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Constructing an efficient and reusable catalyst for catalyzing NaBH 4 hydrolysis for H 2 production is of vital significance. Herein, the Ru particles decorated Co 3 B-CoP heterostructures are obtained by chemical reduction and gas-phase phosphating treatment. The strong electronic interaction and abundant heterojunctions between the Co 3 B-CoP substrate and Ru particles have been elucidated. The optimal Ru 0.063 /Co 3 B-CoP catalyst exhibits a fast hydrogen generation rate (8875.8 mL min−1 g cat −1) and a high turnover frequency (636.0 min−1) at 25 °C, superior to most ever reported catalysts. The excellent NaBH 4 hydrolysis performance can be attributed to the lower activation energy (47.6 kJ mol−1) and the synergy between Co 3 B-CoP substrate and Ru particles. Density functional theory calculations show that electrons penetrate into Ru particles from Co 3 B-CoP substrate, in which the electron-rich Ru particles can selectively adsorb BH 4 − ions, while the electron-deficient Co 3 B-CoP facilitates the capture of H 2 O molecules, thereby synergistically promote the catalyzing NaBH 4 hydrolysis to produce H 2. [Display omitted] • Ru particles decorated Co 3 B-CoP are constructed by three controllable steps. • The heterostructure and electronic interaction of the catalyst have been confirmed. • The catalyst exhibits high HGR and TOF, superior to most ever reported catalysts. • The synergy between Ru and Co 3 B-CoP is the key reason for good performance. [ABSTRACT FROM AUTHOR]

A magnetically separable core-shell-like catalyst Ni-Pd/CB is designed and synthesized via a facile sequential reduction strategy. It is found that the Pd nanocrystals with a thickness of ∼1.67 nm and a length of ∼7.92 nm are intimately coupled with the Ni cores and the formed core-shell-like Ni-Pd nanoparticles are well dispersed on the CB surface with much smaller particle size and narrower size distribution as compared with that of unsupported ones. The ligand-free Ni-Pd/CB nanocatalyst is evaluated for Suzuki-Miyaura coupling reaction and exhibits excellent catalytic activity under mild aerobic conditions without using toxic solvents and inert protective atmosphere, achieving green catalysis. The high catalytic performance of Ni-Pd/CB catalyst can be attributed to its unique core-shell-like nanostructure and the concerted effects between the individual components. The introduction of Ni not only makes the catalyst magnetically separable in a suspension system, but also significantly lowers the cost. [ABSTRACT FROM AUTHOR]

B-doped, B–N co-doped and B–N–F tri-doped TiO 2 catalysts were prepared via a sol–gel method using H 3 BO 3 , NH 4 Cl and NH 4 F as B, N and N–F dopant precursors, respectively. N-doped, N–F co-doped and a pure TiO 2 (undoped) samples were also prepared by the same method as blank samples, for comparison. The catalysts were evaluated for the simultaneous photocatalytic reduction of Cr(VI) and oxidation of benzoic acid (BA). XRD analysis shows the formation of pure TiO 2 anatase phase in all cases, with crystallite size varying from 10.1 nm to 14.6 nm for all doped samples. UV–vis DRS spectra show narrowing of the band gap ( E g ) for all doped samples, compared to the undoped TiO 2 . Concomitant presence of N and F ions i.e. in N–F co-doped and B–N–F tri-doped TiO 2 catalysts, causes the most pronounced decrease of E g while B–N co-doped and B–N–F tri-doped TiO 2 have lower E g values than mono B-doped but higher than N-doped and N–F co-doped TiO 2 . B and N doping also causes an increase of specific surface area and a decrease in mean pore diameter. Electron Paramagnetic Resonance (EPR) spectroscopy was employed for a detailed investigation of the structure and photoexcited species formed in these catalysts. The EPR data show that N-doping forms N b photoexcited species which react as holes, Ti 4+ –O − oxygen vacancies (OVs) and Ti 3+ lattice and surface defects. B-doping enhances the formation of Ti 4+ –O − oxygen vacancies and the quantities of O 2 H and OH radicals. In B-doped and B–N co-doped samples, boron causes the most prominent induction of Ti 3+ lattice centers. Boron in interstitial sites, with oxygen atoms [BO 3 ] behaves as a three-electron donor leading to the formation of B 3+ and reduction of Ti 4+ to Ti 3+ . Under UV–vis irradiation, Cr(VI) reduction followed the trend: TB1 > TBN1 > TBNF1 > TNF1 > TN1 > undoped TiO 2 ; while benzoic acid (BA) oxidation trend was: TB1 > TBNF1 > TBN1 > TNF1 > TN1 > undoped TiO 2 . Cr(VI) reduction and BA oxidation rates are in agreement with EPR-detected Ti 4+ –O − oxygen vacancies and O 2 H, OH photoexcited radicals, respectively. [ABSTRACT FROM AUTHOR]

Trimetallic PdNiAg nanoparticles supported on activated carbon were simply and reproducibly prepared by wet-impregnation followed by simultaneous reduction method without using any stabilizer at room temperature. The characterization of the resulting material was done by the combination of complimentary techniques and the sum of their results shows that the formation of well-dispersed 5.6 ± 2.2 nm PdNiAg nanoparticles in alloy form on the surface of activated carbon. These carbon supported PdNiAg nanoparticles were employed as heterogeneous catalyst in the catalytic decomposition of formic acid, which has great potential as a safe and convenient hydrogen carrier for fuel cells, under mild conditions. It was found that PdNiAg/C can catalyze the dehydrogenation of formic acid with high selectivity (~100%) and activity (TOF = 85 h-1) at 50 °C. More importantly, the exceptional stability of PdNiAg nanoparticles against to agglomeration, leaching and CO poisoning make PdNiAg/C reusable catalyst in the formic acid dehydrogenation. PdNiAg/C catalyst retains almost its inherent activity (>94%) even at 5th reuse in the dehydrogenation of formic acid with high selectivity (~100%) at complete conversion. The work reported here also includes the compilation of kinetic data for PdNiAg/C catalyzed dehydrogenation of formic acid depending on catalyst [PdNiAg], substrate [HCOOH], promoter [HCOONa] concentrations and temperature to determine the rate expression and the activation parameters (Ea, ΔH#, and ΔS#) of the catalytic reaction. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nickel nanoparticles/reduced graphene oxide (Ni/rGO) composite has been synthesized. [•] Ni/rGO can be used as a magnetic recoverable catalyst. [•] Ni/rGO exhibits good catalytic activity for the reduction of 4-nitrophenol. [•] The use of rGO as the catalyst support leads to a synergistic effect. [•] NIR irradiation can enhance the activity of Ni/rGO via photothermal conversion. [ABSTRACT FROM AUTHOR]

Highlights: [•] DeNOx-reaction had a strongly negative impact on the oxidation of elemental mercury. [•] DeNOx-reaction induced reduction of already oxidised mercury. [•] The same reduction occurred when oxidising volatile organic hydrocarbons. [•] Hypothesis will be assumed that the reduction is caused by reduced vanadium species. [ABSTRACT FROM AUTHOR]

