/meso series, both at low and high partial pressures).
Classical methods used for characterization of the materials
with different pore structure morphologies, such as BET or BJH,
failed [23]. Thus, the density functional theory (DFT) model for
cylindrical pores was applied for calculation of pore size distribu-
tions. The DFT pore size distributions (Fig. 1b) clearly show the dis-
tinct pore widths present in the samples. In case of Beta series
three maxima below 2 nm (at about 1.0, 1.4 and 1.7 nm) are pres-
ent. The pore size distribution in the micro-mesoporous samples
exhibits two types of pores – micropores of the same sizes as in
Beta and mesopores in a broad range (between 10 and 35 nm) with
four maxima. It is worth to mention that the contribution of pores
in the micropore range was changed after acidification. A maxi-
mum at about 1 nm significantly decreased in the favor of the peak
at about 1.4 nm. The peaks in the range below 2 nm slightly shifted
to higher pore values (especially in case of the Co-modified series)
after transition metal disposition, what can be connected with a
partial destruction of the zeolite matrix.
Analysis of nitrogen sorption measurements leads to the con-
clusion that application of mesotemplate-free method resulted in
generation of mesopores in Beta/meso series of the samples with
partial preserving of the Beta zeolite microporous matrix.
The XRD powder patterns of the H-, Fe-, Cu- and Co-forms of
Beta and Beta/meso samples are shown in Fig. 2. Reflections char-
acteristic of the BEA topology are present in all diffractograms,
what proves the zeolitic character of the samples of Beta/meso ser-
ies and maintenance of this character in both series during calcina-
tion and ion-exchange. The intensity of reflections obtained for
Beta/meso series is lower in comparison to these recorded for the
samples of Beta series. The mesoporous samples are less crystal-
line, and the intensity of the reflections decreased after ion-
exchange, especially in case of the copper and cobalt modified
samples.
A narrow and intense (302) reflection at about 22.5° is shifted
in case of the Beta/meso sample to lower 2 theta angles indicating
the relaxation of the Beta zeolite matrix [24]. The crystal sizes
obtained using Schererr’s equation (k = 1, k = 0.154 nm) for (302)
reflection are presented in Table 1. All these values are in the range
of 16–26 nm, although it is worth to notice that in case of Beta/
meso series the crystal sizes are slightly larger.
Thermal analysis curves (first derivative curves – DTG) of the
as-synthesized Na-Beta and Na-Beta/meso samples are presented
in Fig. 3. The DTG curve of Beta zeolite exhibit four distinct peaks,
which originate from the weight changes described in the litera-
ture as follows [25,26]: (i) T < 400 K – desorption of zeolitic water
(occluded in zeolite apertures); (ii) 400–625 K – thermal decompo-
sition of tetraethylammonium hydroxide (removal of triethyl-
amine and ethylene, which are the products of TEA+
degradation)
occluded in zeolite pores, non-interacting with the zeolite frame-
work; (iii) 625–750 K – the greatest weight loss related to decom-
position of tetraethylammonium cations, interacting with the
zeolite lattice (chemically bonded to Si–O–Al and Si–O–Si); (iv)
T > 800 K – decomposition of residual TEA+
cations, strongly inter-
acting with Al acidic sites.
The DTG profile obtained for the Na-Beta/meso sample consists
of four weight changes characteristic for Beta zeolite, proving zeo-
litic character of the mesoporous sample. Although, what is impor-
tant to notice, they significantly differ in intensity. The weight
losses in the first and second region are much significant, what
indicate greater amount of water and TEAOH molecules occluded
in the micro-mesoporous structure. On the other hand, the bands
associated to TEA+
cations interacting with the zeolite framework
(III and IV region) are less intensive in comparison to conventional
Beta zeolite. These differences could be related to the disturbed
zeolite structure (lower crystallinity) of the Na-Beta/meso sample.
Fig. 3. DTG profiles of as-synthesized Na-Beta and Na-Beta/meso zeolites.
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6. Fig. 4. DRIFT spectra of the samples of Beta and Beta/meso series.
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7. Mesopores in this sample were created in favor of the zeolite
framework, thereby more unreacted TEAOH molecules reside in
zeolite apertures.
