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Cu-ZSM-5 (Cu-Zeolite Socony Mobil-five) catalysts with different Cu loadings were prepared by ion exchange method. Different Ce loadings were coated on the surface of 0.1Cu-ZSM-5 to form CeO2-Cu-ZSM-5 catalysts. Cu could improve the NH3-SCR activity and broaden SCR temperature window. 0.1Cu-ZSM-5 showed the best catalytic performance (above 90%) in 200–400 ℃. 30% CeO2-Cu-ZSM-5 catalyst was able to increase the NO conversion in the low-temperature region and keep the activity unchanged in the high-temperature region. CeO2 that was coated on the catalysts preferentially reacted with SO2, enhancing the excellent anti-sulfur poisoning performance. TPD, TPR, and XPS results showed that the synergistic effect of Ce and Cu increased the acidic sites and improved the redox capacity of catalysts. According to in situ DRIFTS spectra, Cu-ZSM-5 catalyst followed the Langmuir–Hinshelwood mechanism, and 30% CeO2–0.1Cu-ZSM-5 catalyst followed not only the Langmuir–Hinshelwood mechanism but also the Eley–Rideal mechanism. [ABSTRACT FROM AUTHOR]

Tunable active sites emerged over Cu-ZSM-5 catalysts via modulating Cu contents showed excellent catalytic performance in methane to methanol conversion. The generation of CH 3 OH was operated under the synergetic effect of the Cu x O y NPs and Cu–OH motif, in which multiple mechanisms via methyl intermediates and free radicals (•OH/•OOH) in the liquid phase. [Display omitted] • Methane oxidation toward methanol are achieved at considerable productivity of 15975.73 μmol/g cat /h. • Tunable active species (Cu1+/0, Cu x O y nanoparticles, Cu–OH motif) emerged via modulating Cu contents. • The co-existing Cu x O y nanoparticles and Cu–OH motif synergistically promote methanol generation. • Reactive oxygen species produced by H 2 O 2 take part in the reaction in a parallel way. Copper decorated zeolites are promising candidates for the partial oxidation of methane to generate methanol with elevated energy density, nevertheless, the modulation and possible synergism between multiple Cu active sites still need to be delved in depth. Here, ZSM-5 catalysts with modulated Cu motifs were proposed using copper oxysalts as precursors through a calcination process. By modifying the contents of copper oxysalts precursors, the Cu active sites varied, and a unique M shaped trend of CH 3 OH productivity emerged. Attributed to the synergetic effects of Cu x O y nanoparticles (adsorbing CH 4 and generating *OCH 3 species) and Cu–OH motif (binding CH 4 and forming Si···CH 3), a maximum CH 3 OH yield of 15975.73 μmol/g cat /h (with CH 3 OOH yield of 2155.59 μmol/g cat /h) and methyl oxygenates selectivity up to 72.79 % could be achieved. This work paved an efficient, low cost, and succinct way for the manufacture of catalysts with tunable active sites and high performance over methane to methanol conversion. [ABSTRACT FROM AUTHOR]

The catalyst preparation route is well known to affect the copper loading and its electronic state, which influence the properties of the resulting catalyst. Electronic states of copper ions in copper-containing silicalites with the MFI-framework topology obtained by a solid-state transformation S (SST) were studied with using EPR, UV-Vis DR, XRD, H2-TPR and chemical differentiating dissolution. They were compared with Cu-ZSM-5 and Cu-MFI (silicalite) prepared via the ion-exchange and incipient wetness impregnation. SST route was shown to provide the formation of MFI structure and favor clustering of Cu-ions near surface and subsurface of zeolite crystals. The square-planar oxide clusters of Cu2+-ions and the finely dispersed CuO nanoparticles with the size down to 20 nm were revealed in Cu-MFI-SST samples with low (0.5–1.0 wt.%) and high (16 wt.%) Cu-content. The CuO nanoparticles were characterized by energy band gap 1–1.16 eV. The CuO-like clusters were characterized by ligand-to-metal charge transfer band (CTB L → M) at 32,000 cm−1 and contain EPR-visible surface Cu2+-ions. The low Cu-loaded SST-samples had poor redox properties and activity towards different solvents due to decoration of copper-species by silica; whereas CuO nanoparticles were easily removed from the catalyst by HCl. In the ion-exchanged samples over MFI-silicalite and ZSM-5, Cu2+-ions were mainly CuO-like clusters and isolated Cu2+ ions inside MFI channels. Their redox properties and tendency to dissolve in acidic solutions differed from the behavior of SST-series samples. [ABSTRACT FROM AUTHOR]

NH3‐selective catalytic reduction (NH3‐SCR) is a very effective technical means to control NOx emissions from diesel engines, and Zeolite Selony Mobil No. 5 (SiO2/Al2O3 ratio 53:1) ion exchanged with Cu (Cu‐ZSM‐5) provides support for the high performance of NH3‐SCR within a wide temperature window under diesel engine operating conditions. The mechanism of the NH3‐SCR reaction based on Cu‐ZSM‐5 is established. Resistance analysis, effective factor analysis, and characteristic time analysis are used to analyze the influence of external mass transfer limitation and washcoat diffusion limitation on NH3‐SCR reaction and the transition between the washcoat diffusion control regime, the external mass transfer control regime, and the kinetic control regime of the NH3‐SCR over Cu‐ZSM‐5. It provides the basis for the optimization of the catalyst structure and the support for the improvement of NH3‐SCR performance. [ABSTRACT FROM AUTHOR]

The properties of Pd-modified Cu-ZSM-5 catalysts in liquid-phase methane peroxidation have been studied. The catalysts were prepared by polycondensation of Cu2+ and Pd2+ ions in the zeolite pores. Solutions of ammonia or ammonium complexes of one of the introduced metals were used as an alkaline agent promoting the polycondensation of hydrated metal ions. The electronic states of Cu2+ and Pd2+ ions and the acidic and redox properties of the catalysts, as well as their textural characteristics, were studied. Associated Cu2+ ions and polynuclear hydroxo/oxo complexes of Cu2+/Pd2+ ions were found to form in the pores during polycondensation, which are located in the channels and on the surface of zeolite crystallites. The addition of Pd affects the redox, acidic, and catalytic properties of Cu-ZSM-5, but this effect does not always lead to increased selectivity of the process with respect to liquid oxygenates (methanol and formic acid). Among the bimetallic catalysts, Cu/Pd-ZSM-5 was the most active catalyst, which was most selective for liquid oxidation products; it was synthesized by introducing [Cu(NH3)4]2+ ions after Pd2+ ions. It was assumed that its catalytic characteristics are associated with the lower strength of Cu2+–LAS and higher stability of isolated Cu2+ ions and polynuclear PdO-like clusters against reduction compared with the same characteristics of the sample obtained by simultaneous introduction of Cu2+ and Pd2+. [ABSTRACT FROM AUTHOR]

