Catalytic reduction of NO2 in nanocrystalline NaY zeolite

Article abstract of DOI:10.1016/j.molcata.2004.10.002

In this study, in situ transmission FT-IR spectroscopy was employed to investigate the thermal and selective catalytic reduction of NO₂ with propylene in nanocrystalline NaY zeolite. NO was the major product in the thermal reduction of NO₂. In absence of oxygen and water, selective catalytic reduction of NO₂ with propylene at low temperatures (T ≤ 473 K) resulted in the complete reduction of NO₂ to N₂ and O₂. Isocyanate and nitrile species formed on extra framework alumina sites are found to be important intermediates. Based on kinetic studies, a pathway involving radical reactions appears to be the most plausible mechanism for the complete reduction of NO₂.

Full text of DOI:10.1016/j.molcata.2004.10.002

Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
Catalytic reduction of NO2 in nanocrystalline NaY zeolite
Gonghu Li, Sarah C. Larsen∗∗, Vicki H. Grassian∗
Department of Chemistry, The University of Iowa, Iowa City, IA 52242, USA
Received 30 July 2004; received in revised form 3 October 2004; accepted 4 October 2004
Available online 18 November 2004
Abstract
In this study, in situ transmission FT-IR spectroscopy was employed to investigate the thermal and selective catalytic reduction of NO2
with propylene in nanocrystalline NaY zeolite. NO was the major product in the thermal reduction of NO2. In absence of oxygen and water,
selective catalytic reduction of NO2 with propylene at low temperatures (T ≤ 473 K) resulted in the complete reduction of NO2 to N2 and O2.
Isocyanate and nitrile species formed on extra framework alumina sites are found to be important intermediates. Based on kinetic studies, a
pathway involving radical reactions appears to be the most plausible mechanism for the complete reduction of NO2.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Selective catalytic reduction; NO2; Y zeolite; Propylene; Nanoparticles
1. Introduction
[15,16]. Organic nitro/nitrito compounds are first generated
in the reaction between adsorbed hydrocarbons and surface
nitrate/nitrite species. These compounds are then converted
to isocyanates. Isocyanates will react with NOx from the gas
phase producing dinitrogen. Although the general reaction
scheme can be understood from these steps, many details
still remain elusive, such as the mechanism for the forma-
tion of the nitrogen nitrogen bond in complete reduction.
Ammonium ions or free radicals have been proposed as key
intermediates in the formation of dinitrogen [7,17].
The emission control of nitrogen oxides (NOx) from en-
gine exhaust is of great importance due to their contribution
to processes harmful to the environment [1–3]. Selective cat-
alytic reduction (SCR) of NOx with NH3 or hydrocarbons
(HCs) has emerged as an effective technology using oxide
and zeolite based catalysts [4–6]. Zeolites are considered
particularly promising SCR catalysts because of their cation
exchange capacity and acid–base properties.
Several recent studies have investigated alkali and alka-
line earth-exchanged Y, FAU zeolites in the adsorption and
HC-SCR of NOx [7–14]. NO2 can be stored in zeolite Y
in the form of stable nitrate and nitrite species. The ad-
sorption of NO2 (or NO + O2) in zeolite Y has been sug-
gested to proceed via the disproportionation of N2O4 or
the reaction of NO2 with the residual water in zeolite. As
for the mechanism of HC-SCR, previous studies have sug-
gested isocyanates to be key intermediates in this reaction
Most HC-SCR studies in zeolites have been carried out at
temperatures above 673 K. At these elevated temperatures,
many side reactions can take place [3]. In this study, thermal
reduction and propylene-SCR of NO2 were done at lower
temperatures (T ≤ 473 K) and monitored with in situ FT-IR
spectroscopy. Infrared spectroscopy has been widely used to
investigate the adsorption and the selective catalytic reduc-
tion of NOx [18–22]. In particular, information concerning
the kinetics and mechanism of these reactions may be dis-
cerned from this spectroscopic technique. In addition, syn-
thesized nanocrystalline NaY zeolite was used as the catalyst
instead of commercially available zeolite catalysts. As dis-
cussed in a recent publication, nanocrystalline zeolites may
be particularly useful in environmental applications due to
∗
∗∗
Corresponding author. Tel.: +1 319 335 1392; fax: +1 319 335 1270.
Co-corresponding author.
E-mail addresses: sarah-larsen@uiowa.edu (S.C. Larsen),
vicki-grassian@uiowa.edu (V.H. Grassian).
1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.10.002

26
G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
the small particle size and large internal and external surface
areas [23,24].
sample. The tungsten grid with zeolite sample is placed in-
side of a stainless steel cube. The cube has two BaF2 windows
for infrared measurements and is connected to a vacuum/gas
handling system.
2. Experimental
The stainless steel IR cell is held in place by a lin-
ear translator inside the sample compartment of a Mattson
Galaxy 6000 infrared spectrometer equipped with a narrow-
band MCT detector. The linear translator allows each half of
the sample grid to be translated into the infrared beam. This
permits the detection of gas phase and adsorbed species in
zeolites under identical reaction conditions. Each spectrum
was obtained by averaging 64 scans at an instrument resolu-
tion of 4 cm−1. Each absorbance spectrum shown represents
a single beam scan referenced to the appropriate single beam
scan of the clean zeolites or the blank grid, unless otherwise
noted.
The NaY sample was gradually heated under vacuum at
573 K or higher temperature overnight to remove adsorbed
water. Reactant gases were loaded into the zeolite through the
gas handling system. Two absolute pressure transducers were
used to monitor the pressures. Typically, the zeolite was equi-
librated with each gas prior to a spectrum being recorded. In
pyridine adsorption experiments, adsorption was carried out
by equilibrating the zeolite powder with 1 Torr pressure of
pyridine vapor at room temperatures. The sample was then
evacuated for 30 min before a spectrum was recorded. The
desorption of pyridine was monitored by evacuating the sam-
ple for 30 min at elevated temperatures and cooling back to
room temperature prior to recording a spectrum.
2.1. Zeolite sample preparation and materials
Nanocrystalline NaY zeolite was synthesized according
to methods described in the literature [25]. Two solutions (A
and B) were prepared. Solution A was obtained by dissolving
NaOH and tetramethylammonium hydroxide (TMAOH) in
distilled water and then adding aluminum isopropylate to the
alkali solution. Solution B was prepared by adding tetraethyl
orthosilicate (TEOS) to the remainder of the TMAOH so-
lution. Both solutions were filtered through a 0.2 ␮m filter
paper, then mixed together and stirred overnight at room
temperature. The clear solution mixture obtained was then
heated in a Teflon-lined stainless steel autoclave for 3 days at
403 K. The resulting solution was centrifuged for 30 min at
3400 rmp. The product was washed with distilled water and
dried in air.