Highlights: [•] CeO2-MoO3/TiO2 catalyst is much more active than CeO2/TiO2 for the NH3-SCR. [•] The existed MoO3 can prevent the formation of inactive nitrate species. [•] More Brønsted acid sites formed on the catalyst surface due to the presence of Mo. [•] The activated NH x species react with NO or adsorbed NO2. [ABSTRACT FROM AUTHOR]

Highlights: [•] A multifunctional catalyst/storage material is prepared to maximize NO removal. [•] The role of the different active sites in the lean/rich cycles is established. [•] The cobalt catalytic function oxidizes the NO to NO2. [•] The basic properties of the Co/Mg/Al mixed oxide are enhanced by doping with Na. [•] The introduction of V enables the reduction of the nitrate decomposition products. [ABSTRACT FROM AUTHOR]

Highlights: [•] K2O/Al2O3 and Pt–K2O/Al2O3 with varying K loadings were prepared. [•] K2O(20)/Al2O3 formed more thermally stable nitrate species than K2O(10)/Al2O3 upon NO2 adsorption. [•] Temperature of max. NO x uptake shifted from 573K to 723K with increasing K loadings from 10wt% to 20wt%. [•] Moreover, the efficiency of K for storing NO x increased more than three times. [ABSTRACT FROM AUTHOR]

Abstract: Alumina-supported In2O3, Ga2O3 and B2O3 were investigated as catalysts for lean NO x reduction with DME as reducing agent and compared to pure Al2O3 and In2O3. The In2O3-promoted alumina catalysts showed the highest NO x conversion at low temperatures, although with a narrow temperature window. Pure In2O3, on the other hand, was inactive for NO x reduction with DME. The Ga2O3- and B2O3-promoted alumina catalysts gave the highest NO x conversion at higher temperatures, showed a temperature window similar to pure alumina, but were less sensitive to H2O inhibition. Possible reasons for these observations are discussed. [Copyright &y& Elsevier]

Abstract: Hydrotalcite derived NiMgAl mixed oxide (NiHT) catalysts with different NiMgAl molar ratio were synthesized and tested in the selective gas-phase hydrodechlorination of trichloroethylene to ethylene. The mixed oxide was further promoted by Pd in order to obtain Pd/NiHT catalysts. The catalysts performances for hydrodechlorination of trichloroethylene depend on the Ni/Mg/Al molar ratio, reduction temperature, and method of noble metal incorporation. The main products obtained were ethylene, methane, ethane, chloroethylene and traces of dichloroethylene. The higher the Ni amount in the NiHT support was, the higher were the catalytic activity and ethylene selectivity. Introduction of Pd increases the catalytic activity. Application of higher reduction temperatures improved the selectivity towards ethylene formation due to an increase in the concentration of surface metallic Ni. A better Pd-Ni surface interaction was obtained by impregnation of Pd on a previously reduced (823K) NiHT catalyst, resulting in higher ethylene selectivity (80%). The higher selectivity was associated to metallic Ni promoted by a Pd-Ni alloy, which was detected by HRTEM. [Copyright &y& Elsevier]

Abstract: Sulfur poisoning and regeneration mechanisms for a 2% Ag/γ-Al2O3 catalyst for the H2-assisted selective catalytic reduction of NO x by NH3 are investigated. The catalyst has medium sulfur tolerance at low temperatures, however a good capability of regeneration at 670°C under lean conditions when H2 is present. These heating conditions can easily be established during soot filter regeneration. Furthermore, two types of active sites could be identified with different regeneration capabilities, namely finely dispersed Ag and larger Ag nanoparticles. The most active sites are associated with the finely dispersed Ag. These sites are irreversibly poisoned and cannot be regenerated under driving conditions. On the other hand the larger Ag nanoparticles are reversibly poisoned by direct SO x adsorption. The interpretation of the data is supported by DFT calculations. [Copyright &y& Elsevier]

Abstract: Today, platinum based ammonia oxidation catalysts are applied in automotive exhaust systems to avoid ammonia slip from the SCR catalyst. In this paper we present a dual layer catalyst design with an additional SCR layer on top of the Pt/Al2O3 layer. Laboratory experiments show that the additional SCR layer significantly reduces NO formation, improves N2 selectivity but also reduces the overall NH3 conversion. A mechanistically based kinetic model for NH3 oxidation on platinum is presented. The model is parameterised using experiments with a single layer Pt/Al2O3 catalyst and well describes the NH3 conversion and the selectivities for the products N2, N2O and NO. Additionally NO oxidation to NO2 is included in the model. Based on the mechanistic model for the platinum layer and a previously published model for the SCR layer, a 2-D model of the dual layer catalyst is set up. This model takes into account the diffusion and reaction in the two washcoat layers of one monolith channel. The 2-D model reproduces the experimental data well, with the mechanisms for the two layers parameterised in separate experiments and no additional parameters adjusted for the dual layer model. Finally, the model is used to study the effect of some design parameters such as catalyst size, NO oxidation capacity of the Pt-layer and the thickness or diffusion coefficient of the SCR layer. [Copyright &y& Elsevier]

Abstract: The desulfation mechanisms of pre-sulfated Pt-BaO/γ-Al2O3 lean NOx trap catalysts were investigated under isothermal conditions (600°C) using H2 as the reductant. Sulfates were found to be reduced first with H2 to produce SO2, followed by a reaction between SO2 and H2 to produce H2S. Gas analysis during the rich pulse reveals that the sulfur removal efficiency is initially proportional to the H2 concentration. At constant H2 concentration the overall desulfation efficiency decreases in the order of H2/CO2/H2O>H2/CO2 >H2/H2O>H2, as confirmed by XPS analysis of residual sulfur in the desulfated samples. H2O limits the evolution of SO2 at an early stage of the rich pulse and enhances the production of H2S in later stages of reduction. CO2 is involved in both the formation of COS and the production of H2O (via the reverse water–gas shift reaction), therefore, resulting in an increased overall efficiency. [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: Iron and copper-based zeolites are effective catalysts for the lean selective catalytic reduction (SCR) of NO x with NH3. Cu-zeolites are more active at lower temperatures (≤350°C) while Fe-zeolites are more active at higher temperatures (≥400°C). The effectiveness of a catalytic system comprising Fe- and Cu-based zeolites was examined for the standard (NO+O2 +NH3) and fast (NO+NO2 +NH3) SCR reactions. Experiments carried out with in-house and commercial Fe- and Cu-zeolite monoliths of varying lengths quantified their relative SCR activities. The commercial Cu-zeolite achieved complete NO x conversion for the standard SCR at 250°C while the commercial Fe-zeolite achieved high NO x conversion at higher temperatures (≥400°C) where it out-performed the Cu-zeolite. Subsequently, three configurations of combined Fe and Cu-zeolite catalysts were compared: [•] “Sequential brick” catalyst comprising Fe-zeolite and Cu-zeolite monolith. [•] “Mixed washcoat” catalyst comprising a washcoat layer having equal mass fractions of Fe- and Cu-zeolites. [•] “Dual layer” catalyst comprising monolith coated with individual layers of Fe- and Cu-zeolites of different thicknesses and mass fractions. The sequential brick design with Fe-zeolite brick followed by a Cu-zeolite brick gave a higher conversion than the Cu/Fe sequence of equal loadings with the Fe(33%)/Cu(67%) achieving the highest NO x conversion over a wide range of temperatures. The mixed washcoat catalyst achieved NO x conversion that was nearly an average of the individual Fe-only and Cu-only catalysts. The dual layer catalyst with a thin Fe-zeolite (33% of the total washcoat loading) layer on top of a thicker Cu-zeolite layer (67%) resulted in very high NO x removal efficiencies over a wide temperature range for both the standard and fast SCR reactions. The performance of this dual-layer system was comparable to the series arrangement of Fe and Cu-bricks. The Cu-zeolite on Fe-zeolite dual layer catalyst was not nearly as effective for the same loadings. The Fe/Cu dual layer catalyst also exhibited superior performance for the fast SCR reaction. The results are interpreted in terms of the activities of each catalyst for SCR and ammonia oxidation. An assessment of the extent of washcoat diffusion limitations shows that the dual layer configuration is superior to the sequential brick configuration. The existence of an optimal loading distribution of the Fe- and Cu-zeolite catalysts as well as other intangible benefits of the dual layer SCR catalyst are discussed. [Copyright &y& Elsevier]

