In-containing BEA zeolite for selective catalytic reduction of NOx. Part II. Relation between In active sites and catalytic activity

Article abstract of DOI:10.1016/j.molcata.2006.11.056

In-containing BEA zeolites showed high activity and selectivity for the nitrogen oxides selective catalytic reduction with methane in presence of oxygen. Perturbed angular correlation (PAC) characterization combined with Fourier transformed infrared spectroscopy (FTIR) of intermediates adspecies and reaction experiments, allowed us to correlate the catalytic activity with the nature of the active sites of the catalysts. The catalyst activity was affected by strong Br?nsted sites and the type of In precursor and was influenced by the indium loading methods. Indium species were incorporated into the matrix using two different methods: ion exchange in liquid phase and ion exchange in solid phase, the first one presented a better performance in the SCR reaction.

Full text of DOI:10.1016/j.molcata.2006.11.056

Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
In-containing BEA zeolite for selective catalytic reduction of NOx
Part II. Relation between In active sites and catalytic activity
Oscar A. Anunziataa,∗, Andrea R. Beltramonea,
Eduardo J. Ledeb, Felix G. Requejob
a Grupo Fisicoqu´ımica de Nuevos Materiales/Centro de Investigacio´n y Tecnolog´ıa Qu´ımica (CITeQ), Universidad Tecnolo´gica Nacional,
Facultad Regional Co´rdoba, Maestro Lopez esq. Cruz Roja s/n, 5016 Co´rdoba, Argentina
b Instituto de Investigaciones Fisicoqu´ımicas Teo´ricas y Aplicadas (INIFTA) e Instituto de F´ısica La Plata (IFLP),
Fac. de Cs. Exactas. Universidad Nacional de La Plata, Argentina
Received 4 October 2006; accepted 28 November 2006
Available online 8 December 2006
Abstract
In-containing BEA zeolites showed high activity and selectivity for the nitrogen oxides selective catalytic reduction with methane in presence of
oxygen. Perturbed angular correlation (PAC) characterization combined with Fourier transformed infrared spectroscopy (FTIR) of intermediates
adspecies and reaction experiments, allowed us to correlate the catalytic activity with the nature of the active sites of the catalysts. The catalyst
activity was affected by strong Bro¨nsted sites and the type of In precursor and was influenced by the indium loading methods. Indium species were
incorporated into the matrix using two different methods: ion exchange in liquid phase and ion exchange in solid phase, the first one presented a
better performance in the SCR reaction.
© 2006 Elsevier B.V. All rights reserved.
Keywords: In-BEA; PAC; FTIR of adsorbed species; NOx-SCR
1. Introduction
percentage of crystallinity of the material and diminishes the
content of the template agent, reducing the costs. The incorpo-
ration of indium did not modify the zeolite framework stability.
The incorporation of In by ion exchange in liquid phase dimin-
ished the presence of ammonium cation as counter ion. The
In Part I of this work, we showed the effect of preparation
method of BEA-zeolite and the indium loading method on the
performance for NOx-SCR with methane in presence of oxy-
gen. Temperature programmed ammonium desorption, XRD,
BET, NMR-MAS of 27Al and Fourier transformed infrared spec-
troscopy (FTIR) of pyridine adsorbed on the samples, allowed
us to correlate the catalytic activity with the nature of the active
sites of the catalysts. The catalyst activity was affected by strong
Bronsted sites and the type of In precursor (InCl3 and In2O3)
and was influenced by the indium loading methods. The ion
exchange in liquid phase method resulted in a higher activ-
ity than ion exchange in solid phase method. The BEA zeolite
was obtained by means of a new and fast process of synthesis.
This method reduces the aluminum as octahedral one (EFAL),
diminishes the period of crystallization to 48–60 h, increases the
¨
concentration of strong Bronsted acid sites decreased whereas
the strong Lewis acid sites increased. Pyridine retained for the
zeolite at different temperature followed by FTIR indicated that
new and strong Lewis acid sites in In-HBEA zeolites are formed
in concordance with TPD analysis.
Here we report a new series of PAC experiments performed
on In/H-BEA catalysts prepared by different methods (synthesis
reported in Part I) using 111In as a probe.
The perturbed angular correlation (PAC) technique is a use-
ful characterization tool for catalytic systems as it allows in situ
studies of dispersed and diluted (as low as ppm) phases on cata-
lysts [1–8]. This technique, by measurement of the local electric
field gradient (EFG) at the radioactive probe site, can provide
information on the characteristics (coordination, symmetry, dis-
tortions, etc.) of the different environments of the radioactive
probes, their concentrations, and modifications related to in situ
∗
Corresponding author. Tel.: +54 351 4690585; fax: +54 351 4690585.
E-mail address: oanunziata@scdt.frc.utn.edu.ar (O.A. Anunziata).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.11.056