The synthesized zeolite was characterized using powder
X-ray diffraction (Siemans D5000) to assess the crystallinity
and to verify the identity of the zeolite. Scanning electron
microscopy (SEM, Hitachi S-4000) was used to determine
particle morphology and particle size. The average parti-
cle size was determined to be 80 30 nm from SEM. The
surface area was measured on an automated Quantachrome
Nova 1200 multipoint BET apparatus. The internal and ex-
ternal surface areas of the synthesized zeolite were 474 and
46 m2 g−1, respectively. Based on previous work [26], the
particle size of the zeolite was calculated using the external
surface area to be approximately 88 nm, in reasonable agree-
ment with the SEM measurement. 27Al and 29Si magic angle
spinning (MAS) NMR (300 MHz wide bore, Tecmag) were
performed on the sample. NMR signals from tetrahedral Al
and Si atoms were identified. The Si/Al ratio was determined
to be 1.7 from 29Si MAS NMR.
In SCR reactions, NO2 and propylene (1:1 ratio) were
pre-mixed in a chamber before being introduced into the IR
cell at room temperature. Time course experiments were con-
ducted by automatically scanning the gas phase every 2 min.
The extinction coefficient of individual gases was calibrated
using the characteristic IR absorption bands and measuring
the pressure using an absolute pressure transducer. Assuming
ideal gas behavior, the amount of gas can be calculated from
its pressure and volume of the IR cell.
Research-grade purity oxygen and carbon dioxide were
purchased from Air Products. Research-grade purity nitro-
gen dioxide, propylene, nitric oxide, nitrous oxide and carbon
monoxide from Matheson. All gases were used as received.
Pyridine (99.9%) was purchased from Fisher Scientific. Pyri-
dine was further dehydrated over molecular sieves and puri-
fied before use by several freeze-pump-thaw cycles.
3. Results
3.1. An investigation of the nature of the surface sites on
nanocrystalline NaY
Five absorption bands due to hydroxyl groups were iden-
tified in the infrared spectra after heating the NaY zeolite
overnight under vacuum at temperatures of 573 and 673 K,
as shown in Fig. 1. Although there is an overall decrease
in intensity of the band in this region after heating from
573 to 673 K, the five absorption bands are still evident at
673 K. The relatively intense high frequency absorption band
at 3745 cm−1 is assigned to terminal silanol groups that are
on the external surface of the particles. This feature is of
much weaker intensity in a commercial sample of NaY zeo-
lite that has a much larger particle size [23]. Thus, this result
2.2. Fourier transform infrared spectroscopy
The infrared sample cell used in this study has been de-
scribed previously [27]. Approximately 8 mg of NaY zeo-
lite mixed with some water were coated onto a 3 cm × 2 cm
photoetched tungsten grid held in place by nickel jaws. The
nickel jaws are attached to copper leads so that the sample
can be resistively heated. A thermocouple wire attached to
the tungsten grid is used to measure the temperature of the

G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
27
Fig. 2. FT-IR spectra of propylene adsorbed in nanocrystalline NaY zeolite
at T = 298 K as a function of propylene pressure (P = 0.050, 0.493, 1.019,
2.028 and 4.061 Torr). All spectra shown in Fig. 2 use the clean nanocrys-
talline NaY zeolite prior to adsorption as a reference. In addition, gas-phase
absorptions have been subtracted from each of the FT-IR spectra.
Fig. 1. FT-IR spectra of surface hydroxyl groups in nanocrystalline NaY
zeolite after heating to (a) 573 K and (b) 673 K overnight under vacuum.
The two spectra were recorded at T = 298 K. Five different O–H groups
were identified in the spectrum. The spectrum recorded after heating to
673 K overnight is fit to five bands with Lorentzian line-shapes so that these
bands can be more readily discerned. The blank grid is used as a reference.
Pyridine adsorption, however, revealed the existence of
weaker Bronsted acid sites as well as Lewis acid sites in the
NaY zeolite. It is well known that weakly adsorbed pyridine
with characteristic vibrational frequencies of 1617, 1592,
1574 and 1441 cm−1 desorbs near 470 K [32,33]. In contrast,
pyridinium ions with characteristic vibrational frequencies
of 1632 and 1545 cm−1 generated by reaction with Bronsted
acidsitesdesorbatmuchhighertemperatures. Similarly, pyri-
dine molecules that adsorbed at Lewis acid sites are also more
strongly adsorbed. Pyridine molecules adsorbed at Lewis
acid sites can be identified from characteristic absorptions
at 1621 and 1454 cm−1. All three types of adsorbed pyridine
confirms that the synthesized NaY zeolite consists of small
particles. The next highest frequency absorption band around
3723 cm−1 is associated with hydroxyl groups occurring at
defect sites (also called hydroxyl nests) [28]. The absorption
band at 3694 cm−1 has been assigned to surface hydroxyl
groups near Na+ sites, while the bands at 3654 and 3605 cm−1
are associated with hydroxyl group attached to extra frame-
work alumina (EFAL) species [29,30] and adsorbed water,
respectively.
molecules contribute to the absorption band at 1489 cm−1
.
Several probe molecules were used to detect the pres-
ence of additional surface adsorption sites for the synthesized
nanocrystalline zeolite Y used in this study. The adsorption
of propylene in NaY (see Fig. 2) results in an absorption
band at 1635 cm−1 assigned to the C C stretching mode and
several bands between 1350 and 1500 cm−1 associated with
the CH3 deformation mode and the CH2 scissor mode. Ab-
sorptions due to C H stretching modes between 2800 and
3100 cm−1 were also observed (not shown). All of the ab-
sorption features disappeared after evacuation of gas-phase
propylene at room temperature for several minutes. With ex-
cess propylene in the IR cell, no pronounced change of the
band at 1635 cm−1 was observed at room temperature for 6 h,
indicating that propylene did not undergo polymerization in
the nanocrystalline NaYzeolite. It can therefore be concluded
that strong Bronsted acid sites that initiate propylene poly-
merization are not present in the nanocrystalline NaY zeolite
pretreated at 573 K [31]. The FT-IR spectra shown in Fig. 1
are consistent with this conclusion as strong Bronsted acid
sites are typically bridging OH groups with vibrational fre-
quencies of 3630 and 3560 cm−1 [29,32]. These bands are
not observed in the infrared spectra of nanocrystalline NaY
shown in Fig. 1.
Fig. 3 displays the FT-IR spectra of pyridine molecules ad-
sorbed in the nanocrystalline NaY zeolite following desorp-
tion at three different temperatures (298, 373 and 473 K).
It can be seen from the infrared spectrum at 298 K that all
three types of adsorbed pyridine molecules are observed. Af-
ter heating to higher temperatures, only pyridine molecules
adsorbed on Bronsted and Lewis acid sites are apparent in the
infrared spectra. The Bronsted acid sites may be associated
with the surface hydroxyl groups attached to EFAL species.
