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• A value-added and efficient technology for recycling spent Ag-Al 2 O 3 catalyst is proposed. • High-value-added spherical silver powder is synthesized by a simple chemical reduction method. • A fitted mathematical model of particle size for silver powder is obtained. • The interactions between the factors are investigated. The spent Ag-Al 2 O 3 catalyst is an important silver secondary resource due to its high content of Ag. However, the most commonly used nitric acid leaching method produces toxic and harmful NO x gases. Herein, a novel clean method was proposed to treat the spent Ag-Al 2 O 3 catalyst using the green leaching agent cerium ammonium nitrate instead of nitric acid to effectively avoid the generation of toxic NO x gases. More importantly, value-added monodisperse micro-sized uniform spherical particles were synthesized directly from the leaching solution by a simple chemical reduction method. The influence of leaching conditions on the leaching ratio of Ag and leaching kinetics were discussed in detail. The response surface methodology was applied to optimize the synthesis parameters of silver powder and explore the interactions between the synthesis process parameters. Under the optimal leaching parameters, the leaching ratio of Ag reached 99.69 %. The leaching kinetic analysis of leaching indicated that the leaching reaction of spent Ag-Al 2 O 3 catalyst was controlled by chemical reaction. By the response surface methodology design, a fitted mathematical model of the particle size for silver powder and the optimum synthesis parameters of silver powder were obtained. The optimum synthesis parameters of silver powder were as follows: [Fe2+] = 1.08 mol/L, [Ag+] = 1.01 mol/L, and dispersant dosage of 2.05 wt%. The average experimental particle size of 1.337 μm was very close to the predicted value of 1.343 μm obtained from the fitted model, indicating that the fitted model of particle size for silver powders was very good. This process not only provides a clean and value-added method for recycling the spent Ag-Al 2 O 3 catalyst, but also helps to promote the balanced and high-value utilization of high-abundance cerium. [ABSTRACT FROM AUTHOR]

The use of red mud as a support material was evaluated in this study to develop a novel bimetallic catalyst for highly reactive and selective nitrate removal from water and wastewater. The catalyst was optimized for the selection of promoter metal (i.e., Sn, Cu, In, and Zn) and then for noble metal (i.e., Pd, Pt, and Au). Sn-Pd-red mud and In-Pd-red mud catalysts achieved a complete nitrate removal. Sn-Pd-red mud showed 5.1 times higher removal kinetics (k = 11.57 × 10 −2  min −1 ) than that of In-Pd-red mud (k = 2.27 × 10 −2  min −1 ). The results from characterization study confirmed that the enhanced nitrate removal kinetics of Sn-Pd-red mud was mainly attributed to 1) its high affinity towards nitrate, 2) low alloying effect of Sn on Pd, 3) high reduction potential of Sn, and 4) high H 2 activation by Pd, as compared to those of other red mud supported bimetallic catalysts. We also found that the interaction between CaO and Fe 2 O 3 was the driving force for the enhanced nitrate reduction and high N 2 selectivity in this study. A complete nitrate removal with high N 2 selectivity (>88%) was preserved during the 11 times of recycling tests with consistent reduction kinetics (k = 10.87 ± 0.48 × 10 −2  min −1 ), indicating that red mud could be an excellent support material for efficient and durable bimetallic catalyst for the enhanced selective nitrate reduction. [ABSTRACT FROM AUTHOR]

Uniform mesoporous iron titanium (CT-FeTi) catalysts were synthesized by a CTAB-assisted process and exhibited good catalytic activity and H 2 O resistance when tested in the selective catalytic reduction (SCR) of NO with NH 3 at low temperature. BET, TPD, TPSR and in situ DRIFTS were carried out to reveal the inhibition mechanism of H 2 O on SCR reaction and determine the role of CTAB in the improved H 2 O resistance during low-temperature SCR processes. Results showed that H 2 O inhibited the adsorption of NO on the surface of CT-FeTi catalysts, as well as the formation of the intermediate species (–NH 2 ), which was produced by the reaction Fe 3+ + NH 3 → Fe 2+ - NH 2 + H + . CTAB acted as a “structural” and “chemical” promoter, not only optimizing the pore size to avoid being excessively enlarged in the presence of H 2 O, but also enhancing the adsorption of bridging nitrate and NH 3 species on Lewis acid sites, thus improving the catalytic activity and H 2 O resistance. [ABSTRACT FROM AUTHOR]