N,N-Dimethylformamide (DMF), a nitrogen-containing volatile organic compound (NVOC) with high emissions from the spray industry, has attracted increasing attention. In this study, Cu-ZSM-5 catalysts with different CuO particle sizes of 3, 6, 9 and 12 nm were synthesized and tested for DMF selective catalytic oxidation. The crystal structure and physicochemical properties of the catalyst were studied by various characterization methods. The catalytic activity increases with increasing CuO particle size, and complete conversion can be achieved at 300–350 °C. The Cu-12 nm catalyst has the highest catalytic activity and can achieve complete conversion at 300 °C. The Cu-6 nm sample has the highest N2 selectivity at lower temperatures, reaching 95% at 300 °C. The activity of the catalysts is determined by the surface CuO cluster species, the bulk CuO species and the chemisorbed surface oxygen species. The high N2 selectivity of the catalyst is attributed to the ratio of isolated Cu2+ and bulk CuO species, and weak acidity is beneficial to the formation of N2. The results in this work will provide a new design of NVOC catalytic oxidation catalysts. [ABSTRACT FROM AUTHOR]

HCN catalytic hydrolysis mechanism over Cu-ZSM-5 was investigated based on the density functional theory (DFT) with 6-31++g (d, p) basis set. Five paths (A, B, C, D, and E) were designed. For path A and path B, the first step is the nucleophilic attack of water molecule. Next, the hydrogen atom of H2O is transferred to the nitrogen atom first for path A, while in path B, the hydrogen atom of the HCN is first transferred to the nitrogen atom. In path C, HCN isomerizes to HNC initially, and the remaining steps are similar to that of path A. The H atom of HCN shifts to Cu-ZSM-5 initially in path D, and the H atom is transferred to N atom subsequently. The last step is the attack on water molecule. The first step for path E is similar to that of path D. The next step is the attack on water molecule, in which the H atom of water molecule shifts to N atom, and the H on Cu-ZSM-5 shifts to the N atom. Meanwhile, the H atom of oxygen atom is transferred to the N atom. The results show that path C is the most favorable path, with the lowest free energy barrier (35.45 kcal/mol). The results indicate that the Cu-ZSM-5 strongly reduces the energy barrier of HCN and isomerizes to HNC, making it an effective catalyst for HCN hydrolysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfibrous-structured Cu-ZSM-5/Al-fiber catalysts with different Si/Al molar ratios were synthesized for SCR reaction. • Adsorbed bridged nitrates species is in accordance with the enhanced NO degradation activity. • Microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer. Selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) is one of the most efficient technologies to remove NO x emissions. The copper ion-exchanged zeolites with broad temperature windows and high N 2 selectivity are very promising for this process. In this work, we synthesized a series of microfibrous-structured Cu-ZSM-5/Al-fiber catalysts for SCR reaction by changing the Si/Al molar ratios. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NH 3 adsorption results show that the Cu-ZSM-5/Al-fiber catalysts with higher Si/Al molar ratios have higher NH 3 adsorption capacity. The subsequent NO adsorption results show that the amount of adsorbed bridged nitrates species is in accordance with the enhanced NO x degradation activity. At moderate temperature, Cu-ZSM-5/Al-fiber catalyst shows better NH 3 -SCR performance under higher gas hourly space velocity (GHSV), indicating microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer. [ABSTRACT FROM AUTHOR]

The impact of water on catalyst activity remains inconclusive due to its dependence on the specific reaction environment. To maximize the exploitation of water's promoting effect, we employed ammonia selective catalytic reduction (NH 3 -SCR) as a probe reaction and proposed a phosphorus modification strategy for Cu-ZSM-5 catalysts. The objective of this approach was to construct water-adaptive microstructures through directional arrangement. To investigate the effect of phosphorus on the transformation of framework copper sites in humid environments, we conducted comprehensive characterizations and density functional theory calculation. Results reveal that water molecules cleave the oxygen bridges between phosphorus oxide and copper, leading to the formation of active isolated [Cu(OH)] + groups and phosphate. The phosphate species weaken the interaction between exchanged Cu 2+ groups and the zeolite framework, leading to the generation of highly migratory hydrated Cu 2+ species. This work will potentially guide the rational design of water-adaptive catalysts for gas pollution abatement in a humid environment.

Copper-exchanged ZSM-5 (Cu-ZSM-5) is a promising catalyst thanks to the Cu redox pair. A particular feature of this material consists in the presence of spontaneous isothermal oscillations which take place during N 2 O decomposition reaction, depending on the operating conditions. In the present work, a set of five Cu-ZSM-5 catalysts was synthesised by three procedures and three different copper precursor concentrations: i) wet impregnation, ii) single ion exchange, and iii) double ion exchange. Catalytic tests revealed that the ion-exchanged samples exhibit a low catalytic activity and no oscillatory behaviour, except for the twice-exchanged sample which achieves an average N 2 O conversion of 26 % at 400 °C. Conversely, the impregnated samples reach higher levels of N 2 O conversion (66 % for Cu 5 ZSM5_WI and 72 % for Cu 10 ZSM5_WI) and demonstrate a similar oscillating pattern. Further investigations disclosed that the most active catalysts, characterised by the presence of oscillatory behaviour, have more abundant and easily reducible copper species (ICP, EDX and H 2 -TPR) which interact better with the zeolitic support (FT-IR). Catalytic tests under a long time on stream (TOS) suggest that either self-organised patterns or deterministic chaos can be achieved during the reaction, depending on the operating conditions, such as temperature and contact time., (© 2024 Wiley-VCH GmbH.)