O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
273
conditions. This is possible because of the hyperfine interac-
tion between the nucleus of the probe and the EFG produced
by the extranuclear (ion and electronic) charges [3]. A brief
and clear description of this technique and of the typical equip-
ment setup was published by Vogdt et al. [9]. PAC gives direct
information on site structure. Moreover, PAC experiments are
a powerful aid to quantify the concentrations of molybdenum
species identified by these techniques. Compounds containing
molybdenum have the advantage that after neutron irradiation
the PAC probe 99Mo is formed from natural 98Mo present in
the samples. Thus, the extracted information is reliable since
the PAC probe does not introduce an impurity. In the case of
In-supported catalysts, the time differential observations of the
perturbed angular correlation of ␥-rays emitted from radioac-
tive 111In (probe) allowed the characterization of different In
sites (and In species). Since the EFG depends on r−3 (where r
is the distance between the probe and the charge), PAC char-
acterizations are very sensitive to distances, the PAC technique
becoming a local environment characterization technique. Thus,
PAC experiments are very appropriate for characterizing species
with different local environments and/or short range order (as in
the case of species exchanged in zeolites).
Wodniecki et al. [10] studied nickel–indium intermetallic
compounds of different stoichiometries by means of the per-
turbed angular correlation spectroscopy. They measured the
temperature dependence of the hyperfine interaction parameters
for 111Cd probes in the crystal lattices of Ni3 In7 and Ni2 In3
and found a T character of the electric field gradient temperature
dependence.
It has been suggested that the activity of the In-ZSM5 catalyst
for the SCR reaction is due to the presence of (InO)+ groups
[11]. We have previously reported the first PAC characterization
of this species [12]. We supported the fact that the activation of
methane is initiated by NO2 and NO3− chemisorbed species on
InO+ sites of the In-ZSM-5 zeolite [13].
• Sample AM: “as made”, In2O3-HBEA prepared by ionic
exchange in solid phase, Si/Al molar ratio: 23, In content:
2% w/w.
• Sample B: AM Sample reduced under H2 flow of 5 ml/min
and 2 ◦C/min from 100 ◦C to 500 ◦C, holding this temperature
during 12 h, then it is oxidized at 500 ◦C under oxygen flow
of 10 ml/min and 2 ◦C/min from 100 ◦C and calcined during
12 h at 500 ◦C.
• Sample C: AM Sample reduced under H2 atmosphere from
100 to 300 ◦C and then oxidized at 500 ◦C.
2.2. Catalytic activity
The studies on the catalytic activity were carried out using a
flow reactor of simple step, made of silica fused with an inter-
nal diameter of 5 mm and 300 mm in length, loaded with 0.5 g
of catalyst, at atmospheric pressure. The reactant mixture was
obtained from independent gases lines and controlled by con-
trollerofmassflow, toobtain1000 ppmofNO, 1000 ppmofCH4
and 10% of O2, using He as carrier gas. The resulting GHSV
was set to 30,000 h−1 based on the bed density of 0.5 g/cm3
for zeolites. The range of temperatures used was between 300
and 600 ◦C. The reaction products were analyzed by gas chro-
matography, using a column of silica–alumina/Porapak Q of 2 m
in length and a TC-Mass detector.
2.3. Catalysts characterization
2.3.1. Studies by Fourier transformed infrared spectroscopy
Infrared analysis of H-BEA and In-HBEA were performed
on a JASCO 5300 spectrometer using a thermostatized cell with
CaF2 windows connected to a vacuum line, with a self-supported
wafer adsorbed at 10−3 Torr and desorbed at 350–400 ◦C at
10−3 Torr for 4 h. NO/CH4/O2 co-adsorption experiments with
In-HBEA samples were carried out using a thermostatized cell
with CaF2 windows connected to a vacuum line, with a self-
supported wafer.
For NO adsorption, the samples were purged in vacuum for
6 h before NO was introduced into the cell. All spectra were
recorded at room temperature as a function of exposure time. For
the quantitative comparison of absorbance, we took the absolute
value of absorbance per milligram of sample at different wave
numbers. These values were obtained from the FTIR spectra. A
reference spectrum of the sample before exposure of NO was
subtracted from each spectrum.
In Part I we showed the effect of BEA zeolite topology [14],
and the incorporation of active In species by IELP (ion exchange
liquid phase) and IESP (ion exchange in solid phase) on the
catalytic activity.
In this work, PAC characterization combined with FTIR of
NO/CH4/O2 co-adsorption experiments and the earlier results
of XRD, TPAD and the reaction experiments reported in Part I,
will help us to elucidate the nature of the In species present in
the catalysts, and the intermediate NOx adspecies responsible of
the selective reduction of NOx with methane in the presence of
excess oxygen.
2.4. Perturbed angular correlation technique
2. Experimental
The time differential observation of the perturbed angular
correlation of ␥-rays emitted from radioactive 111In allows us to
characterize different In species by means of hyperfine interac-
tions. The principle of the application of PAC to In can be found
elsewhere [15]. This technique by means of the determination of
the gradient of local electric field in the site of a probe atom, can
give information on the characteristics (coordination, symmetry,
distortion, etc.) of the different surroundings from the probe, its
concentrations and modifications by in-situ analysis conditions
2.1. Catalysts preparation
The preparation methods of the catalysts were reported in
Part I of this work. A summary of the different samples used in
this study are listed below:
• Sample A: In-HBEA prepared by ion exchange in liquid
phase, Si/Al molar ratio: 23, In content: 2% w/w.