Abstract: This study investigates how sulfur affects the NO x reduction activity over a commercial vanadium based urea-SCR catalyst for marine applications, especially at low temperatures, and in combination with H2O. The addition of SO2 in the absence of H2O promotes the NO x reduction at 350°C, while the addition of H2O, in the absence of SO2, gives rise to a decrease in the NO x reduction and also an inhibition of the N2O formation. The same trends are observed at transient temperatures, but no promotional effect by SO2 is seen at temperatures below 230°C. Further, long term effects of SO2 and H2O were investigated and the NO x reduction remains stable, also after long term exposure of SO2. The ammonia desorption is investigated using temperature programmed desorption (TPD) experiments, both in the presence and in the absence of SO2. In general in the presence of both H2O and SO2 the catalyst does not show any sign of deactivation at temperatures above 300°C and fairly low space velocities (below 12,200h−1). However, at lower temperatures (250°C) and/or higher space velocities the catalytic performance for NO x reduction decreases with time. [Copyright &y& Elsevier]

Abstract: The selective catalytic reduction of NO by ethanol under strongly oxidizing conditions (ethanol-SCR) in the wide-temperature range of 150–400°C has been studied over Ag supported on a series of metal oxides (e.g., MgO, Y2O3, CuO, CeO2, SiO2, MgO-CeO2-Al2O3). The Ag/MgO, Ag/CeO2 and Ag/Al2O3 solids showed the best catalytic behavior with respect to N2 and CO2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Ag solids. An optimum 25wt% MgO-25wt% CeO2-Al2O3 support composition was found in terms of specific reaction rate of N2 production (mol N2/gcat s) and CO2 selectivity. High NO conversions (60–90%), N2 selectivities (95–99%) and CO2 selectivities (>97%) were also obtained in the 150–400°C range at a GHSV of 40,000h−1 with the low 0.1wt% Ag loading and using a feed stream of 0.05vol% NO, 0.1vol% ethanol, 5vol% O2, 5vol% H2O and He as balance gas. Moreover, the latter catalytic system exhibited a high stability in the presence of 50ppm SO2 in the feed stream. N2 selectivity values higher than 98% and CO2 selectivities higher than 97% were obtained over the 0.1wt% Ag/MgO-CeO2-Al2O3 catalyst in the 150–400°C range in the presence of water and SO2 in the feed stream. The above-mentioned results led to the submission of a patent application for the commercial exploitation of Ag/MgO-CeO2-Al2O3 catalyst towards a new NO x control technology in the low-temperature range of 150–250°C using ethanol as reducing agent. DRIFTS studies after adsorption of NO, and transient titration of the adsorbed surface intermediate NO x species with H2 experiments, have revealed some preliminary important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., number and location of possible active NO x intermediate species). [Copyright &y& Elsevier]

Abstract: Copper loaded hydroxyapatite prepared by ion exchange were characterized by XRD, FTIR, BET, UV–vis, H2-TPR and evaluated in the selective catalytic reduction of NO by NH3 under oxidizing atmosphere. The Cu-Hap catalysts, without the libethenite phase presence, have been found to be active, and selective in the NH3-SCR process. The highly dispersed CuO clusters on Ca-Hap surfaces were responsible for the NO conversion in the low temperature range in the NO-SCR with NH3. The presence of 2.5% of H2O in the feed mixture strongly affects the NO conversion in the whole temperature range. [Copyright &y& Elsevier]

Abstract: Platinum plays an important, multi-functional role during NOx storage and reduction (NSR). Understanding and predicting the effect of Pt loading is essential to optimize the lean NOx trap. In this study, a microkinetic model is developed for NOx storage on a series of Pt/BaO/Al2O3 catalysts with a range of Pt loadings (0–3.7wt.%). A classification of the Ba sites into two storage site populations, proximal and non-proximal (bulk), is presented. A simple model for estimating the capacities of the two Ba site populations using the Pt loading is used to explain trends in the storage of NO/O2 and NO2/O2. The model integrates existing literature models for NO2 storage on BaO/Al2O3, Pt-catalyzed NO oxidation to NO2, and spillover chemistry involving NO2. Wherever possible, simplifications in the model are made based on sensitivity analyses. Literature estimates of kinetic parameters are adjusted if estimates of spillover rate constants are not sufficient to predict the storage data. The dual-site model comprises proximal storage sites that participate in the spillover chemistry and non-proximal sites that involve NO2 that is generated by the Pt-catalyzed NO oxidation. The model shows reasonable agreement with the measured storage of NO and NO2 in O2 at 340°C for a range of storage times and Pt loading. The model helps to elucidate the storage dynamics and the roles of Pt and should be useful for incorporation into a complete NOx storage and reduction model. Some further refinements to the model are discussed. [Copyright &y& Elsevier]

Abstract: Carbon-supported Ag/Mn y O x composites were prepared by a one step synthesis method, i.e., silver permanganate pyrolysis at different temperatures. The physical and electrochemical properties of the obtained composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV). The electrochemical activity, selectivity and stability for the Ag/Mn y O x /C composites toward oxygen reduction reaction (ORR) in alkaline media were investigated by rotating (ring)-disk electrode (R(R)DE) technique. The XRD results show that the manganese oxides were converted from MnO2 to Mn3O4 and then to MnO gradually with increasing temperature. Among all the Ag/Mn y O x /C composites, Ag/Mn3O4/C obtained at 400°C exhibits the highest activity toward the ORR. Compared with the Ag/C, Mn3O4/C and the physical mixture of Ag/C and Mn3O4/C with the same metal loadings, the ORR activity of the Ag/Mn3O4/C is improved significantly, suggesting a synergic effect between Ag and Mn3O4. At an overpotential of 0.35V, the calculated apparent activation energy for the ORR on the Ag/Mn3O4/C catalyst is 56kJmol−1, which is apparently higher than that on a Pt/C catalyst (36kJmol−1). The results from both Koutecky–Levich plots of the ORR and the RRDE measurements suggest that the ORR proceeds via a 4-electron pathway on the Ag/Mn3O4/C composite. Moreover, the presence of methanol has little influence on the ORR activity toward the Ag/Mn3O4/C catalyst. The accelerated aging tests indicate that the Ag/Mn3O4/C is more stable than the Pt/C in 0.1M NaOH solution. [Copyright &y& Elsevier]