In this work, a series of Cu-ZSM-5 catalysts with different SiO 2 /Al 2 O 3 ratios (25, 50, 100 and 200) were synthesized and investigated in n -butylamine catalytic degradation. The n -butylamine can be completely catalytic degradation at 350°C over all Cu-ZSM-5 catalysts. Moreover, Cu-ZSM-5 (25) exhibited the highest selectivity to N 2 , exceeding 90% at 350°C. These samples were investigated in detail by several characterizations to illuminate the dependence of the catalytic performance on redox properties, Cu species, and acidity. The characterization results proved that the redox properties and chemisorption oxygen primarily affect n -butylamine conversion. N 2 selectivity was impacted by the Brønsted acidity and the isolated Cu2+ species. Meanwhile, the surface acid sites over Cu-ZSM-5 catalysts could influence the formation of Cu species. Furthermore, in situ diffuse reflectance infrared Fourier transform spectra was adopted to explore the reaction mechanism. The Cu-ZSM-5 catalysts are the most prospective catalysts for nitrogen-containing volatile organic compounds removal, and the results in this study could provide new insights into catalysts design for VOC catalytic oxidation. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• The reactivity of a pair of Cu+ ions within a 10-membered ring of Cu-ZSM-5 was simulated. • The model explains and integrates experimental data available in the literature. • Cu+ ions react as a Cu+ pair. • Three mechanisms were identified for the complete NO decomposition. • Only one of the spin-allowed mechanisms appears to be feasible. The decomposition of NO catalysed by Cu+ pairs coordinated at the Al-substituted T3 sites of the 10-membered rings of Cu-ZSM-5 was studied by means of DFT/ONIOM calculations. Three mechanisms for NO decomposition were defined on the active site, all based on the formation and further decomposition of an hyponitrite anion, which gives the N 2 O molecule and a [Cu‒O‒Cu]2+ bridge, where both copper ions are oxidized. N 2 O can react with the oxidized active site according to two different spin-allowed mechanisms which give immediately the products, N 2 + O 2. Otherwise, N 2 O reacts with a new reduced site according to a spin-forbidden mechanism which gives N 2 and a second [Cu‒O‒Cu]2+ bridge. When the latter mechanism occurs, reduced sites are restored by further reaction of [Cu‒O‒Cu]2+ with NO and desorption of NO 2 , which is finally decomposed on a second [Cu‒O‒Cu]2+ site, giving O 2 + NO. Turnover frequencies (TOFs) calculated by means of the Energetic Span model showed that one of the spin-allowed mechanisms should be relatively fast, whereas the spin-forbidden one is expected to be extremely slow. Computational results were discussed with reference to experimental data available in the literature. [Display omitted] [ABSTRACT FROM AUTHOR]

Cu(Fe)-containing zeolites are promising catalysts for biomimetic functionalization of light hydrocarbons. Catalysts with various copper states have been elaborated and studied in the peroxide oxidation of methane to methanol and formic acid. ICP-AES, UV–vis DR, EPR, NH3-TPD, H2-TPR, and N2 adsorption techniques were used for the characterization of the Cu(II) states, the textural, acidic and redox properties of the catalysts. The prepared zeolites contained the following Cu species: (1) isolated Cu2+ ions, (2) square planar binuclear oxo/hydroxo complexes ([Cu2(OH)2]2+) in the zeolite channels, (3) CuO- and/or Cu(OH)2-like clusters and nanoparticles on the zeolite external surface. UV–vis DR spectroscopy also was used for studying the ability of different Cu-ZSM-5 to form Cu peroxocomplexes with H2O2. Three types of peroxocomplexes were detected. These were terminal Cu–OOH originated from the isolated Cu2+ ions, binuclear Cu(II) with a terminal OOH group and the binuclear Cu(II) with a bridging OO-group formed from the Cu-species with extra lattice oxygen. 1H and 13C NMR analysis revealed the formation of methylhydroperoxide, formaldehyde, and CO2 as side products during peroxide oxidation of methane. Two pathways of methane oxidation with hydrogen peroxide involving both binuclear Cu-species with extra-lattice oxygen and isolated Fe-sites and/or oligomer oxo-clusters of Fe(III) ions were supposed. [ABSTRACT FROM AUTHOR]

• Intracrystalline and effective diffusivity of NO and NH 3 within Cu-ZSM-5. • Validation of equation for estimation of NO diffusivity within Cu-ZSM-5. • Kinetic study for NH 3 -SCR of NO by Cu-ZSM-5 with different crystal size. • NO diffusion rate control overall reaction rate of NO reduction with NH 3. Micropore diffusivities of NO and NH 3 were experimentally measured for Cu-ZSM-5 using constant volumetric method at a temperature range from 373 K to 423 K. Intracrystalline diffusivities and effective diffusivities of NO were lower than those of NH 3 , and the activation energy for intracrystalline diffusivity of NO (21 kJ mol−1) was higher than that of NH 3 (6.3 kJ mol−1). The intracrystalline diffusivity of NO in Cu-ZSM-5 catalysts at 373 K was independent of Cu content and Si/Al ratio of Cu-ZSM-5. We proposed an equation for calculation of effective diffusivity of NO in Cu-ZSM-5 which was validated by the experimental data. Kinetic studies for NH 3 -SCR and NH 3 oxidation were carried out using Cu-ZSM-5 with different crystal thickness. The apparent reaction rate of NH 3 -SCR at 523 K depended on the zeolite crystal thickness; the rates by a small Cu-ZSM-5 (0.088 μm) was 2.75 times higher than that by a large crystal catalyst (2.7 μm), corresponding to the effectiveness factor of 0.36. The apparent reaction rate of NH 3 oxidation did not depend on the zeolite crystal size. It is concluded that NH 3 -SCR is controlled by intracrystalline diffusion of NO, or in other words, the active sites in zeolite crystal are not fully utilized due to the NO diffusion limitation. The effective diffusivity of NO in Cu-ZSM-5 estimated by the catalytic study was close to that calculated using the NO diffusivity results, which supported our conclusion. [ABSTRACT FROM AUTHOR]

