Micro-/mesoporous copper-containing zeolite Y applied in NH3-SCR, DeNOx

Microporous and Mesoporous Materials 334 (2022) 111793

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Microporous and Mesoporous Materials
journal homepage: www.elsevier.com/locate/micromeso

Micro-/mesoporous copper-containing zeolite Y applied in
NH3-SCR, DeNOx
Rujito S.R. Suharbiansah a, Kamila Pyra b, Michael Liebau a, David Poppitz a,
ra-Marek b, Roger Gla
ăser a, Magdalena Jabon
ska a, *
Kinga Go
a
b

Institute of Chemical Technology, Universită
at Leipzig, Linnestr. 3, 04103, Leipzig, Germany
Faculty of Chemistry, Jagiellonian University in Krakow, Gronostajowa 2, 30-387, Krakow, Poland

A R T I C L E I N F O

A B S T R A C T

Keywords:
Zeolite Y
Micro-/mesoporous zeolites
Copper
NH3-SCR
Time-resolved FT-IR

Zeolite Y was prepared by a dense-gel method and subsequently modified either by treatment with diethylamine
(DEA), sodium hydroxide (NaOH) or disodium ethylenediaminetetraacetate (Na2H2EDTA), or by sequential
treatment (H4EDTA-NaOH or H4EDTA-NaOH-Na2H2EDTA). Individual treatment did not succeed in introducing
mesoporosity in the parent zeolite Y, while the sequential treatment lead to formation of mesopores. After
introduction of Cu2+ ions, the obtained materials were studied as catalysts for the selective catalytic reduction of
NOx by NH3 (NH3-SCR, DeNOx). The catalytic investigations reveal a similar NO conversion for all Cu-containing
catalysts up to 450 ◦ C, independent of the introduced mesoporosity. Insights into the dynamics of NH3-SCR
intermediates through rapid scan FT-IR show that for Cu–Y, the rate-determining step is the formation of the
mixed [Cu(O− )(NH3)n-1(NO)]2+ complexes, which initiate the NH3-SCR reaction.

1. Introduction
Selective catalytic reduction of NOx by NH3 (NH3-SCR, DeNOx) is
used as an efficient technology to eliminate NOx from diesel exhaust
gases. Several research groups have reported property-activity
relationship for Cu-containing molecular sieves, e.g., Cu-ZSM-5 or CuSSZ-13 [1]. However, the catalytic properties of zeolite Cu–Y have
been less extensively investigated compared to other Cu-containing
zeolites. For instance, Kwak et al. [2] showed a significant loss of ac­
tivity for Cu–Y (n(Si)/n(Al) = 2.6, 7.2 wt.-% of Cu) above 300 ◦ C.
Furthermore, after hydrothermal treatment (800 ◦ C, 16 h, 10 vol.-%
H2O), the Cu–Y catalyst completely lost its activity in NH3-SCR. Also,
Zhou et al. [3] showed high SCR-activity of Cu–Y below 300 ◦ C, while
activity at higher temperatures was not provided. Additionally, Wang
et al. [4] showed that the Cu–Y catalyst (n(Si)/n(Al) = 5.10, 4.97 wt.-%
of Cu) possesses similar (up to 300 ◦ C) and even higher activity (above
300 ◦ C) than the other copper-exchanged straight-channel zeolites
(Cu-ZSM-5, Cu-Beta). Furthermore, some studies (e.g., Refs. [5,6]) show
that the presence of mesopores in the zeolite-based catalysts leads to
high dispersion of the metal component in comparison to conventional
microporous materials and thus also enhanced activity and N2 selec­

tivity during the NH3-SCR. Also, Komatsu et al. [7] identified modified

(in an aqueous solution of HNO3) USY as an effective support for the
formation of highly dispersed copper species (based on adsorbed NO).
The authors showed that the activity of Cu-USY increased for materials
from n(Si)/n(Al) = 7.5 to 50. Cu-USY (n(Si)/n(Al) = 50, 11 wt.-% of Cu)
reached maximum NO conversion of 70–80% in the range of
227–527 ◦ C. Verboekend et al. [8] pointed out that tetrapropylammo­
nium hydroxide (TPAOH) or diethylamine (DEA) yielded micro-/­
mesoporous USY zeolites featuring crystallinities even higher than those
obtained from applying mixtures of NaOH and tetrabutylammonium
bromide (TPABr) [8]. Recently Jabło´
nska et al. [9] reported that the
microporous structure was necessary for the formation of isolated
Cu+/Cu2+, and thus enhanced NO conversion over Cu-ZSM-5 (contrary
to micro-/mesoporous Cu-containing catalysts with support
post-modified with an aqueous solution of NaOH or NaOH/TPAOH).
Thus, in order to clarify the effect of the introduced mesoporosity on the
catalytic properties of Cu-containing zeolite Y in the NH3-SCR, DeNOx,
in the present study, zeolite Y (n(Si)/n(Al) = 2.5) was synthesized and
exposed to a variety of post-synthetic treatments (i.e., in an aqueous
solution of diethylamine (DEA), disodium ethylenediaminetetraacetate
(Na2H2EDTA) or sodium hydroxide (NaOH), sequential treatment with
ethylenediaminetetraacetic acid (H4EDTA) and NaOH, as well as
following treatment with Na2H2EDTA). The Cu-containing zeolites were

* Corresponding author.
E-mail address: (M. Jabło´
nska).
/>Received 16 December 2021; Received in revised form 14 February 2022; Accepted 25 February 2022