3.2. Adsorption and thermal reduction of NO2
The adsorption and reaction of NO2 on surfaces have been
extensively studied due to its environmental importance. FT-
IR spectra recorded of the NaY zeolite as a function of NO2
pressure are shown in Fig. 4. It is evident from the spectra
that exposure to NO2 results in the formation of several sur-
face species whose frequencies fall into two spectral regions:
1200–1660 cm−1 due to NO3− and NO2− 1900–2300 cm−1
due to NO+. Previous studies on nitrogen oxide adsorption
make the assignment of the spectra relatively straightforward
[34–39]. At low pressures, a doublet with absorbance max-

28
G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
The absorption bands within the spectral region between
1900 and 2300 cm−1 are assigned to nitrosonium ions (NO+)
[11,40]. At low pressures, two bands at 2024 and 2124 cm−1
are due to the formation of NO+ species adsorbed onto dif-
ferent cationic position in the zeolite framework. At high
pressures, an absorption feature at 2187 cm−1 develops. This
feature can be assigned to the N O stretching mode from
[NO+][NO2] or [NO+][N2O4] adducts adsorbed onto Lewis
base sites [11,12]. Two other bands at 2450 and 1764 cm−1
can be assigned to an overtone and combination bands of
adsorbed nitrates [22].
In the hydroxyl group region, loss of three bands at 3694,
3716 and 3746 cm−1 was observed because of either the dis-
placement or interaction of hydroxyl groups with adsorbed
−
NOx species. Perturbed hydroxyl groups on EFAL species
gave rise to two absorptions at 3649 and 3560 cm−1 [12]. At
low NO2 pressure, a negative peak around 1658 cm−1 was
visible, indicating the consumption of residual H2O in the
zeolite upon NO2 adsorption.
Fig. 3. FT-IR spectra of pyridine molecules adsorbed in nanocrystalline NaY
zeolite at T = 298 K following pyridine desorption at (a) 298 K, (b) 473 K
and (c) 573 K. The inset shows the spectral region extending from 3635 to
3760 cm−1. The spectra were recorded at 298 K. All spectra shown in Fig. 3
use the clean nanocrystalline NaY zeolite prior to adsorption as a reference.
In addition, gas-phase absorptions have been subtracted from each of the
FT-IR spectra. The peaks in the spectra are assigned to weakly adsorbed
pyridine and pyridine adsorbed on acid sites. See text for further details.
Thermal reduction of NO2 at temperatures from 298 to
573 K was investigated. FT-IR spectra of the gas phase were
taken at 2 min time intervals. The concentration of the gases
in the infrared cell can be determined from the integrated
absorbances of the bands at 1616 cm−1 (NO2), 1875 cm−1
(NO) and 2224 cm−1 (N2O) using calibrated extinction co-
efficients. The time course concentration of gas-phase prod-
ucts in thermal reduction of NO2 at 373 K is shown in Fig. 5.
Immediately after heating began, the concentration of NO2
in the gas phase jumped to a maximum and then decreased
quickly. Clearly a large amount of NO2 was released from the
NaY zeolite upon heating, possibly via the reaction of highly
active surface nitrate [41]. NO and N2O were the only other
gas-phase products detected by the FT-IR spectroscopy.
The product distribut−ion and conversion of both gaseous
NO2 and adsorbed NO3 at three different temperatures are
listed in Table 1. In thermal reduction of NO2, NO was the
major product. N2O accounted for less than 2% of the prod-
ima at 1410 and 1386 cm−1 can be attributed to the ν3 mode
splitting of surface nitrate (NO3−) adsorbed on Na+ sites. At
higher loading, the doublet converges into a singlet with a fre-
quency of 1407 cm−1. This broadening of the nitrate bands
is most likely due to intermolecular interactions [11,12]. The
absorption at 1230 cm−1 is associated with adsorbed nitrite
(NO2−). Absorption bands at 1627, 1581 and 1554 cm−1 are
associated with nitrate absorptions on the EFAL bonded in
different coordinations (bridging, bidendate and monoden-
tate, respectively) [2]. The absorption at 1327 cm−1 is also
associated with nitrate adsorption on EFAL sites.
Fig. 4. FT-IR spectra of NO2 adsorbed in nanocrystalline NaY zeolite
at T = 298 K as a function of NO2 pressure (P = 0.055, 0.107, 0.498 and
1.033 Torr). All spectra shown in Fig. 4 use the nanocrystalline NaY zeolite
prior to adsorption as a reference. In addition, gas-phase absorptions have
been subtracted from each of the FT-IR spectra.
Fig. 5. Time evolution of gas phase NO2, NO and N2O during the thermal
reduction of NO2 in nanocrystalline NaY at 373 K. Spectra were recorded
every 2 min.

G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
29
Table 1
Table 2
−
Product distribution and conversion of gas-phase NO2 and adsorbed NO3
Assignment of infrared absorption bands observed following adsorption of
NO2 and propylene (1:1) mixture in nanocrystalline NaY zeolite
in the thermal reduction of NO2 at different temperatures after 6 h of reaction
time
Bands (cm−1
)
Assignments
Possible species
Reference
Gas products (␮mol L−1
)
%Conversionb
a
Reaction
temperature (K)
3300–3150
2985
2317
2272
2239
2187
1969
1943
1723, 1694
1647
1598, 1483
1557, 1387
1528
1508
1354
ν(OH)
Oximes
RCH=CH2
SiNCO
HNCO
RNCO
RCN
NO (a)
N2O3 (a)
Carbonyl species
RONO (or RCONH2)
Carbonaceous species
RNO2
Carbonate ion
Formate ion
RCH3
[18,47]
[42]
−
NO3
ν(=CH2)
ν(NCO)
ν(NCO)
ν(NCO)
ν(CN)
ν(N O)
ν(N=O)
ν(C=O)
ν(ONO)
–
NO
N2O
NO2
[43,44]
[7,44]
[19,48–52]
[48,51,52]
[35]
298
373
473
a
10.1
23.6
51.3
0
0.2
0.8
79
71
92
11
64
90
In thermal reduction, the total loading of NO2 was controlled to be
50 5 ␮mol L−1; the initial concentration of gas-phase NO2 after adsorption
[35]
equilibrium at 298 K was 14 2 ␮mol L−1
.
[7,47]
[7,20,21,47]
[46]
[7,20,21,47]
[42]
[42]
[7]
[45]
b
Co−nversion of NO2 refers to change of NO2 in gas phase; conversion
of NO3 describes the change associated with the integrated absorbance in
the entire 1240–1660 cm−1 spectral region.
ν(NO2)
2−
ν(CO3
)
ν(COO−)
δ(CH3)
ucts in the temperature range studied. More than 70% of gas-
phase NO2 decomposed after reaction at 373 K for 6 h. The
efficiency reached 100% when the temperature was above
523 K. The concentration of N2 and O2 couldn’t be mon-
itored in this study. However, based on the nitrogen mass
balance, it appears that little N2 and O2 were formed in the
thermal reduction of NO2.
1282
ν(C O)
RONO
nitrates > Al-nitrates > nitrites [12]. In our work, nitrates also
appear to be the more stable species relative to nitrites and
nitrosonium ions.