• A model for NH 3 -SCR based on kinetics and computational fluid dynamics (CFD). • Model validation with SCR by monolithic Cu-ZSM-5. • Inhibition of effect of hydrocarbons in engine emission tests. A simple kinetic model for the standard NH 3 -SCR reaction by Cu-ZSM-5 catalysts has been developed by assuming three reaction steps: NH 3 adsorption (desorption), reactions of adsorbed NH 3 with O 2 (NH 3 oxidation) and NO (NH 3 -SCR). The model is based on Arrhenius parameters for NH 3 -SCR and NH 3 oxidation by a powder catalyst, combined with models for heat and mass transport and parameters of monolithic catalysts. The model is validated with the experimental results, not included in the estimation of the model, for NH 3 -SCR by monolithic catalysts with different parameters (catalyst loading and cell density). NOx removal from diesel exhaust, generated by engine bench, was also carried out by using monolithic Cu-ZSM-5 and Cu-AFX catalysts. The results suggest the poisoning effect of hydrocarbons in the exhaust emissions on NOx conversion is more significant for Cu-ZSM-5 than Cu-AFX. [ABSTRACT FROM AUTHOR]

• Cu-exchanged zeolites achieving both high C 2 H 3 CN conversion and N 2 selectivity. • Oxidation/hydrolysis mechanism was proposed on experimental and theoretical approaches. • Change transfer during nitrile elimination was analyzed by Mulliken method. A series of Cu (5 wt%) modified microporous zeolites (ZSM-5, Beta, MCM-22, MCM-49, and Y) was investigated for selective catalytic combustion of acrylonitrile (C 2 H 3 CN-SCC), associated with N 2 yield order of Cu-ZSM-5 (SiO 2 /Al 2 O 3 = 26) > Cu-MCM-49 > Cu-MCM-22 > Cu-Beta > Cu-Y. Various characterizations of XRD, N 2 adsorption, H 2 -TPR, NH 3 -TPD and XPS were employed to reveal structure-activity relationship. It was suggested that (i) isolated Cu cation acting as active center played a major role in C 2 H 3 CN-SCC; (ii) lowering SiO 2 /Al 2 O 3 ratio could enhance ion-exchanging capacity and thereby improve the zeolitic catalytic behavior; (iii) Cu-ZSM-5 (SiO 2 /Al 2 O 3 = 26) possessed the largest amounts of Cu cations as well as the highest Cu2+ → Cu+ redox ability, being responsible for its excellent catalytic behavior. C 2 H 3 CN-SCC mechanism over Cu-ZSM-5 was further investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) and density functional theory (DFT) calculation. C 2 H 3 CN-SCC mainly followed an oxidation mechanism via intermediate of NCO in absence of H 2 O; however, after an introduction of H 2 O hydrolysis mechanism was dominated involving NH 3 intermediate. DFT simulation majorly focusing on NCO formation mechanism reveals that C 2 H 3 CN could be initially adsorbed on active center Cu of Cu-ZSM-5 through its N, associate with atomic C of CN being adsorbed with a dissociated atomic O. Such kind of adsorption mode greatly favored C 2 H 3 CN bond fracture to produce NCO, of which the energy barrier was calculated to be 17.0 kcal mol−1. Mulliken charge transfer (CT) analysis was further conducted, based on which the electronic properties of active center Cu, zeolite framework and dissociated atomic O were well illustrated. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • La doping effectively improves the dispersion of the Cu species. • Ni doping benefits the formation of the (Cu2+-O2−-Cu2+)2+. • Co-doping with La and Ni shows synergistic effects of the two promoters. • La-Ni-Cu-ZSM-5 shows a higher activity than that in the single doped sample. Abstract A number of M-Cu-ZSM-5 (M = La, Ni, La-Ni) samples were prepared via an aqueous solution ion-exchange method. The co-doping with Ni and La into a Cu-ZSM-5 catalyst enhanced the NO decomposition activity in a temperature range 350–550 °C. The characterization results indicate that doping with La effectively improved the dispersion of the Cu species forming more Cu2+ ions in the sample, while the effect of Ni is likely to facilitate the implantation of Cu2+ to form (Cu2+-O2–-Cu2+)2+ dimers. The synergistic effect of La and Ni contributes to the increased (Cu2+-O2−-Cu2+)2+ content in the co-doped sample, thus enhancing the NO decomposition activity. [ABSTRACT FROM AUTHOR]

The properties of dihydroxycarbonate (malachite) and trihydroxynitrate of copper were studied in order to apply their ammonia solutions for the synthesis of copper-substituted ZSM-5 zeolites. Copper concentration and NH 4 OH/Cu2+ ratio in the solutions varied 1–12 g/l and 6–30, respectively. The parameters of Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms revealed the favorability of the chosen conditions and the chemical nature of [Cu(NH 3) n ]2+ ions sorption by zeolite. For both copper salts, the sorption capacity of H-ZSM-5 for Cu2+ ions was higher in the solutions having NH 4 OH/Cu2+ = 6–10 compared to 30. To identify the synthesis and structure – activity relationship correlations, the ammonia solution and Cu-ZSM-5 samples were characterized by EPR, UV–visible spectroscopy, temperature-programmed reduction by hydrogen (H 2 -TPR). The calcined Cu-ZSM-5 samples produced at NH 4 OH/Cu2+ = 6–30 contained two types of the isolated Cu2+ ions (bare Cu2+ and [Cu(OH)]+), differing in their Redox properties. Their reducibility improved with an increase in the copper loading and with a decrease in NH 4 OH/Cu2+. At NH 4 OH/Cu2+ = 6–10, the samples additionally comprised the structures of Cu2+ ions with extra-lattice oxygen (ELO), which were formed due to hydrolysis of [Cu(NH 3) n (H 2 O)]2+ to [Cu(NH 3) n (OH)]+ and then to [Cu(OH) 2 Cu]2+. Cu2+–ELO structures possessed a greater ability to complete reduction than both types of isolated Cu2+ ions. Correlations with DeNOx properties in selective catalytic reduction (SCR) of NO by propane and ammonia are discussed. [Display omitted] • Synthesis of ion-exchanged Cu-ZSM-5 using ammonia solutions of copper hydroxysalts. • NH 4 OH/Cu2+ in solution affect copper content and type of Cu-ions loaded in ZSM-5. • At NH 4 OH/Cu2+ = 30, there is 2 types of isolated Cu2+ ions differing in Redox. • At NH 4 OH/Cu2+ = 6–10, reducibility is improved due to Cu2+–ELO structures. • Cu2+–ELO structures enhance SCR NO performance compared with isolated Cu2+ ions. [ABSTRACT FROM AUTHOR]