Available online 28 February 2022
1387-1811/© 2022 The Author(s).
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R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

characterized with respect to structure and morphology (XRD, SEM,
ICP-OES), texture (N2 sorption), acidic properties (FT-IR studies of
pyridine sorption), the nature of the copper species (DR UV–Vis, TEM,
TPD-NOx, FT-IR studies of CO sorption), and were investigated as cat­
alysts for the NH3-SCR reaction, DeNOx. Furthermore, this study aims to
provide insight into the reaction mechanism of the NH3-SCR by rapid

scan FT-IR spectroscopy under realistic application conditions (contrary
to the ex situ technologies proposed in the literature), providing insight
for the future SCR catalyst design.

commercial zeolite Na–Y (Zeolyst, CBV 100, n(Si)/n(Al) = 2.55) has
been applied to prepare the Cu–Y_com sample.
The copper-containing Y materials were characterized concerning
structure and morphology (XRD, SEM, ICP-OES), texture (N2 sorption),
acidity (IR studies of pyridine sorption), the nature of copper species (DR
UV-Vis, TEM, TPD-NOx, CO sorption followed by FT-IR), catalytic ac­
tivity and selectivity (NH3-SCR). The reaction mechanism was investi­
gated through time-resolved IR measurements. The details of the
experimental procedure can be found in the Supplementary data.

2. Experimental

3. Results and discussion

Synthesis gel with the composition of 8 Na2O: Al2O3: 10 SiO2: 410
H2O was prepared according to the procedure described by Dabbawala
et al. [10]. Briefly, the obtained gel was sealed and: 1) aged at room
temperature (RT, ca. 25 ◦ C) for 24 h and afterward hydrothermally
crystallized in the oven at 100 ◦ C for 12 h or 21 h (Na–Y/24RT-12HT,
Na–Y/24RT-21HT); 2) hydrothermally crystallized in the oven at 100 ◦ C
for 21 h (Na–Y/0RT-21HT). For further post-synthetic modification or
modification with copper species, Na–Y/24RT-21HT has been applied, i.
e., the material with aging for 24 h at room temperature and for 21 h at
100 ◦ C. The calcined zeolite Y was treated by an aqueous solution of 1)
diethylamine (Y_DEA), 2) sodium hydroxide (Y_NaOH), 3) disodium
ethylenediaminetetraacetate

(Y_Na2H2EDTA),
4)
ethyl­
enediaminetetraacetic acid (H4EDTA) and NaOH (Y_H4EDTA_NaOH) as
well as treatment with 5) Na2H2EDTA (H4EDTA_NaOH_Na2H2EDTA).
All materials were ion-exchanged in an aqueous solution of copper ni­
trate for 24 h at room temperature, separated by filtration, washed with
distilled water, and finally calcined. For comparative purposes also the

3.1. Structural and textural properties of zeolite Y and Cu–Y
Fig. SI1a shows the X-ray powder diffractograms of zeolite Na–Y with
varied aging time (0 or 24 h at room temperature) and hydrothermal
treatment (12 h or 21 h at 100 ◦ C). For all materials, the XRD pattern
shows the typical peaks of the zeolite Y at 2θ = 6.3, 10.3, 12.2, 16, 19.1,
20.7, 23.3, 24.1, 27.6, 31.4, 32, and 34.8◦ . The obtained XRD results
indicated that no changes in the characteristic peaks for materials pre­
pared with varied aging time and hydrothermal treatment (Na–Y/24h21HT, Na–Y/24h-12HT, Na–Y/0RT-21HT) were observable. Indeed, a
high degree of crystallinity of the zeolite Y also after modification can be
concluded from the high intensity and narrow peaks. All materials
reveal similar crystal size determined by the Scherrer equation in the
range of 85–102 nm (Table. SI1). The Cu-containing zeolite Y exhibits
similar XRD patterns (Fig. SI1b,c) to the zeolite Na–Y, while the crystal
size of the samples varies in the range of 79–102 nm. The crystallinity
declined which was caused either by post-synthetic alkali- and acid-

Fig. 1. SEM images of zeolite Na–Y: a) Na–Y/24RT-21HT, b) Na–Y/0RT-21HT, and c) Cu–Y, d) Cu–Y_DEA. The particle size distribution (inlay in c and d) was
obtained by counting 100 particles from SEM images.
2

R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

treatments or the subsequent calcination. No amorphous phase or other
copper phase were detected. All these findings indicate that in all Cucontaining zeolite Y, very small crystal sizes below 1 nm or maybe
atomically dispersed copper species are present.
Fig. 1 presents SEM images of zeolite Na–Y and Cu-containing zeolite
Y. The zeolite Na–Y with 24 h of aging time at room temperature (Na–Y/
24RT-21HT) possessed a smaller particle size in the range of 0.43–0.69
μm than zeolite Na–Y obtained without the aging step at room tem­
perature (Na–Y/0RT-21HT), having particle sizes in the range of
2.48–6.81 μm. Aging of the synthesis mixture before crystallization is a
common method used to tailor the size of zeolite crystals. For instance,
ărog
lu et al. [11] showed that lower temperature (4 ◦ C versus 25 ◦ C)
Ko
favored the formation of smaller zeolite Y crystals (after 120–432 h of
aging time), especially when a less alkaline gel composition was applied
(4.16 Na2O: 1 Al2O3: 10 SiO2: 205 H2O versus 5.3 Na2O: 1 Al2O3: 10
SiO2: 205 H2O). Also, Ginter et al. [12] pointed out that a longer period
of aging times (up to 48 h) at room temperature in the preparation of
zeolite Na–Y could accelerate the crystallization by decreasing the
crystal size (from 4 μm at 0 h to 1.1 μm at 48–86 h). This seems to be
valid also for our studies, i.e., the aging in the room temperature for 24 h
results in the decrease of the crystal size (Na–Y/24RT-21HT,
Na–Y/0RT-21HT, Fig. 1a and b). Comparing the results (zeolite Na–Y
with approx. particles size of 400 nm) obtained by Dabbawala et al.
[10], higher average particle size in the present case could be a result of
longer hydrothermal treatment time (21 h in our case instead of 12 h).

