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[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]

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]

• 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]

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]

[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]

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]

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]

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]

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: [•] 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]

Abstract: H-ZSM-5 is an excellent catalyst to produce light olefin in naphtha cracking. But it is difficult to avoid the deactivation by coke formed, so the frequent regeneration of H-ZSM-5 by calcination is necessary. A little steam is generated during the calcination, resulting in the permanent deactivation by dealumination. We found that Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of oxygen and a comparable activity for heptane cracking in the reductive atmosphere, compared with H-ZSM-5. These results are attributed to a low Brønsted acidity in the presence of oxygen and a high Brønsted acidity in the reductive atmosphere. [Copyright &y& Elsevier]

Abstract: The adsorption of NO has been investigated in the temperature range 50–150°C on Cu-ZSM-5 and La-Cu-ZSM-5 also in the presence of water and O2 in a continuous flow reactor. TPD experiments have been performed after each adsorption test monitoring all desorbed NO x species. Water has been found to displace NO from copper sites strongly reducing its adsorption except for nitrate-like species which are partially preserved also in the presence of water. O2 addition, although decreasing NO adsorption, limits the negative effect of water. Lanthanum co-exchange results in improving the NO adsorption capacity of the zeolite both in the absence and in the presence of water. [Copyright &y& Elsevier]

Abstract: The present computational study investigates the mechanism of NO decomposition catalyzed by Cu-ZSM-5. It was considered that the active site could be of two kinds: (i) pairs of Cu+ ions located at opposite sides of the ten-membered rings of the zeolite, in the region at the intersection of the linear and sinusoidal channels; (ii) isolated Cu+ ions. DFT calculations were performed by using the B3LYP functional on cluster models suited to reproduce the geometrical constraints of the ZSM-5 structure. It was shown that both the Cu+-pair mechanism and that catalyzed by a single-Cu+ site proceed through the formation of N2O as a reaction intermediate, which further reacts with the oxygen atom of a ZCu–O–CuZ or ZCuO unit (Z=zeolite) to give O2 +N2. The latter step displayed a larger activation energy in the Cu+-pair mechanism, which is therefore unfavored although the pathway associated to Cu+-pairs occurs at lower energy than that associated to a single-Cu+ site. Such a large activation energy is associated to the stability of the ZCu–O–CuZ fragment. A quantitative analysis, performed by means of the energetic span model of Kozuch and Shaik, reinforced the just outlined observations. [Copyright &y& Elsevier]

Abstract: The aim of the present study is to investigate the de-NOx performance of a Cu-ZSM-5 catalyst to which ZrO2 additives are added to improve the low-temperature activity and durability of the selective catalytic reduction (SCR) catalyst for diesel vehicles. The main experimental parameters are the amount of ZrO2 added, hydrothermal aging temperature, type of hydrocarbon (HC) and concentration of sulfur (S). The results showed that the NOx conversion of the Cu-ZSM-5-ZrO2 (2wt%) catalyst was improved by 10–20% compared to that of the Cu-ZSM-5 or Fe-zeolite catalyst in the temperature range of 200–300°C, because the addition of an appropriate amount of ZrO2 additive can improve the activation of the Cu-ZSM-5-ZrO2 (2wt%) catalyst by enhancing the acidity of the SCR catalyst. The Cu-ZSM-5-ZrO2 (2wt%) catalyst was the (most?) resistant against hydrothermal aging, (because the?) ZrO2 additives can advance the activation of the Cu-ZSM-5 catalyst by promoting its thermal stability. Alkenes such as propylene (C3H6) containing a double bond in the reaction gases had a more negative effect on the de-NOx performance of the Cu-ZSM-5 catalysts than other hydrocarbons. The curve of the de-NOx performance of the Cu-ZSM-5 catalysts in the presence of C3H6 decreased rapidly in the range of 200–350°C and then increased again to form an M-shaped curve due to the blocking of the SCR reaction. Although the recovery rate of the de-NOx performance for Cu-ZSM-5-ZrO2 (2wt%) from sulfur poisoning was not reversible, it was higher than those of the Cu-ZSM-5-ZrO2 (0 and 4wt%) catalysts, because it contained the proper amount of ZrO2. The proper amount of ZrO2 for the Cu-ZSM-5 SCR catalyst was 2wt%. [Copyright &y& Elsevier]