In order to measure the thermal stability of the various
surface species in the zeolite, NO2 was first adsorbed in
nanocrystalline NaY zeolite at 298 K and the sample was
then heated to different temperatures. Fig. 6 shows the FT-
IR spectra of surface species adsorbed in NaY zeolite after
evacuating the zeolite at different temperatures. Surface ad-
sorbed NO+ was removed completely by evacuating at 298 K
for 30 min, while less than 10% of the original NO3− species
still remained adsorbed in the zeolite after heating to 573 K.
The quantitative study by Sedlmair et al. has shown the rel-
ative stability of the NOx surface species as following: Na+-
3.3. Adsorption of NO2 and propylene (1:1) mixture
In the propylene-SCR reaction, NO2 and propylene were
pre-mixed (1:1 mole ratio) in a chamber prior to being intro-
duced into the infrared cell. The FT-IR spectra of the result-
ing mixture adsorbed in NaY zeolite at 298 K are shown in
Fig. 7. In comparison to the adsorption of NO2 a−lone, similar
absorption features were observed in the NO3 region. In
addition, several new absorption bands were also observed.
Assignments of these bands are given in Table 2. Most of
Fig. 6. FT-IR spectra of NO2 adsorbed in nanocrystalline NaY zeolite after
adsorption at (a) 298 K in the presence of the gas phase and (b) after evacu-
ation of the gas phase. The sample was then heated to (c) 373 K, (d) 473 K
and (e) 573 K for 30 min. All spectra were recorded at T = 298 K. All spectra
shown in Fig. 6 use the nanocrystalline NaY zeolite prior to adsorption as
a reference. In addition, gas-phase absorptions have been subtracted from
each of the FT-IR spectra.
Fig. 7. FT-IR spectra of NO2 and propylene (1:1) mixture adsorbed in
nanocrystalline NaY zeolite at 298 K recorded as a function of increasing
total pressure (P = 0.100, 0.200, 0.623, 1.005 Torr). All spectra shown in Fig.
7 use the nanocrystalline NaY zeolite prior to adsorption as a reference. In
addition, gas-phase absorptions have been subtracted from each of the FT-IR
spectra.

30
G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
these assignments are based on previous studies reported in
the literature [42–52].
These organic compounds may be intermediates or possibly
final products in the SCR reaction.
It is important to note that the spectra contain a wealth
of information and there is some considerable overlap of
some of the bands in several spectral regions. For example,
both Na+-nitrates and surface adsorbed organic nitro com-
pounds can contribute to the intensity of the observed band
at 1387 cm−1. The absorption at 1647 cm−1 is assigned to
organic nitrito species, but it may also, in part, be due to
the formation of carbonyl groups in primary amides or the
C N stretching mode of oximes [47,48]. Therefore, care-
ful analysis of the FT-IR spectra is important in identifying
the adsorbates present. Thermal stability of the surface com-
pounds was investigated to assist in making these spectral
assignments. The NaY zeolite was equilibrated with NO2
and propylene (1:1) mixture for 30 min. After evacuating the
gas phase, the NaY zeolite was heated for 30 min and cooled
backtoroomtemperaturebeforerecordingeachofthespectra
shown in Fig. 8.
Surface adsorbed NO (1969 cm−1
)
and N2O3
(1943 cm−1) appear upon adsorption of the NO2 and
propylene mixture. These species are stable up to hours at
room temperature. However, they disappeared quickly upon
heating to 373 K. Another surface species that appears to
have similar stability is identified as NCO species on Si4+
sites. NCO is identified by the absorption band at 2317 cm−1
and has been identified in previous studies using isotope
labels [7]. Two surface species characterized by fairly
intense absorption bands at 1557 and 1647 cm−1 appear to
be more thermally stable than NO, N2O3 and NCO as these
bands persist in the spectra even after heating to 373 K.
Yeom et al. investigated the adsorption and reactions of
nitromethane in zeolite Y [7]. Based on their isotopic studies,
the two intense absorption bands are assigned to organic
nitro (1557 cm−1) and nitrito (1647 cm−1) compounds,
respectively. Another possible stable intermediate that some
consider to be important in the SCR reaction is oxime.
Oxime may be responsible for the broad absorbance between
3150 and 3300 cm−1 [18].
Adsorption of the NO2 and propylene mixture results in
the formation of several oxygenated and nitrogen-containing
organic compounds. As seen in Figs. 7 and 8, adsorbed oxy-
genated hydrocarbons (CxHyOz) with absorptions at 2985,
1723, 1694, 1528, 1508 and 1354 cm−1 appear immediately
in the spectrum recorded at 298 K. Carbonyl group contain-
ing compounds may come about from the direct oxidation
Most of the absorption bands decreased in intensity af-
ter the nanocrystalline NaY zeolite was heated at elevated
temperature. Ketones or aldehydes are produced at 373 K as
indicated by the band at 1694 cm−1 but then convert into
other products by heating to 473 K. Surface adsorbed carbon
dioxide (2355 cm−1) and isocyanic acid (2272 cm−1) [7] de-
velop in the zeolite upon heating to 373 and 473 K (Fig. 8).
At elevated temperature, two other absorption peaks appear
in the spectra at 2239 and 2187 cm−1 (Fig. 8). These two fea-
tures have been assigned to organic isocyanate and nitrile in
several previous studies using alumina-supported materials
as SCR catalysts [19,48–52]. The assignments of isocyanate
and nitrile have been supported by other experiments involv-
ing NO + CO reactions [50]. Since there is EFAL detected in
the nanocrystalline NaY zeolite used in our study, these two
absorptions are assigned to organic isocyanate and nitrile ad-
sorbed on EFAL sites. They most likely come from the ther-
mal reaction of organic nitro/nitrito compounds or oxime.
Unlike the band at 1557 cm, the absorption at 1647 cm−1
persists even after heating to 473 K. This may indicate the
formation of a primary amide, which can be generated via
the hydrolysis of nitriles and/or thermal reaction of organic
nitro/nitrito species. The assignment for the bands at 1598
and 1483 cm−1 is difficult since there are numerous litera-
ture assignments for bands at these two frequencies and are
most likely due to the presence of unsaturated carbonaceous
residues or coke [46]. Organic isocyanates and coke are the
only compounds adsorbed in NaY zeolite after evacuating
the sample overnight at 673 K.
−
of adsorbed propylene by adsorbed NOx [22,41,53]. Two
bands at 1528 and 1508 cm−1 develop quickly after the co-
adsorption of NO2 and propylene. These have been previ-
ously assigned to carbenium ions formed upon adsorption of
olefins on acidic zeolites [54]. Since there are no strong Bron-
sted acid sites in the nanocrystalline NaY zeolite used in our
study, these two bands are most likely due to the formation of
monodentate carbonate and formate ions, respectively [55].