The crystallinity of the samples of Beta and Beta/meso series
can be determined beside the XRD also by IR-DRIFT method
(Fig. 4). In the range of 500–600 cmÀ1
all the samples show two
bands characteristic of five (525 cmÀ1
) and six (575 cmÀ1
) mem-
bered rings present in the Beta zeolite structure [27]. Intensity of
these bands is lower in case of Beta/meso series, what corresponds
with the results of XRD analysis and indicates lower crystallinity of
the micro-mesoporous samples. Intensity of these bands slightly
decreased after ion-exchange, especially in case of the samples of
Beta/meso series modified with Cu and Co. Additionally, the contri-
bution of the zeolitic phase in the samples of Beta and Beta/meso
series corresponds to intensity of the band located at 1230 cmÀ1
and attributed to the asymmetric stretching of strained siloxane
bridges (with the same bond length) present in the zeolite lattice
[28].
In the OH stretching region of the spectra, the band at
3745 cmÀ1
is assigned to the terminal Si-OH groups present on
the external surface [29]. An increase in intensity of this band cor-
responds to a decrease in the crystals sizes. In case of Beta/meso
series it could be related to development of the external surface
through the generation of mesopores. The band at about
3630 cmÀ1
, assigned to hydroxyl stretching vibrations (Si–(OH)–
Al), corresponds to Brønsted acidity in the zeolite framework.
Intensity of this band is comparable for the Beta and Beta/meso
samples in H-forms. Deposition of Fe, Cu, and Co decreased inten-
sity of this band for a series of the Beta/meso samples. The broad
band in the range of 2000–3500 cmÀ1
is assigned to the presence
of internal OH groups (strong hydrogen bonds between neighbor-
ing silanols). Intensity of this band is related to internal Si-OH
defects, whereby proving the looseness of the structure in case of
Beta/meso series. It could be a result of partial dealumination of
the samples [30].
The content of transition metals introduced to the samples by
ion-exchange method, as well as the Si/Al ratio, was analyzed using
Table 3
Transition metals content, Si/Al ratio and total NH3 uptake measured for the samples
from the Beta and Beta/meso series modified with Fe, Cu and Co.
Sample M*
[%] Si/Al NH3 uptake [mmol/g]
Fe-Beta 2.1 27 0.977
Fe-Beta/meso 1.6 42 0.508
Cu-Beta 6.7 23 1.211
Cu-Beta/meso 6.5 32 0.802
Co-Beta 2.2 20 0.982
Co-Beta/meso 2.2 37 1.641
*
M = Fe, Cu or Co.
Fig. 5. UV–vis-DR spectra of conventional and mesoporous Beta zeolites exchanged with Fe (a), Cu (b) and Co (c).
Fig. 6. NH3-TPD profiles of conventional and mesoporous Beta zeolites exchanged
with Fe, Cu and Co. Conditions: 10,000 ppm NH3 in He; gas flow 20 ml/min; weight
of catalyst – 0.05 g.
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8. ICP method (Table 3). Transition metal content in the samples is
significantly different, despite the use of the same ion-exchange
conditions. The content of metals in the samples can be presented
in the following order: Cu P Co > Fe. The variations in particular
metals content are probably connected with differences in the
hydrated radiuses of the exchanged cations, which are equal to
4.19, 4.23 and 4.28 Å for Cu2+
, Co2+
and Fe2+
, respectively [31]. It
seems that for smaller hydrated cations the penetration of microp-
ores is facilitated, thus they can reach more ion-exchange positions
and the resulting metal content is higher. The differences in metal
contents between Beta and Beta/meso series can be observed in
case of the Fe and Cu modified samples, while in case of exchange
with cobalt the same amount was introduced to Beta and Beta/
meso.
Smaller content of Fe and Cu in Beta/meso can be related to the
higher Si/Al ratios in these samples. Lower Al content in the micro-
mesoporous samples (what was also evidenced by IR-DRIFT) can
be connected with disturbed and incomplete crystallization of
the samples of Beta/meso series. It is worth to notice that the Si/
Al ratios of the samples of conventional Beta zeolite series is close
to the expected ratio ($21). A slightly higher values of this ratio
can be assigned to partial dealumination of the samples during
their calcination.