Abstract: NO oxidation is considered as the rate determining step of the standard selective catalytic reduction (SCR) reaction (NO+NH3 +O2) on metal-exchanged zeolite catalysts. A comprehensive experimental and kinetic modeling study of NO oxidation reaction was carried out and a comparison made between Fe-ZSM-5, Cu-ZSM-5 and recently developed small pore Cu-chabazite catalysts. Steady state integral measurements of NO oxidation show Fe-zeolite to be a more active NO oxidation catalyst than Cu-zeolite. Both NO2 temperature programmed desorption and decomposition experiments show that the NO2 is more strongly bound on the Cu-chabazite compared to Fe-ZSM-5. Increasing amounts of NO2 in the NO x feed decrease the NO oxidation activity on both the catalysts. Differential kinetic studies show a positive order rate dependence of NO oxidation reaction with respect to both NO (∼1) and O2 (∼0.5) while showing a negative order dependence with respect to NO2 (−0.5 to −1), which confirms that the NO2 inhibits the NO oxidation reaction. NO2 inhibition on NO oxidation was found to be more severe on Cu-chabazite (∼ −1 order) compared to Fe-ZSM-5 (∼ −0.5 order). The overall activation energy of NO oxidation was found to be 39kJ/mol on Fe-ZSM-5 compared to 56kJ/mol on Cu-chabazite. The presence of feed water strongly inhibits the NO oxidation reaction. Transient NO2 uptake experiments reveal nitrate formation on both catalysts. Catalysts pretreatments by different oxidizing/reducing agents (O2, NO2, H2 and NH3) did not affect steady state NO oxidation results. Experiments with monolith catalysts having the same washcoat volume but different washcoat thicknesses rule out the presence of washcoat diffusion limitations for NO oxidation. A global kinetic model is developed which accurately predicts the experimentally observed reaction orders, NO conversions and NO2 and water inhibition effects for a wide temperature range and different feed conditions. The kinetic model accounts for the experimentally observed instability of nitrates in the presence of feed NO and shows that the steady state NO oxidation data can be predicted with a global kinetic model assuming the surface reaction between adsorbed O atoms and gaseous NO as the rate determining step. [Copyright &y& Elsevier]

Abstract: The interaction of NO with Cu-ZSM-5 has been investigated in a temperature range (25–225°C) in which no steady-state reactions occur. The study has been conducted by performing adsorption tests at variable exposure times and analysing the phenomena that occur by continuous monitoring of the gaseous effluents as well as by performing a subsequent TPD. The effect of temperature, catalyst pre-treatment and composition of the adsorbing mixture (NO/He, NO/O2/He, N2O/He and N2/He) have been evaluated. In situ FTIR experiments have been also carried out under similar conditions. The main observed phenomena are: (i) reduced Cu+ sites are quickly re-oxidized by NO producing large amounts of N2O; (ii) adsorbed NO slowly reacts with gaseous NO to give surface nitrates and still N2O in the gas phase regardless the copper oxidation state. A mechanism of copper re-oxidation and nitrates formation under the different conditions explored has been proposed on the basis of these findings. [Copyright &y& Elsevier]

Abstract: ONIOM calculations for the direct catalytic decomposition mechanism of NO2 and NO by Cu–ZSM-5 were carried out. In two layer calculations, Density Functional Theory and Universal Force Field were employed for the high and low level models, respectively. ΔH° and ΔG° evaluations were performed in order to determine the thermodynamically more favored way for catalytic decomposition of NO2 and NO. The results show that a novel copper κ2 mononitrosyl species (Z–2Cu–κ2NO) is in equilibrium with the Z–2CuNO and Z–2CuON species. According to our results, the Z–2Cu–κ2NO species is the intermediary key of the direct catalytic decomposition mechanism of NO2 and NO by Cu–ZSM-5. [Copyright &y& Elsevier]