Fig. 8. FT-IR spectra of adsorbed species following adsorption of an NO2
and propylene (1:1) mixture at (a) 298 K and heating to (b) 373 K and (c)
473 K. All spectra shown in Figs. 8 use the nanocrystalline NaY zeolite prior
to adsorption as a reference. In addition, gas-phase absorptions have been
subtracted from each of the FT-IR spectra.
3.4. Low temperature propylene-SCR of NO2
Propylene-SCR of NO2 at different temperatures was in-
vestigated next. The FT-IR spectra of the gas phase as a func-

G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
31
Table 3
−
Product distribution and conversion of gas-phase NO2 and adsorbed NO3
in propylene-SCR of NO2 at different temperatures after 6 h of reaction time
Reaction
temperature (K)
Product distribution
%Conversionb
(␮mol L−1
NO N2O CO
12.5 3.0
)
a
−
CO2
NO2
NO3
298
373
473
473c
0
0
1.6
8.6
82
100
100
100
100
0
3
29
68
87
0
0
0.4
0
24.7
28.1
40.9 3.7
25.1 4.6
6.4 13.9
1.3 40.7
d
473, O2
a
The total loading of NO2 was 50 5 ␮mol L−1; in the absence of oxy-
gen the initial concentration of gas-phase NO2 after adsorption equilibrium
at 298 K was 16 4 ␮mol L−1
.
b
Co−nversion of NO2 refers to the change of NO2 in gas phase; conversion
of NO3 describes the change associated with the integrated absorbance in
the entire 1230–1600 cm−1 spectral region (because of overlapping absorp-
tion bands due to other adsorbed species, this estimate could be in error by
as much as 20%).
Fig. 9. FT-IR spectra of the gas phase following propylene-SCR of NO2 in
nanocrystalline NaY at 473 K for (a) 0 min, (b) 10 min, (c) 30 min, (d) 1 h
and (e) 4 h.
c
Propylene-SCR of NO2 was done using a partially deactivated zeolite
catalyst (see text for further details).
d
tion of time at a temperature of 473 K is shown in Fig. 9.
The concentration of the gases was again calculated from
the integrated absorbance of the individual band using the
calibration procedure discussed in the experimental section.
Fig. 10 shows the amount of the various gaseous species as a
function of time in propylene-SCR of NO2 at 473 K. Immedi-
ately after the heating process begins, gaseous NO2 decreases
and is completely gone after 25 min. The concentrations of
NO and N2O initially increase until a maximum is reached
at approximately t = 10 min, then gradually decrease to zero.
Propylene (1459 and 1657 cm−1), CO (2143 cm−1) and CO2
(2348 cm−1) were the only carbon-containing molecules de-
tected in the gas phase. Although not directly measured, N2
and O2 most likely form as well, based on the estimated ni-
trogen mass balance. Some water is apparent in the gas-phase
spectra as well. A similar time course experiment was done at
T = 373 K. These data are summarized in Table 3 with some
additional experiments as well.
Propylene-SCR of NO2 with O2 present in the IR cell.
Table 3 summarizes the gas-phase product distribution
and percent conversion of gas-phase NO2 and adsorbed
nitrate (vide infra) in propylene-SCR of NO2 at three
different temperatures (298, 373 and 473 K). Based on the
nitrogen balance, the complete reduction of NO2 into N2
and O2 was found at 473 K after 6 h of reaction. Although
a small amount of N2O existed after 6 h at 373 K, it was
expected that it too would disappear with longer reaction
time. CO and CO2 were generated as the major carbon
containing products in the gas phase.
−
It should be pointed out that the conversion of NO3 in
Table 3 stands for the conversion of species responsible for
the absorption bands between 1230 and 1600 cm−1. Even
though some of the absorptions in the region are due to other
adsorbates,−it can still be an approximate measure of how
−
much NO3 species reacted since NO3 accounts for most
of the absorbance in that region (estimated to be ∼90%).
Complete conversion of NO2 did not occur when coke
accumulated in the NaY zeolite (referred to as “partially de-
activated NaY zeolite” in Table 3). Propylene-SCR of NO2
at 473 K in a partially deactivated NaY zeolite converted ap-
proximately 90% of loaded NO2 into NO and N2O. The evo-
lution of NO2, NO and N2O with time was similar to that
of thermal reduction, except for the higher concentration of
N2O. Compared to SCR reaction in active NaY zeolite, less
propylenewasconsumed, buttheCO2 toCOratioandconver-
−
sion of NO3 were much higher. More undesired products,
i.e. partially oxidized organics, were generated in the zeolite
as well. These products include surface adsorbed carbonyl
compounds (1723 and 1694 cm−1).
Although an excess amount of oxygen is present under
typical lean burn conditions, only propylene and NO2 were
included in the starting reaction mixture in this study for sev-
eral reasons. First, an intermediacy of NO2 in SCR of NO has
been suggested [6]. Furthermore, the oxidation of propylene
Fig. 10. Evolution of gaseous N-containing species during propylene-SCR
of NO2 in nanocrystalline NaY at 473 K. The inset shows the decay and
evolution of propylene and carbon monoxide, respectively. Spectra were
recorded every 2 min.

32
G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
Table 4
Reaction 1 is the minor path since only a trace amount of wa-
ter is left in the zeolite after heating to 673 K under vacuum.
However, adsorption of NO2 happens preferentially via reac-
tion 1 in the presence of water, as indicated by the formation
of nitrite (1230 cm−1) in the spectra shown in Fig. 4.
In this study, decomposition of NO2 should involve the
participation of NO2 from the gas phase. An equilibrium
might exist between surface NOx− species and gaseous NO2
(reaction 3). At elevated temperature, NO2 was released from
the NaY zeolite and reacted with surface cationic sites (reac-
tion 4a) or nitrite (reaction 4b). Mn+ represents Na+ or EFAL
sites.
Initial reaction rates (10−2 ␮mol L−1 s−1) in first 10 min
Reaction
temperature (K)
Thermal (NO)
Propylene-SCR
NO2 (loss)
PE (loss)
CO
298
373
473
473a
a
0.1
1.0
2.8
0.4
2.1
2.0
0.9
0
0
0.7
0.8
0.3
2.9
2.6
0.4
Propylene-SCR of NO2 was done using a partially deactivated zeolite
catalyst (see text for further details).
by oxygen competes with the SCR reaction. This is confirmed
by the propylene-SCR of NO2 in nanocrystalline NaY zeolite
at 473 K in the presence of oxygen, propylene was found to
be consumed within 2 h at 473 K. The concentration of NO
reached a maximum and then decreased slowly.
