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).
Microporous and Mesoporous Materials 334 (2022) 111793 Contents lists available at ScienceDirect 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 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: magdalena.jablonska@uni-leipzig.de (M Jabło´ nska) https://doi.org/10.1016/j.micromeso.2022.111793 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) Published by Elsevier Inc This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/) access article under the CC BY-NC-ND license 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 Experimental Results and discussion Synthesis gel with the composition of 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 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 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 nm or maybe atomically dispersed copper species are present Fig 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: Al2O3: 10 SiO2: 205 H2O versus 5.3 Na2O: 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 μm at 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 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 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 R.S.R Suharbiansah et al Microporous and Mesoporous Materials 334 (2022) 111793 Table 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− [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− 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 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− 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 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− 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 V(MES)/cm3 g− V(MIC)/cm3 g− R.S.R Suharbiansah et al Microporous and Mesoporous Materials 334 (2022) 111793 Fig a,c) N2 sorption isotherms and b,d) pore width distribution of Cu-containing zeolite Y after different types of treatment Fig 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), R.S.R Suharbiansah et al Microporous and Mesoporous Materials 334 (2022) 111793 Fig 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− (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− The peaks at 2179 and 2151 cm− observed only in the spectra of Cu–Y are attributed to dicarbonyls Cu+exch(CO)2 Fig 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) = vol.-%, He balance, FTOT = 120 ml min− R.S.R Suharbiansah et al 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− 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− The varied intensity of 2142 and 2130 cm− 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 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) = vol.-%, (c(H2O) = vol.-%), He balance, FTOT = 120 ml min− 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, h, 100 ◦ C), and subsequently modified with 3.3 Catalytic investigation over Cu-containing zeolite Y Fig 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 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) = vol.-%, c(H2O) = vol.-%, He balance, FTOT = 120 ml min− R.S.R Suharbiansah et al Microporous and Mesoporous Materials 334 (2022) 111793 Table 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) = vol.-%, He balance * c(NO) = 500 ppm, c(NH3) = 575 ppm, c(O2) = vol.-%, c (H2O) = vol.-%, He balance, GHSV = 30,000 h− 125–400 ◦ C *175–400 ◦ C