Abstract: Adsorption of 12C16O–13C18O isotopic mixtures was used to establish polycarbonyl structures formed with Cu+ ions in Cu–ZSM-5. The principal Cu+(12C16O)2 dicarbonyls are characterized by νs at 2178cm−1 and νas at 2151cm−1. In excellent agreement with theory, Cu+(12C16O)(13C18O) mixed-ligand species were found to absorb at 2168 and 2065cm−1. Another kind of dicarbonyls, characterized by νs at 2183cm−1, was also unambiguously detected. Tricarbonyls are characterized by two IR modes, at 2191 and 2166cm−1. Different bands of Cu+(12C16O) x (13C18O) y (x + y =3) species were established. The use of isotopic mixtures also helped in the assignment of a shoulder at 2194cm−1 to Cu2+–CO adducts. [Copyright &y& Elsevier]

Abstract: A range of ethers, alcohols and alkanes were compared as reducing agents for NO x over a Cu-ZSM-5 lean NO x catalyst. The nature of the reducing agent was found to determine the degree of NO x reduction. Methanol and DME were virtually inactive as reductants over this catalyst, while higher ethers and alcohols showed high NO x conversion. A detailed study was performed to investigate the differences. Among the studied variables, the chemical structure of the reductant was found to be especially important. Despite having a lower reducing capacity than DME, ethylene glycol was active for NO x reduction. It is concluded that a C–C bond in the reducing agent is required for lean NO x reduction over Cu-ZSM-5. The absence of this bond in DME and methanol explains their low activity for NO x reduction over this catalyst. [Copyright &y& Elsevier]

Several Cu-exchanged and Fe-exchanged ZSM-5 catalysts were prepared and studied for the decoloration, degradation and mineralization of Rhodamine 6 G in catalytic wet peroxide oxidation (CWPO). The Cu-ZSM-5 catalysts were shown to be more effective than the parent H-ZSM-5 zeolites (containing Fe-ions as impurity) and Fe-exchanged ZSM-5 to Rhodamine 6 G oxidation by hydrogen peroxide. Effects of copper loadings, Si/Al ratio, structure of copper species, and initial pH were ascertained on catalytic behavior of Cu-ZSM-5 and copper leaching under CWPO conditions. At acid pH, the highest decoloration of Rhodamine 6 G was typical of Cu-ZSM-5 with Si/Al equal to 30 and Cu content of ca. 0.5 – 0.65 wt% having isolated Cu2+ ions, whereas the maximal conversions of total organic carbon (TOC) were exhibited by catalysts with 1.5 – 2.8 wt% Cu and CuO-like clusters on the external zeolite surface. At alkali pH, the over-exchanged 2.8% Cu-ZSM-5 with CuO-like clusters was more active than under-exchanged 0.5% Cu-ZSM-5 to decoloration of Rhodimine 6 G, while both catalysts provided identical TOC conversions. Catalyst with 0.5 wt% copper loading showed reproducible activity up to 7th cycle. According to UV-Vis DR and EPR studies, the high efficiency of Cu-ZSM-5 to Rhodamine 6 G oxidation in acid solution is provided by the isolated Cu2+ ions, while the nanostructured square-planar CuO-like clusters (on the zeolite surface) ensure activity at alkali pH. Two mechanisms of organic substrate oxidation, i.e. radical (Fenton-like) mechanism activated by isolated Cu2+ ions and nucleophilic substitution via copper-hydroperoxide complex generation, were discussed. [Display omitted] • Cu-ZSM-5 efficiently degrades Rhodamine 6 G in CWPO at 50 °C. • pH and Cu-state are key to control the decoloration and mineralization of R6G. • At acidic pH, 80% mineralization of R6G is due to isolated Cu2+ ions. • At alkaline pH, more active in R6G mineralization are CuO-like clusters. • High performance of 0.5%Cu-ZMS-5 showed in seven consecutive CWPO cycles. [ABSTRACT FROM AUTHOR]