Fig. 5 shows UV–vis-DR spectra of the samples of Beta and Beta/
meso series, exchanged with Fe, Cu and Co. The samples modified
with iron (Fig. 5a) exhibit absorption bands in the range of 200–
650 nm. The spectra were deconvoluted into four Gaussian sub-
bands corresponding to monomeric Fe3+
ions in tetrahedral
(k < 250 nm) or octahedral (250 < k < 300 nm) coordination, small
oligomeric FexOy species (300 < k < 400 nm) and Fe2O3 nanoparti-
cles (k > 400 nm). The spectra of the both Fe-Beta and Fe-Beta/
meso samples show four distinct absorption bands, although they
differ in proportions between the particular iron forms. In case of
the Beta/meso sample more iron was introduced in the form of
small oligonuclear FexOy species, while in case of the Beta sample
relatively greater amount of Fe2O3 nanoparticles was deposited,
possibly on the outer surface of the sample. A wide bandwidth of
maximum at about 380–400 nm indicates the presence of oligonu-
clear iron clusters of various sizes and geometries [32]. Absorption
below 300 nm is related to CT transitions O ? isolated Fe3+
and the
position of this band depends on the iron coordination number. It
was reported [32–34] that absorption band below 250 nm is
assigned to tetrahedrally coordinated Fe3+
ions (in framework posi-
tions or in other matrices), while the bands located between 250
and 300 nm are assigned to octahedrally coordinated Fe3+
ions in
the extra framework positions. An appearance of the absorption
at about 225 nm in the spectra of the calcined samples is a very
interesting result. A similar phenomenon was observed by Pérez-
Ramiréz et al. [32] and explained by the release of water ligands
during calcination, which resulted in a decrease of iron coordina-
tion degree.
The UV–vis-DR spectra for the Cu-modified samples are pre-
sented in fig. Fig. 5b. Both samples (Cu-Beta and Cu-Beta/meso)
show the absorption below 400 nm, attributed to monomeric
Cu2+
ions interacting with oxygen of the zeolite structure (maxi-
mum at about 230 nm), and oligomeric [Cu2+
–O2-
–Cu2+
] species
(at about 280 nm) [35]. Moreover, the adsorption band, present
above 500 nm, is related to hydrated Cu2+
cations in octahedral
coordination [35], what proves a very high dispersion of the depos-
ited copper species.
Fig. 5c shows the UV–vis-DR spectra collected for the cobalt
modified samples. In both spectra of Co-Beta and Co-Beta/meso
the bands characteristic of Co3O4 spinel at about 250, 380 and
670 nm appeared, while in case of the mesoporous sample the
intensity of these bands is significantly higher [36–48]. Also in
the both calcined samples a triplet of absorption bands at about
510, 590 and 650 nm, characteristic of tetrahedral Co2+
coordina-
tion, appeared [36].
Temperature-programmed desorption of ammonia (NH3-TPD)
was used to determine the surface acidity (surface concentration
and strength of acid sites) of the catalysts modified with Fe, Cu
and Co (Fig. 6). NH3-TPD profiles with two desorption peaks were
obtained for all the examined samples. First of them could be
attributed to NH3 bonded to weak acid sites, such as silanol groups,
while the second one to ammonia interacting with framework Al
[38]. In case of a series modified with iron the strength of acid cen-
ters in Fe-Beta is higher than for Fe-Beta/meso, what is indicated
by the position of the peaks (at about 480 and 640 K for conven-
tional zeolite Beta and at about 420 and 580 K for the mesoporous
sample). Also the total NH3 uptake (Table 3) is higher in case of the
Fe-Beta sample. Higher acidity of conventional Beta zeolite can be
connected with a significantly larger amount of iron introduced to
this sample. Similar results were obtained in case of Cu-modified
series, however its worth to notice that the total NH3 uptake for
this series was higher in comparison to the Fe-exchanged samples.
For Co series an opposite effect was observed. Higher concentra-
tion of stronger acid sites was found for the micro-mesoporous
sample. It is worth to notice that Co-Beta/meso possess stronger
acidic properties despite the same Co content in the both
Co-modified samples and higher Si/Al ratio in this sample in
Fig. 7. Temperature dependence of N2O conversion (a) and reaction rate (b) for Fe, Cu and Co modified Beta and Beta/meso. Conditions: 1000 ppm N2O; He as balancing gas;
total flow rate – 50 ml/min; weight of catalyst – 0.1 g.
8 M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx
Please cite this article in press as: M. Rutkowska et al., Micropor. Mesopor. Mater. (2014), http://dx.doi.org/10.1016/j.micromeso.2014.10.011

9. comparison to Co-Beta. Thus, the acidic properties could be
related to form of introduced cobalt, which is different in the both
samples (Co-Beta/meso contains more cobalt in the form Co3O4
spinel). Among the examined samples the highest NH3 uptake
1.641 mmol/g was found for the Co-Beta/meso sample.
