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Graphical abstract Highlights • Dry SO 2 streams poison Z 2 Cu and ZCuOH sites in Cu-SSZ-13. • SCR kinetics are consistent with 1:1 SO 2 poisoning of each Z 2 Cu site. • New H+ sites are formed after SO 2 poisoning of Z 2 Cu sites. • SO 2 -poisoned Cu sites are less mobile than NH 3 -solvated Cu sites. • Z 2 Cu sites are more resistant to SO 2 poisoning and easier to regenerate. Abstract The effects of sulfur poisoning on Cu-SSZ-13 zeolites, used commercially for the selective catalytic reduction (SCR) of nitrogen oxides (NO X) with ammonia, were studied by exposing model Cu-zeolite powder samples to dry SO 2 and O 2 streams at 473 and 673 K, and then analyzing the surface intermediates formed using spectroscopic and kinetic assessments. Model Cu-SSZ-13 zeolites were synthesized to contain distinct Cu active site types, predominantly either divalent Cu2+ ions exchanged at proximal framework Al (Z 2 Cu), or monovalent CuOH+ complexes exchanged at isolated framework Al (ZCuOH). SCR turnover rates (473 K, per Cu) decreased linearly with increasing S content to undetectable values at equimolar S:Cu ratios, consistent with poisoning of each Cu site with one SO 2 -derived intermediate. Cu and S K-edge X-ray absorption spectroscopy and density functional theory calculations were used to identify the structures and binding energies of different SO 2 -derived intermediates at Z 2 Cu and ZCuOH sites, revealing that bisulfates are particularly low in energy, and residual Brønsted protons are liberated at Z 2 Cu sites as bisulfates are formed. Molecular dynamics simulations also show that Cu sites bound to one HSO 4 − are immobile, but become liberated from the framework and more mobile when bound to two HSO 4 −. These findings indicate that Z 2 Cu sites are more resistant to SO 2 poisoning than ZCuOH sites, and are easier to regenerate once poisoned. [ABSTRACT FROM AUTHOR]

The influence of phosphorus on the catalytic properties, durability, sulfur resistance and kinetics of Cu-SSZ-13 for NO x reduction by ammonia selective catalytic reduction (NH 3 -SCR) were systematically investigated to obtain a deeper understanding of the deactivation of Cu-SSZ-13 in the presence of phosphorus-containing impurities in diesel exhaust. An enhanced effect on NO conversion at low phosphorus loading was found above 450 ℃, probably due to the reduction of copper oxides that promote NH 3 oxidation at high temperatures. As the phosphorus loading reached 0.4 mmol/g catal , the framework dealumination and decrease of the BET specific surface area, acidity, and isolated Cu 2+ ions accounted for the decrease in activity and hydrothermal stability over the entire temperature range. Simultaneously, the activity of phosphorus-impregnated samples tested in the presence of SO 2 indicates that phosphorus accelerates the deactivation of Cu-SSZ-13 in the presence of SO 2 at low temperatures, primarily due to the severe decrease of the Cu 2+ ion content and partial coverage of the acid sites and active sites by phosphate and sulfate species. Additionally, kinetic analysis further demonstrated that phosphorus has an inhibitory effect on the SCR reaction rates at low temperatures and high phosphorus addition changes the NH 3 -SCR reaction kinetic parameters. The data presented herein provide a comprehensive picture of the interaction between phosphorus and Cu-SSZ-13. [ABSTRACT FROM AUTHOR]