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O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
(temperature, atmosphere, pressure, etc.). Often, a probe of PAC
is introduced as an impurity but in this case, the information of
the PAC turns out to be more reliable since the probe does not
constitute an impurity but that it is a natural component of the
catalyst.
3. Results and discussion
3.1. Studies by Fourier transformed infrared spectroscopy
FTIR data of acid sites as a function of pyridine retained at
350 and above 400 ◦C are shown in Table 1 (data reported in
Part I).
3.2. Adsorption of nitrogen monoxide
The introduction of NO (250 Torr, equilibrium pressure for
30 min, followed by a 15 min evacuation) to the calcined In-
HBEA samples and subsequent evacuation (10−1 Torr) is shown
in Fig. 1 When NO was introduced to the samples, two strong
peaks were observed from FTIR spectrum of Samples A, B
and C at room tempe−rature, the bands at 1665 cm−1 is likely
due to adsorbed NO3 [16–18] and the band at 1620 cm−1 is
assigned to NO2 adsorbed over InO+ site [13,19] (see Fig. 1
A–C). This suggests that NO molecules are weakly adsorbed
and some of them were oxidized to NO2 and nitrate species
by the residual O2 species weakly adsorbed on the catalyst. The
results of the adsorption of NO (250 Torr) at 400 ◦C on In-HBEA
samples are showed in Fig. 1 A1–C1. We can observe, at this
temperature, that only the 1620 cm−1 band remains in all the
samples.
The comparison between the intensities of the peaks for the
different species adsorbed in the three samples at room temper-
ature is illustrated in the Fig. 2a. The band at 1620 cm−1 has
higher intensity in Sample A than B or C. This specie is one of
the most important intermediates in the CH4-SCR process. The
1665 cm−1 band is more intense in Samples A and C. Fig. 2b
shows the intensities of the peaks in the three samples at 400 ◦C.
At this adsorption temperature the intensity of the bands dimin-
ished sharply, but NO2 specie remains adsorbed over the samples
in an appreciable amount. This fact indicates that NO2 species
adsorbed over In-sites are the intermediates for the reduction of
NO to N2.
Fig. 1. FTIR spectra of NO adsorbed (250 Torr equilibrium pressure, after of
vacuum activation at 500 ◦C) on In-HBEA, Samples A, B and C, (A, B, C: NO
adsorbed at 25 ◦C; A1, B1 and C1: NO adsorbed at 400 ◦C).
3.3. Co-adsorption of nitrogen monoxide, methane and
oxygen at 400 ◦C
The results of the co-adsorption of NO, CH4 and O2 (250 Torr
of NO, 250 Torr of CH4, 250 Torr of O2 equilibrium pres-
sure for 30 min, followed by a 15 min evacuation) at 400 ◦C
on In-HBEA samples are shown in Fig. −3. According to our
experimental results, the NO2 and NO3 adspecies showed
an increase when oxygen and methane was introduced with
NO. Oxygen improved NO adsorption, clearly due to oxida-
Table 1
FTIR data of acid sites as a function of pyridine retained at 350 ◦C and above
400 ◦C, respectively on H-BEA and In-HBEA
Catalysts
Bro¨nsted sitesa
Lewis sitesa
temperature [◦C] desorption
of pyridine
350
400
350
400
H-BEA
0.180
0.032
0.065
0.100
0.180
0.150
0.014
0.030
0.080
0.150
0.040
0.170
0.120
0.090
0.040
0.020
0.140
0.090
0.070
0.020
Sample A
Sample B
Sample C
Sample AM
a
FTIR, pyridine mmol/g retained at different temperatures before desorption
at 10−4 Torr for 4 h.
Fig. 2. Adsorption of NO over In-HBEA, Samples A, B and C, (a) NO adsorbed
at 25 ◦C; (b) NO adsorbed at 400 ◦C.