The samples of Beta and Beta/meso series, modified with Fe, Cu
and Co were tested as catalysts in the process of N2O decomposi-
tion. The results of measurements performed in inert conditions
are presented in Fig. 7a. The samples activity depends on the intro-
duced transition metal and the following order of their activation
effect: Cu > Co > Fe was observed. The N2O conversion over the
most active Cu-modified sample started at about 598 K and
reached 100% at about 723 K. Among the catalysts doped with Cu
and Co more active were found to be the samples of Beta series,
while in case of zeolites modified with Fe slightly higher conver-
sion was obtained for Fe-Beta/meso.
Because the samples differ in surface area the most accurate
method for comparison of their activity is the temperature depen-
dence of the reaction rate (Fig. 7b). The reaction rate (understood
as a number of N2O molecules, which were converted on defined
Fig. 8. Temperature dependence of N2O conversion for the Fe, Cu and Co modified samples from the Beta and Beta/meso series in the presence of different compositions of
reaction mixture. Conditions: 1000 ppm N2O and optionally: 40,000 ppm O2, 200 ppm NO, 30,000 ppm H2O; He as balancing gas; total flow rate – 50 ml/min; weight of
catalyst – 0.1 g.
M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx 9
Please cite this article in press as: M. Rutkowska et al., Micropor. Mesopor. Mater. (2014), http://dx.doi.org/10.1016/j.micromeso.2014.10.011

10. surface area (1 m2
) the catalyst during defined time (1 s)) was cal-
culated basing on observed N2O conversion using the following
equation: r ¼
_nN2O
mÁSBET
Á X, where n – molar flow rate of N2O [mol/s],
m – catalyst weight [kg], SBET – BET surface area [m2
/g] and X –
N2O conversion. It can be seen that the reaction rate reached the
highest values over the copper and cobalt modified micro-meso-
porous samples. Transition metal species present in Co-Beta and
Cu-Beta are more active than in the adequate samples of Beta/
meso series (higher values of the reaction rate at lower tempera-
tures). Whereas in case of the catalysts modified with iron the
slight difference in activity (in favor of Fe-Beta/meso) was
observed.
Thus, it could be concluded that Cu species, present in the Cu-
Beta and Cu-Beta/meso samples, are the most active in N2O decom-
position (in inert gas atmosphere). This high catalytic activity can
be attributed to the presence of Cu dimmers, bridged by two oxy-
gen atoms, so called bis(l-oxo)dicopper species ([Cu2(l-O)2]2+
).
Groothaert et al. [39–41] investigated formation of such Cu-species
in ZSM-5 by an operando optical fiber UV–vis spectroscopy and in
situ XAFS combined with UV–vis-near-IR. The bis(l-oxo)dicopper
species are able to storage the peroxy species generated from
N2O activation and release O2.
The mechanism of N2O decomposition is complex and despite
extensive studies still not clearly defined [42,43]. An influence of
additional components of waste gases make the kinetic analysis
even more complicated. Thus, the studies of O2, NO and H2O (pres-
ent in waste gases emitted from nitric acid plants) impact on the
N2O decomposition mechanism were done. The results of these
studies performed in the presence of different components of the
reaction mixture over conventional and micro-mesoporous Beta
zeolites modified with Fe, Cu and Co are presented in Fig. 8.
In case of the iron and cobalt modified samples an addition of
oxygen to the reaction mixture only slightly influenced the N2O
conversion. In case of Cu-modified zeolites oxygen inhibition
effect was observed. Transition metal species, which play a role
of catalytically active sites, can be oxidized by surface oxygen
(O) species released upon N2O decomposition (Eq. (1)) or by the
adsorptive dissociation of oxygen from gaseous phase (Eq. (2)).
The second mentioned reaction is predominating at high oxygen
pressures in the reaction inlet. The surface oxygen can be
removed by reaction with N2O molecule according to the Eley–
Rideal mechanism (Eq. (3)) or by recombination of two surface
oxygen (O) species according to the Langmuir–Hinshelwood
mechanism (Eq. (4)) [44].