The effect of NH4OH/Cu2+ in a copper-acetate solution on the properties of ion-exchanged Cu-ZSM-5 catalysts in the selective catalytic reduction of NO by NH3 (NO-NH3 SCR) has been studied. The temperature programmed desorption of ammonia (NH3-TPR) on Cu-ZSM-5 and the ammonia adsorption-desorption dynamics at 75-300 °C were studied to identify and quantify the nature of acid sites and ammonia desorption heat of Cu-ZSM-5. The Cu-ZSM-5 catalysts containing Cu-structures with extra-lattice oxygen were active in the low-temperature SCR, whereas those with isolated Cu2+ ions were active in the high-temperature SCR. It was shown that Cu-structures with extra-lattice oxygen were generated during the ion exchange of H-ZSM-5 with a water-ammonia solution of copper-acetate where the NH4OH/Cu2+ ratio was in the range of 6-15. Isolated Cu2+ ions were produced in the ion-exchange mode with the ammonia-free solution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The spin-forbidden N 2 O decomposition on Cu(I) pair in Cu-ZSM-5 is investigated. • The addition of NO to the oxidised [Cu O Cu]2+ occurs without activation energy. • The reduced [Cu⋯Cu]2+ active site is obtained, plus coordinated NO 2. • NO 2 desorption from the active site is almost 40 kcal mol−1 endothermic. • NO 2 decomposition on a second [Cu O Cu]2+ active site yields NO + O 2. Abstract The reactivity between NO and the oxidized form of a short-distance dinuclear Cu-ZSM-5 catalyst (ZCu 2 O) was investigated. ZCu 2 O, which contains the [Cu O Cu]2+ bridge coordinated at the opposite T11 positions of the M6 ring of ZSM-5, is obtained by the spin-forbidden decomposition of N 2 O on the reduced form of the catalyst, ZCu 2 , with an activation energy of about 18 kcal mol−1. The further addition of NO to the [Cu O Cu]2+ unit of ZCu 2 O occurs in the doublet state without activation energy and gives NO 2. After desorption, which requires 39.9 kcal mol−1, NO 2 decomposes on a second ZCu 2 O site, giving NO again and O 2. Three reaction paths were defined for the latter reaction, with activation energies ranging from about 30 to 42–43 kcal mol−1. Final O 2 desorption is endothermic. The effect of enthalpy and Gibbs free energy contributions at 298.15 and at 773 K was also shown and discussed. According to the present calculations, the [Cu O Cu]2+ bridge can easily be broken by reaction with NO but the desorption and further decomposition of NO 2 are characterized by energetics which make the above mechanism slower than the spin-allowed decomposition of N 2 O on similar sites, already reported in the literature. The above conclusions were based on a kinetic analysis according to the Energetic Span Model. [ABSTRACT FROM AUTHOR]

New composite catalysts were synthesized by pyrolysis of carbon-containing compounds supported of Cu-substituted ZSM-5 zeolite. Three series of the catalysts containing 12 wt% of carbon and 1 wt% of copper were prepared (powder, honeycomb monolith and extruded trefoils) and characterized by TEM, XPS, N 2 adsorption. Kinetics of catalytic wet peroxide oxidation (CWPO) of phenol was studied in the presence of the composite catalysts using batch and flow reactors. The substrate conversion in the batch reactor was reached 45% in two minutes over the composite catalyst but no more than 8% in five minutes over the zeolite catalyst. Studies of the granulated composites (monoliths and trefoil) in the flow reactor demonstrated a higher efficiency of the trefoil catalyst. The conversion of phenol at the flow rate 20 mL min −1 was 35% higher over the composite trefoils than over the carbon-free zeolite. The obtained kinetic data allowed the conclusion to be made about different mechanisms of CWPO over zeolite and composite catalysts. The developed kinetic model of phenol CWPO over the composite catalyst described the formation and destruction of intermediate products of phenol oxidation. It was established that inhibiting of phenol oxidation by the substrate was less pronounced in the presence of the composite catalysts than in the presence of the carbon-free catalysts. The flow reactor for phenol oxidation was modeled with account for the external and internal diffusion deceleration of the reaction over real catalyst granules of different geometry to provide adequate description of the experimental results. [ABSTRACT FROM AUTHOR]