O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
275
Table 2
Catalytic activity of In-HBEA at different temperatures for NO-SCR
Sample
NO conversion to N2
(mol%)
Methane conversion
(mol%)
A
B
C
A
B
C
Temperature (◦C)
400
450
500
550
60
80.5
78
60
79
78
76
59
72
77
64.8
33
55
77.5
99
49
80
99
99.1
69
94
100
100
76
NO conversion to N2, and methane conversion for Sample A: IELP activated in
air at 500 ◦C; Sample B: IESP reduced at 500 ◦C under H2 and then oxidized at
500 ◦C; Sample C: IESP reduced under H2 at 300 ◦C and then oxidized in air a
500 ◦C.
In-containing zeolite, in agreement with our recent work [13]
and Ogura et al. [11].
3.4. Catalytic activity
The results of the catalytic activity for the selective reduction
of NO with methane in the presence of oxygen are summa-
rized in Table 2. As we can see, the conversion of NO reached
approximately an 80% for Samples A and B at 450 ◦C and the
methane conversion was 55 and 80% for the Samples A and B,
respectively.
With the objective to analyze the concerted action of active
In-species and H+ sites of the catalysts (Samples A, B and C),
we chose the reaction temperature of 400 ◦C, taking in account
that at this temperature we studied the adsorbed species from
NO/CH4/O2 reaction system and pyridine determined by FTIR.
At this temperature the NO conversion to N2 was 60 mol% for all
the samples, but the methane conversion was different for each
Fig. 3. FTIR spectra of NO + CH4 + O2 (NO: 250 Torr; CH4: 250 Torr, O2:
250 Torr) co-adsorbed on In-HBEA at 400 ◦C, Samples A, B and C.
tion of NO to NO2 and nitrate species. The NOy adspecies, with
high intensities, were observed on the NO2 adsorbed over sev-
eral zeolites [20–22], suggesting stronger adsorption for NO2
than NO.
Comparing the data of absorbance from the spectra obtained
at 400 ◦C, we observe that the Sample A possesses more inter-
mediate species adsorbed (NO2–In-site) than the others samples,
particularly than the Sample C (see Fig. 4).
The bands assigned to these adspecies are present even, at the
−
catalytic reaction temperature, indicating that NO2 and NO3
adspecies might play an important role in the SCR of NOx over
Fig. 5. Relationship between methane conversion at 400 ◦C and (−NO2)
Fig. 4. Co-adsorption of NO + CH4 + O2 over In-HBEA at 400 ◦C, Samples A,
B and C.
adsorbed specie and Bro¨nsted sites for Samples A, B and C.