N2OþÃ
! OÃ
þ N2 ð1Þ
O2 þ 2Ã
! 2OÃ
ð2Þ
OÃ
þ N2O ! N2 þ O2þÃ
ð3Þ
2OÃ
! O2 þ 2Ã
ð4Þ
The presence of O2 in the reaction mixture could increase the
efficiency of N2O conversion if the rate of reaction 3 is faster than
reaction 2. The inhibiting effect of oxygen, observed in case of the
copper modified samples, proves that the oxygen removal from the
catalyst surface is slower than the step described by Eq. (2). Less
significant influence of oxygen presence on the Fe and Co contain-
ing samples can be explained by the comparable rates of the reac-
tions 2 and 3, or the elementary steps, involving adsorption of
oxygen from the gas phase on active centers, are negligible. These
results are in agreement with the kinetic analysis of the N2O
decomposition over Cu and Co modified ZSM-5 zeolite carried
out by Kapteijn et al. [43].
An introduction of NO to the reaction mixture significantly
increased the N2O conversion over the Fe-Beta and Fe-Beta/meso
catalysts. In case of the Cu and Co modified samples the presence
of NO did not influence the N2O decomposition rate. According to
Pirngruber et al. [42] and Pérez-Ramírez et al. [46] the role of NO
in nitrous oxide decomposition over the ion-containing samples
is purely catalytic. Probably NO molecules adsorb on the catalyst
surface and react with chemisorbed oxygen liberating active site
for the next catalytic cycle (Eqs. (5), (6)).
NOÃ
þ OÃ
! NOÃ
2þÃ
ð5Þ
NOÃ
2 þ OÃ
! 2Ã
þ NO þ O2 ð6Þ
Opposite, strongly deactivating effect caused by the presence of
NO in a feed mixture was observed for noble metal based catalysts
[47,48]. NO molecules adsorb on active centers making them
unavailable for N2O activation and diffusive recombination of oxy-
gen. The difference in the role of NO molecules observed for the Fe
modified samples can be connected with the presence of different
sites for NO and N2O (alpha-oxygen sites) adsorption [45,48].
The presence of water vapor in the reaction mixture signifi-
cantly decreases the N2O conversion over all the studied samples
(both conventional and micro-mesoporous materials). Probably
this effect is connected with occupying of active centers by H2O
molecules. The OHÀ
surf species produced by water adsorption are
Fig. 9. Temperature dependence of N2O conversion (a) and reaction rate (b) for Fe, Cu and Co modified Beta and Beta/meso. Conditions: 1000 ppm N2O, 40,000 ppm O2,
200 ppm NO, 30,000 ppm H2O; He as balancing gas; total flow rate – 50 ml/min; weight of catalyst – 0.1 g.
10 M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx
Please cite this article in press as: M. Rutkowska et al., Micropor. Mesopor. Mater. (2014), http://dx.doi.org/10.1016/j.micromeso.2014.10.011

11. responsible for the selective blocking of active sites. Selmachowski
et al. [49,50], investigated the blocking of the sites present on
MgO, Co-MgO and Co3O4 crystallite corners, edges and terraces by
hydroxylation, using H2O-TPD, IR-measurements and DFT molecular
modeling. Their results show that the stability of adsorbed hydroxyl
species is much higher than that of peroxy species. The formed
OH-
surf groups effectively block the active site, both for N2O activa-
tion and diffusive recombination of oxygen. Piskorz et al. [51] stud-
ied the water inhibition in N2O decomposition over Co3O4 in
simultaneous presence of oxygen in the feed. Water adsorbed on
active center is stabilized by neighboring surface oxygen atoms,
what strength the inhibiting effect of both molecules.
An influence of the simultaneous presence of O2, NO and H2O in
the reaction mixture on the N2O conversion is an imposition of
impact of all components. Only in case of the iron modified sam-
ples their catalytic activity measured in the presence of O2, NO
and H2O was higher than under ambient gas conditions. The posi-
tive influence of NO on the Fe-catalysts balanced with a surplus the
water inhibition. In case of Cu and Co series lower activity deter-
mined in a test performed in the presence of all additional compo-
nents of the nitric acid plants waste gases, was manly connected
with a negative influence of H2O.
The comparison of the catalysts activity in the conditions simu-
lating the composition of waste gases emitted from nitric acid
plants is presented in Fig. 9. The profiles of the N2O conversion
curves (Fig. 9a) are more similar to each other than in case of inert
conditions (Fig. 7a). The Fe-Beta sample was found to be the most
resistant for the process conditions, while the Co-Beta/meso sam-
ple showed the lowest activity. Fig. 9b presents temperature
dependence of the reaction rate related to the surface areas of
the samples. The reaction rate reached the highest values in the
presence of the Cu-Beta/meso catalyst. What proves, that under
conditions prevailing in waste gases emitted from nitric acid
plants, the highest activity among the tested transition metals
exhibits copper.