Phosphorus were employed to investigate the influences on the acid sites and reaction mechanism of FeTiO x SCR catalyst. The introduction of phosphorus inhibited the SCR activity by suppressing the redox property, decreasing the surface acidity and reducing the surface area. In particular, phosphorus preferentially bonded to the electron-deficient Ti 4+ and Fe 3+ cations on the surface as P-O-Fe and P-O-Ti, thereby blocking the Lewis acid sites (Fe-NH 3 or Ti-NH 3 ). Although phosphate provided additional Brønsted acid sites (P-O-NH 4 + ), the larger decrease of Lewis acid sites results in the decrease of total surface acidity. The newly formed Brønsted acid sites showed less SCR active at low temperature and exhibited high thermal stability and reactivity at high temperature, which leads to a new pathway following the L-H mechanism and an enhancement of high temperature performance. [ABSTRACT FROM AUTHOR]

The stability of MnO x based low temperature SCR catalysts remained to be a serious issue. This report explored use of multi-walled carbon nanotubes (MWCNTs) network with uniform structure as a “rigid” pore template for synthesis of mesoporous MnO x -TiO 2 SCR catalyst with high surface area and high stability. The results showed that MWCNT network imposed MnO x -TiO 2 catalyst a mesoporous porosity with a narrow pore size distribution centered on ∼13.2 nm and a surface area of 131.6 m 2 g −1 stabilized at 500 °C. The mesoporous structure was formed by interconnected nanoparticles, comprised of crystallized rutile TiO 2 core surrounded by amorphous MnOx, with an average diameter of ∼8 nm. The catalyst exhibited an excellent low temperature SCR activity and selectivity as well as high resistance to deactivation and poison by H 2 O and SO 2 . SnO 2 modification led to degradation of catalytic performance in low temperature (60–180 °C) side, but improvement at high temperature side (240–360 °C), especially at high gas velocity, which can be attributed to change in structure, reactivity of MnO x and surface acidity induced by SnO 2 addition. [ABSTRACT FROM AUTHOR]

A series of WO 3 -doped Mn–Zr mixed oxide catalysts were investigated for the selective catalytic reduction of NO x by NH 3 (NH 3 –SCR). It was found that the added WO 3 significantly enhanced the catalytic performance of Mn–Zr mixed oxide catalyst for NH 3 –SCR of NO x . In situ diffuse reflectance infrared transform spectroscopy (DRIFTS) studies revealed that the highly dispersed WO 3 not only resulted in more acid sites formed on the catalyst surface, but also inhibited the adsorption of the inactive nitrate specie, leaving more active sites available for the adsorption of NH 3 . In addition, the synergetic effect between W and Mn contributes to improving the redox property of the catalyst. Therefore, the high catalytic deNO x performance was obtained over WO 3 -promoted Mn–Zr mixed oxide catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] Highly efficient Pd/CNF catalyst for bromates reduction in water is presented. [•] Production of carbon nanofibre support scaled to 10g. [•] LCA study of carbon nanofibrous catalyst was developed. [ABSTRACT FROM AUTHOR]

Highlights: [•] AuNPs can be immobilized on dead yeast cell by reacting Pichia pastoris with HAuCl4. [•] NH2 and OH were demonstrated to play a crucial role in the biosorption process. [•] Mannocarolose may be responsible for the bioreduction of [AuCl4]−. [•] Au/P. pastoris exhibited good catalytic activity for the reduction of 4-NP. [•] The catalytic activity is closely related to the interaction between AuNPs and yeast. [Copyright &y& Elsevier]

A functional GO/AgNPs nanocomposite was obtained by in situ reduction of positively charged AgNO3 precursors which were adsorbed on the negatively charged surface of GO through electrostatic attraction. GO/Ag −Fe3O4 magnetic nanoparticles (GAMNs) were generated via an amidation reaction in the presence of 1-ethyl-3-(3-dimethyaminopropyl) carbodiimide and N-hydroxysuccinnimide for the first time. The catalysis property of the nanocomposite was studied by degrade 4-nitrophenol. The characterized results proved that AgNPs and Fe3O4 have been successfully decorated on GO nanosheets. The GAMNs possess high catalytic capacity and good reusability, and exhibit great potential in environmental pollutant degradation. [Copyright &y& Elsevier]