Sb was used as the additive to enhance the NH 3 -SCR performance of MnTiO x catalyst. Experimental results revealed that MnSbTiO x -0.2 demonstrated outstanding NH 3 -SCR activity in a wide temperature window (100–400 ℃) and high resistance to SO 2 . Characterization results indicated the introduction of Sb into MnTiO x catalyst could improve the dispersity of active species and generate more surface acid sites, Mn 4+ and surface adsorbed oxygen species. In situ DRIFT spectra proved that the presence of Sb in MnSbTiO x -0.2 catalyst could form new Brønsted acid sites, along with the increased surface Lewis acidity. The improved adsorption of NH 3 and NO x species over MnSbTiO x -0.2 catalyst had a stimulating effect on the NH 3 -SCR reaction over it through Langmuir−Hinshelwood (L-H) route. Moreover, Sb species in MnSbTiO x -0.2 could improve the reactivities of ad-NH 3 and ad-NO x species in SCR reaction. All these factors contributed to the excellent performance of MnSbTiO x -0.2 catalyst. [ABSTRACT FROM AUTHOR]

Our previous studies suggested that the biomass tar derived from pyrolysis of distilled spirit lees (DSL) is an attractive agent for lowering NOx emission in the circulating fluidized bed decoupling combustion (CFBDC) process. The present work is furthered to evaluate the capabilities of other tar agents including sawdust (SD) tar and Xianfeng (XF) coal tar for NO reduction in a lab-scale drop-tube reactor. Additionally, five representative model tar compounds including phenol, benzene, acetic acid, methyl acetate and heptane were also tested to clarify the contribution of the main components in tar agents to NO reduction. The realized NO reduction efficiency by tar obviously varied with the reburning stoichiometric ratio (SR) and reaction temperature. At a specified mass feeding rate of reductant, say 0.15 g/min, the NO reduction realized by the SD tar is higher than that by the XF coal tar, and was even better than that by the DSL tar obtained in our previous study. Testing the NO reduction by model tar compounds revealed that phenol plays an important role in enabling its good NO reduction for the SD tar. The major understanding from the work is that the compounds containing at least an aromatic ring (e.g. phenol, benzene, etc.) are the major contributor for reducing NO in either biomass tar or coal tar. [ABSTRACT FROM AUTHOR]

The selective catalytic reduction (SCR) of NOx with C 3 H 6 in the presence of O 2 on silica sub-microtubes with platinum nanoparticles was studied in order to establish a possible reaction mechanism at different experimental conditions. This catalyst showed a high NO conversion with very high selectivity to N 2 at mild conditions in the presence of excess oxygen when using C 3 H 6 as reducing agent. The influence of both NO and C 3 H 6 concentrations on their conversions was analyzed at different space times. The obtained results suggest that the three reactants (C 3 H 6 , NO, and O 2 ) are adsorbed on Pt sites. The kinetic model proposed considers that both dissociative adsorption of NO and activation of the hydrocarbon can take place simultaneously. Nevertheless, the value of the parameters obtained by the resolution of the model equations indicates that the first one presents a major relevance. These results are in concordance with the high selectivity to N 2 observed, because the preponderance presence of dissociated NO avoids the formation of N 2 O by the reaction of molecular NO with N dissociated from NO. Furthermore, both NO reduction and C 3 H 6 oxidation conversions are represented reasonably well by the model presented. [ABSTRACT FROM AUTHOR]

Catalytic performance of CeO 2 -MO x (0.25) (M = Mn, Fe and Cu) mixed oxide nanocatalysts were investigated in NO + CO reduction. Sol-gel method was used to synthesize nanocrystalline mixed oxides. Catalysts were characterized by XRD, BET, SEM, TEM and H 2 -TPR analysis. The Ce-Cu mixed oxide catalyst showed superior activity than other catalysts (with 80% NO and 72% CO conversions), due to its better reduction properties. To model and optimize the NO and CO conversions, a neuro-genetic approach was employed. This approach established by combining an artificial neural network with a genetic algorithm. The results showed that the ANN model is accurate with R 2 = 0.991, 0.979 and 0.960 for training, validation and testing, respectively. Catalyst design factors (Cu/Ce molar ratio, citric acid/nitrate and calcination temperature) were optimized by GA. The optimum values were 0.49, 0.98 and 500 °C. For Cu/Ce molar ratio, citric acid/nitrate and calcination temperature, correspondingly. NO conversion predicted through ANN-GA system and obtained via experimental at 300 °C were 91% and 90%, respectively. [ABSTRACT FROM AUTHOR]