To examine stability of the catalysts in a flow of N2O, O2, NO and
H2O, the extended isothermal catalytic tests (50 h at 773 K) were
done (Fig. 10). In case of the samples modified with Fe and Co
any significant changes in the catalytic activity were observed.
While, for the copper containing samples, the N2O conversion
decreased by about 20% during first 30 h of the test and then
reached nearly constant level. The comparison of time dependence
of the reaction rate is presented in Fig. 11. The most active and sta-
ble species (under conditions simulating the composition of real
gases emitted from nitric acid plants) were generated in Cu-Beta/
meso.
4. Conclusions
The undertaken studies allowed the comparison of the catalytic
performance of different transition metal (Fe, Cu and Co) species
introduced to conventional and mesopore-modified Beta zeolite
in N2O decomposition reaction. The results of the undertaken
research can be analyzed from two points of view – physicochem-
ical properties of the catalysts and their activity:
Fig. 10. Time dependence of N2O conversion (Stability tests: 50 h at 773 K) of the Fe,
Cu and Co modified samples of Beta and Beta/meso series. Conditions: 1000 ppm
N2O, 40,000 ppm O2, 200 ppm NO, 30,000 ppm H2O; He as balancing gas; total flow
rate – 50 ml/min; weight of catalyst – 0.1 g.
Fig. 11. Time dependence of reaction rate (Stability tests: 50 h at 773 K) of: Fe-Beta
(j), Fe-Beta/meso (h),Cu-Beta (d), Cu-Beta/meso (s), Co-Beta (N) and Co-Beta/
meso (D). Conditions: 1000 ppm N2O, 40,000 ppm O2, 200 ppm NO, 30,000 ppm
H2O; He as balancing gas; total flow rate – 50 ml/min; weight of catalyst – 0.1 g.
M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx 11
Please cite this article in press as: M. Rutkowska et al., Micropor. Mesopor. Mater. (2014), http://dx.doi.org/10.1016/j.micromeso.2014.10.011

12. Applied mesotemplate-free method resulted in the formation of
zeolitic materials (Beta zeolite) with the hierarchical micro-
mesoporous structure (N2 sorption measurements). The pre-
serving of BEA properties in the micro-mesoporous samples
was confirmed by different techniques, such as XRD, TG and
IR-DRIFT. Differences in the pore architecture between both
series of the samples influenced the formation of different tran-
sition metals species deposited on the catalyst surface (UV–vis-
DRS).
All the studied catalysts were active in the process of nitrous
oxide decomposition. The following order of the transition
metal activation effect was observed in tests performed with
gas mixtures containing N2O diluted in helium: Cu Co Fe.
The N2O conversion over the most active Cu-Beta catalyst
started at about 598 K. The highest rate of N2O decomposition
(in a gas mixture containing O2, NO and H2O) was obtained over
the Cu-Beta/meso sample, what proves the generation of the
sites, most active in this reaction, in the micro-mesoporous
sample. The zeolite catalysts doped with Fe or Co were found
to be stable (50 h, 773 K) in the presence of typical gases emit-
ted from nitric acid plants (O2, NO, H2O), while for the samples
modified with copper a drop in N2O conversion by about 20%
was measured. Detailed analysis of the influence of other com-
ponents emitted (beside N2O) from nitric acid plants, as well as
the stability tests, enabled the selection of the most active cat-
alyst Cu-Beta/meso. Despite similar forms of copper introduced
to Cu-Beta/meso and Cu-Beta, the former catalyst present sig-
nificantly higher activity, what could be explained by better
accessibility of acid centers in the micro-mesoporous sample.
On the other side the highest N2O conversion (under conditions
simulating the composition of gases emitted from nitric acid
plants) was obtained over the Fe-Beta catalyst. This result,
together with high hydrothermal stability (50 h, 773 K), makes
this catalyst the most interesting for the application in industry
in a studied series of the samples.
Acknowledgements
M.R. acknowledges the financial support from the International
PhD-studies programme at the Faculty of Chemistry Jagiellonian
University within the Foundation For Polish Science MPD
Programme co-financed by the EU European Regional
Development Fund. The research was carried out with the
equipment purchased thanks to the financial support of the
European Regional Development Fund in the framework of
the Polish Innovation Economy Operational Program (contract no.