Abstract: Experimentally, Cu-exchanged IM-5 zeolite has been found to exhibit excellent catalytic activity in NO x reduction. Unfortunately, the origin of such property still remains obscure due to the rather complex structure of IM-5. In this paper, we made the first attempt to provide a theoretical rationalization. By calculating the (Al, Cu) location energies, the stability of both Cu2+ and hydroxyl-Cu2+ (i.e., [CuOH]+) was considered and compared to those in ZSM-5. It was shown that [CuOH]+ located in IM-5 is comparable to that in ZSM-5. The most favorable location of Cu2+ cation is in 6-membered ring in the wall of unusual two-dimensional medium-pore channel of IM-5. Moreover, through calculating the interaction of NO with copper-exchanged zeolite (Cu-IM-5), the most active center is Cu2+ located in the 5-membered ring. The relatively high adsorption energies and numerous active centers in Cu-IM-5 might rationalize why Cu-IM-5 is more active than Cu-ZSM-5 in experiment of NO reduction. Thus, our theoretical results provide support that Cu-IM-5 is a more active and hydrothermically more stable catalyst than Cu-ZSM-5. [Copyright &y& Elsevier]

• A new coordination for a pair of Cu+ ions at the M6 ring of Cu-ZSM-5 was found. • The new coordination is much more stable than those in the literature. • Cu+ ions react as single ions and not as a Cu+ pair. • Two mechanisms were identified for NO decomposition. • The site is inactive due to high activation energies. By DFT calculations, a new coordination was found for a pair of Cu+ ions at the M6 ring of ZSM-5, with Al located at the T11 and T11' positions. This coordination is 27 kcal mol−1 more stable than other structures previously reported in the literature. In the present structure, one of the Cu+ ions is tetracoordinated to the framework oxygens, whereas the other one is nearly pentacoordinated. After NO adsorption, Cu+ ions are split apart and do not show the typical reactivity of a Cu-pair. The bridged [Cu‒O‒Cu]2+ structure is 30 kcal mol−1 less stable than the structures where only one of the copper ions is oxidised. Because of the high degree of coordination of both copper ions, the adsorption energy of NO does not exceed 10–15 kcal mol−1. Two mechanisms for NO decomposition were defined for the present site, but when contributions to Gibbs free energy were accounted for, all intermediates and transition states turned out to be strongly destabilised at 773.15 K, with a consequent drop of the reaction rate. Since M6 rings and similar structures are widely represented within ZSM-5, the findings of the present work rule out many possibilities in the search of the actual active site for NO decomposition. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper studied nitrous oxide decomposition over a series of transition metal exchanged ZSM-5 zeolites prepared by solid-state ion-exchange method. Crystallographic structure of the catalysts has been investigated with the aid of XRD analysis. The texture of the prepared catalysts was investigated using nitrogen sorption. FTIR measurements applying pyridine as a probe molecule have been carried out in order to investigate the nature of the acid sites of the different catalysts. In situ electrical conductivity measurements were carried out in order to relate the activity of this series of catalysts to their electrical conductivity variation in the presence of N2O. The obtained results revealed that the N2O decomposition activity is related to the relative conductivity decrease upon the admission of N2O over metal exchanged ZSM-5 zeolites. Further studies have been performed over Co-, Cu- and Fe-ZSM-5 catalysts since they showed the highest activity patterns among all the tested catalysts. Such studies included the effect of changing Si/Al ratio, the exchange level, the calcination temperature and the milling time. [Copyright &y& Elsevier]