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O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
samples. Therefore, in Fig. 5 we show only the methane conver-
like will be able to be seen in the following section about PAC
characterization.
¨
sionasafunctionofNO2-adspeciesabsorbanceandtheBronsted
acid sites at 400 ◦C (according to the data of Figs. 3 and 4, and
Table 1, respectively).
3.5. PAC Characterization of In-HBEA zeolite
The graph shows that the methane conversion is indeed
higher over the Sample C, accordingly with the highest value of
3.5.1. In-HBEA, IELP
¨
Bronsted sites. For this sample, methane conversion increases
Fig. 6 shows the spectra of precession of spin (R(t)) and its
Fourier transform for Sample A. The values of the fitted hyper-
fine parameters are shown in Table 3. The fit was made proposing
three hyperfine interactions and the obtained results indicate the
presence of at least two In species. The sites associated with the
assemblies of parameters 1 and 2 correspond with reported for
In2O3 [15]. The parameter 3 correspond to a different In-site,
more likely due to In exchanged by ammonium ions in zeolite
framework. This specie was previously associated to InO+ in
In-ZSM-5 [15].
with the reaction temperature (>400 ◦C), but the NO conversion
is constant or decreases. Methane is converted to CO and CO2
over H+ sites, but it is not consumed to reduce NO at these tem-
peratures. Sample A possesses more NO2-adspecies and less
¨
Bronsted sites and these sites are capable to convert methane
selectively to reduce NO to N2. So, the selective methane con-
version for the samples presents the following order: Sample
A > B > C in concordance with NO2-species and Lewis acids
sites of the catalyst.
For Samples A and B the active sites are capable to form
species with high thermal stability [23], therefore, chemisorbed
NOx begin to reduce it self to N2 at lower temperature than on In-
ZSM-5 zeolite [15]. In that case, the maximum NO conversion to
N2 using methane as reducer was 80 mol% at 540 ◦C. However,
for In-HBEA, Samples A and B reach similar conversion levels
but at lower temperature (450 ◦C). In the case of In-ZSM-5, the
conversion was 30 mol%lowerthan forIn-HBEAatthisreaction
temperature [15].
3.5.2. In-HBEA, IESP
The PAC spectrum showed in Fig. 7, correspond to the
obtained R(t) and its Fourier transform for In-HBEA. In Sample
AM: as made, the spectrum shows the characteristic signal of
the In2O3 that we used in its preparation and it does not show
any interaction with the zeolite. The values of the fit hyperfine
parameters (sites AM.1 and AM.2 in Table 3) confirm it.
Considering that the IESP of In2O3 over NH4-BEA, was
These differences seem to indicate that the amount and/or
nature of the active sites in both zeolites are not quite similar,
´
interpreted by Mihalyi et al. [24] as the reduction of In2O3
to univalent indium concomitantly incorporated by solid-state
Fig. 6. PAC Spectra (left) and its Fourier transform (right) of Sample A, measured at 500 ◦C in air. The arrows indicate the three harmonic components for each
hyperfine interaction.

O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
277
Fig. 7. PAC Spectra (left) and its Fourier transform (right) of In-HBEA by IESP: Sample AM; Sample B; Sample B1; Sample C.