A series of metal modified zeolite including Cu-(Beta, FER, MCM-22, MCM-49, MOR) and M-(M = Cu, Co, Fe, Mn, Ni)-ZSM-5 was prepared by impregnation method and characterized by BET, XRD, and H 2 -TPR. HCN-SCC (selective catalytic combustion) activity measurement results suggest that Cu-ZSM-5 exhibiting excellent HCN conversion activity (T 90 = 350 °C) and N 2 yield (>95% at T > 350 °C) constitutes one kind of promising candidate for HCN catalytic abatement. The HCN-SCC mechanism was further investigated by density functional theory (DFT) over constructed 20T-Cu-ZSM-5 models, which suggests that: (i) the 20T-Cu-ZSM-5 containing double active [Cu] + site was much more favorable than that of 20T-Cu-ZSM-5 with single active [Cu] + site during NCO generation step, being mainly related to the cooperation effect of double active [Cu] + site; (ii) NCO + NO → N 2 + CO 2 was confirmed to the one kind of probable reaction pathway for N 2 and CO 2 generations, wherein the NO could be produced through oxidation of NCO; (iii) the DFT energy calculation results as well as the microkinetic analyses suggested that the NCO formation step possessing the highest energy barrier (10.4 kcal mol −1 ) was proposed to be the rate determining step of the whole catalytic cycle. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction of NO with ammonia (NH3–SCR) was studied over Cu-ZSM-5 nanocatalysts which were prepared by several methods, including conventional ion-exchange (IE), conventional impregnation (IM), ultrasound-enhanced impregnation (UIM), and conventional deposition–precipitation (DP) using NaOH and homogeneous deposition–precipitation (HDP) using urea. The nanocatalysts were subsequently characterized by Fourier transform infrared spectroscopy, temperature-programmed reduction with hydrogen (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscope, and Brunauer–Emmett–Teller. The catalytic activity of the Cu-ZSM-5 nanocatalysts for NO removal decreased in the following order: Cu-ZSM-5 (HDP) > Cu-ZSM-5 (UIM) > Cu-ZSM-5 (IM) > Cu-ZSM-5 (IE) > Cu-ZSM-5 (DP). The effect of various preparation methods for Cu-ZSM-5 on the activity of NO conversion was compared and catalytic experiments revealed a strong correlation between the acid sites’ strength and easily reducible isolated Cu2+with NO conversion. Catalyst (HDP) (which showed excellent deNO activity) mainly contains easy reducibility of isolated Cu2+ions, more strong acid sites, and higher specific surface area when compared with other catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanism of NO decomposition by Cu-ZSM-5 was investigated. • DFT calculations were performed on simple cluster models. • Pairs of Cu(I) ions located at a short distance were considered as the active site. • Three different pathways were identified. • The slow steps of the process are N 2 O decomposition and O 2 desorption. The complete NO decomposition catalyzed by short-distance Cu+ pairs in Cu-ZSM-5 was studied by means of DFT calculations. After adsorption of two NO molecules, an hyponitrite species is formed. Further decomposition of hyponitrite occurs with activation energies ranging from about 4 to 24 kcal mol−1, depending on the initial geometry of the substrate-catalyst complex. An oxidized form of the catalyst, [Cu O Cu]2+ and a copper-coordinating N 2 O molecule are obtained. Further N 2 O decomposition may occur with oxygen transfer from N 2 O to [Cu O Cu]2+ and formation of N 2 and O 2 , both adsorbed on the catalyst. Three different kinds of transition states were identified for the latter step, which appears to be rate-determining due to activation energies ranging from 39–40, to 44–45, and to 50–52 kcal mol−1, respectively. After this, N 2 desorption occurs easily, whereas O 2 desorption is endothermic (from 28.8 to 36.5 kcal mol−1), the highest value being associated to reductive O 2 desorption from a peroxide-like complex. It turned out that the best way for N 2 O elimination is the direct, spin-forbidden decomposition on a reduced Cu+⋯Cu+ pair, with formation of [Cu O Cu]2+ and N 2 , as already suggested in the literature. The problem of how the reduced catalyst may be regenerated is left open. [ABSTRACT FROM AUTHOR]

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir's monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in NO decomposition. The amount of Cu that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO properties of Cu-ZSM-5 depend considerably on the NHOH/Cu ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NHOH/Cu = 6-10 stabilize, in the Cu-ZSM-5 structure, Cu ions bonded with extraframework oxygen, which are more active in DeNO than isolated Cu ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NHOH/Cu = 3). [ABSTRACT FROM AUTHOR]

The surface of Cu-ZSM-5 catalyst was modified by chemical liquid deposition (CLD) of tetraethoxysilane (TEOS) for enhancing its hydrothermal stability in the selective catalytic reduction of NO with NH 3 . After hydrothermal aging at 750 °C for 13 h, the catalytic performance of Cu-ZSM-5-Aged catalyst was significantly reduced for NO reduction in the entire temperature range, while that of Cu-ZSM-5-CLD-Aged catalyst was affected very little. The characterization results indicated that an inert silica layer was deposited on the surface of Cu-ZSM-5 and formed a protective layer, which prevents the detachment of Cu 2+ from ZSM-5 ion-exchange positions and the dealumination of zeolite during the hydrothermal aging process. Based on the data it is hypothesized to be the primary reason for the high hydrothermal stability of Cu- Z SM-5-CLD catalyst. [ABSTRACT FROM AUTHOR]

Catalytic dehydration of ethanol to ethylene on HMOR (Si/Al = 6.5), HZSM-5 (Si/Al = 29), Cu-HZSM-5 (Si/Al = 98) and Fe-HZSM-5 (Si/Al = 151) was studied at atmospheric pressure and 120oC - 300ºC. ZSM-5 supported catalysts were active at temperatures over 260ºC, achieving more than 60% conversion. Ethylene was predominantly produced as a dehydration product. Incorporating Cu did not significantly improve catalytic activity compared to HZSM-5. H-MOR was very active at low temperatures but deactivated rapidly at 240ºC, most probably due to coke formation.

The mono(μ-oxo) dicopper cores present in the pores of Cu-ZSM-5 are active for the partial oxidation of methane to methanol. However, copper on the external surface reduces the ratio of active, selective sites to unselective sites. More efficient catalysts are obtained by controlling the copper deposition during synthesis. Herein, the external exchange sites of ZSM-5 samples were passivated by bis(trimethylsilyl) trifluoroacetamide (BSTFA) followed by calcination, promoting selective deposition of intraporous copper during aqueous copper ion exchange. At an optimum level of 1-2 wt % SiO2, IR studies showed a 64 % relative reduction in external copper species and temperature-programmed oxidation analysis showed an associated increase in the formation of methanol compared with unmodified Cu-ZSM-5 samples. It is, therefore, reported that the modified zeolites contained a significantly higher proportion of active, selective copper species than their unmodified counterparts with activity for partial methane oxidation to methanol. [ABSTRACT FROM AUTHOR]

The wet peroxide oxidation of phenol over the extruded 1.5%Cu/(80%H-ZSM-5 + 20%Al 2 O 3 ) catalysts of the different geometric forms and sizes (cylinders with diameters 1, 2, 3 mm, trefoils, spheres and monoliths with size of channels 1.0 × 1.0, 1.5 × 1.5 mm) was studied in a flow reactor. The geometric form and size of the catalyst granules exert a pronounced effect on the apparent kinetics of the process. The highest efficiency toward phenol destruction was observed for the catalysts with a greater geometric surface area (trefoils and monolith with high channel density). The conversions of phenol and TOC at flow rate 5 mL min −1 equal to 100 and ∼90% were achieved over these catalysts. Application of the spherical shape catalyst with lowest geometric surface gave only 80% conversion of phenol at the same reaction conditions. The proposed mathematical model of the process, accounting for internal and external diffusion limitations on the base of the pseudo-first order simplification of the apparent kinetic rates, provide reasonably accurate description of the experimental data and reproducing all important process regularities. [ABSTRACT FROM AUTHOR]