Abstract: Kinetic modeling, in combination with flow reactor experiments, was used in this study for simulating NH3 selective catalytic reduction (SCR) of NO x over Cu-ZSM-5. First the mass-transfer in the wash-coat was examined experimentally, by using two monoliths: one with 11wt.% wash-coat and the other sample with 23wt.% wash-coat. When the ratio between the total flow rate and the wash-coat amount was kept constant similar results for NO x conversion and NH3 slip were obtained, indicating no significant mass-transfer limitations in the wash-coat layer. A broad range of experimental conditions was used when developing the model: ammonia temperature programmed desorption (TPD), NH3 oxidation, NO oxidation, and NH3 SCR experiments with different NO-to-NO2 ratios. 5% water was used in all experiments, since water affects the amount of ammonia stored and also the activity of the catalyst. The kinetic model contains seven reaction steps including these for: ammonia adsorption and desorption, NH3 oxidation, NO oxidation, standard SCR (NO+O2 +NH3), rapid SCR (NO+NO2 +NH3), NO2 SCR (NO2 +NH3) and N2O formation. The model describes all experiments well. The kinetic parameters and 95% linearized confidence regions are given in the paper. The model was validated with six experiments not included in the kinetic parameter estimation. The ammonia concentration was varied from 200 up to 800ppm using NO only as a NO x source in the first experiment and 50% NO and 50% NO2 in the second experiment. The model was also validated with transient experiments at 175 and 350°C where the NO and NH3 concentrations were varied stepwise with a duration of 2min for each step. In addition, two short transient experiments were simulated where the NO2 and NO levels as well as NO2-to-NO x ratio were varied. The model could describe all validation experiments very well. [Copyright &y& Elsevier]

Abstract: The mechanism of acrylonitrile (AN) decomposition, that is, conversion of the nitrogen atoms in AN molecules to N2, over Cu-ZSM-5 was investigated. Oxygen was found to be necessary for AN decomposition and H2O in the reactant gas enhanced the reaction between AN and O2. The dependence of AN decomposition on contact time indicated that HCN, HNCO, NH3, and NO x behaved like intermediates. Temperature-programmed surface reaction of adsorbed AN revealed that H2O suppressed desorption of AN and lowered the temperature of N2 evolution. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed that AN was mostly converted to isocyanate (–NCO), which was probably converted to adsorbed NH3 by hydrolysis. N2 was formed by the reaction of adsorbed NH3 and adsorbed nitrate or by oxidation of adsorbed NH3. [Copyright &y& Elsevier]

Abstract: The decomposition activities of nitrogen monoxide (NO) were investigated for the copper ion-exchanged ZSM-5 zeolites (Cu-MFI) containing the rare-earth elements: La, Ce, Pr, Nd, Sm, and Gd. It was found that Sm and Gd acted as promoter for NO decomposition over Cu-MFI with 60–70% of the exchange level of copper ion, while the addition of the other rare-earth elements to Cu-MFI showed no positive effect on NO decomposition activity. The introduction of Sm and Gd to Cu-MFI had little influence on the effectiveness of each copper ion for NO adsorption in the MFI zeolite. The presence of Sm and Gd stabilized Cu+ as an active center. [Copyright &y& Elsevier]

Abstract: The hydrothermal synthesis of Cu-modified ZSM-5 by introducing Cu ions during zeolite synthesis (Cu/ZSM-5in) and by conventional impregnation (Cu/ZSM-5imp) has been compared. The catalysts were characterized by X-ray diffraction (XRD), FTIR spectroscopy in the T–O–T vibrations rang, scanning electron microscope (SEM), FTIR of pyridine adsorption and N2 adsorption. They were subjected to FTIR of NO adsorption for evaluating reactivity of Cu species changed with preparation method. The heterogeneous nature of Cu/ZSM-5imp is stressed with preponderance of CuO particles on the external zeolite surface. Contrary to this result, Cu/ZSM-5in showed evidence for highly dispersed and isolated Cu2+ centers in coordination with lattice oxygen of zeolite. Results of NO-FTIR experiments showed a clear performance for direct NO dissociation where Cu/ZSM-5in is favored over Cu/ZSM-5imp. This result, however, appears to correlate with the nature of Cu ions in the samples. The tetrahedral geometry of Cu2+ ions in the lattice of Cu/ZSM-5in served in a noticeable development of Brönsted acid sites (BAS) compared with analogies on Cu/ZSM-5imp. The nitrosyl complexes observed over Cu/ZSM-5in were N2O, NO–Cu2+, O–NO δ+, NO2 − and mono- and bidentate NO3 −. Similar species were observed on Cu/ZSM-5imp, together with evidence for concurrent appearance of two spectral features due to stable NO3 − species at 1713 and 1327cm−1. When these results are compared with those obtained over parent ZSM-5 and Cu/ZSM-5in, the latter species is associated mainly with the Cu2+ ions in discrete CuO phase which led to deactivation of Cu/ZSM-5imp. [Copyright &y& Elsevier]