The copper-exchanged zeolite Y (Cu–Y) shows a homogeneous particle
size distribution in the range of 350–650 nm (Fig. 1c). SEM

investigations of samples with modified support (Cu–Y_DEA shown as an
example, Fig. 1d) reveal no obvious differences among them (particle
sizes of 300–700 nm). It should be mentioned that SEM imaging shows
the topography of the samples and thus particle sizes (accumulation of
crystallites) were measured, different from XRD analysis where crys­
tallite size was obtained. By means of TEM (Fig. 2a–c) and HAADF-STEM
material contrast imaging (Fig. 2d–f), the size and distribution of the
copper species within the zeolite Y particles is shown. A homogenous
distribution of the copper species is observed for all investigated sam­
ples. The particle size distribution data (Fig. 2) allow for conclusions on
the higher dispersion of copper-oxide species in Cu–Y_DEA and Cu–Y
than in a commercially available Na–Y material (after introduction of
Cu2+ ions) despite the lower Cu content in the latter material (Table 1).
Table 1 gathers the results of the elemental analysis of the zeolite
Na–Y and Cu-containing zeolite Y. The n(Si)/n(Al) ratio obtained for
Na–Y/24RT-21HT was similar to that obtained for the zeolite Y without
aging at room temperature (Na–Y/0RT-21HT). These results also
approve the investigations presented by Dabbawala et al. [10]. The
relatively high content of Na (8.9–9.2 wt.-%) was also reported for
commercial zeolite Na–Y (n(Si)/n(Al) = 2.55, 6.79–6.80 wt.-% of Na)
[13,14], also for the one included in our studies (Zeolyst, CBV 100, n
(Si)/n(Al) = 2.55, 8.7 wt.-% of Na). The prepared Na–Y zeolites were
exchanged with an aqueous solution of Cu(NO3)2, where one Cu2+
cation substitutes two Na+ sites or two surface hydroxyl groups. After Cu
exchange, the Na content significantly decreases, as well as the n(Si)/n
(Al) ratio. The total loading of Cu species in all samples varies in the
range of 6.5–9.1 wt.-%. As shown, in Table 1, the Cu loading slightly

Fig. 2. TEM images of Cu-containing zeolite Y: a) Cu–Y_com; b) Cu–Y, and c) Cu–Y_DEA and HAADF-STEM material contrast images d-f. The particle size distribution
(inlay in a-c) of copper species was obtained by counting 100 particles randomly from TEM images.
3


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Microporous and Mesoporous Materials 334 (2022) 111793

Table 1
Results of elemental analysis of the zeolite Na–Y and Cu-containing zeolite Y by ICP-OES: (ωi: mass fractions).
Sample

ωAl/wt.-%

ωSi/wt.-%

ωNa/wt.-%

ωCu/wt.-%

n(Si)/n(Al)

Na–Y/24RT-21HT
Na–Y/0RT-21HT
Y_com

11.4
11.1

10.5

29.6
28.4
25.2

9.2
8.9
8.7

–
–
–

2.49
2.45
2.30

Cu–Y
Cu–Y_com
Cu–Y_DEA
Cu–Y_NaOH
Cu–Y_Na2H2EDTA

10.2
8.3
10.8
10.5
10.0

17.0
19.8
19.2
17.6
18.6

2.9
2.3
2.9
2.8
2.9

8.2
6.5
8.3
8.7
9.0

1.60
2.29
1.70
1.61
1.78

Cu–Y_H4EDTA_NaOH
Cu–Y_H4EDTA_NaOH_2
Cu–Y_H4EDTA_NaOH_Na2H2EDTA_2

10.1
10.9

9.9

19.2
20.1
19.2

2.5
2.8
2.4

9.0
9.1
8.5

1.82
1.77
1.86

0.28–0.37 cm3 g− 1 [19–21], respectively. The specific surface area and
the pore volume of the Cu–Y sample decrease after the ion-exchange due
to blockage of the pores or cavities by copper oxo-species located on the
external crystal surface blocking the micropore entrances, and/or
located directly in micropores [22]. For the copper form of the
post-synthetically modified zeolite Y (in the presence of DEA, NaOH or
Na2H2EDTA), no additional mesoporous characteristics were detected
(Fig. 3a and b). Again, it is demonstrated that the post-synthetic treat­
ment of the bulk phase of zeolite Y with a low n(Si)/n(Al) ratio of ca. 2.5
is not effective, as concluded previously from chemical analysis
(Table 1). The N2 isotherms of the Cu-containing materials based on the
sequentially treated Y support (Fig. 3c) display an uptake at low relative

pressure compared to others. The pore width distribution shown in
Fig. 3d in the range of 20–50 nm corresponds to the introduction of
mesoporosity [16,23]. The specific surface area significantly drops (to
111–121 m2 g− 1) for the materials with sequentially treated zeolite Y,
while total pore volume increases to ca. 0.51–0.72 cm3 g− 1. These sig­
nificant textural changes for H4EDTA treated materials, supported by a
loss of crystallinity (XRD studies, Fig. SI1c), indicate a significant
deterioration of microporosity of zeolite Y caused by sequential leach­
ing. Indeed, the hysteresis loop confirms the presence of mesopores.