−
M
n+ − NO3
→ NO2 + Mn+ − O−(at elevated temperature)
(3)
Table 4 summarizes the initial reaction rates in catalytic
reduction of NO2. The initial reaction rates were obtained by
linear fitting the concentration of individual gaseous species
in the first 10 min of the reaction. NO for thermal reduc-
tion, NO2, propylene and CO for SCR reaction were chosen
because their concentration changed monotonically with re-
action time. In thermal reduction of NO2, the initial reaction
rates increased with temperature. Propylene-SCR of NO2 did
not occur to any great extent in nanocrystalline NaY zeolite at
room temperature. In propylene-SCR of NO2, the initial re-
action rates at 373 K were approximately the same as those at
473 K. This reveals a free radical behavior for the early stage
of SCR reactions as the reaction rates are independent of tem-
perature once a certain threshold temperature is reached in
which the free radicals are formed. The high CO to CO2 ratio
in Table 3 also suggests a free radical pathway [7].
−
Mn+ + 2NO2 → Mn+ − NO3 + NO
(4a)
(4b)
n+ − NO2 + NO2 → Mn+ − NO3 + NO
−
−
M
The small amount of N2O produced in thermal reduction
of NO2 might come from the disproportionation of NO
[12,38,56]. Significant thermal reduction of NO to N2O was
observed only at temperature above 573 K.
Notably, the concentration of NO reached a maximum at
t = 150 min and was constant thereafter (Fig. 5). Conversion
of surface NO3− species increased from 64% at 373 K to 90%
at 473 K (Table 1). This means that some of the NO3− species
are more strongly adsorbed and less reactive. Two different
reactivity classes of surface nitrates in zeolite Y have been
observed in other studies [7].
4.2. Formation of NO and N2O in the adsorption of NO2
and propylene mixture at room temperature
4. Discussion
The concentration of NO and N2O upon adsorption of the
NO2 and propylene mixture (Fig. 10) was consistently higher
than that after the adsorption of NO2 alone (Fig. 5). Surface
adsorbed NO and N2O3 (1969 and 1943 cm−1, respectively)
were observed upon exposure of the mixture to NaY zeolite
(Fig. 7), but not in the adsorption of NO2 alone (Fig. 4).
Although NO+ was not observed in the adsorption of NO2
and propylene mixture, it could play an important role due
to its low thermal stability and high reactivity. Gerlach et
al. studied the reactivity of NO+ towards propylene over
acidic Mordenite [18]. Their study demonstrated that oxime
was produced in the reaction between NO+ and propylene
at 393 K and converted into nitrile at higher temperature. In
this study, the disappearance of NO+ by propylene adsorp-
tion was observed at room temperature. First the NaY zeolite
was equilibrated with NO2 at room temperature. Then propy-
lene was introduced to NO2 pre-adsorbed NaY zeolite. NO+
vanished immediately upon the introduction of propylene. At
the same time, surface adsorbed NO and N2O3 are observed.
Other new surface species observed in adsorption of NO2 and
propylene mixture (Fig. 7) appear within 1 min after adsorp-
4.1. Formation of NO in thermal reduction of NO2
In earlier studies it was found that the adsorption of NO2
on ion exchanged Y zeolite occurred preferentially via sur-
face nitrates on exchangeable metal cation sites and partly on
cationic EFAL [12]. A second pathway has been proposed
involving the reaction between strongly adsorbed water and
NO2 [9,11]. Other studies indicate the possibility that nitrate
is formed via two or more different mechanisms that populate
different sites [7]. The disproportionation of NO2 has been
suggested to explain the formation of surface species and NO
over CuZSM-5 [41]. Underwood and co-workers proposed a
mechanism involving the formation of nitrite first followed
by nitrate [37].
Based on the experimental observations, the formation of
surface nitrate and nitrite in NaY zeolite can be best explained
by reactions 1 and 2.
2NO2 + H2O → HNO3 + HONO
(1)
(2)
−
2NO2 → NO+ + NO3

G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
33
tion. The intensity of 1407 cm−1 band characterizing surface
Na+-nitrates didn’t change significantly. This implies that at
T = 298 K surface Na+-nitrate is inactive toward reaction with
adsorbed propylene [7].
It is difficult to write the balanced reaction for propylene-
SCR of NO2 in the presence of excess oxygen because of the
multiple reaction pathways involved and the complexities of
these reactions. Complete oxidation of propylene by oxygen
to CO2 and water does occur in nanocrystalline NaY zeo-
lite at 473 K. This can be seen by the high CO2 to CO ratio
(Table 3) and the existence of surface adsorbed water after
SCR reaction for 6 h. As mentioned previously, NO reduc-
tion occurred very slowly once propylene was completely
consumed. The low SCR reaction rate is possibly due to a
combination of no propylene and the presence of surface ad-
sorbed water. Although oxygen does decrease the zeolite de-
activation by oxidizing carbonaceous deposits [6,59], overall
it is detrimental to the propylene-SCR of NO2.
Thus it is suggested from the data that NO+ and NO3− on
EFAL produced upon adsorption of NO2 (reaction 2) react
readily with adsorbed propylene to form NO and organic
nitro/nitrito compounds (reactions 5 and 6).
NO+ + CH3− CH CH2 → [CH3 CH CH2]+ + NO (5)
M
n+ − NO3 + [CH3 CH CH2]+
→ C3H5NO2 + Mn+ − OH
(6)
The high reactivity of the ␣-H in propylene and the stabiliza-
tion of allylic species by cations in zeolite Y could facilitate
these two reactions [57,58]. Reaction 6 can lead to the gen-
eration of acidic hydroxyl groups. This is consistent with the
appearance of a broad band at 3562 cm−1 associated with hy-
droxyl groups on EFAL (Fig. 7). Oxime was then produced
in the reaction between NO+ and adsorbed propylene in pres-
ence of the weak Bronsted acidic sites. It is also possible that
organic nitro/nitrito compounds came from the direct reac-
tion between adsorbed propylene and certain nitrate species,
most likely those attached to EFAL sites populated on the
external surface of the nanocrystalline NaY zeolite used in
this study.
4.4. A mechanism for propylene-SCR of NO2 at low
temperature
Several studies have focused on the mechanism for HC-
SCR of NOx. Most of them have suggested that isocyanate
is an important intermediate. The most controversial and
least understood aspect of the selective catalytic reduction
of NO2 is the formation of the nitrogen-nitrogen bond which
is necessary for the production of N2. In the SCR reaction
over Fe/ZSM-5, isotopic studies have shown that the nitro-
gen in N2 comes from both the gas phase NOx and surface
nitrogen-containing species [60]. Radical mechanisms in-
volving azoxy or dinitroso species have been proposed to ex-
plain the formation of dinitrogen in zeolites containing transi-
tion metals [17,57]. Others have considered –NH complexes
as the key intermediate [48]. Recently, Yeom et al. studied
the reactions of acetaldehyde, acetic acid and nitromethane
with NO2 on BaNa-Y zeolite [7]. Their study led to the con-
clusion that the formation of ammonium nitrite (NH4NO2)
is a crucial step for DeNOx catalysis. They also suggested
a parallel reaction channel involving free radicals to explain
reaction pathways which result in a high CO to CO2 ratio
[7].