Abstract: Cu-exchanged ZSM-5 zeolites finely coated with CeO2 nanoparticles were tested in this work as catalysts for the selective catalytic reduction (SCR) of NO with C3H6. The CeO2 coated Cu/ZSM-5 shows lower maximum NO conversion activity compared to the non-coated Cu/ZSM-5 catalyst at relatively high temperatures (ca. 450°C) but the former catalyst is significantly more active at lower temperatures (ca. 350°C), especially at lower space velocities, both under dry and wet feed conditions. Under simultaneous addition of both SO2 and water in the feed, the beneficial effect of the CeO2 coating at lower reaction temperatures was retained only at low space velocities. The same Cu/ZSM-5 based samples were evaluated as fluid catalytic cracking (FCC) catalytic additives for the in situ reduction of NOx formed during regeneration of the coked FCC catalyst. The amounts of NO and CO emitted during regeneration of the spent FCC catalyst at 700°C in the presence of Cu/ZSM-5 based additives were compared with those obtained when a commercial CO promoter was used in the FCC catalyst inventory. All Cu/ZSM-5 additives exhibited significant NO reduction ability, which was further enhanced by increasing the Cu loading or the amount of additive in the FCC catalyst. The CeO2-coated sample reached the highest deNOx performance (up to 78% NO reduction); however, all additives presented insufficient activity for CO oxidation. Simultaneous NO reduction and CO oxidation was achieved only when the CeO2-Cu/ZSM-5 additive was promoted with Rh or when the non-promoted additives were combined with a commercial CO promoter. Preliminary studies suggested that the Rh-promoted CeO2-Cu/ZSM-5 additives can be very effective for both NO reduction by CO and CO oxidation at certain O2 concentrations, such as in the O2-deficient zones of the FCC regenerator. Further studies are in progress in order to elucidate the reaction mechanism and optimize the additive''s formulation. [Copyright &y& Elsevier]

Abstract: Conventional Cu-ZSM-5 has for many years been recognized as a unique catalyst for direct NO decomposition. Zeolite-based catalysts have a crystallographically well-defined microporous structure. In such microporous catalysts, the creation and accessibility of the active sites is often influenced by the geometry of the pore system. To improve these catalysts, secondary mesoporous systems can benefitially be introduced into the structure of conventional zeolites. Here, this approach was used with Cu-containing ZSM-5 and ZSM-11 type mesoporous zeolite catalysts, which were used as catalysts for direct NO decomposition. It was discovered that introducing mesoporosity into the conventional materials leads to a significant improvement of the catalytic activity. Additionally, mesoporous Cu-ZSM-11 catalyst was found to be about twice as active as mesoporous Cu-ZSM-5. This difference is attributed to the fact that ZSM-11 has only straight microporous channels, while ZSM-5 has both straight and sinusoidal channels. Apparently, there is a preferential formation of active sites and/or improved accessibility in the straight channels compared to the sinusoidal channels, which make the ZSM-11 material a better catalysts than ZSM-5. All samples were characterized by XRPD, SEM, TPD-NH3, in situ EPR and N2 physisorption measurements. Thus, this confirms our previous observation that the special pore structure of Cu-ZSM-5 is not a decisive factor for the catalytic activity in NO decomposition. [Copyright &y& Elsevier]