Abstract: The behaviour of a perovskite SrTiCuO3 as NSR catalyst has been studied by simultaneous DRIFTS and activity measurement. The amount of NOx stored on the perovskite SrTiCuO3 (41μmol/m2 at 300°C) is much higher, when compared on a surface area basis, than on noble metal-containing reference catalysts (0.3–23μmol/m2). The perovskite SrTiCuO3 is able to perform both the NO oxidation to NO2 and the NOx storage, and copper enhances both the NO oxidation and NOx chemisorption capacities of copper-free SrTiO3 perovskite. During NOx chemisorption on SrTiCuO3, the following process have been identified (i) NO chemisorption and nitrite formation or NO oxidation to gas phase NO2 and further chemisorption of NO2 with nitrites or nitrates formation, (ii) nitrite oxidation to nitro and/or nitrates, and (iii) nitro and/or nitrate decomposition with release of NO2. NOx chemisorption at 300°C is more effective than chemisorption at 350°C, while regeneration at 350°C is more effective than regeneration at 300°C because: (i) decreased NOx slip (only for CO regeneration) and (ii) maintains the same chemisorption capacity of the perovskite after regeneration. H2 is a better reductant than CO, and the differences between both reducing gases are much higher at 300°C than at 350°C. [Copyright &y& Elsevier]

Abstract: In order to elucidate the effect of washcoat composition on lean NO x trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of Pt, Rh and BaO were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that in all cases aging resulted in deterioration of the NO x conversion as a consequence of impaired NO x storage and NO x reduction functions, while increased selectivity to NH3 was observed in the temperature range 250–450°C. Elemental analysis, H2 chemisorption and TEM data revealed two main changes which account for the degradation in LNT performance. First, residual sulfur in the catalysts, associated with the Ba phase, decreased catalyst NO x storage capacity. Second, sintering of the precious metals in the washcoat occurred, resulting in decreased contact between the Pt and Ba, and hence in less efficient NO x spillover from Pt to Ba during NO x adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NO x spillover during catalyst regeneration. For the aged catalysts, halving the Pt loading from 100 to 50g/ft3 was found to result in a significant decrease in overall NO x conversion, while for catalysts with the same 100g/ft3 Pt loading, increasing the relative amount of Pt on the NO x storage components (BaO and La-stabilized CeO2), as opposed to an Al2O3 support material (where it was co-located with Rh), was found to be beneficial. The effect of Rh loading on aged catalyst performance was found to be marginal within the range studied (10–20g/ft3), as was the effect of BaO loading in the range 30–45g/L. [Copyright &y& Elsevier]

Abstract: In the present work we studied the N2O decomposition activity of nano-Ru/γ-Al2O3 catalysts prepared by in situ reduction with ethylene glycol (EG), in comparison to catalysts prepared via typical incipient wetness procedure. The metal content, particle size, dispersion and reduction characteristics of the supported Ru catalysts were studied by means of ICP-AES, XRD, HRTEM, TPR-H2 and TPD-H2. The EG reduction method favored the formation of almost spherical metallic Ru nanoparticles with the size of 1–3nm (HRTEM) and dispersion of 70–35% (TPD-H2), at Ru loading levels of 0.4–1wt.%. The impregnated-calcined catalysts exhibited larger Ru nanoparticles (10–80nm, TEM) with very low degree of dispersion (∼10%). The activity of the EG-prepared catalysts for the decomposition of N2O in oxygen rich feeds and in the absence or presence of NO, H2O, SO2, CO and CO2, was significantly higher compared to that of the impregnated-calcined samples and comparable with that of the most active catalytic systems reported in the literature for the treatment of combustion processes off-gases. The superior activity of the former catalysts, especially of the sample with low Ru content (0.4wt.% Ru, 1–2nm particle size), was attributed both to the high dispersion of Ru (70% dispersion), i.e., the high surface area of Ru metal available for reaction, and to the higher intrinsic activity and lower apparent activation energy of the very small supported Ru nanoparticles prepared by the EG reduction method. The EG-prepared nano-Ru/γ-Al2O3 catalysts could retain their high N2O decomposition activity (higher than 90%) for long time-on-stream by applying intermediate, short term regenerations in reducing atmosphere at moderate temperatures (i.e., 500°C); treatment of the partially deactivated catalysts under reducing (H2/He) atmosphere leads to elimination of Ru(SO4)2 that is usually formed during reaction via reduction of Ru4+ to active Ru metallic phase. [Copyright &y& Elsevier]

Abstract: A dual catalyst system for the Selective Catalytic Reduction of NO x with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NO x emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NO x reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NO x reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase. [ABSTRACT FROM AUTHOR]

Abstract: The selective catalytic reduction of nitrates (NO3 −) in water mediums towards N2 formation by the use of H2 and in the presence of O2 (air) in the gas feed has been investigated under a continuous flow process over Pd–Cu supported on various mixed metal oxides, x wt.% M x O y /γ-Al2O3 (M x O y =CeO2, MgO, Mn2O3, Cr2O3, Y2O3, MoO2, Fe2O3 and TiO2). It is demonstrated for the first time that a remarkable improvement of both catalysts activity and N2 reaction selectivity can be achieved when increasing the liquid flow rate in the continuous flow process. In particular, it was found that NO3 − reduction rates up to more than two times higher and NH4 + selectivity values up to twenty times lower can be obtained when increasing the liquid flow rate from 2 to 6mL/min. Moreover, it was proven for the first time, in a continuous flow process, that the presence of oxygen (or air) has a remarkable positive effect on the reaction''s selectivity towards nitrogen. The reaction''s selectivity towards NH4 + can be decreased by up to three times when 20vol.% air is added in the gas feed of the NO3 −/H2 continuous flow reaction. The Pd–Cu clusters supported on TiO2-, CeO2- and MgO-coated γ-Al2O3 spheres showed the best catalytic behaviour compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. In addition, it was found that the initial concentration of nitrates in the liquid feed can significantly affect catalysts activity and reaction''s selectivity. A positive apparent reaction order towards nitrates of 0.9 was calculated on Pd–Cu/TiO2/Al2O3. [Copyright &y& Elsevier]

Abstract: Hollandite-type manganese oxides with K+ or H+ cations in the tunnels (K-Hol or H-Hol) were successfully synthesized and investigated in low-temperature selective catalytic reduction of NO by NH3. The results of the catalytic tests revealed that both K-Hol and H-Hol with almost same catalytic activities had much higher reaction rates than β-MnO2 under the same conditions, and even at a high gas hourly space velocity of 160,000h−1, K-Hol obtained more than 90% conversions of NO in a wide temperature window of 100–300°C. The high resolution transmission electron microscopy observations showed that both K-Hol and β-MnO2 were tetragonal prism-shaped nanorods with same exposed {110} planes, and the atoms in the {110} planes of K-Hol arranged to form semitunnel structures, while the {110} planes of β-MnO2 were relatively smooth surfaces. The temperature-programmed reduction by H2 and thermal gravimetric analyses indicated that active surface lattice oxygen atoms of K-Hol were around 1.6% with respect to total lattice oxygen atoms. The transition reactions of NH3 demonstrated that K-Hol with special semitunnel structured surface and active surface lattice oxygen showed much stronger ability to efficiently adsorb and activate NH3 molecules than β-MnO2. Hence, both efficient semitunnel structured external surfaces and high active surface lattice oxygen atoms predominantly accounted for the high catalytic activities. [ABSTRACT FROM AUTHOR]