4.3. Reaction stoichiometry in propylene-SCR of NO2
In the absence of oxygen, the balanced reaction for com-
plete reduction of NO2 by propylene can be written either
as
(9/2)NO2 + C3H6 ꢀ 3CO2 + (9/4)N2 + 3H2O
3NO2 + C3H6 ꢀ 3CO + (3/2)N2 + 3H2O
(7)
(8)
assuming CO2 or CO as the only carbon-containing products,
respectively.
As shown in Table 3, a high CO to CO2 ratio was ob-
served at both 373 and 473 K. Therefore, it can be concluded
that the majority of the propylene-SCR of NO2 in nanocrys-
talline NaY zeolite occurs via reaction 8 at low temperatures.
The concentration of CO2 was much higher at 473 K than
373 K. This can be easily understood since higher tempera-
ture promotes decomposition of oxygenated species and the
oxidation of CO to CO2. The initial reaction rates for NO2
and CO at both 373 and 473 K are approximately three times
that found for propylene (Table 4). Thus, the stoichiometry
shown in reaction 8 is in agreement with the measured rate
data.
Water was also observed in the gas phase in propylene-
SCR of NO2 at both 373 and 473 K (Fig. 9). However, surface
adsorbed water was not present to any great extent in the
zeolite after SCR reaction for 6 h. It is most likely that surface
adsorbed water was consumed in the hydrolysis of surface
species, such as organic nitrile.
Based on the observed kinetics and the discussion of the
literature above, a mechanism involving free radicals appears
to be the most plausible pathway for propylene-SCR of NO2
in nanocrystalline NaY zeolite. Thermal treatment is neces-
sary for C H bond dissociation in propylene [61]. At elevated
temperature, the SCR reaction is initiated by the abstraction
of H from adsorbed propylene to yield the allyl radical, ac-
cording to reaction 9 [62,63].
NO2 + CH3 CH CH2 → CH2 CH CH2 + HNO2 (9)
The allylic radical can react with HNO2 to give oxygenated
species and NO (reaction 10).
HNO2 + CH2 CH CH2 → C3H6O + NO
(10)
Upon thermal treatment, surface nitrogen containing com-
pounds (organic nitro/nitrito species and oximes) adsorbed
on EFAL sites are converted to nitrile or isocyanate. Acry-

34
G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
lamide species can be produced via the hydrolysis of organic
nitrile or isocyanate. The reaction between acrylamide and
HNO2 (reaction 11) provides one possible pathway for the
dinitrogen formation [64,65].
References
[1] G. Delahay, B. Coq, Catal. Sci. Ser. 3 (2002) 345.
[2] V.H. Grassian, Int. Rev. Phys. Chem. 20 (2001) 467.
[3] S. Bhattacharyya, R.K. Das, Int. J. Energy Res. 23 (1999) 351.
[4] R. Burch, J.P. Breen, F.C. Meunier, Appl. Catal. B: Environ. 39
(2002) 283.
RCONH2 + HNO2 → RCOOH + N2 + H2O
(11)
[5] Y. Traa, B. Burger, J. Weitkamp, Micro. Meso. Mater. 30 (1999) 3.
[6] M. Shelef, Chem. Rev. 95 (1995) 209.
[7] Y.H. Yeom, B. Wen, W.M.H. Sachtler, E. Weitz, J. Phys. Chem. B
108 (2004) 5386.
[8] B. Wen, Y.H. Yeom, E. Weitz, W.M.H. Sachtler, Appl. Catal. B:
Environ. 48 (2004) 125.
[9] J. Szanyi, J.H. Kwak, C.H.F. Peden, J. Phys. Chem. B 108 (2004)
3746.
[10] S.J. Schmieg, B.K. Cho, S.H. Oh, Appl. Catal. B: Environ. 49 (2004)
113.
[11] J. Szanyi, J.H. Kwak, R.A. Moline, C.H.F. Peden, Phys. Chem.
Chem. Phys. 5 (2003) 4045.
[12] C. Sedlmair, B. Gil, K. Seshan, A. Jentys, J.A. Lercher, Phys. Chem.
Chem. Phys. 5 (2003) 1897.
[13] A. Sultana, R. Loenders, O. Monticelli, C. Kirschhock, P.A. Jacobs,
J.A. Martens, Angew Chem. Int. Ed. 39 (2000) 2934.
[14] O. Monticelli, R. Loenders, P.A. Jacobs, J.A. Martens, Appl. Catal.
B: Environ. 21 (1999) 215.
Another possible channel is the reaction between acrylamide
and N2O3 in the presence of water.
In propylene-SCR of NO2, isocyanate radical
(2317 cm−1) and isocyanic acid (2272 cm−1) were generated
as stable species containing one atom each of nitrogen, car-
bon and oxygen. Isocyanic acid adsorbed in nanocrystalline
NaY zeolite very strongly and can be removed by heating to
573 K under vacuum. It was considered as the precursor of
ammonia, which is essential for the formation of dinitrogen
[7,66]. In our study, a minor pathway for nitrogen-nitrogen
bond formation might involve the reactions of isocyanate
radical and isocyanic acid as evidenced by the presence of
these species in the FT-IR spectra [51].
[15] R. Brosius, J.A. Martens, Top. Catal. 28 (2004) 119.
[16] V.A. Sadykov, V.V. Lunin, V.A. Matyshak, E.A. Paukshtis, A.Y. Ro-
zovskii, N.N. Bulgakov, J.R.H. Ross, Kinet. Catal. 44 (2003) 379.
[17] R.H.H. Smits, Y. Iwasawa, Appl. Catal. B: Environ. L6 (1995) 201.
[18] T. Gerlach, F.W. Schutze, M. Baerns, J. Catal. 185 (1999) 131.
[19] Y. Yu, H. He, Q. Feng, H. Gao, X. Yang, Appl. Catal. B: Environ.
49 (2004) 159.
[20] M. Haneda, Y. Kintaichi, M. Inaba, H. Hamada, Catal. Today 42
(1998) 127.
[21] T. Tanaka, T. Okuhara, M. Misono, Appl. Catal. B: Environ. 4 (1994)
L1.
[22] A. Satsuma, T. Enjoji, K. Shimizu, K. Sato, H. Yoshida, T. Hattori,
J. Chem. Soc., Faraday Trans. 94 (1998) 301.
[23] W. Song, G. Li, V.H. Grassian, S.C. Larsen, Environ. Sci. Tech.
(2004), in press.
[24] S.C. Larsen, V.H. Grassian, in: J.A. Schwarz, C.I. Contescu, K. Puty-
era (Eds.), Encyclopedia of Nanoscience and Nanotechnology, Mar-
cell Dekker Publishing Co., NY, 2004, 1137.
[25] Q. Li, D. Creaser, J. Sterte, Chem. Mater. 14 (2002) 1319.
[26] W. Song, R.E. Justice, C.A. Jones, V.H. Grassian, S.C. Larsen, Lang-
muir 20 (2004) 4696.