The SCR performances of CaO poisoning CeO 2 –WO 3 and V 2 O 5 –WO 3 /TiO 2 catalysts were prepared and compared for selective catalytic reduction of NO with NH 3 (NH 3 –SCR). It was found that the CeO 2 –WO 3 catalyst showed better calcium resistance than V 2 O 5 –WO 3 /TiO 2 catalyst even when the CaO mass percentage reached up to 5 wt%. In order to further understand the resistance mechanism, XRD, Raman, XPS, H 2 -TPR, NH 3 -TPD and in situ DRIFTS were used to analyze and explore the changes of CeO 2 –WO 3 catalysts before and after the CaO deactivation. The results manifested that the introduction of Ca species not only affected CeO 2 lattice but also led to CaWO 4 formation on the surface. Additionally, although CaO increased the surface chemisorbed oxygen and Ce 4+ species, the reducibility and Lewis acid sites, NH 3 chemisorbed amount and Brønsted acid sites were greatly inhibited after deactivation. Furthermore, the enhanced NO 2 adsorption capacity after the alkaline Ca species introduction could partially offset the negative effect in the loss of acid sites over the catalyst surface, which might be the primary reason for stronger CaO resistance of CW catalyst than traditional V 2 O 5 –WO 3 /TiO 2 catalyst. [ABSTRACT FROM AUTHOR]

Zero-valent iron (ZVI) reductive dechlorination is a promising approach for the abatement of chlorinated organic pollutants in the environment. In this study, ZVI and Ni/Fe bimetal nanoparticles were synthesized and applied for the treatment of chloronitrobenzenes (CNBs) in water. The pre- and post-reaction nanoparticles samples were characterized by SEM and XRD respectively. Here we show that ZVI nanoparticles can effectively perform the selective reduction of p -CNB to p -chloroaniline ( p -CAN) with a selectivity of ca. 100% in 10 min without dechlorination throughout the research. Catalytic reduction of p -CNB over Ni/Fe nanoparticles could be divided into two sequential processes: the first is the conversion of p -CNB to p -CAN, and the second is the reductive hydrodechlorination of p -CAN with aniline formation. Direct catalytic hydrodechlorination of p -CNB as a side route was also observed. Results indicate that ZVI initiates the electron transfer process for the reduction of p -CNB to p -CAN, whereas Ni catalyst is in favor of hydrogen transfer as the dominant pathway for the dechlorination reactions. The complete reduction mechanisms of p -CNB over ZVI and Ni/Fe nanoparticles were discussed, and the kinetics of dechlorination of CNBs were found to be pseudo-first order. The effects of different experimental parameters, such as solution pH, dosage of Ni/Fe nanoparticles, initial concentration of p -CNB and the Ni loading on the catalytic reduction of p -CNB were carefully investigated. Under the several reaction conditions tested, a complete dechlorination could be attained in 2 h. The dechlorination reactivity for mono-CNBs decreases in the order: p -CNB > o -CNB > m -CNB. The energy gap between HOMO and LUMO is firstly indicated as a descriptor to evaluate the dechlorination reactivity of mono-CNBs, which may provide a new insight in predicting the dechlorination reactivity for other organic chlorides. [ABSTRACT FROM AUTHOR]