Abstract: The performance trends of a homemade Pt–Ba/Al2O3 monolith catalyst for NO x storage and reduction at different temperatures and varying the hydrogen concentration fed during the regeneration period have been found by the response surface methodology. NO x trapping efficiency during the lean period, selectivity to N2/N2O/NH3 and global NSR efficiency have been used as the response for describing the performance of the monolith. Maximum NO x trapping efficiency (80%) was found when operating at relative low temperature (240°C) and high reductant concentration (>2% H2) but with limited selectivity to N2, whereas maximum selectivity to N2 (above 90%) was achieved at high temperature (>300°C) and hydrogen in defect (<1%) but with limited NO x trapping efficiency. As both response should be as high as possible for NSR commercial systems, they are combined in the global NSR efficiency or production of N2 related to NO in the feedstream (vol.%). Maximum NSR efficiency (65%) was achieved at 270°C and 1% H2, with NO x trapping efficiency of 77% and N2 selectivity of 85%. It has been verified the consistency of data obtained with mechanistic aspects already reported in the literature. The role of ammonia as an intermediate that reacts with NO x stored has been confirmed and also the primary routes of H2 which reacts with stored NO x and the sequential route of stored NO x reacting with H2 and then NH3 reducing with stored NO x downstream. N2/NH3/N2O distribution at the reactor exit depends on the extent of each route in the reaction network and is a complex function of temperature, gas phase and surface compositions. [Copyright &y& Elsevier]

Abstract: In industrial fluidized bed processes, the system often involved a change in volumetric flow. Defluidization occurs when reactions involving a decrease in gas volume are carried out in a fluidized catalyst bed. This is due to decrease in gas velocity below the minimum fluidization velocity in the emulsion phase. One method to improve fluidization quality is to supply an inert gas with reactant gases: similar effect can be obtained by supplying an excessive amount of one of the reactants. In the present study, the effect of a diluted reactant gas on fluidization quality is quantitatively analyzed by performing CO2 hydrogenation in a fluidized catalyst bed. Stable operation can be established by operating the fluidized bed to avoid the conditions contained in the defluidization zone using two parameters that influence fluidization quality. [Copyright &y& Elsevier]

Abstract: A pseudo 1-D model of an industrial NO x storage and reduction (NSR) catalyst has been developed under isothermal conditions. The Pt/Ba proximity or the presence of barium in different chemical forms such as BaO and BaCO3 can result in a wide range of storage rates. To represent these multiple storage sites, an idealized storage particle with a spherical configuration is proposed where the outer layer is assumed to represent the sites with the highest storage capacities/rates while subsequently deeper layers represent the sites with relatively lower storage capacities. It is further assumed that the NO x species first react with the particles in the outer layer, followed by the particles in subsequent deeper layers. To model the progressively decreasing storage rates, a shrinking core approach is used with a diffusivity coefficient, decreasing nonlinearly along the particle depth. The degree of nonlinearity depends on the complexity of the catalyst and therefore, depending on the catalyst, being studied, one can calibrate this function instead of quantifying different types of storage sites. During cyclic operation starting with a completely regenerated catalyst, model predictions for the NO x concentration profiles are in a good agreement with the experimental data during both the transient and steady cycle-to-cycle regimes. It is also shown that with limited amount of reductant, the regeneration of storage sites takes place only in the front portion of the catalyst up to a certain length and the remaining part of the catalyst is only involved in the storage reactions. After a certain number of cycles, the back of the catalyst reaches its saturation limit for storing NO x and from then on, only the amount of catalyst being regenerated in the front part of the catalyst during the rich phase participates in storage. [Copyright &y& Elsevier]

Abstract: The mass transfer of wire mesh honeycomb is investigated, and a new correlation Sh =1.108 Re 0.5 Sc 1/3 is proposed based on data for the mass transfer limited performance for selective catalytic reduction of NO x by NH3 over wire mesh honeycomb catalysts. The numerical model is developed to evaluate the performance of wire mesh honeycomb, which is verified by the experiments. By measuring the NO x conversion over wire mesh honeycomb catalysts with different washcoat thickness and cell density, the intraporous diffusion and interphase diffusion are studied. The pressure drop of wire mesh honeycomb is low. Compared to ceramic monolith, wire mesh honeycomb catalysts possess high catalyst utilization relative to the geometric surface area and the catalyst weight. [ABSTRACT FROM AUTHOR]