Abstract: The over-loaded Cu-ZSM-5 under heating treatment (50–910°C) in oxidative conditions exhibits the formation of copper aggregates, which show different oxidation states as a function of temperature (Cu0, Cu2O and CuO). At room temperature the excess of copper is not detectable by X-ray diffraction (XRD). It is likely present as divalent copper species (Cu x (OH) y ) dispersed on the zeolite surface that appear amorphous at XRD. This is confirmed by the UV–Vis diffuse reflectance spectroscopy data. From Rietveld refinement of room temperature and high temperature diffraction data, there are no indications of the presence of copper clusters inside the zeolite cavities. As the heating treatment proceeds, the dispersed copper species transform to metallic copper particles with increasing diffracting domains as a function of temperature. Above 510°C the metallic copper starts to progressively oxidise to Cu2O and finally CuO. During heating treatment the ZSM-5 framework does not show relevant structural modifications. The transition from monoclinic to orthorhombic form was observed in the early stages of the temperature ramp (ca. 100°C). [Copyright &y& Elsevier]

Abstract: Decane-SCR-NO x in the presence of water vapor and NO decomposition were investigated over Cu ions exchanged in ZSM-5 zeolites with various Si/Al and Al distribution. The local environment of the Cu ions in cationic sites was characterized by the combination of 29Si MAS NMR, Vis–NIR spectroscopy of Cu(II) ions, Cu(I) Vis emission spectroscopy and UV–Vis spectroscopy of Co(II) ions as probes for the presence of Al pairs in the framework. The Cu(II) ions coordinated to four framework oxygens of the α- or β-type cationic sites containing Al-O-(Si-O)2-Al sequences represent the most active sites in decane-SCR-NO x . On contrary, the Cu(I) ions coordinated to two or three framework oxygens and located at the channel intersection adjacent to the single Al atoms in the α- or β-site control predominantly reaction of NO decomposition. [Copyright &y& Elsevier]

Abstract: The selective catalytic reduction of nitrogen oxides (NO x ) with ammonia over ZSM-5 catalysts was studied with and without water vapor. The activity of H-, Na- and Cu-ZSM-5 was compared and the result showed that the activity was greatly enhanced by the introduction of copper ions. A comparison between Cu-ZSM-5 of different silica to alumina ratios was also performed. The highest NO conversion was observed over the sample with the lowest silica to alumina ratio and the highest copper content. Further studies were performed with the Cu-ZSM-5-27 (silica/alumina=27) sample to investigate the effect of changes in the feed gas. Oxygen improves the activity at temperatures below 250°C, but at higher temperatures O2 decreases the activity. The presence of water enhances the NO reduction, especially at high temperature. It is important to use about equal amounts of nitrogen oxides and ammonia at 175°C to avoid ammonia slip and a blocking effect, but also to have high enough concentration to reduce the NO x . At high temperature higher NH3 concentrations result in additional NO x reduction since more NH3 becomes available for the NO reduction. At these higher temperatures ammonia oxidation increases so that there is no ammonia slip. Exposing the catalyst to equimolecular amounts of NO and NO2 increases the conversion of NO x , but causes an increased formation of N2O. [Copyright &y& Elsevier]

Abstract: The effect of ion exchange conditions, such as Si/Al ratio, precursor copper salt, pH and concentration of the solution, on the catalytic activity in SCR of NO by propane and on the electronic state of copper ions in Cu-ZSM-5 has been studied. The NO conversion in NO SCR by C3H8 has been found to reach a maximum value at Cu/Al ratio about 0.37–0.4 and remain constant at higher Cu/Al. ESR and UV–vis DR spectroscopy have been used to elucidate stabilization conditions of copper ions in Cu-ZSM-5 zeolites as isolated Cu2+ ions, chain copper oxide structures and square-plain oxide clusters. The ability of copper ions for reduction and reoxidation in the chain structures may be responsible for the catalytic activity of Cu-ZSM-5. These transformations of copper ions are accompanied by the observation of intervalence transitions Cu2+–Cu+ and CTLM of the chain structures in the UV–vis spectra. [Copyright &y& Elsevier]