increases after the modification indicating that the Cu exchange
capacity of the Y zeolite is enhanced by the post-synthetic treatment.
For the Cu-containing materials with modified zeolite Y (with DEA,
NaOH or Na2H2EDTA), a very similar n(Si)/n(Al) ratio of 1.61–1.78 is
obtained. The post-synthetic treatment of zeolite Y is influenced by the
density of Al ions. Zeolite Y with low n(Si)/n(Al) ratio (n(Si)/n(Al) < 20)
has a high concentration of AlO4− which protects the zeolite framework
against attacks by OH− . For zeolites with n(Si)/n(Al) > 20, introduction
of mesopores is more efficient [15]. Thus, Verboekend et al. [16]
claimed that to obtain micro-/mesoporous Y zeolite (with n(Si)/n(Al)
ca. 2.5), post-synthetic modification with acid treatment in
ethylenediaminetetraacetic acid (H4EDTA) followed by alkaline
treatment in NaOH should be applied. Treatment with aqueous
Na2H2EDTA is commonly used to remove extra-framework Al from
steamed USY zeolites [17]. Contrary to the results presented by
Verboekend et al. [16], the sequential treatment – in terms of time
or additional step of treatment with Na2H2EDTA - does not vary
significantly with respect to the n(Si)/n(Al) ratio between the studied
materials.
Fig. SI2 shows the isotherms and pore width distribution of zeolite

Na–Y, while Table 2 summarizes its textural properties. The zeolite Na–Y
samples (Na–Y/0RT-21HT, Na–Y/24RT-21HT) exhibit type IV isotherms
with a H4 hysteresis loop [18] at a partial pressure in the range of
0.5–0.9. The Na–Y/24RT-21HT material shows also a wider hysteresis
loop in the partial pressure region of 0.8–1.0, indicating the increase of
the specific mesopore volume (from 0.02 to 0.04 cm3 g− 1). This material
possesses also a higher specific surface area (647 m2 g− 1) than the one
obtained without aging (Na–Y/0RT-21HT, 564 m2 g− 1). For compara­
tive purposes, the specific surface area and pore volume of zeolite Na–Y
reported in the literature vary in the range of 574–681 m2 g− 1 and

3.2. Nature of copper species in Cu-containing zeolite Y
The results of NH3-SCR (chapter 3.3.) indicate that modification of
the zeolite Y did not significantly influence the activity and selectivity of
the investigated materials. Thus, the nature of copper species was
evaluated for the selected materials through DR UV–Vis (Fig. 4a), TPDNOx (Fig. 4b) as well as IR studies of CO sorption (Fig. 5). Among the
investigated materials, copper species are mainly present as isolated

Table 2
Textural properties determined from the N2-sorption isotherms: specific surface area (AS(BET)), specific total pore volume (V(TOT)), micropore (V(MIC)), and mesopore
volume (V(MES)).
Sample

AS(BET)/m2 g−

1

V(TOT)/cm3 g−

Na–Y/0RT-21HT

Na–Y/24RT-21HT
Cu–Y

564
647
510

0.30
0.36
0.29

0.02
0.04
0.05

0.28
0.32
0.24

Cu–Y_com
Cu–Y_DEA
Cu–Y_NaOH
Cu–Y_Na2H2EDTA

589
500
514
541

0.32

0.28
0.30
0.31

0.04
0.05
0.06
0.07

0.28
0.23
0.24
0.24

Cu–Y_H4EDTA_NaOH
Cu–Y_H4EDTA_NaOH_2
Cu–Y_H4EDTA_NaOH_Na2H2EDTA_2

120
111
121

0.51
0.72
0.64

0.49
0.70
0.62

0.02
0.02
0.02

4

1

V(MES)/cm3 g−

1

V(MIC)/cm3 g−

1


R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

Fig. 3. a,c) N2 sorption isotherms and b,d) pore width distribution of Cu-containing zeolite Y after different types of treatment.

Fig. 4. a) DR UV–Vis spectra of Cu-containing zeolite Y, b) TPD-NOx profiles of Cu-containing zeolite Y.

which indicates the presence of d-d transition of Cu2+ ions in
pseudo-octahedral coordination (e.g., Cu(H2O)62+). Additional bands in
the range of 250–600 nm detected mainly for Cu–Y_Na2H2EDTA indicate
the presence of CuO species and [Cu–O–Cu]2+ species [4,9]. Among the
studied materials, the Cu–Y_com exhibits lower relative abundance of

the copper oxo-species, which is in line with the lower loading of Cu
(6.5 wt.-%) in this sample. The status of copper species was also

cations (the light blue colored ion-exchanged materials) or aggregated
copper species (the grey color of zeolite Y modified with an aqueous
solution of Na2H2EDTA) [24]. All samples reveal similar profiles with
the dominant broad band in the range of 200–250 nm, which can be
assigned to the charge transfer from framework oxygen to isolated Cu+
and/or Cu2+ ions stabilized in the zeolite framework. Besides, broad
bands are found for all samples in the wavelength region (600–900 nm),
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Microporous and Mesoporous Materials 334 (2022) 111793

Fig. 5. a) FT-IR spectra of CO adsorbed at room temperature on Cu-containing zeolite Y, b) Copper monocarbonyls bands intensity plotted as the function of Lewis
acid sites density derived from Py sorption.

investigated in NOx thermodesorption studies. In this approach, reagent
molecules was used to characterize the copper centers. Fig. 4b shows
TPD-NOx profiles of selected Cu-containing zeolite Y. Three main
desorption peaks centered at about ca. 220, 350, and 480 ◦ C for the
Cu-containing zeolite Y are found. An additional broad peak appears
below 150 ◦ C, which was assigned by some authors (e.g., Refs. [25,26])
to the physical adsorption of NO. In our case, the NO weakly bonded to
the catalyst surface was desorbed during the purging step in pure He,
before temperature-programed desorption. The desorption peak
centered at 220 ◦ C dominating for the Cu–Y_com, corresponds to the NO

molecules that desorbed from the isolated Cu+/Cu2+ (which demon­
strates the highest abundance in DR UV–Vis studies). Also this sample
reveals the highest NOx adsorption capacity of 32 μmol g− 1 (compared
to the other Cu-containing zeolite Y – 13–24 μmol g− 1). The peak
centered at ca. 350 ◦ C in the spectra of all materials indicates thermal
decomposition of nitrate and/or nitrite species generated by NO
adsorption on [Cu–O–Cu]2+: 2NO + [Cu–O–Cu]2+ → Cu+-NO +