Abstract: Efficient ZnO based visible-light photocatalysts, Cu(II) modified Cd x Zn1−x O were developed by adopting a hybrid approach, consisting of band-engineering by formation of a solid solution and surface modification of co-catalysts. The Cd x Zn1−x O solid solution exhibited the visible-light activity for decomposing gaseous acetaldehyde, while bare ZnO showed negligible activity under visible-light. Further, the visible-light activity of Cd x Zn1−x O photocatalysts was greatly improved by the surface modification of Cu2+ ions. Photogenerated electrons in Cd x Zn1−x O are injected into the modified Cu2+ ions under visible-light irradiation, and electrons in Cu2+/Cu+ redox couples cause the efficient reduction of absorbed oxygen molecules. The strategy in the present study is a promising approach for applying ZnO-based photocatalysts for indoor applications. [ABSTRACT FROM AUTHOR]

Abstract: Zeolites In,H-ZSM-5 (Si/Al=29.7, 1.7wt% In) and In,H-mordenite (In,H-M, Si/Al=6.7, 3.5 wt% In) were prepared by reductive solid state ion exchange (RSSIE) method and studied in the selective catalytic reduction of NO (NO-SCR) by methane. The results suggested that the methane oxidation reactions proceed by redox type mechanisms over In+/InO+ sites. The NO reduction selectivity was shown to be related to the relative rates of In+ oxidation by NO and O2. Regarding the relative rates, the In+ density of the zeolite was the most important. Above about 673K the In,H-ZSM-5 (T-atom/In=102) had higher NO reduction selectivity than the In,H-mordenite (T-atom/In=46). The operando DRIFTS examinations suggested that NO+ and NO3 − surface species were formed simultaneously on InO+Z− sites, and were consumed together in the NO-SCR reaction with methane. The reduction of the NO3 − by methane gave an activated N-containing intermediate, which further reacted with the NO+ species to give N2. The NO-SCR properties could be significantly improved by adding small amount of Pd to the In,H-zeolite catalyst. The promoting effect of Pd was interpreted as a concerted action of InO+ and the Pd n+ sites. The interplay between these sites is twofold: the Pd speeds up the equilibration of the NO/O2 mixture, thereby, increases the formation rate and the steady state concentration of the activated nitrate species, whereas the In+/InO+ sites prevent the transformation of Pd-nitrosyls to less reactive isocyanate and nitrile species. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study of Pt/Ba/Al2O3, Co/Ba/Al2O3, Pt/Co/Al2O3 and Pt/Co/Ba/Al2O3 was performed in regards to their NO x storage capacities and NO oxidation abilities as a function of temperature. The nitrate stability and dynamic behaviors of NO x storage reduction during lean/rich fuel cycles using hydrogen as a reductant were also investigated over these catalysts. It was found that Pt/Co/Ba/Al2O3 possessed the largest NO x storage capacity within the temperature range of 200–350°C. The existence of Co not only improved the oxidation of NO to NO2 under lean conditions, but also enhanced the release and reduction of NO x during the rich phase. The Pt and Co co-supported catalysts showed better NO x storage reduction activity and higher N2 selectivity than Pt supported Ba/Al2O3 catalysts within the tested temperature range. As for Pt/Co/Ba/Al2O3, high conversion was obtained at either a low reductant concentration with long duration time or a high reductant concentration with short duration time during the rich phase. In situ FTIR studies showed that NO x adsorption over Co-containing catalysts takes “nitrite route” as an important pathway. The intimate contact of Co and Ba/Al could accelerate nitrite/nitrate formation and the synergistic effect of Pt and Co could accelerate NO x reduction. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic reduction of two textile azo dyes (Orange II and Reactive Black 5) was investigated in upflow stirred packed-bed reactors (USPBRs) with biological activated carbon (BAC) system. The bioreactors were prepared with tailored activated carbons (ACs) having different textural properties and various surface chemistries. A kinetic model proposed previously was able to describe the catalytic azo reduction in all cases. Decolourisation with very high reduction rates took place in the case of each AC. Best dye removals were ensured by the AC having the highest surface area: conversion values above 88% were achieved in the case of both azo dyes at a space time of 0.23min or higher, corresponding to a very short hydraulic residence time of about 0.30min at the most. The decolourisation rates were found to be significantly influenced by the textural properties of AC and moderately affected by its surface chemistry. The results confirmed the catalytic effects of carbonyl/quinone sites and, in addition, delocalized π-electrons seemed to play a role in the catalytic reduction in the absence of surface oxygen groups. [Copyright &y& Elsevier]

Abstract: V2O5/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH3 at around 200°C and resistant to SO2 deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH3 over V2O5/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH3 take place mainly at V V2O5. A higher V2O5 loading results in more NH3 adsorption on the catalyst. V2O5 contains both Brϕnsted and Lewis acid sites; NH4 + on Brϕnsted acid sites is less stable and easier to be oxidized than NH3 on Lewis acid sites. Gaseous O2 promotes interaction of NH3 with AC and oxidation of NH3 over V2O5/AC. NH3 is oxidized into NH2 and acylamide structures and then to isocyanate species, which is an intermediate for N2 formation. [Copyright &y& Elsevier]

Abstract: A nanocomposite of Al2O3 and ZrO2–TiO2 solid solution (AZT) was synthesized for NO x storage-reduction (NSR) catalysts Pt/Rh/Ba/K/AZT, and the effect of calcination temperature on thermal stability was investigated. The catalyst containing AZT calcined at 1073K (AZT catalyst) had a high NO x storage capacity after thermal aging. This enhanced storage capacity was attributed to the fact that ZrO2–TiO2 solid solution (ZT) was crystallized and stabilized. The solid-state reaction of potassium, which was added as a NO x storage material, was inhibited in the AZT catalyst, relative to those containing AZT calcined at a low temperature. The AZT catalyst also showed excellent NO x storage performance after sulfur aging at 973K or higher, compared with the catalyst containing physically mixed Al2O3 and ZT (physically mixed catalyst). Furthermore, AZT catalysts inhibited the solid phase reaction of potassium with support materials and kept a high ratio of active potassium, which can store NO x . Further, because the barium in the AZT catalyst prevented sulfur poisoning, the ratio of active barium in the AZT catalyst was also larger than that in the physically mixed catalyst, probably because of the low basicity and high Pt dispersion of AZT. [Copyright &y& Elsevier]

Abstract: The effect of axial length on the NO x reduction performance of two different commercial Lean NO x Trap (LNT) monolithic catalysts was experimentally investigated in a bench flow reactor. The washcoat composition of one of the catalysts consisted of Pt and K on γ-Al2O3; whereas the other catalyst contained a complex mixture of Pt, Pd, Rh, Ba, Ce, Zr, Mg, Al and others. The NO x removal characteristics of cylindrical monolith segments of constant diameter (2.22cm) and axial lengths of 2.54, 5.08 and 7.62cm were evaluated using a simulated lean engine exhaust containing water and carbon dioxide at a constant space velocity of 30,000h−1. No significant effects of length were observed when the catalysts were fully reduced with hydrogen between NO x capture phases. However when the catalysts were only partially regenerated NO x reduction efficiency increased with monolith length. Intra-catalyst H2 measurements at different axial locations indicated that at least some of the efficiency loss during partial regeneration occurred when back-mixed H2 was directly oxidized and became unavailable for nitrate reduction. [Copyright &y& Elsevier]