Abstract: The catalytic decomposition of acrylonitrile (AN) over Cu-ZSM-5 prepared with various Cu loadings was investigated. AN conversion, during which the nitrogen atoms in AN were mainly converted to N2, increased as Cu loading increased. N2 selectivities as high as 90–95% were attained. X-ray diffraction measurements (XRD) and temperature-programmed reduction by H2 (H2-TPR) showed the existence of bulk CuO in Cu-ZSM-5 with a Cu loading of 6.4wt% and the existence of highly dispersed CuO in Cu-ZSM-5 with a Cu loading of 3.3wt%. Electron spin resonance measurements revealed that Cu-ZSM-5 contains three forms of isolated Cu2+ ions (square-planar, square-pyramidal, and distorted square-pyramidal). The H2-TPR results suggested that in Cu-ZSM-5 with a Cu loading of 2.9wt% and below, Cu+ existed even after oxidizing pretreatment. The activity of AN decomposition over Cu/SiO2 suggested that CuO could form N2, but, independent of the CuO dispersion, nitrogen oxides (NO x ) were formed above 350°C. Cu+ and the square-pyramidal and distorted square-pyramidal forms of Cu2+ showed low activity for AN decomposition. Temperature-programmed desorption of NH3 suggested that N2 formation from NH3 proceeded on Cu2+, resulting in the formation of Cu+. The Cu+ ions were oxidized to Cu2+ at around 300°C. Thus, high N2 selectivity over Cu-ZSM-5 with a wide range of temperature was probably attained by the reaction over the square-planar Cu2+, which can be reversibly reduced and oxidized. [Copyright &y& Elsevier]

Abstract: Selective catalytic reduction of NO x (SCR-NO x ) with decane, and for comparison with propane and propene over Cu-ZSM-5 zeolite (Cu/Al 0.49, Si/Al 13.2) was investigated under presence and absence of water vapor. Decane behaves in SCR-NO x like propene, i.e. the Cu-zeolite activity increased under increasing concentration of water vapor, as demonstrated by a shift of the NO x –N2 conversion to lower temperatures, in contrast to propane, where the NO x –N2 conversion is highly suppressed. In situ FTIR spectra of sorbed intermediates revealed similar spectral features for C10H22– and C3H6–SCR-NO x , where –CH x , R–NO2, –NO3 −, Cu+–CO, –CN, –NCO and –NH species were found. On contrary, with propane –CH x , R–NO2, NO3 −, Cu+–CO represented prevailing species. A comparison of the in situ FTIR spectra (T–O–T and intermediate vibrations) recorded at pulses of propene and propane, moreover, under presence and absence of water vapor in the reaction mixture, revealed that the Cu2+–Cu+ redox cycle operates with the C3H6–SCR-NO x reactions in both presence/absence of water vapor, while with C3H8–SCR-NO x , the redox cycle is suppressed by water vapor. It is concluded that decane cracks to low-chain olefins and paraffins, the former ones, more reactive, preferably take part in SCR-NO x . It is concluded that formation of olefinic compounds at C10H22–SCR-NO x is decisive for the high activity in the presence of water vapor, while water molecules block propane activation. The increase in NO x –N2 conversion due to water vapor in C10H22–SCR-NO x should be connected with the increased reactivity of intermediates. These are suggested to pass from R–NO x →–CN→–NCO→NH3; the latter reacts with another activated NO x molecule to molecular nitrogen. The positive effect of water vapor on the NO x –N2 conversion is attributed to increased hydrolysis of –NCO intermediates. [Copyright &y& Elsevier]

Abstract: The effect of framework aluminum content and local density on the NO x reduction with decane under lean burn conditions, i.e. in high excess of oxygen and water vapor (12%) over Cu-ZSM-5 zeolites with various Cu/Al and Si/Al ratios was investigated. The concentration of “Al pairs” located in one ring and balanced by divalent cations was estimated using divalent cobalt ions as probes. The portion of Cu ions located in vicinity of “Al pairs” or adjacent to a single framework AlO2 − entity was monitored by vis–NIR spectra of Cu2+ ions. The most active and stable Cu ions in C10H22-SCR-NO x under lean burn conditions appeared to be those located in vicinity of two Al atoms in one ring coordinated the cation. [Copyright &y& Elsevier]