[Cu–NO2]+. The peak centered at around 480 ◦ C can be assigned to the
desorption of NO2 formed in the reaction between NO and the
[Cu–O–Cu]2+ active species: NO + [Cu–O–Cu]2+ ▫ NO2 + [Cu- ▫ -Cu]2+ (
▫ represents surface oxygen vacancy) [9]. The NO3− and NO2− species
are also of heterogeneous nature, thus located in various crystallo­
graphic extraframework positions, which can be deduced from the
complexity of the profile at ca. 350 ◦ C. The NO oxidation to NO2 on
Cu–Y_Na2H2EDTA is less efficient compared to the other materials, due
to the presence of significant contribution of CuO species, which pres­
ence was confirmed by DR UV–Vis studies.
Deeper insight into the speciation of copper sites was obtained from
FT-IR studies of CO adsorption. Fig. 5a presents the IR spectra of CO
adsorbed at room temperature up to the saturation of all accessible Cu+
cations in selected Cu-containing zeolites. The binding of CO to Cu+ sites
results in the formation of the Cu+exch(CO) monocarbonyls identified by
the band at ca. 2155 cm− 1. The peaks at 2179 and 2151 cm− 1 observed
only in the spectra of Cu–Y are attributed to dicarbonyls Cu+exch(CO)2

Fig. 6. NO conversion for NH3-SCR over Cu-containing zeolite Y based on: a) zeolite Y modified with DEA, NaOH or Na2H2EDTA, or b) zeolite Y modified with
H4EDTA-NaOH or H4EDTA-NaOH-Na2H2EDTA. Reaction conditions: mK = 0.2 g; GHSV = 30,000 h− 1, c(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2) = 4 vol.-%, He
balance, FTOT = 120 ml min− 1.
6

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Microporous and Mesoporous Materials 334 (2022) 111793

that are formed at the expense of the Cu+exch(CO) species. The Cu+
cations in the form of oxide-species dispersed in zeolite are also able to
ligate CO molecules forming Cu+oxo(CO) adducts. Those Cu+ cations
surrounded by O2− ions are of stronger electron-donor properties than
exchangeable Cu+ sites, thus their monocarbolnyl bands appear at lower
wavenumbers, ca. 2140-2130 cm− 1. The position of the Cu+exch(CO)
monocarbonyls band does not vary in all the zeolites and therefore the
electron-donor properties of Cu+exch cations are assumed to be identical.
In contrast, the Cu+oxo(CO) species are heterogeneous concerning their
electron-donor properties, as manifested by the presence of two bands at
2142 and 2130 cm− 1. The varied intensity of 2142 and 2130 cm− 1 bands
is also indicative of a different mutual population of the Cu+oxo centers
in the Cu-containing zeolite Y. However, the most interesting feature is
the diversity in the abundance of isolated exchangeable cations and
oxide forms in alkaline-leached zeolites. Alkaline treatment of the sup­
port appears to lead to a decrease in Cu+ cations in exchange positions
largely which adversely affects the number of copper oxide forms
accessible to CO molecule. This effect is particularly visible in the case of
the Cu–Y_DEA, where the amount of copper(I) oxides is significantly less
affected than exchangeable Cu+ cations in comparison to native Cu–Y.
The intensity of copper monocarbonyls bands (with an exception of the
band at 2179 cm− 1) is linearly dependent on the Lewis acid sites density
derived from Py sorption studies (Table SI2, Fig. SI3). This suggests that
the copper sites serve as Lewis acid sites in all the zeolites studied. The

limited accessibility of copper sites for both of the probes manifested as
the decrease the intensities of CO and Py bands (Fig. 5) results from the
copper species agglomeration.

Fig. 8. NO conversion for NH3-SCR over (8.2 wt.-%)Cu–Y. Reaction conditions:
mK = 0.2 g; GHSV = 30,000 h− 1, c(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2)
= 4 vol.-%, (c(H2O) = 5 vol.-%), He balance, FTOT = 120 ml min− 1 and (4.9 wt.%)Cu-SSZ-13(2) [33].

active sites in NH3-SCR, e.g., Komatsu et al. [28] or Kieger et al. [13].
´ ska et al. [29] assigned the observed
More recently, Ochon
low-temperature activity of the ultrastabilized Cu-USY (n(Si)/n(Al) =
4.5, 2.4 wt.-% of Cu) catalyst to the high abundance of Cu+ sites. Similar
conclusions were drawn by Zhou et al. [3]. The Cu+ species present in
the sodalite cages of Cu-USY (n(Si)/n(Al) = 2.6, 5.0 wt.-% of Cu) appear
to be the main catalytically active sites for low-temperature NH3-SCR
(below 200 ◦ C). The effect of Ce (1–12 wt.-%) addition in the Cu-USY
zeolite is shown to increase the oxygen mobility due to CuOx present
in the zeolite and increase the concentration of Cu+ sites that were
considered as active sites of the NH3-SCR.
Cu–Y_Na2H2EDTA can be considered as a catalyst for ammonia
oxidation (NH3–SCO) [30]. Similar activity towards ammonia oxidation
(a significant drop in the activity at 300–400 ◦ C during NH3-SCR) was
reported earlier by Rutkowska et al. [31] over commercial chabazite
(CHA, SAPO-34) zeolite modified with an aqueous solution of
Na2H2EDTA (0.2 M, 4 h, 100 ◦ C), and subsequently modified with