POIG.02.01.00-12-023/08).
References
[1] Directive 2009/29/EC of the European Parliament and of the Council of 23 April
2009 amending Directive 2003/87/EC so as to improve and extend the
greenhouse gas emission allowance trading scheme of the Community, 2009.
[2] The Kyoto Protocol, United Nations Framework Convention on Climate Change,
COP 3, Kyoto, Japan, December 11, 1997.
[3] J. Pérez-Ramiréz, F. Kapteijn, K. Schöffel, J.A. Moulijn, Appl. Catal. B 44 (2003)
117–151.
[4] J. Pérez-Ramiréz, Appl. Catal. B: Environ. 70 (2007) 31–35.
[5] M. Hartmann, Angew. Chem. Int. Ed. 43 (2004) 5880–5882.
[6] J. Cˇejka, S. Mintova, Cat. Rev. 49 (2007) 457–509.
[7] J.C. Groen, Sònia Abelló, L.A. Villaescusa, J. Pérez-Ramírez, Micropor. Mesopor.
Mater. 114 (2008) 93–102.
[8] A. Omegna, M. Vasic, J.A. van Bokhoven, G. Pirngruber, R. Prins, Phys. Chem.
Chem Phys. 6 (2004) 447–452.
[9] A.A. Campus, L. Dimitrov, C.R. da Silna, M. Wallau, E.A. Urquieta-González,
Micropor. Mesopor. Mater. 95 (2006) 92–103.
[10] A.A. Campus, C.R. Silna, M. Wallau, L.D. Dimitrov, E.A. Urquieta-González, Stud.
Surf. Sci. Catal. 185A (2005) 573–580.
[11] K. Egeblad, Ch.H. Christensen, M. Kustova, C.H. Christensen, Chem. Mater. 20
(2008) 946–960.
[12] A. Corma, U. Diaz, M.E. Domine, V. Fornés, Angew. Chem. Int. Ed. 39 (2000)
1499–1501.
[13] A. Corma, U. Diaz, V. Fornés, J.M. Guil, J. Martínez-Triguero, E.J. Creyghtony, J.
Catal. 191 (2000) 218–224.
[14] M. Rutkowska, L. Chmielarz, D. Macina, Z. Piwowarska, B. Dudek, A. Adamski,
S. Witkowski, Z. Sojka, L. Obalová, C. Van Oers, P. Cool, Appl. Catal. B: Environ.
146 (2014) 112–122.
[15] M. Rutkowska, L. Chmielarz, D. Macina, B. Dudek, C. Van Oers, P. Cool, J. Chem.
Adv. Mater. Soc. 1 (2013) 48–55.
[16] C.J. Van Oers, M. Kurttepeli, M. Mertens, S. Bals, V. Meynen, P. Cool, Micropor.
Mesopor. Mater. 185 (2014) 204–212.
[17] C.J. Van Oers, W.J.J. Stevens, E. Bruijn, M. Mertens, O.I. Lebedev, G. Van
Tendeloo, V. Meynen, P. Cool, Micropor. Mesopor. Mater. 120 (2009) 29–34.
[18] M. Rutkowska, L. Chmielarz, M. Jabłon´ ska, C.J. Van Oers, P. Cool, J. Porous
Mater. 21 (2014) 91–98.
[19] N. Liu, R. Zhang, B. Chen, Y. Li, Y. Li, J. Catal. 294 (2012) 99–112.
[20] C. Dai, Z. Lei, Y. Wang, R. Zhang, B. Chen, Micropor. Mesopor. Mater. 167 (2013)
254–266.
[21] J. Rouquerol, P. Llewellyn, F. Rouquerol, Stud. Surf. Sci. Catal. 160 (2007) 49.
[22] M. Thommes, Chem. Ing. Tech. 82 (2010) 1059–1073.
[23] J. Landers, G.Yu. Gor, A.V. Neimark, Colloid Surf. A 437 (2013) 3–32.
[24] S. Dzwigaj, P. Massiani, A. Davidson, M. Che, J. Mol. Catal. A: Chem. 155 (2000)
169–182.
[25] D.S. Kim, J.-S. Chang, J.-S. Hwang, S.-E. Park, J.M. Kim, Micropor. Mesopor.
Mater. 68 (2004) 77–82.
[26] Z. Huang, J.-F. Su, Y.-H. Guo, X.-Q. Su, L.-J. Teng, Chem. Eng. Comm. 196 (2009)
969–986.