The development of more efficient zeolite catalyst for selective catalytic reduction of NO x (DeNO x -SCR) requires the analysis of the real-time state of the catalyst (e.g. NH 3 storage level) and the reaction mechanism. Impedance spectroscopy (IS) allows to electrically sense the uptake of NH 3 into proton conducting catalysts. By means of IS we reveal that Cu-SAPO possesses higher response to NH 3 than Cu-ZSM-5 over a broad temperature range from 80 °C to 450 °C. IS can thus be used to determine the NH 3 storage and to monitor the SCR reaction in situ . Simultaneous IS and DRIFTS study under in situ conditions unveiled that the proton conductivity of Cu-SAPO is related to the ammonium nitrate intermediate, NH 3 species bounded to both Cu sites and Brønsted acid sites. However, the contribution of each species to the conductivity varied in different reaction conditions. This correlation of integral electrical response with molecular processes paves a new route for the in situ monitoring and mechanistic understanding of zeolite-catalyzed SCR reactions. [ABSTRACT FROM AUTHOR]

The peroxide oxidation of model substrates (formic acid and phenol) was studied in the presence of copper- and iron-containing catalysts (0.5 % Cu-ZSM-5-30 and 0.65 % Fe-ZSM-5-30). The aim was to develop optimal kinetic models for describing the kinetics of peroxide oxidation. The real kinetics of phenol and formic acid oxidation in the presence of these catalysts at varied reaction parameters (concentrations and temperature) was studied. The copper-containing catalysts were more active to formic acid oxidation than the iron-containing catalyst over all the temperature range studied. The rate of destruction of pollutants decreases with a decrease in the HO concentration and the catalyst weight. The observed rate dependences on the initial substrate concentration appeared to be different for the substrate used. With formic acid, an increase of initial concentration leads to a slight increase in the reaction rate. In the case of phenol peroxide oxidation, the negative order with respect to the substrate concentration was observed. This may be explained by strong inhibition of the reaction rates by phenol and intermediates (hydroquinone, catechol, etc.) of its oxidation. The mathematical modeling of the kinetics was performed for various types of kinetic equations that correspond to different hypotheses on the kinetic reaction scheme. The selected kinetic models based on logical kinetic schemes allowed describing the peroxide oxidation of model substrates at an appropriate accuracy. [ABSTRACT FROM AUTHOR]

Silicalite-1 particles with an average size of 260 nm were used as seeds to prepare Silicalite-1@ZSM-5 core-shell crystals with sizes on the order of 500 nm. A Silicalite-1@Cu-ZSM-5 catalyst was then prepared by ion exchange with copper acetate. Upon appropriate pretreatment in He at 500 °C, the core-shell catalyst showed much higher activity in N 2 O decomposition than Cu-ZSM-5 prepared using commercial ZSM-5 as the precursor. Characterization of relevant samples was conducted employing N 2 adsorption-desorption, XRD, ICP, XRF, SEM, TEM, XPS, CO-IR, H 2 -TPR, and O 2 -TPR. It was found that Silicalite-1@Cu-ZSM-5 has more dimetric Cu + upon thermal pretreatment in He. In addition, less O 2 can be adsorbed on Silicalite-1@Cu-ZSM-5. Both factors contribute to the much higher activity of Silicalite-1@Cu-ZSM-5. The effect of co-fed O 2 and H 2 O vapor on the catalytic performance was also studied. [ABSTRACT FROM AUTHOR]

The coordination of Cu+ at the T1 and T7 positions of the M7 ring of Cu-ZSM-5, and the interaction of NO with coordinated Cu+ were investigated by means of DFT/ONIOM calculations. The B3LYP, BLYP, PBE1PBE, PBE, M06, and M062X functionals with the def2-TZVP (def2-QZVP for Cu) basis set were used in the high-level part of ONIOM calculations, with the HF/3-21G, B3LYP/LANL2DZ, M06/LANL2DZ, and M062X/LANL2DZ methods in the low-level part. The ability of suitable combinations of the above methods to reproduce (i) the crystallographic structure of purely siliceous ZSM-5, (ii) the tendency of Cu+ to be twofold or fourfold coordinated by framework oxygen atoms of Cu-ZSM-5, and (iii) the interaction energy and the NO stretching frequency of adsorbed nitrogen oxide are discussed, showing that different results are obtained depending on the adopted computational approach. With reference to above properties, some considerations about the employment of the ONIOM approximations are also included. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We performed n -heptane cracking over Cu-ZSM-5, Ag-ZSM-5, and P/H-ZSM-5 before and after steaming under various conditions. The reduced Cu-ZSM-5 and Ag-ZSM-5 exhibited similar n -heptane cracking activities to H-ZSM-5 due to generation of Brønsted acid sites by reduction of metal cations. The order of steaming stabilities in the presence of O 2 was Cu-ZSM-5 > Ag-ZSM-5 ≫ P/H-ZSM-5, which was the reverse order of cumene cracking activities in the presence of O 2 . Cumene cracking activity is a function of Brønsted acidity. Therefore, these findings indicate that the steaming stability of a catalyst is strongly related to its Brønsted acidity. Cu 2+ and Cu + cations in the 194%Cu-ZSM-5 were not reduced to Cu 0 at a high temperature of 1023 K in the presence of O 2 and, therefore, 194%Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of O 2 . The Brønsted acidity of 95%Ag-ZSM-5 was extremely low, almost equal to 194%Cu-ZSM-5. However, the thermal reduction of Ag + took place during steaming even in the presence of O 2 at a high temperature of 1023 K and, therefore, the steaming stability of 95%Ag-ZSM-5 in the presence of O 2 was much lower than that of 194%Cu-ZSM-5. [ABSTRACT FROM AUTHOR]

ZSM-5 nanosheets were prepared using [C 18 H 37 -N + (CH 3 ) 2 -C 6 H 12 -N + (CH 3 ) 2 -C 6 H 13 ]Br 2 as a template and then ion-exchanged with Cu cations. The catalytic performance of the obtained Cu-ZSM-5 nanosheets in N 2 O decomposition was investigated and compared with that of conventional Cu-ZSM-5. Higher activity as well as better stability was observed for Cu-ZSM-5 nanosheets although the Cu contents of the catalysts were identical. Relevant characterization was conducted using XRF, ICP, XRD, N 2 adsorption–desorption, SEM, TEM, CO-IR, H 2 -TPR and O 2 -TPD. The data show that the better catalytic performance of Cu-ZSM-5 nanosheets is probably due to better accessibility of active sites, better reducibility of active Cu + species, and the weakened interaction between oxygen and Cu + sites. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Cu-ZSM-11 catalysts are firstly used in direct N2O decomposition. [•] Cu-ZSM-11 is obviously more active than Cu-ZSM-5 with the same Si/Al ratio. [•] Enhanced activity is due to better reducibility and accessibility of Cu+ species. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydrothermal deactivation depends on stability of Al in the zeolite framework. [•] Cu–Al clusters are formed during deactivation of Cu-ZSM-5 and Cu-IM-5. [•] Cu–Al clusters resemble CuAl2O4 but without the periodicity and symmetry. [•] An overall deactivation mechanism is proposed for Cu-ZSM-5 and Cu-IM-5. [ABSTRACT FROM AUTHOR]