5. Conclusions
Catalytic reduction of NO2 in nanocrystalline NaY zeo-
lite was investigated using in situ transmission FT-IR spec-
troscopy. NO2 was stored in the NaY zeolite as nitrate and
nitrite. Because of the relatively high external surface area of
the nanocrystalline zeolite, there was considerable adsorp-
tion on the EFAL sites. Thermal reduction of NO2 showed
high selectivity to NO in the temperature range studied.
In the absence of oxygen, the selective catalytic reduc-
tion of NO2 with propylene at low temperature (T ≤ 473 K)
resulted in complete reduction of NO2 to N2 and O2 in
nanocrystalline NaY zeolite. Upon adsorption of propylene
and NO2 mixtures at room temperature, surface organic ni-
tro/nitrite compounds were produced together with other sur-
face species. Isocyanate and nitrile species formed on EFAL
sites are found to be important intermediates. Based on ki-
netic studies, a pathway involving radical reactions appeared
to be the most plausible mechanism for the complete reduc-
tion of NO2. In the proposed mechanism, complete reduction
of NO2 was initiated by H abstraction from propylene. The
resulting radical, HNO2, then continues on to form N2.
[27] G. Li, M. Xu, S.C. Larsen, V.H. Grassian, J. Mol. Catal. A: Chem.
194 (2003) 169.
[28] H.G. Karge, Micro. Meso. Mater. 22 (1998) 547.
[29] S. Khabtou, T. Chevreau, J.C. Lavalley, Micro. Mater. 3 (1994) 133.
[30] P.O. Fritz, J.H. Lunsford, J. Catal. 118 (1989) 85.
[31] Y. Xiang, S.C. Larsen, V.H. Grassian, J. Am. Chem. Soc. 121 (1999)
5063.
[32] F. Thibault-Starzyk, B. Gil, S. Aiello, T. Chevreau, J. Gilson, Micro.
Meso. Mater. 67 (2004) 107.
[33] M.R. Basila, T.R. Kantner, K.H. Rhee, J. Phys. Chem. 68 (1964)
3197.
Acknowledgements
The authors thank Hassan Alwy for providing the
nanocrystalline NaY zeolite sample. Although the research
described in this article has been funded wholly or in part by
the Environmental Protection Agency through grant number
EPA R829600 to SCL and VHG, it has not been subjected to
the Agency’s required peer and policy review and therefore,
does not necessarily reflect the views of the Agency and no
official endorsement should be inferred.
[34] A.L. Goodman, E.T. Bernard, V.H. Grassian, J. Phys. Chem. A 105
(2001) 6443.
[35] K.I. Hadjiivanov, Catal. Rev. Sci. Eng. 42 (2000) 71.
[36] A.L. Goodman, T.M. Miller, V.H. Grassian, J. Vacuum Sci. Tech. A
16 (1998) 2585.
[37] A.L. Goodman, G.M. Underwood, V.H. Grassian, J. Phys. Chem. A
103 (1999) 7217.
[38] C.C. Chao, J.H. Lunsford, J. Am. Chem. Soc. 93 (1971) 71.
[39] C.C. Chao, J.H. Lunsford, J. Am. Chem. Soc. 93 (1971) 6794.

G. Li et al. / Journal of Molecular Catalysis A: Chemical 227 (2005) 25–35
35
[40] K. Hadjiivanov, J. Saussey, J.L. Freysz, J.C. Lavalley, Catal. Lett.
52 (1998) 103.
[54] I. Kiricsi, H. Foerster, G. Tasi, J. Mol. Catal. 65 (1991)
L29.
[41] K. Hadjiivanov, D. Klissurski, G. Ramis, G. Busca, Appl. Catal. B:
Environ. 7 (1996) 251.
[55] T.E. Hoost, K.A. Laframboise, K. Otto, Appl. Catal. B: Environ. 7
(1995) 79.
[42] S.V. Gerei, E.V. Rozhkova, Y.B. Gorokhovatskii, J. Catal. 28 (1973)
341.
[56] T. Weingand, S. Kuba, K. Hadjiivanov, H. Knoezinger, J. Catal. 209
(2002) 539.
[43] B.A. Morrow, I.A. Cody, J. Chem. Soc., Faraday Trans. 1 (71) (1975)
1021.
[57] N.W. Hayes, R.W. Joyner, E.S. Shpiro, Appl. Catal. B: Environ. 8
(1996) 343.
[44] F. Solymosi, T.J. Bansagi, J. Catal. 156 (1995) 75.
[45] V.H. Grassian, J. Phys. Chem. A 106 (2002) 860.
[46] J.M. Garcia-Cortes, J. Perez-Ramirez, J.N. Rouzaud, A.R. Vaccaro,
M.J. Illan-Gomez, C. Salinas-Martinez De Lecea, J. Catal. 218
(2003) 111.
[58] T. Beutel, B. Adelman, W.M.H. Sachtler, Catal. Lett. 37 (1996)
125.
[59] J.L. d’Itri, W.M.H. Sachtler, Appl. Catal. B: Environ. 2 (1993)
L7.
[60] H.Y. Chen, T. Voskoboinikov, W.M.H. Sachtler, J. Catal. 186 (1999)
[47] A.L. Smith, Applied Infrared Spectroscopy: Fundamentals, Tech-
niques, and Analytical Problem Solving, 1979.
[48] M. Haneda, N. Bion, M. Daturi, J. Saussey, J. Lavalley, D. Duprez,
H. Hamada, J. Catal. 206 (2002) 114.
91.
[61] E. Finocchio, G. Busca, V. Lorenzelli, R.J. Willey, J. Catal. 151
(1995) 204.
[62] J. Vassallo, E. Miro, J. Petunchi, Appl. Catal. B: Environ. 7 (1995)
[49] Y. Ukisu, S. Sato, A. Abe, K. Yoshida, Appl. Catal. B: Environ. 2
(1993) 147.
65.
[63] A.D. Cowan, R. Duempelmann, N.W. Cant, J. Catal. 151 (1995)
[50] G.R. Bamwenda, A. Ogata, A. Obuchi, J. Oi, K. Mizuno, J.
Skrzypek, Appl. Catal. B: Environ. 6 (1995) 311.
[51] W. Schiesser, H. Vinek, A. Jentys, Appl. Catal. B: Environ. 33 (2001)
263.
356.
[64] P.A.S. Smith, The Organic Chemistry of Open-Chain Nitrogen Com-
pounds, vol. I, 1965.
[65] H.Y. Chen, T. Voskoboinikov, W.M.H. Sachtler, J. Catal. 180 (1998)
[52] S. Sumiya, H. He, A. Abe, N. Takezawa, K. Yoshida, J. Chem. Soc.,
Faraday Trans. 94 (1998) 2217.
[53] K. Hadjiivanov, L. Dimitrov, Micro. Meso. Mater. 27 (1999) 49.
171.
[66] N.W. Cant, D.C. Chambers, A.D. Cowan, I.O. Liu, A. Satsuma, Top.
Catal. 10 (2000) 13.