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O.A. Anunziata et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 272–279
Table 3
Values of the fitted hyperfine parameters in the spectra showed in Figs. 6 and 7
Catalyst
Site
Population f (%)
Frequency ωQ (Mrad./s)
Asymmetry parameter (n)
Distribution δ (%)
Sample A
A.1
A.2
A.3
AM.1
AM.2
B.1
B.2
B.3
C.1
C.2
33(12)
57(4)
10(4)
20.1 (5)
80(2)
16(3)
36(3)
48(9)
16(2)
7(1)
24.9 (2)
19.3 (1)
28.7 (2)
24.72 (6)
19.09 (3)
24.96 (9)
19.10 (3)
29(2)
25.5 (4)
19.2 (1)
33.1 (9)
24.38 (8)
18.71 (8)
0.17 (3)
0.71 (1)
0.33 (2)
0.02 (4)
0.699 (3)
0.11 (3)
0.705 (5)
0.42 (6)
0.18 (8)
0.76 (2)
0.50 (5)
0
5.8 (9)
5.8 (6)
2(1)
0.2 (3)
1.2 (1)
1.1 (6)
0.7 (3)
21(4)
5(2)
AMa
Sample B
Sample C
0(2)
C.3
In1
In2
78(16)
23(2)
77(2)
19(3)
0.16 (6)
0.22 (6)
b
In2O3
0.71 (1)
a
AM: As made, ion exchange solid phase. Sample B without the oxidizing process (B1) can be fitted with a relaxation for all In-sites (f = 100%).
Hyperfine parameters of bulk In2O3 measured at 600 ◦C [15].
b
ion to form 2In+Z− and the degree of oxidation by oxygen to
InO+-Z− is a function of the temperature (450 ◦C to reduce and
the oxidation process), we reduced at 300 and 500 ◦C and oxi-
dized at 500 ◦C to observe the effect in the formation of InO+
species (Sample B and C). The reductive pretreatment temper-
ature of the catalysts (500 ◦C) for Sample B, was chosen to be
below the dehydroxylation temperature of the zeolite but suffi-
ciently high for complete reduction of In2O3. Sample B reduced
in controlled atmosphere of H2 during 2 h at 500 ◦C and later
oxidizing in air at 500 ◦C for 1 h, was analyzed by PAC and the
R(t) spectra and its Fourier transform are clearly different from
the previous ones, admit an adjustment with three interactions.
The presence of In on sites with similar surroundings to In in
In2O3 is again observed. We found hyperfine parameters asso-
ciated to a second specie of In interacting with the BEA zeolite
(see Table 3, B.1, 2, 3 sites). To show the effect of the reduction
of In-HBEA, we prepared other sample reduced at 500 ◦C but its
PAC measurements was made without oxidizing it. The results
are indicated as Sample B1 (see Fig. 7). In these conditions the
PAC spectrum showed a remarkable change. The interpretation
of this signal is not even conclusive but it could be due to sta-
tionary dynamic at the probe’s surrounding, like chemisorption
and desorption of H2, which would take place in the order of few
nseg. Similar results were previously reported through TDPAC
experiments on In/H-ZSM5, In/FER and InPt/FER in presence
of H2 [25,26].
Sample C obtained by a processing of reduction in controlled
atmosphere by constant flow of H2 during 2 h at 300 ◦C and
later oxidizing in air at 500 ◦C for 1 h, was measured by PAC
at 500 ◦C in air. An appreciable change in comparison with AM
is observed. This spectra was fit with three interactions, two of
which (sites C.1 and C.2 in Table 3) are in agree with both sites
of Indium in In2O3. The third interaction (site C.3 in Table 3)
would correspond to second specie of In interacting with the
zeolite framework, with high population but at higher frequency
(ωQ) and with higher asymmetry parameter than for the specie
present in the Sample A. These values suggest that the indium
species interacting with BEA zeolite (Sample C) seem to be
quiet different to the indium species found in Sample A. In the
same way, the high EFG (electric field gradient) distribution
of B.3 and C.3 (21 and 19, respectively, see Table 3) would
also explained by several anchoring configurations of the (InO+)
species because of the size of this species can be found within
the channel of the zeolite. Thus, not all of B.3 and C.3 can
be assigned to active InO+ species [27]. However, a very low
distribution of A.3 is found for Sample A (δ (%) = 2 in Table 3),
indicating that, even at low concentration compared with the
other samples, this signal is attributed to InO+ active sites for
SCR of NO, in concordance with the results of the catalytic
activity and NO2 intermediate adspecies showed in the FTIR
analysis for Sample A.
4. Conclusions
A good correspondence between the catalytic activity and
characterization of the materials was observed. The PAC tech-
nique allowed us to determine the presence of active sites such
as InO+ in Sample A (IELP) activated in air at 500 ◦C, showing
hyperfine interactions (A.3 in Table 3) attributed to the pres-
ence of (InO)+-BEA species and two In2O3 signals (hyperfine
interactions A.1 and A.2). The samples prepared by IESP (B
and C) reduced at 500 and 300 ◦C under H2, respectively, and
then oxidized at 500 ◦C, show two characteristic signals of In2O3
crystals. The third interaction (site B.3 and C.3 in Table 3) would
correspond to a second specie of In interacting with the zeolite
framework, with high population but at higher frequency (ωQ)
and with higher asymmetry parameter, thus not all of this sig-
nal (specially in Sample C) corresponds to InO+ species as we
found in Sample A.
FTIR of pyridine indicated that new and strong Lewis acid
sites in In-HBEA zeolites are formed i−n concordance with TPD
analysis. NO adsorption showed NO3 and NO2 adspecies are
the intermediate of the reaction.
The results obtained with In-HBEA prepared by IELP and
IESP (reduced at 500 ◦C and then oxidized at 500 ◦C) are more
active for the reduction of NO with methane than In-ZSM-5
[15]. In the same way, with these catalysts, methane is con-
sumed selectively for the reduction of NO to N2 at 450–500 ◦C,

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279
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and A.R.B. are grateful to CONICET Argentine, PIP
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