Methoxychlor [or 4,4′-(2,2,2-trichloroethane-1,1-diyl)bis(methoxybenzene)], a common environmental pollutant, has been catalytically reduced with nickel(I) salen electrogenerated in situ at carbon cathodes in dimethylformamide (DMF) containing 0.050 M tetra- n -butylammonium tetrafluoroborate (TBABF 4 ). Cyclic voltammograms for reduction of nickel(II) salen in the presence of various concentrations of methoxychlor provide evidence for catalytic reduction. Cathodic peak currents for the nickel(II) salen–nickel(I) salen redox couple increase in proportion to the concentration of methoxychlor, whereas the anodic peak current associated with reoxidation of nickel(I) salen diminishes; in addition, a cathodic prepeak appears at higher concentrations of methoxychlor. Controlled-potential (bulk) electrolyses of nickel(II) salen at reticulated vitreous carbon cathodes in the presence of methoxychlor allowed the n value for reduction of methoxychlor to be determined. With the aid of gas chromatography–mass spectrometry, major electrolysis products have been identified as 4,4′-(2-chloroethene-1,1-diyl)bis(methoxybenzene) and 4,4′-(ethene-1,1-diyl)bis(methoxybenzene), and the product distribution was determined by means of gas chromatography. Adducts arising from the combination of fragments derived from methoxychlor and DMF have also been detected and confirmed, and a mechanistic scheme is proposed to account for the various products. [ABSTRACT FROM AUTHOR]

The steady-state kinetics of the selective catalytic reduction (SCR) of nitrogen oxides (NO and NO 2 ) with ammonia over a commercial iron zeolite catalyst were studied in the temperature range of 250 to 450 °C using an integral tubular reactor. Special attention was paid to the stoichiometric ratio of the conversion of ammonia and nitrogen oxides. For this purpose, both systematic SCR measurements at different feed gas compositions and independent studies of the catalytic oxidation of ammonia in the absence of NO and NO 2 were carried out. Under all reaction conditions, a considerable deviation from the expected 1:1 stoichiometry was observed. The steady-state kinetics of the reacting system could be described by global Langmuir–Hinshelwood-type rate equations for standard SCR, fast SCR, NO/NO 2 equilibrium and NH 3 oxidation. For the correct calculation of the ammonia oxidation it was necessary to include two terms. A first one describing the reaction of NH 3 with O 2 , which becomes important at temperatures above 400 °C, and a second rate equation which is not only proportional to NH 3 and O 2 but also to the NO concentration and which is of particular relevance at low reaction temperatures. Additional measurements with different catalyst particle sizes including industrial extrudates could be successfully described with the aid of a reactor model which took film and pore diffusion phenomena into account. [ABSTRACT FROM AUTHOR]

A new branched-dumbbell Pt/NiFe nanostructure was fabricated through a controllable microwave route followed by the element lithographic process. In this nanostructure, Pt nanoparticles (Nps) are embedding on the surface of NiFe branched-dumbbells. Owing to the three-dimensional (3D) hierachical framework with large surface area, Pt/NiFe branched-dumbbell nanostructure has an advantage for the reactant diffusion and transport. The synergistic action between the high catalytic selectivity of NiFe nanoalloy and the superior catalytic activity of Pt Nps can result in remarkably efficiency catalytic of Pt/NiFe branched-dumbbells toward the reduction of nitro-aromatic compounds under ambient atmosphere at room temperature. The morphologies, structures and properties were characterized by SEM, XRD, XPS, EDS, VSM, and UV–vis. Owing to the good soft-magnetic behavior, branched-dumbbell Pt/NiFe nanostructures can be easily separated and recycled by an external magnet field for application. [ABSTRACT FROM AUTHOR]

Highlights: [•] The catalyst structure and activity of viral-templated Pd nanocatalysts are tunable by manipulating the synthesis conditions. [•] Dichromate reduction shows size-dependent behavior, where larger Pd particles sparsely coated along TMV show higher catalytic activity. [•] Pd catalyzed dichromate reduction with formic acid follows Langmuir–Hinshelwood surface reaction mechanism. [•] The adsorption of formic acid on Pd surface is substantially higher than dichromate ions. [Copyright &y& Elsevier]