Abstract: Selective catalytic reduction of NOx with propene has been investigated over SnO2/Al2O3 catalysts prepared by impregnation and single step sol–gel methods. Catalyst preparation method exerts significant influence on the catalytic performance, and SnO2/Al2O3 prepared by the sol–gel method is more active than the impregnated catalyst. Moreover, its resistance against water is higher. The high surface area and the strong interaction between SnO2 and Al2O3 may be responsible for the high reduction activity of sol–gel SnO2/Al2O3 catalyst. The presence of oxygen strongly favours the NOx reduction process. FT-IR results have revealed that the role of oxygen is to contribute to the formation of formate, acetate and nitrate species, all of which are reactive intermediates for NOx reduction. [ABSTRACT FROM AUTHOR]

Abstract: Fructose and invert sugar (fructose/glucose mixture) were hydrogenated over bimetallic amorphous nano-catalysts of CoNiB and polymer polyvinylpyrrolidone (PVP)-stabilized CoNiB (PVP-CoNiB), prepared by chemical reduction, to yield mannitol and sorbitol. The parameters of catalysts and the reaction conditions were discussed. CoNiB and PVP-CoNiB catalysts were much more active than NiB, CoB and Raney nickel in the hydrogenations of fructose and invert sugar. The selectivity of mannitol changed slightly even as the catalysts and the reaction conditions were altered. The highly active catalysts of CoNiB and PVP-CoNiB are promising to replace Raney nickel in the hydrogenations of fructose and invert sugar, although the selectivity of mannitol improved slightly. [Copyright &y& Elsevier]

Abstract: Carbon-coated catalysts doped with tungsten and vanadia oxides with different V and W loadings have been prepared by the ionic exchange method and characterized. The surface, structure and composition have been investigated by XPS, Raman, N2 sorption at 77K, TPD-NH3 and reactivity tests for the SCR of NO with NH3 at low temperatures. Under reaction conditions, NO conversions were found to go through a maximum with vanadia surface coverage at approximately half a monolayer. The observed decrease in the SCR activity at higher vanadia loadings can be attributed to either a loss of dispersion or loss of textural properties. Maximum NO conversion is ascribed to the higher Brönsted proton acidity (V4+) of the centres that decreases with increasing vanadia loadings up to 3wt% loading due to the increase of V4+/V5+ ratio. Large amounts of tungsten (5%, w/w) upon or before addition of vanadia do not provide an enhancement of activity. The results indicate that W addition increases surface acidity leading to stronger Brönsted or even Lewis acid centre creation. [Copyright &y& Elsevier]

Abstract: Common sources of chromium in wastewater are electroplating and leather industries. Hexavalent chromium is more toxic and carcinogenic compared to its trivalent counterpart. Conversion of Cr(VI) to Cr(III) in an aqueous medium by photocatalytic reduction using UV radiation and ZnO semiconductor catalyst has been investigated using potassium dichromate as the model compound. Effects of the process parameters such as ZnO loading (0–3g/L) and intensity of UV radiation (0–125W medium pressure Hg vapour lamp) on photocatalytic reduction were investigated. Initial concentration of substrate solution was varied from 40 to 120mg/L. A comparison of the performance of the ZnO photocatalyst achieved in this study with that reported in the literature for photocatalytic and conventional processes is presented. The initial rate of the photochemical method was found to be independent of the concentration of potassium dichromate. Methanol was added as a hole scavenger for enhancement of the photo-reduction. Initial rate of photo-reduction was found to be independent of the concentration of methanol above a particular value. A probable mechanism and the corresponding kinetic model have been proposed for the photo-reduction and tested by experimental results. An alternative rate equation based on the LHHW model compares well with the mechanistic rate equation. [Copyright &y& Elsevier]