Abstract: In the selective catalytic reduction (SCR) of NO by dimethyl ether (DME), the formation of unexpectedly high amounts of NO2 over 300°C has previously been reported. In this study, we explain this phenomenon by radical reactions initiated by DME and O2, during which DME is partly oxidized and NO2 is formed in the presence of NO. For the design criteria of a DME-SCR catalyst, these gas phase reactions have mainly three consequences: (i) another type of reducing agent than that fed into the reactor reaches the catalyst, (ii) no activation of the reducing agent such as partial oxidation is required, and (iii) several of the proposed intermediate species for HC-SCR, e.g. NO2, HONO, CH3–NO2, and CH3–NO form already in the gas phase. An efficient DME-SCR catalyst should thus have high selectivity for reduction of NO x predominately by partially oxidized C1-compounds, and it should not have particularly strong oxidizing properties to avoid non-selective oxidation of these C1-compounds. These two requirements appear to be reasonable well met by the acidic zeolite H-ZSM-5. [Copyright &y& Elsevier]

Abstract: Phosphorous-doped NiMo/Al2O3 hydrodesulfurization (HDS) catalysts (nominal Mo, Ni and P loadings of 12, 3, and 1.6wt%, respectively) were prepared using ethyleneglycol (EG) as additive. The organic agent was diluted in aqueous impregnating solutions obtained by MoO3 digestion in presence of H3PO4, followed by 2NiCO3·3Ni(OH)2·4H2O addition. EG/Ni molar ratio was varied (1, 2.5 and 7) to determine the influence of this parameter on the surface and structural properties of synthesized materials. As determined by temperature-programmed reduction, ethyleneglycol addition during impregnation resulted in decreased interaction between deposited phases (Mo and Ni) and the alumina carrier. Dispersion and sulfidability (as observed by X-ray photoelectron microscopy) of molybdenum and nickel showed opposite trends when incremental amounts of the organic were added during catalysts preparation. Meanwhile Mo sulfidation was progressively decreased by augmenting EG concentration in the impregnating solution, more dispersed sulfidic nickel was evidenced in materials synthesized at higher EG/Ni ratios. Also, enhanced formation of the so-called “NiMoS phase” was registered by increasing the amount of added ethyleneglycol during simultaneous Ni–Mo–P–EG deposition over the alumina carrier. That fact was reflected in enhanced activity in liquid-phase dibenzothiophene HDS (batch reactor, T =320°C, P =70kg/cm2) and straight-run gas oil desulfurization (steady-state flow reactor), the latter test carried out at conditions similar to those used in industrial hydrotreaters for the production of ultra-low sulfur diesel (T =350°C, P =70kg/cm2, LHSV=1.5h−1 and H2/oil=2500ft3/bbl). [Copyright &y& Elsevier]

Abstract: This work addresses the low-temperature NO x abatement under oxygen-rich conditions using H2 as reductant. For this purpose Pt/ZrO2 and Pt/WO3/ZrO2 catalysts are developed and characterised by temperature-programmed desorption of H2 (H2-TPD), N2 physisorption (BET) and powder X-ray diffraction (PXRD). The most active catalyst is a Pt/WO3/ZrO2 pattern with a Pt load of 0.3wt.% and a W content of 11wt.%. This material reveals high deNO x activity below 200°C and high overall N2 selectivity of about 90%. Additionally, the catalyst exhibits outstanding hydrothermal stability as well as resistance against SO x . Furthermore, the transfer from the powder level to real honeycomb systems leads to promising performance as well. Diffuse reflectance Fourier transform infrared spectroscopic studies, kinetic modelling of temperature-programmed desorption of O2 (O2-TPD) and NO x -TPD examinations indicate that the pronounced H2-deNO x performance of the Pt/WO3/ZrO2 catalyst is related to the electronic interaction of WO3 with the precious metal. The tungsten promoter increases the electron density on the Pt thus activating the sample for H2-deNO x and N2 formation, respectively. Contrary, NO x surface species formed on the WO3/ZrO2 support are not supposed to be involved in the H2-deNO x reaction. [Copyright &y& Elsevier]

Abstract: A nanocomposite of Al2O3 and a ZrO2–TiO2 solid solution (AZT) doped with Ti (Ti–AZT) was synthesized as a support for a NO x storage-reduction (NSR) catalyst in order to achieve sulfur durability. Ti–AZT maintained the original structure of AZT after the Ti doping step and exhibited lower basicity. Energy dispersive X-ray spectroscopy revealed that the Ti concentration on the Al2O3 particles was more than 10at.% on average for a sample containing 3.3at.% of doped titanium. Doped titanium was homogeneously distributed on the surface without the formation of discrete TiO2 particles. SO2-temperature programmed desorption at less than 823K indicated that the catalyst containing Ti–AZT had larger sulfur desorption than that containing AZT. After sulfur aging tests, the Ti–AZT catalyst provided a large amount of NO x storage. The improved sulfur durability in the NSR catalyst resulted from the presence of TiO2 as a Al2O3–TiO2 solid solution in Ti–AZT. [Copyright &y& Elsevier]

Abstract: A selective NO x reduction in lean conditions on Rh-based catalysts using CO and hydrogen as reductants was investigated. Over specified Rh-based catalysts, NO x has been found to be selectively reduced with CO as a main reductant at a high efficiency when hydrogen is concomitant as an assistant reductant. Furthermore, the presence of SO x in reaction gases drastically enhances this selective NO x reduction and the activity increases with time, followed by saturation of the NO x reduction. A reaction mechanism of this NO x reduction is proposed based on results of in situ FTIR. In addition, the highly active Rh supported on a beta-zeolite is characterized using TEM, XRD and XPS. [Copyright &y& Elsevier]

Abstract: Several Ir/WO3 catalysts were prepared, which were different in the loading of Ir (up to 10wt.%) and in the pretreatment conditions, and used for the reduction of NO (500ppm) with CO (3000ppm) in the presence of excess O2 (5%), SO2 (2ppm), and H2O (1%). The rate of NO conversion per unit mole of Ir was found to be maximal at a small Ir loading of 0.5–1.0wt.%. The good catalytic performance was achieved when the Ir precursors (IrO x ) supported on WO3 were reduced under mild conditions by He at 400°C or H2/He at a lower temperature of 130°C. The catalysts were characterized by XRD, FTIR after CO adsorption, and H2-TPR. The characterization results show that the active sites are exposed zero-valent Ir species, in accordance with previous works using Ir on WO3 and other supports, and that the fraction of these active species is larger for a higher degree of Ir dispersion (smaller Ir particles). The preparation conditions for highly active Ir/WO3 catalysts were confirmed and possible reaction mechanisms were discussed. [Copyright &y& Elsevier]