Abstract: The catalytic effect of coal gangue hollow ball with open pores on NO reduction by CO in fluidized bed was investigated, and the kinetics for the catalytic reduction of NO using CO was evaluated. In the absence of water vapor at 773–923K, the reaction rate constant was NO reduction ratio rapidly increased with reaction residence time at initial stage (<1s) and T>873K; high NO reduction ratio was achieved by increasing reaction temperature when the initial concentration ratio of CO to NO was less than 4. In the presence of water, the catalytic effect of coal gangue hollow ball on NO reduction was weakened, and the reaction rate constant was NO reduction ratio is less than 0.2 when reaction residence time was 2.5s at T≤923K when the initial concentration ratio of CO to NO was 4, and the initial concentration ratio of CO to NO had negligible effect on NO reduction ratio at T≤923K. [Copyright &y& Elsevier]

Abstract: To broaden and lower the narrow temperature window of the selective non-catalytic reduction (SNCR) of nitric oxide (NO), the use of activated ammonia as the reduction agent was examined. A 172nm VUV (vacuum ultraviolet) excimer lamp was employed as the excitation source for molecular ammonia. Activated ammonia generated by VUV radiation in a photochemical reactor was injected into a model flue gas (NO/O2/N2) at room temperature. The effects of reaction temperatures, oxygen concentrations, and NH3/NO molar ratios (MRs) on NO removal were investigated in a lab-scale plug flow reactor. Temperatures ranged from 500°C to 850°C. A temperature window enlargement of 150°C was achieved at the lower boundary of the temperature window. The results are the first clear observations of low temperature SNCR by activated ammonia. Above 600°C, NO removal was affected by injection of activated ammonia, while around 750°C, conventional SNCR by injection of molecular ammonia was effective. An approximate 80% NO removal was attained at 700°C with an MR =2.0 and 8.3% O2. Although the chemical compositions of activated ammonia remained unknown during the present study, the results suggested that effective chemical species for NO removal such as NH2 and H2 were produced from activated ammonia above 600°C. The number of photons emitted per mole of molecular ammonia, Np , was proposed to evaluate the effects of NH3 concentrations and residence times of NH3 gas in the photochemical reactor. The optimum Np range was found to be the point at which maximum NO removal was attained. [Copyright &y& Elsevier]

Abstract: This study was aimed at developing an approach for correcting the gas and particle partitioning of PCDD/F congeners for samples collected from the flue gas of an iron ore sinter plant. An iron ore sinter plant equipped with an electrostatic precipitator (EP) and a selective catalytic reduction (SCR) was selected. Flue gas samples were collected at EP inlet, EP outlet and SCR outlet. Both particle- and gas-phase PCDD/Fs were analyzed for each collected sample. PCDD/F contents in EP ashes (EPash) were also analyzed and used to correct the gas and particle partitioning of PCDD/F congeners of the collected flue gas samples. Results show that PCDD/Fs in the flue gas were dominated by the gas-phase. Before correction, the removal efficiencies for the gas- and particle-phase PCDD/Fs for EP were −58.1% and 64.3%, respectively, and SCR were 39.4% and 83.9%, respectively. The above results were conflict with the expected results for both EP and SCR indicating the need for correcting the gas and particle partitioning of PCDD/F congeners for all collected flue gas samples. After correction, the removal efficiencies become more reasonable for EP (=4.22% and 97.7%, respectively), and SCR (=54.7% and 62.0%, respectively). The above results confirm the effectiveness of the approach developed by this study. [Copyright &y& Elsevier]

Abstract: The use of urea based selective catalytic reduction (SCR) technology for the reduction of NOx from the exhaust of diesel-powered vehicles has the potential to emit at least six thermal decomposition by-products, ammonia, and unreacted urea from the tailpipe. These compounds may include: biuret, dicyandiamine, cyanuric acid, ammelide, ammeline and melamine. In the present study, a simple, sensitive and reliable hydrophilic interaction liquid chromatography (HILIC)-electrospray ionization (ESI)/mass spectrometry (MS) method without complex sample pre-treatment was developed for identification and determination of urea decomposition by-products in diesel exhaust. Gradient separation was performed on a SeQuant® ZIC-HILIC column with a highly polar zwitterionic stationary phase, and using a mobile phase consisting of acetonitrile (eluent A) and 15mM ammonium formate (pH 6; eluent B). Detection and quantification were performed using a quadrupole ESI/MS operated simultaneously in negative and positive mode. With 10μL injection volume, LODs for all target analytes were in the range of 0.2–3μg/L. The method showed a good inter-day precision of retention time (RSD<0.5%) and peak area (RSD<3%). Satisfactory extraction recoveries from spiked blanks ranged between 96 and 98%. Analyses of samples collected during transient chassis dynamometer tests of a bus engine equipped with a diesel particulate filter (DPF) and urea based SCR technology showed the presence of five target analytes with cyanuric acid and ammelide the most abundant compounds in the exhaust. [Copyright &y& Elsevier]