[27] M.L. Kantam, B.P.C. Rao, B.M. Choudary, K.K. Rao, B. Sreedhar, Y. Iwasawa, T.
Sasaki, J. Mol. Catal. A: Chem. 252 (2006) 76–84.
[28] O. Collart, P. Van Der Voort, E.F. Vansant, D. Desplantier, A. Galarneau, F. Di
Renzo, F. Fajula, J. Phys. Chem. B 105 (2001) 12771–12777.
[29] M. Mauvezin, G. Delahay, B. Coq, S. Kieger, J.C. Jumas, J. Olivier-Fourcade, J.
Phys. Chem. B 105 (2001) 928–935.
[30] M.A. Camblor, A. Corma, S. Valencia, Micropor. Mesopor. Mater. 25 (1998) 59–
74.
[31] E.R. Nightingale, J. Phys. Chem. 63 (1959) 1381–1387.
[32] J. Pérez-Ramiréz, J.C. Groen, A. Brückner, M.S. Kumar, U. Bentrup, M.N.
Bebbagh, L.A. Villaescusa, J. Catal. 232 (2005) 318–334.
[33] J. Gurgul, K. Ła˛tka, I. Hnat, J. Rynkowski, S. Dzwigaj, Micropor. Mesopor. Mater.
168 (2013) 1–6.
[34] S. Dzwigaj, J. Janas, T. Machej, M. Che, Catal. Today 119 (2007) 133–136.
[35] L. Martins, R.P.S. Peguin, M. Wallau, E.A. Urquieta, Stud. Surf. Sci. Catal. 154
(2004) 2475–2483.
[36] C. Chupin, A.C. van Veen, M. Konduru, J. Després, C. Mirodatos, J. Catal. 241
(2006) 103–114.
[37] J. Zhang, W. Fan, Y. Liu, R. Li, Appl. Catal. B: Environ. 76 (2007) 174–184.
[38] Q. Shen, L. Li, C. He, X. Zhang, Z. Hao, Z. Xu, Asia-Pac. J. Chem. Eng. 7 (2012)
502–509.
[39] M.H. Groothaert, K. Lievens, H. Leeman, B.M. Weckhuysen, R.A. Schoonheydt, J.
Catal. 220 (2003) 500–512.
[40] M.H. Groothaert, J.A. van Bokhoven, A.A. Battiston, B.M. Weckhuysen, R.A.
Schoonheydt, J. Am. Chem. Soc. 125 (2003) 7629–7640.
[41] P.J. Smeets, B.F. Sels, R.M. van Teeffelen, H. Leeman, E.J.M. Hensen, R.A.
Schoonheydt, J. Catal. 256 (2008) 183–191.
[42] L. Obalová, V. Fila, Appl. Catal. B: Environ. 70 (2007) 353–359.
[43] F. Kapteijn, G. Marbán, J. Rodriguez-Mirasol, A. Moulijn, J. Catal. 167 (1997)
256–265.
[44] L. Obalová, K. Jirátová, F. Kovanda, M. Valášková, J. Balabánová, K. Pacultová, J.
Mol. Catal. A: Chem. 248 (2006) 210–219.
[45] G.D. Pirngruber, J.A.Z. Pieterse, J. Catal. 273 (2006) 237–247.
[46] J. Pérez-Ramiréz, F. Kapteijn, G. Mul, J.A. Moulijn, J. Catal. 208 (2002) 211–223.
[47] G. Centi, A. Galli, B. Montanari, S. Perathoner, A. Vaccari, Catal. Today 35 (1997)
113–120.
[48] J.A.Z. Pieterse, G. Mul, I. Melian-Cabrera, R.W. van den Brink, Catal. Lett. 99
(2005) 41–44.
[49] P. Stelmachowski, F. Zasada, W. Piskorz, A. Kotarba, Catal. Today 137 (2008)
423–428.
[50] P. Stelmachowski, G. Maniak, A. Kotarba, Z. Sojka, Catal. Commun. 10 (2009)
1062–1065.
[51] W. Piskorz, F. Zasada, P. Stelmachowski, A. Kotarba, Z. Sojka, Catal. Today 137
(2008) 418–422.
12 M. Rutkowska et al. / Microporous and Mesoporous Materials xxx (2014) xxx–xxx
Please cite this article in press as: M. Rutkowska et al., Micropor. Mesopor. Mater. (2014), http://dx.doi.org/10.1016/j.micromeso.2014.10.011