3.3. Catalytic investigation over Cu-containing zeolite Y
Fig. 6 presents the results of catalytic investigations for NH3-SCR
over Cu-containing zeolite Y. The post-synthetic modification of the

zeolite, including sequential treatment, did not influence the results of
the NH3-SCR. Thus, in case for all catalysts, nearly full NO conversion is
found at 150–350 ◦ C. Only in the case of Cu–Y_Na2H2EDTA the NO
conversion significantly drops above 350 ◦ C due to the side reaction of
NH3 oxidation. These results confirm that isolated Cu ions and
[Cu–O–Cu]2+ species are the active sites for this reaction, while CuO
species mainly catalyze the side reaction. Copper ions are reported to be
preferentially located at Site I’ (on the face of the d6r subunits) and Site
II (on the 6-MR faces of the sodalite cages) on the surface of the 12-MR
channel (faujasite cage) rather than the highly coordinated Site III (on the
4-MR facing the supercages) [4,27]. Much of the early literature con­
cerning Cu-containing zeolite Y suggests mainly [Cu–O–Cu]2+ as the

Fig. 7. a) NO conversion, b) N2O yield for NH3-SCR over Cu-containing zeolite Y in the presence of H2O. Reaction conditions: mK = 0.2 g; GHSV = 30,000 h− 1, c
(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2) = 4 vol.-%, c(H2O) = 5 vol.-%, He balance, FTOT = 120 ml min− 1.
7


R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

Table 3
Comparison of the catalytic activity of Cu-containing zeolite Y catalysts with those reported in the literature.
Sample

Reaction conditions

Operation temperature for achieving
>80% NO conversion

Formation of by-products

Ref.

Cu–Y n(Al)/n(Si) = 1.6
ωCu = 8.2 wt.-%

c(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2) = 4 vol.-%, He
balance
* c(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2) = 4 vol.-%, c
(H2O) = 5 vol.-%, He balance,
GHSV = 30,000 h− 1

125–400 ◦ C
*175–400 ◦ C

<21% (113 ppm) N2O
(125–400 ◦ C)
*<15% (81 ppm) N2O
(175–400 ◦ C)
<22% N2O (125–450 ◦ C)
*<9% N2O (150–450 ◦ C)

this
work

Cu–Y_com n(Al)/n(Si) =
2.29
ωCu = 6.5 wt.-%

Cu–Y n(Al)/n(Si) = 2.6
ωCu = 7.2 wt.-%
Cu–Y n(Al)/n(Si) = 4.52
ωCu = 6.5 wt.-%
Cu–Y n(Al)/n(Si) = 5.1
ωCu = 4.97 wt.-%
Cu-USY supported on
‘kanthal’ plates
n(Al)/n(Si) = 4.5
ωCu = 2.4 wt.-%
Cu-USY n(Al)/n(Si) = 2.6
5.0 wt.-% of Cu
ωCu = 5 wt.-%

c(NO) = 350 ppm, c(NH3) = 355 ppm, c(O2) = 14 vol.-%, c
(H2O) = 10 vol.-%, He balance,
GHSV = 30,000 h− 1
c(NO) = 2500 ppm, c(NH3) = 2500 ppm, c(O2) = 2.5 vol.-%
O2, He balance,
GHSV not shown
c(NO) = 1000 ppm, c(NH3) = 1000 ppm, c(O2) = 6 vol.-%, c
(H2O) = 5 vol.-%, He balance,
GHSV = 300, 000 h− 1
c(NO) = 2000 ppm, c(NH3) = 2000 ppm, c(O2) = 5 vol.-%,
He balance,
GHSV = 128, 000 h− 1
c(NO) = 500 ppm, c(NH3) = 500 ppm, c(O2) = 5 vol.-%, Ar
balance,
GHSV = 48, 000 h− 1

copper ions. This effect was described to the textural changes in
SAPO-34 (decrease of the external surface area) and reduction of the
number of acid sites (extraction of framework aluminum), thus the
formation of a significant amount of oligomeric CuOx species was
favored. Also, in our case, the Cu–Y_Na2H2EDTA catalyst possesses CuO
species (based on DR UV–Vis and TPD-NOx analyses). In the presence of
5 vol.-% H2O, the low-temperature NO conversion shifts to a tempera­
ture higher by about 50 ◦ C. H2O competes with NH3 for the active sites,
thus, a higher NO conversion is also found for Cu–Y_Na2H2EDTA
(Fig. 7a). Also, the activity of Cu–Y treated for 5 h in 10 vol.-% of H2O at
500 ◦ C remains stable (Fig. 8). Table 3 provides the comparison of the
catalytic activity of Cu-containing zeolite Y catalysts prepared with
those reported in the literature. Clearly, the activity of the catalysts
presented in this studies remains in the range of the other catalysts
presented in the literature, however indicating a lower operation tem­
perature for achieving NO conversion >80%. On the other side, a
significantly higher amount of N2O concentration compared to the other
authors [2–4,29,34] is found.
N2O is a major side product during NH3-SCR, mainly formed through
the oxidation of NH3. Fig. 7b displays N2O outlet concentration as a
function of temperature during the reaction. Similar to the NO conver­
sion, the N2O yield (with a maximum between 350 and 450 ◦ C below
26% (140 ppm, for NH3-SCR both without H2O and in the presence of
H2O)) does not change significantly across the investigated materials,
and it is a major side product during NH3-SCR in the range of
250–450 ◦ C. The catalyst based on commercial zeolite Y (Cu–Y_com)
reveals more than 80% of NO conversion between 125 and 450 ◦ C.
Contrary to the present data, Kwak et al. [2] reported that NO conver­
sion significantly dropped above 300 ◦ C for the same copper-exchanged
zeolite Na–Y (Zeolyst, CBV 100, n(Si)/n(Al) = 2.6, ion-exchanged with