[Display omitted] • A chemical looping methane-nitric oxide dry reforming process is proposed to integrate CO 2 and NO conversion. • Carbon deposited during methane reforming can serve as reactant during the subsequent NO reduction. • Complete conversion of carbon and NO can be achieved via rational adjustment of operating conditions. • The inherent temporal-spatial separation of reactions enables the process to flexibly adapt to the CO 2 and NO sources. Carbon deposits typically enforce shutdowns of chemical reactors to periodically regenerate their active materials, a continuous challenge for industry and scientists alike. This downside can however be turned to benefit by utilizing carbon's reductive power. Here, we integrate dry reforming of methane (DRM) and selective reduction of nitric oxide (SRN) in a novel chemical looping process, coupled by the periodic deposition and removal of surface carbon, which participates in both reactions. Carbon formed on the catalyst during dry reforming is subsequently used as reductant for nitric oxide (NO) conversion into N 2 , hence not only achieves stable CO 2 utilization and NO reduction with cyclic catalyst regeneration, but also reduces the consumption of valuable energy resources demanded by NO removal. In contrast to co-feeding all reactants in a single step, the inherent temporal-spatial separation of reactions in chemical looping allows for complete conversion of carbon and NO, ensuring a higher exergetic efficiency (70 % more efficient). Also, adaptation of the relative duration of the DRM and SRN steps to the conditions of the CO 2 and NO industrial point sources allows to account for the differences in supply of carbon and NO, offering an attractive strategy for selective catalytic reduction of NO with greenhouse gases rather than NH 3. [ABSTRACT FROM AUTHOR]

Abstract: Differences in the NO x storage-reduction (NSR) behavior of Pt/Ba/CeO2 and Pt/Ba/Al2O3 have been identified and traced to their different chemical and structural properties. The results show that Pt/Ba/CeO2 exhibits inferior NO x storage and, particularly, reduction (regeneration) activity compared to the Al2O3 supported catalyst. The incomplete reduction of the stored NO x -species in Pt/Ba/CeO2 seems to be caused by a faster and more profound reoxidation of Pt particles during the lean period as evidenced by in situ X-ray absorption spectroscopy. Interestingly, the reduction activity could be significantly improved by a pre-reduction step at mild conditions. Exposure of the Pt/Ba/CeO2 catalyst to reducing H2 atmosphere in the temperature range 300–500°C lead to a moderate increase of Pt particle size which beneficially influenced the regeneration activity. In contrast, pre-reduction at temperatures above 500°C was unfavorable and resulted in a severe decrease of the regeneration activity, probably due to migration of the partially reduced CeO2 onto the surface of Pt particles. [Copyright &y& Elsevier]

Abstract: The effectiveness of Ag/Al2O3 catalyst depends greatly on the alumina source used for preparation. A series of alumina-supported catalysts derived from AlOOH, Al2O3, and Al(OH)3 was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, O2, NO+O2-temperature programmed desorption (TPD), H2-temperature programmed reduction (TPR), thermal gravimetric analysis (TGA) and activity test, with a focus on the correlation between their redox properties and catalytic behavior towards C3H6-selective catalytic reduction (SCR) of NO reaction. The best SCR activity along with a moderated C3H6 conversion was achieved over Ag/Al2O3 (I) employing AlOOH source. The high density of Ag–O–Al species in Ag/Al2O3 (I) is deemed to be crucial for NO selective reduction into N2. By contrast, a high C3H6 conversion simultaneously with a moderate N2 yield was observed over Ag/Al2O3 (II) prepared from a γ-Al2O3 source. The larger particles of Ag m O (m >2) crystallites were believed to facilitate the propene oxidation therefore leading to a scarcity of reductant for SCR of NO. An amorphous Ag/Al2O3 (III) was obtained via employing a Al(OH)3 source and 500°C calcination exhibiting a poor SCR performance similar to that for Ag-free Al2O3 (I). A subsequent calcination of Ag/Al2O3 (III) at 800°C led to the generation of Ag/Al2O3 (IV) catalyst yielding a significant enhancement in both N2 yield and C3H6 conversion, which was attributed to the appearance of γ-phase structure and an increase in surface area. Further thermo treatment at 950°C for the preparation of Ag/Al2O3 (V) accelerated the sintering of Ag clusters resulting in a severe unselective combustion, which competes with SCR of NO reaction. In view of the transient studies, the redox properties of the prepared catalysts were investigated showing an oxidation capability of Ag/Al2O3 (II and V)>Ag/Al2O3 (IV)>Ag/Al2O3 (I)>Ag/Al2O3 (III) and Al2O3 (I). The formation of nitrate species is an important step for the deNO x process, which can be promoted by increasing O2 feed concentration as evidenced by NO+O2-TPD study for Ag/Al2O3 (I), achieving a better catalytic performance. [Copyright &y& Elsevier]

Abstract: Experimental results describing the product distribution during the reduction of NO by H2 on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts are presented in the temperature range 30–500°C and H2/NO feed ratio range of 0.9–2.5. A microkinetic model that describes the kinetics of NO reduction by H2 on Pt/Al2O3 is proposed and most of the kinetic parameters are estimated from either literature data or from thermodynamic constraints. The microkinetic model is combined with the short monolith flow model to simulate the conversions and selectivities corresponding to the experimental conditions. The predicted trends are in excellent qualitative and reasonable quantitative agreement with the experimental results. Both the model and the experiments show that N2O formation is favored at low temperatures and low H2/NO feed ratios, N2 selectivity increases monotonically with temperature for H2/NO feed ratios of 1.2 or less but goes through a maximum at intermediate temperatures (around 100°C) for H2/NO feed ratios 1.5 or higher. Ammonia formation is favored for H2/NO feed ratios of 1.5 or higher and intermediate temperatures (100–350°C) buts starts to decompose at a temperature of 400°C or higher. The microkinetic model is used to determine the surface coverages and explain the trends in the experimentally observed selectivities. [Copyright &y& Elsevier]

Abstract: Remarkable progress towards implementation of catalytic technology for N2O mitigation in nitric acid plants has been experienced in recent years. EnviNOx®, one of the commercial processes developed by Uhde, accomplishes the tail-gas abatement of N2O and NO x over a single reactor using iron-containing zeolite catalysts. Two variants of the process are available depending on the tail-gas temperature. This manuscript evaluates the low-temperature abatement process (<700K), where NO x and N2O are selectively reduced by NH3 and CH4, respectively. To this end, activity tests in mixtures with N2O, O2, NO, NH3, and CH4 at different temperatures and partial pressures of reactants were carried out over steam-activated FeZSM-5. Ammonia and nitric oxide strongly inhibit the selective catalytic reduction (SCR) of N2O by CH4, shifting the temperature for N2O conversion over 700K. Controlled ammonia dosing is required for the efficient operation of the low-temperature EnviNOx® variant over the particular iron zeolite used in this study. The optimal inlet NH3 concentration is determined by the NO concentration in the tail-gas and its temperature. In the absence of NO and NH3, the CH4-SCR of N2O over FeZSM-5 is effective above 623K. Still, this process cannot retrofit a number of existing plants with lower tail-gas temperatures. [Copyright &y& Elsevier]