Abstract: Species including N2H4, NH3 and N2O are known to be present near the surface of burning hydrazinium nitroformate (HNF). In this paper, planar laser induced fluorescence from the near surface region of burning HNF pellets is reported indicating the presence of NO2. These four species are formed in the upper (foamy) layer of the solid phase. A burning rate modifier might be selected to induce reactions between the gaseous species in this layer. Selective catalytic reduction (SCR) is able to start highly exothermic reactions at relatively low temperatures. The SCR catalyst V2O5 increases the burning rate of HNF by a factor of 11 at 0.1MPa. The pressure exponent is reduced to 0.28, far below the target value of 0.5 required for practical application of HNF in propellant formulations. As far as SCR catalysts have been tested as burning rate modifiers of HNF, they are effective, yet incompatible. To overcome this incompatibility remedies might possibly be found in high-temperature catalysts, or in coating particles. [Copyright &y& Elsevier]

Abstract: NO x storage-reduction experiments were performed using a coupled LNT-SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu–zeolite SCR catalyst. Cycling experiments revealed that when a CO+H2 +C3H6 mixture or C3H6 by itself was used as the reductant, the NO x conversion over the SCR catalyst exceeded the conversion of NH3 over the same catalyst. This is explained by the presence of propene, which slipped through the LNT catalyst and reacted with the LNT NO x slip. Separate experiments, conducted under continuous flow and lean-rich cycling conditions, confirmed the ability of propene, as well as ethene, to function as a NO x reductant over the SCR catalyst. Cycling experiments also revealed that the SCR catalyst was able to store propene, such that NO x reduction by stored propene continued into the lean phase (after the switch from rich conditions). According to adsorption experiments, significant co-adsorption of NH3 and propene occured in the SCR catalyst, while under lean-rich cycling conditions the contributions of NH3 and C3H6 to NO x conversion were found to be essentially additive. These findings suggest that under actual driving conditions, NO x reduction by non-NH3 reductants (olefins and possibly other hydrocarbons) in the SCR catalyst can contribute to the mitigation of lean and rich phase NO x . [Copyright &y& Elsevier]

Abstract: A numerical simulation is designed in order to better understand the selective catalytic reduction of NO x by propane (C3H8-SCR) in the presence of hydrogen. The simulation was designed for a single channel of a monolith typical for automotive catalytic converters, coated with a silver alumina catalyst (Ag/Al2O3). The complicated physical and chemical processes occurring during the reactions are solved by computational fluid dynamics (CFD) coupled with a surface-reaction mechanism. This mechanism is developed based on detailed microkinetic analysis. The elementary-step-like surface reaction mechanism (consisting of 94 reactions, 24 gas-phase species and 24 adsorbed surface species) is applied to investigate the effect on the conversion of NO x to N2 of chemical kinetic steps, such as intermediate species. Results from the modelling emphatically agree with the experimental data. The modelling can predict the NO x conversion at various operating conditions. Furthermore, the modelling can also provide information that is difficult to measure, for example predicts the channel wall temperature and surface coverage of surface species. [Copyright &y& Elsevier]