an aqueous solution of Cu(NO3)2, 7.2 wt.-% of Cu, GHSV 30,000 h− 1).
They reported also a significant formation of N2O of ca. 70 ppm at
450 ◦ C. Also, Wang et al. [4] applied zeolite Na–Y (Zeolyst, CBV-100, n
(Si)/n(Al) = 2.6, ion-exchanged with an aqueous solution of Cu(NO3)2,
4.97 wt.-% of Cu, GHSV 300,000 h− 1). The comparison of the
Cu-containing zeolites Y, Beta, and ZSM-5 with the same intended
loading of 5 wt.-% of Cu species reveal the highest NO conversion over
Cu–Y. Nevertheless, also a significant amount of N2O was detected (ca.
5%). The origin of the N2O formation over Cu–Y is controversially dis­
cussed in the literature. For instance, Kieger et al. [13,32] claim that
N2O (as a by-product) is formed over Cu–Y on residual CuO clusters

125–450 ◦ C
*150–450 ◦ C

this
work

250–325 ◦ C

<40 ppm N2O (250–325 ◦ C)
<80 ppm N2O (150–550 ◦ C)

[2]

200–475 ◦ C

<5% N2O (200–475 ◦ C)
>95% N2 selectivity
(200–475 ◦ C)

<5% N2O yield
(225–450 ◦ C)

[34]

150–500 ◦ C

100% N2 selectivity
(100–500 ◦ C)

[29]

175–300 ◦ C

>80% N2 selectivity
(175–300 ◦ C)

[3]

225–450 ◦ C

[4]

(around ca. 267 ◦ C) as well as above 377 ◦ C on neighboring Cu ions in
small (sodalite) cages within the FAU framework and/or [Cu–O–Cu]2+
dimers. Wang et al. [4] reported that low- (100–350 ◦ C) and
high-temperature (350–450 ◦ C) N2O formation is favored over dimeric
[Cu–O–Cu]2+ in Cu–Y. The N2O formation at lower temperatures
(<350 ◦ C) originated mainly from the decomposition of NH4NO3. Above
350 ◦ C, the formation of N2O is due to the unselective oxidation of NH3.

Our last investigations [9] over Cu-ZSM-5 and Na–Cu-ZSM-5 revealed
that [Cu–O–Cu]2+ sites enhanced N2O formation.
3.4. Insight into the dynamics of NH3-SCR intermediates
Fig. 9 presents the FT-IR spectra of Cu–Y contacted with the mixture
of NH3, NO, O2, and H2O (c(NH3):c(NO):c(O2):c(H2O) = 4:4:1:8) at
100 ◦ C. The spectra shown in Fig. 9a, and a’ were collected over a 10 min
reaction course in rapid scan mode by collecting one spectrum in 1 s. It is
well seen that the adsorption of ammonia leads to the marginal
perturbation of the external silanols (3745 cm− 1). The effects related to
the N–H bands intensification are assigned to ammonia binding to Lewis
acid sites and formation of hydrogen bond between ammonia and
Brønsted acid species. The spectral region of the N–H stretching vibra­
tion is complex due to the distortion of ammonia molecule induced by
adsorption which finally leads to the activation of νN-H sym mode and the
splitting of the νN-H asym modes. The bending modes of NH3-Lewis ad­
ducts, δasym, are represented by the band at 1621 cm− 1. The nature of
these sites could be either Al species related to framework and extraframework positions and also copper Lewis acid sites such as Cu2+/
Cu+. According to the literature, ammonia bonded coordinatively to
Cu2+ sites give rise to the bands at 3356 and 3182 cm− 1 [35]. Simul­
taneously, in the lower wavenumber region (2000-1300 cm− 1), the
interaction of NO with redox sites is detected: the bands of copper(II)
appear at 1943 and 1910 cm− 1. No bands of Cu+(NO) mononitrosyls
were detected in the spectra (1810-1780 cm− 1). Only the
oscillation-rotational spectrum of gaseous NO is visible (1875 cm− 1).
This suggests that the oxidation of Cu+ to Cu2+ species by O2− in the
ammonia presence is fast enough to not be detected in this time reso­
lution. Therefore, the bands at 1943 and 1910 cm− 1 were assigned to
isolated Cu2+ cations possessing an adjacent O− anion (i.e., the structure
of the adsorption site is Cu2+-O-) [36–38]. The Cu(II) mononitrosyl band
at 1943 cm− 1 is rapidly eroded completely within the first 3 min of re­

action duration while the lower frequency mononitrosyl band at 1910
8


R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

Fig. 9. Time-resolved rapid scan FT-IR spectra presenting the gaseous and surface-bonded species involved in NH3-SCR over Cu–Y in the presence of water vapor in
600 s (a and a’) and 100 min (b and b’) reaction course in the frequency region typical of stretching N–H modes (a, b) and deformation modes of the NOx- and NH3originated species (a’, b’).