Abstract: A series of Pt–Ba/MO2 (MO2 =CeO2, SiO2, ZrO2) catalysts, containing 1wt.% Pt and different Ba-loadings (4.5–28wt.%), was investigated concerning NO x storage and reduction of the stored NO x species by propene using pulse thermal analysis combined with mass spectrometry and temperature-programmed reaction-desorption (TPRD). Well-characterized standard Pt/Al2O3 and Pt–Ba/Al2O3 catalysts were used as references. Exposure of the catalysts to NO/O2 pulses showed that the NO x storage capacity of the Ba-free as well as Ba-loaded catalysts was strongly affected by the nature of the support. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption on the Ba-free catalysts revealed that the distribution of CO chemisorbing sites also depends on the nature of the support. Among the Ba-free catalysts Pt/CeO2 exhibited the highest NO x uptake. No NO x uptake was observed with Pt/SiO2. With all supports the NO x storage capacity increased with the Ba-loading, but differently depending on the support. TPRD of catalysts after exposure to NO x pulses revealed that the thermal stability of the stored NO x species is affected by the nature of the support and the Ba-loading. Up to ca. 10wt.% of Ba, Pt–Ba/CeO2 showed the highest NO x uptake, whereas at the highest Ba-loading (28wt.%) Pt–Ba/Al2O3 and Pt–Ba/ZrO2 afforded highest NO x storage. The NO x storage capacity depended strongly on the relative abundance of the differently stable BaCO3 phases. To test the storage-reduction behavior, the catalysts were subjected to alternating pulses of NO/O2 and propene at 300°C. Depending on the support different reduction behavior was observed. While reduction occurred rapidly on Pt–Ba(16.7)/Al2O3 and Pt–Ba(16.7)/CeO2, it was relatively slow and incomplete on Pt–Ba(16.7)/ZrO2. This behavior was attributed to the low surface area of the ZrO2 support which at higher Ba-loading seems to result in partial blocking of active Pt sites. [Copyright &y& Elsevier]

Abstract: Carbon-based SCR catalysts for the reduction of NO with NH3 at low temperatures have been prepared using activated carbons obtained from a local Spanish coal, doped with several vanadium compounds. Among them, the ashes of a petroleum coke (PCA) were also employed. Both the catalysts and the carbon supports have been characterized by means of N2 and CO2 physisorption, NH3 and O2 chemisorption and temperature programmed desorption (TPD). The activity of the catalysts has been tested in a laboratory-scale unit, measuring significant conversions of NO (above 50%) with almost 100% selectivity toward N2 at 150°C. The feasibility of using the petroleum coke ashes as the active phase was confirmed comparing the activity of the catalysts doped with these residues, with the one measured for the catalysts prepared using model vanadium compounds. The physical–chemical features of the carbon support resulted of key importance for achieving a considerable catalytic activity. The values of apparent energy of activation calculated for the catalysts presented in this paper were very similar to other carbon-based catalysts and smaller than the ones corresponding to TiO2-supported systems. The gas residence time on the catalytic bed influences the catalytic activity to a great extent, thus being a determinant parameter for designing the SCR de-NO x unit. To avoid ammonia slip, inlet concentrations of NH3 has to be little under the stoichometric NH3/NO ratio (∼0.7). The catalysts stability was tested in terms of carbon support gasification followed by termogravimetric analysis and gas chromatography. The activity of the catalysts was maintained at least over 24h of reaction. [Copyright &y& Elsevier]

A highly dispersed Pt/Al2O3 catalyst was used for the selective catalytic reduction of NOx using propene (HC-SCR). Contact with the reaction gas mixture led to a significant activation of the catalyst at temperatures above 523 K. According to CO chemisorption data and HRTEM analysis, Pt particles on the activated catalyst had sintered. The redox behavior of the fresh and sintered catalysts was investigated using Multitrack, a TAP-like pulse reactor. If Pt particles on the catalyst are highly dispersed (average size below ∼2 nm), only a small part (∼10%) of the total number of Pt surface sites as determined by CO chemisorption (Ptsurf) participates in H2/O2 redox cycles (Ptsurf,redox) in Multitrack conditions. For a sintered catalyst, with an average particle size of 2.7 nm, the number of Ptsurf and Ptsurf,redox sites are in good agreement. Similar results were obtained for both catalysts using NO as the oxidant. The low number of Ptsurf,redox sites on highly dispersed Pt/Al2O3 is explained by the presence of a kinetically more stable—probably ionic—form of Pt&z.sbnd;O bonds on all surface sites of the smaller Pt particles, including corner, edge and terrace sites. When the average particle size shifts to ∼2.7 nm, the kinetic stability of all Pt&z.sbnd;O bonds is collectively decreased, enabling the participation of all Pt surface sites in the redox cycles.A linear correlation between the NOx conversion in HC-SCR, and the amount of Ptsurf,redox was found. This suggests that redox-active Pt sites are necessary for catalytic activity. In addition, the correlation could be significantly improved by assuming that Ptsurf,terrace sites of the particles larger than 2.7 nm are mainly responsible for HC-SCR activity in steady state conditions. Implications of these results for the pathway of HC-SCR over Pt catalysts are discussed. [Copyright &y& Elsevier]

Selective reduction of NO (0.1%) with propylene (0.1%) in the presence of oxygen (5%) with He balance was carried out over Ag supported on Al2O3, H-ZSM5 and H-Y catalysts. Although their activities were different, all three catalysts showed high selectivity to N2 (around 95%). Through several characterizations, it was concluded that silver was present in the form of Ag2O clusters, but not in metallic form for the three catalysts. High selectivity to N2 on all the catalysts is attributed to the same active phase of silver oxide. The difference in catalytic activity is considered to be due to the amounts and the size of Ag2O clusters. Normalized activity per Ag site (TOF) was not the same (Ag/Al2O3>Ag-ZSM5>Ag-HY), which is explained by the carbon depositions and facile transformation of Ag species under redox condition over zeolite-based catalysts. [Copyright &y& Elsevier]

A bimetallic RhNi/Al 2 O 3 catalyst prepared by galvanic replacement (GR) offers enhanced catalytic CO 2 hydrogenation to selectively produce methane. • Galvanic replacement offers a facile route to bimetallic Rh@Ni core–shell catalysts. • Bimetallic Ni@Rh core–shell catalysts offer significant rate enhancements for CO 2 methanation. • Operando IR identifies reactively-formed CO as the key intermediate to CH 4 production. • Surface formate is a catalytic spectator in methanation. CO 2 utilisation as a chemical feedstock could transform fuels production and help mitigate climate change. Direct CO 2 reduction for energy production requires the development of active, stable, and low-cost catalysts selective for methane. A bimetallic Ni@Rh core–shell catalyst prepared by galvanic replacement (GR) exhibits a 3.5-fold rate enhancement for CO 2 methanation relative to an analogue prepared by chemical reduction (CR) and is twice as active as monometallic Rh/Al 2 O 3. Superior performance of RhNi/Al 2 O 3 (GR) is attributed to Rh dispersion as an atomically thin RhO x shell encapsulating Ni nanoparticles, stabilised by a strong Rh-Ni interaction. Operando IR spectroscopy identifies reactively-formed CO from the dissociative chemisorption of CO 2 over Rh as the key intermediate for methane production. Surface formate from the dissociative chemisorption of CO 2 and subsequent hydrogenation (via spillover from Rh sites) over alumina is a catalytic spectator. This mechanistic insight paves the way to high activity nanostructured catalysts for CO 2 methanation. [ABSTRACT FROM AUTHOR]