Abstract: We present a systematic kinetic investigation of the full NO/NO2/N2O–NH3 SCR reacting system performed over a commercial Fe-promoted zeolite catalyst in the form of powder in a representative temperature range (150–550°C) at high space velocities. The well-known reactions of the NO/NO2–NH3 SCR system, namely NH3 adsorption, NH3 and NO oxidation, standard-, fast- and NO2-SCR reactions, ammonium nitrate formation, and N2O formation are considered. In addition, dedicated runs with N2O added to the feed stream showed that two more reactions, namely N2O reduction by NO (N2O+NO→N2 +NO2) and N2O reduction by NH3 (2NH3 +3N2O→4N2 +3H2O) become significant at T >330°C and need to be considered for kinetic modelling. The kinetic runs were fitted by multiresponse nonlinear regression to obtain estimates of the intrinsic rate parameters. Such parameters, as well as the relevant geometrical and morphological catalyst properties, were then successfully used to simulate on a purely predictive basis additional transient SCR runs performed over core honeycomb samples of the same Fe-zeolite catalyst, revealing modest effects of mass transfer limitations. In comparison with other published SCR kinetic models, the model herein developed accounts also for the N2O reactivity with NO and NH3, which is shown to be an important feature in order to accurately reproduce high-T operation of SCR converters based on Fe-zeolite catalysts. [Copyright &y& Elsevier]

Abstract: Cu-MOR, Cu-MFI, Co-MOR, Co-MFI and Mn-MFI were prepared by ion-exchange of Na-MOR or Na-MFI. On all samples, the catalytic activity for N2O decomposition, CH4 +N2O, CH4 +O2, and for the selective catalytic reduction (SCR) of N2O in the presence of O2 was studied in a flow apparatus with GC analysis of reactants and products. Extensively exchanged Cu-MOR and Cu-MFI were active for N2O decomposition. Cu-MOR and Cu-MFI exchanged at about 20% were much less active. All Co-MOR and Co-MFI catalysts, irrespective of the exchange-extent, were active for the same reaction. Mn-MFI was nearly inactive up to 773K. All catalysts were active for CH4 +N2O. Cu-MOR and Cu-MFI were active for CH4 +O2, whereas Co-MOR, Co-MFI and Mn-MFI were much less active for this reaction. Irrespective of the exchange extent, Cu-MOR, Cu-MFI, Co-MOR, and Co-MFI were active for the SCR of N2O with CH4. Conversely, Mn-MFI was not active for this reaction. Turnover frequency was slightly higher for the various reactions on Me-MFI (Me=Cu or Co) than for the corresponding reactions on Me-MOR. We conclude that on Cu- and Co-zeolites, the SCR of N2O with CH4 consists of two nearly independent reactions: CH4 +N2O prevails at high temperature (673–773K), and CH4 +O2 at lower temperature. The two reactions involve different catalytically active oxygen species: CH4 +O2 involves a molecular form, and CH4 +N2O a monoatomic form, arising from N2O. Because Co-MOR and Co-MFI are also active for the SCR of NO x , we suggest that these materials are promising catalysts for the simultaneous SCR of N2O and NO x with CH4. [Copyright &y& Elsevier]

Abstract: A model including coupled surface reactions, liquid-phase equilibrium and mass transfer steps was developed for the reaction of catalytic reduction of nitrates with H2 over bimetallic catalysts. The model was constructed from the molecular mechanism of NO3 − and NO2 − reduction including description of the roles of mono- and bimetallic active sites. The model was validated against experimental data and was used to obtain detailed information on the concentrations of surface species, thus providing mechanistic insights into the influence of operating conditions on reactivity and selectivity. Simulation of the model with different experimental conditions showed that the presence of external mass transfer resistances strongly affects the surface species NO* and NH* and results in deterioration of selectivity to N2. The obtained knowledge is being used to design a more optimised ‘reaction environment’ in the specific case of the nitrates reduction reaction, using new capabilities of nano-scale materials and process intensification. A modeling approach adopted in this study can be generalised as a methodology of investigating complex reaction systems. [Copyright &y& Elsevier]