Highlights: [•] Adsorption of NO on Cu-ZSM-5 causes disproportionation of Cu2+ to Cu+ and Cu3+ ions. [•] The process occurs with participation of associated [Cu–O–Cu]2+ sites even at 100K. [•] The Cu3+ ions form two kinds of mononitrosyl species (1960 and 1947cm−1). [•] The Cu3+–NO species can accept a second NO molecule thus forming dinitrosyls. [•] At ambient temperature, Cu3+ ions are reduced by NO to Cu+ and Cu2+. [ABSTRACT FROM AUTHOR]

Highlights: [•] Metal foams of enhanced mass and heat transfer properties. [•] Metal foams generates low pressure drop and offer considerable reduction of a reactor size. [•] Cu-ZSM-5 directly synthesized on metal foams active in NH3-SCR reaction. [•] Short channel structures as an alternative for honeycomb monoliths and packed bed of spheres. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cu-ZSM-5 was immobilized on glassy carbon electrode obtained so-called ZME. [•] The redox couple Cu2+/Cu+ acts like charge mediator in the reduction of nitrite. [•] The copper inside of zeolite framework show high catalytic activity toward nitrite reduction. [•] The acidity necessary for the electrochemical reduction of nitrite was provided by the zeolite. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cu- and Fe-substituted zeolites in CWPO of formic acid were systematically examined. [•] Cu-ZSM-5-30 (0.5–1.5wt% Cu) catalysts are most promising for CWPO. [•] High efficiency is provided by square-planar Cu oxide clusters in zeolite channels. [Copyright &y& Elsevier]

Abstract: Cu-zeolites are highly promising heterogeneous catalysts for a variety of chemical reactions. Knowledge of the location and coordination of copper in the zeolite lattice is key to fully understand its fascinating catalytic properties. Various methods exist to introduce Cu in zeolites, cation exchange being commonly used. The location of Cu in the zeolite structure has been researched for many years and an overview is presented here for the common zeolite topologies. Besides simple Cu-ion exchange, also ligated copper complexes are included in the pores and cages of zeolites. Irrespective of their introduction method, the zeolite does not merely serve as the inorganic host. As Cu interacts with the zeolite framework, while being located in a unique constraint microenvironment, a distinctly different Cu coordination chemistry often exists in the zeolites. Effects thereof on the activity of various Cu complexes are discussed in relation to oxidation chemistry and catalysis. An interesting case is the (re)activity of Cu, when exchanged in a ZSM-5 zeolite. Cu–ZSM-5 is for instance able to catalytically decompose NO x in its elements very rapidly and, even more intriguing, recent research shows that some Cu species in Cu–ZSM-5, and by extension also in Cu–MOR, selectively oxidizes methane into methanol after activation with O2 or N2O. This review summarizes the latest advances and discussions on the identification of the reactive intermediates and their particular role in the reaction cycle of the methane to methanol conversion. Interestingly, recent spectroscopic and kinetic (isotopically labeled) studies on the Cu–ZSM-5 system have shed new light on the activation of small molecules on Cu-sites. The structural and mechanistic details have already been and will be very useful and instructive to understand the working fundamentals of Cu-containing biomimics and enzymes. Prof. Edward I. Solomon greatly contributed to this pioneering work. [Copyright &y& Elsevier]

Abstract: The present work studies RedOx properties and reactivity in N2O decomposition and selective catalytic reduction of NO (NO-SCR) by propane of Cu-modified ZSM-5 catalysts prepared by hydrolytic polycondensation (HPC). Their characteristics are compared with properties of Cu-ZSM-5 samples having the same copper content (1wt.%) and produced by ion exchange (IEX) with water–ammonia solutions of copper chloride at NH4OH/Cu2+ equal to 6–30. The HPC method consists in the treatment of the copper-impregnated zeolite by water–ammonia solution for polycondensation of hydrolyzed copper ions in the zeolite pores. It is shown that varying the NH4OH/Cu2+ ratio allows a regulation of the size and structure of copper active complexes. The copper-impregnated zeolite contains copper as CuO-like particles after calcination. At NH4OH/Cu2+ equal to 1–3, active sites in dried samples are disordered polynuclear copper-hydroxo complexes, which are characterized by symmetric ESR signal with g 0 =2.18. Increase of NH4OH/Cu2+ to 6–30 lead to the orbital ordering of Cu2+ ions in the copper–ammoniate complexes, observed as the rhombic ESR signals (g z ex,1 =2.18, g y ex,1 =2.08, g x ex,1 =2.03 and g ∥ ex,2 =2.24, g ⊥ ex,2 =2.03), and to dispersion of CuO-like particles during following thermal treatment at 500°C. The dried 1%Cu(30)ZSM-5-HPC sample prepared at NH4OH/Cu2+ =30 has a higher amount of isolated tetraammine–copper complex and a lower number of weak associates of Cu2+ ions among samples. The addition of ammonia solution to the copper-impregnated zeolite for hydrolytic polycondensation has a favorable impact on the Cu-ZSM-5 activity in DeNOx processes. In N2O decomposition, the ion-exchanged CuZSM-5 catalysts were more reactive in the low-temperature region, while the ex-polycondensation catalysts provided a high N2O conversion at high temperatures. In NO-SCR by propane, the more reactive were the ion-exchanged catalysts, and NO reduction rate increased with NH4OH/Cu2+ grew for 10. It is suggested that the ordered associated Cu2+ ions of ex-polycondensation and ion-exchanged catalysts have higher reactivity and selectivity in both DeNOx processes as compared to the isolated copper ions. [Copyright &y& Elsevier]