cm− 1 develops in time (Fig. 9). It should be noted that the accessibility of
Cu2+ cations for the reagent molecules is significantly increased by the
coordination of ammonia to Cu(II). Solvation by ammonia confers
mobility to single Cu ions. Only the Cu2+ cations withdrawn by
ammonia from sodalite cages to the supercages can react with NO
molecules. The [Cu(O− )(NH3)n]2+ complexes migration depends on the
reaction temperature. In our case, we observed an obvious time
dependence: only [Cu(O− )(NH3)n]2+ adducts easily accessible are able
to ligate NO molecules, thus the band at 1910 cm− 1 of monositrosyls
increased over time. After 7 min of reaction, the 1910 cm− 1 band
reached the maximum intensity, implying that all the copper(II) sites are
transformed in [Cu(O− )(NH3)n-1(NO)]2+ complexes. Taking all the
above considerations into account, the 1943 cm− 1 band can be assigned
to Cu(II) mononitrosyls [Cu(NO)]2+ converted into [Cu(NH3)n-1(NO)]2+
complexes in the further course of the reaction. The ligation of NO to [Cu
(O− )(NH3)n]2+ is also reflected in the development of the nitrate/nitrite
detected as the bands in the range of 1630-1430 cm− 1. As previously
mentioned, the bending modes of NH3-Lewis adducts, δasym, are

represented by the complex band located at 1621-1629 cm− 1. After 7
min of the process, the 1629 cm− 1 band becomes clearly visible and its
growth is associated with the 1436 cm− 1 bands. All these findings
indicate the formation of the mixed ammine nitro/nitrite complexes [Cu
(NO3)(NH3)n-1]2+, identified by the bands at 1629 and 1451 cm− 1.
Indeed, such intermediates (i.e., Cu2+(NH3)3(NO3)) were recently re­
ported for Cu-CHA at low reaction temperatures [39]. Paolucci et al.
[39] showed that Cu2+ ions migrate through zeolite windows and form
transient ion pairs that participate in an oxygen (O2)–mediated Cu+ →
Cu2+ redox stage by combing kinetic measurements, X-ray absorption
spectroscopy, and first-principles calculations. The reversible formation
of multinuclear sites [(NH3)2Cu2+–O2–Cu2+(NH3)2] from single atoms
(NH3)2Cu2+ induced by ammonia coadsorption was defined as inherent
to the NH3-SCR. These authors claimed also that when the activation of
O2 is not rate-controlling, the Cu ions solvated by ammonia are cata­
lytically equivalent. Therefore, the zeolite framework itself has only a
marginal influence on the SCR rate because it functions as a ligand that
is overtaken by NH3 molecules. Indeed the same catalytic activity was
9


R.S.R. Suharbiansah et al.

Microporous and Mesoporous Materials 334 (2022) 111793

confirmed also for CHA – a cage-like structure similar to FAU (Fig. 8)
[33]. Our earlier spectroscopic studies [40] provided evidence that the
framework geometry is a decisive factor for the accessibility of the
copper sites and the saturation with ammonia molecules while the n
(Si)/n(Al) ratio governs the copper sites speciation and ammonium ions

stabilization. Herein, we show that for Cu–Y, the determining rate is the
formation of mixed [Cu(O− )(NH3)n-1(NO)]2+ complexes [40]. When
considering prolonged contact time of reagents with the catalyst surface
(10–100 min, called as standard scanning, one spectrum collected in 30
s) (Fig. 9b and b’) we can undeniably conclude on the consumption of
[Cu(O− )(NH3)n-1(NO)]2+ mononitrosyls (1910 cm− 1) accompanied by
the 1629 and 1621 cm− 1 bands. A prominent growth of the higher fre­
quency component is observed. In the O–H and N–H stretching vibra­
tions region the 3567 and 3500 cm− 1 together with 3396 and 3298 cm− 1
bands are the dominating spectral features, while the 3356 and 3182
cm− 1 bands of ammonia bonded coordinately to Cu2+ are reduced. The
presence of 3567 and 3500 cm− 1 bands unquestionably points to water
formation: these bands arise from O–H stretching vibrations of water
molecules which accumulates on the catalyst surface both by
hydrogen-bonding to the silanols (the 3745 cm− 1 band is eroded with
time) and by the coadsorption to [Cu2+(NH3)n] complexes. The
destruction of [Cu2+(NH3)n] complexes detected as a reduced intensity
of the 3356 and 3182 cm− 1 bands suggests both coadsorption of water
and ammonia on the same copper site or the replacement of ammonia by
water molecules. Paolucci et al. [41] showed that NH3 outcompetes with
other gases present under standard NH3-SCR conditions, including H2O,
for binding at both Cu+ and Cu2+ ions. However, the most vital reason
for the vanishing of the 3356 and 3182 cm− 1 bands is the regeneration of
the Cu+ cations that do not provide the aforementioned spectral fea­
tures. It cannot be however excluded that at temperature of 100 ◦ C,
ammonia and water molecules are attached to the same copper(II)
cation, and at higher temperature water molecules are released,
restoring the original complex.

Declaration of competing interest

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgments
ăt Leipzig: Pre-Doc Award 2019/2020. R.S.R.
Funding from Universita
S. acknowledges the DAAD scholarship programme. M.J. acknowledges
the DFG Research Grant JA 2998/2-1. K.G.M. and K.P. acknowledge the
Grant No. 2021/41/B/ST4/00048 from the National Science Centre,
Poland.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.micromeso.2022.111793.
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CRediT authorship contribution statement
Rujito S.R. Suharbiansah: Investigation, Data curation, Method­
ology, Writing – original draft, Writing – review & editing. Kamila Pyra:
Investigation, Data curation. Michael Liebau: Investigation, Data
´ racuration. David Poppitz: Investigation, Data curation. Kinga Go
Marek: Investigation, Data curation, Writing review & editing. Roger
ăser: Writing review & editing, Supervision. Magdalena Jabłon
´­
Gla
ska: Investigation, Data curation, Conceptualization, Methodology,
Writing – original draft, Writing – review & editing, Supervision.

10


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