Abstract: The influence of two different washcoats deposited on ceramic honeycombs (alumina and carbon) on the catalytic and mechanical properties of catalysts are examined in this work. A series of carbon and alumina washcoated samples was prepared through a dip-coating method and subsequently cured and treated to reach a suitable chemistry surface. Carbon-coated monoliths present a high washcoat homogeneity, high integrity and a suitable chemistry surface that favour NO reduction at low temperatures. The carbon washcoat was bonded perfectly to the ceramic monoliths. The high adherence between both materials, checked by vibrational tests, provides higher resistance indexes against axial compression and prevents crack propagation. Both facts are a consequence of the high mechanical strength of the catalyst. On the other hand, alumina coatings present better temperature resistance, although their adherence to ceramic monoliths is not as good as in carbon-coated samples. The properties of alumina coatings are strongly dependent on the slurry viscosities, which influence the integrity of the washcoat, mechanical properties and even NO conversion. Both series of catalysts have shown a good NO conversion under on-board conditions, although the key parameters of each washcoat are completely different. [Copyright &y& Elsevier]

• Epitaxial growth of CoO on Co 9 S 8 can be regulated by TAA's amount. • Strong interactions between Co 9 S 8 and CoO caused by Jahn-Teller effect result in the lattice distortion in Co 9 S 8 and CoO. • The built-in electric field contributes accelerated electron transfer from CoO to Co 9 S 8. • CoO engineered Co 9 S 8 can increase the binding energy of CO 2 and decrease the energy barriers of intermediates. Fabricating highly active surface and rapid electron-transfer interface is an appealing route to develop an efficient catalyst to realize visible light driven photocatalytic CO 2 reduction into value-added chemicals. Herein, we successfully synthesized the epitaxy of Co 9 S 8 material with tiny CoO by using assembly-calcination method through controlling the amount of added thioacetamide as sulfur resource. As CoO is strongly anchored on the Co 9 S 8 , the bonding interaction between Co 9 S 8 and CoO leads to the lattice distortion inside the material, attributing to the Jahn-Teller effect. The as-formed heterojunction between Co 9 S 8 and CoO can create the built-in electric field, which drives the electron transfer from CoO to the Co sites of Co 9 S 8 through the Co-O and Co-S covalent bonds. The existence of CoO also enhances the adsorption affinity of CO 2 on the Co 9 S 8 surface, as well as expands the bond length of C = O, which triggers the activation of CO 2 molecule on the catalyst surface. While using [Ru(bpy) 3 ]Cl 2 (bpy: 2,2′-bipyridine) as photosensitizer and triethanolamine as sacrificial agent, Co 9 S 8 /CoO@C displays excellent photocatalytic performance to realize the CO 2 reduction to syngas. And the evolution rate of CO and H 2 is 1.71 × 104 and 4.75 × 103 μmol h−1 g−1 respectively. The DFT calculations demonstrate that the Co 9 S 8 /CoO heterojunction obviously reduces the kinetic barrier for the formation of intermediates during the photochemical reduction of CO 2. [ABSTRACT FROM AUTHOR]

Abstract: The kinetics of the selective catalytic reduction of NO in the presence of vanadium loaded carbon-based catalysts has been studied, by means of different techniques, such as transient response analysis, temperature programmed desorption and DRIFT spectrometry. The results point out to a reaction mechanism involving adsorbed species of ammonia, which react with the NO from the gas phase. The role of oxygen will be the regeneration of the spent catalytic sites. Finally, the Mars van Krevelen kinetic model was successfully used to fit the experimental data. [Copyright &y& Elsevier]

Abstract: The aim of this investigation is to check the possibility of using, after Pd extraction, the residue of deactivated alumina–palladium catalyst as a component of an oxide composite, as well as to establish the effect of Pd on the catalyst activity. In order to do so, Cu–Co active phase was impregnated on catalyst containing Pd residue (synthesized catalyst 3KN). The polyoxide composition obtained is intended for a catalyst to be used in reduction of NO with CO and oxidation of CO to CO2 in gas mixtures. For comparison Cu–Co oxide catalysts (KA1–KA3) and regenerated Pd catalyst with content of 2% Pd (catalyst KN) were used. It was established that not only the catalyst activity towards NO reduction with CO, but also the resistance to poisoning with SO2 increased in the presence of Pd in combination with the synthesized fresh active Cu–Co phase. In this way the 3KN catalyst is suitable to be used as a catalyst for purification of polluted gases. [Copyright &y& Elsevier]