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The paper is focused on evaluation of active centres and impact of adsorbed species on (10%Co+0.5%Pd) / Al2O3 catalyst system performance aiming selectivity optimization. Application of different sets of precursor pretreatment and reduction resulted in catalysts exhibiting high CO conversion or high methane selectivity. A sample of high selectivity was prepared by pretreatment in hydrogen and the performance was determined by lower amount of strongly adsorbed CO, strongly adsorbed carbonate species, and higher amount of reduced metal and bimetallic particles. A more active system was formed by pretreatment in air leading to larger amount of unreduced metal and CO-bridged species on the surface, stable coverage of hydroxyl groups on the support, and medium-strength sites for adsorption of carbonates. Ratios of hydrogen to carbon monoxide adsorption (H/CO) and of strongly to weakly adsorbed CO species appeared as important criteria for catalyst efficiency together with supported metal state, amount of unreduced ions, bimetallic particle formation, and alumina's ability to adsorb CO and CO2. [ABSTRACT FROM AUTHOR]

Catalytic oxidation of bis (2-chloroethyl) ether (CEE) was carried over 6 wt.% nanocatalyst (VTN) in the presence of ozone. The VTN was prepared by sol–gel method, while the impregnated catalyst (VTI) was prepared for the sake of comparative study. The catalysts were characterized by BET-SA, CEE-TPD, NH 3 -TPD, H 2 -TPR, XRD, SEM EDAX and TEM analyses. TPR and TPD data reveal that more acid and redox site was observed on nanocatalyst compared to that of conventional catalyst. The Brønsted acid sites were relatively more on nanocatalyst which were responsible for the higher ozone decomposition at low temperatures. The effects of O 3 /CEE ratio, reaction temperature, gas hourly space velocity (GHSV) and relative humidity (RH) were also investigated. The nanocatalyst exhibited the better performance, at low temperature (150 °C) with high selectivity to carbon oxides. The transmission electron microscope data reveal that the sol–gel catalysts' average particles size was 14. At 10% of RH, the complete conversion of CEE into carbon oxides was observed for nanocatalyst at 100 °C with long-term stability. The ozone decomposition data reveal that the particle size and acidity had significant influence up to 100 °C, whereas the thermal effects are predominant over the particle size above 150 °C. A plausible reaction mechanism was proposed based upon the experimental data. [ABSTRACT FROM AUTHOR]

Sulfated zirconia is a very strong solid acid catalyst which can be utilized for various reactions. The present study focuses on synthesis of zirconia-based catalyst with high acidity and high surface area, particularly for isomerization reaction. Sulfated zirconia has been obtained by sulfation of zirconia prepared by hydrothermal route. The catalyst was developed by impregnating tungstophosphoric acid on sulfated zirconia by wet incipient method. The catalyst was characterized through Brunauer–Emmett–Teller (BET) surface area, temperature-programmed desorption of ammonia, temperature program reduction of hydrogen, Fourier transmission infrared spectroscopy, and thermogravimetric analysis. The results revealed that the catalyst is crystalline in nature with surface area 190–225 m2 g−1 and acidity 0.135–0.558 mmol g−1. Twenty-five percent conversion was obtained (as confirmed by gas chromatography) at 225°C using n-hexane as model hydrocarbon in fixed-bed microreactor. [ABSTRACT FROM AUTHOR]

Se prepararon catalizadores de CeTbO X/La2O3-Al2O3, CeO2/La2O3-Al2O3, CeTbO X/SiO2 y CeO2/SiO2, utilizando la técnica de impregnación a humedad incipiente a partir de soluciones acuosas de cloruros de cerio, terbio y lantano. Los catalizadores fueron caracterizados mediante las técnicas de Fluorescencia de rayos X (XRF), Área superficial, Reducción a Temperatura Programada (TPR), Desorción a Temperatura Programada de H2 (TPD-H2), Capacidad de Almacenamiento de Oxígeno (OSC). El comportamiento catalítico de las muestras sometidas a distintos tratamientos térmicos fue evaluado a través de la reacción de oxidación de metano. Los estudios de TPR muestran que la adición del ión Tb mejora la reducibilidad del óxido de cerio. En los perfiles de TPR se observan cambios en la naturaleza de las fases presentes en superficie luego de ser sometidas a distintos tratamientos térmicos y que los óxidos soportados en sílice se reducen en un rango de temperatura menor que los correspondientes a los catalizadores soportados sobre alúmina modificada, efecto que es ventajoso pero que no tiene correlación con los valores obtenidos de OSC y actividad catalítica. La mayor OSC y conversión fueron obtenidas para el catalizador CeTbO X/La2O3-Al2O3. La reacción de oxidación de metano se desfavorece con el incremento de la presión parcial de oxígeno.The CeTbO X/La2O3-Al2O3, CeO2/La2O3-Al2O3, CeTbO X/SiO2 and CeO2/SiO2 catalysts were prepared by incipient wetness impregnation technique from aqueous solutions of cerium, terbium and lanthanum chlorides. The catalysts were characterized by X-ray fluorescence (XRF), Surface area, Temperature-programmed reduction (TPR), Temperature-programmed desorption of hydrogen (TPD-H2), Oxygen storage capacity (OSC). The catalytic behavior was studied using methane oxidation reaction after different thermal treatments. The TPR study showed that the addition of Tb ion improves the reduction properties of cerium oxide. TPR profiles showed appreciable changes in the nature of the superficial phases in surface after the different thermal treatments, and that the oxides supported on silica reduce in a temperature range lower than those corresponding to the modified alumina-supported catalysts; this effect is advantageous but it does not correlate with the low values of OSC and catalytic activity. The higher OSC and the higher conversions were obtained with CeTbO X/La2O3-Al2O3 catalyst. The methane oxidation reaction is not favored with the increase of the oxygen partial pressure.

Zinc oxides modified with chromium were prepared by the co-precipitation method. Samples were calcined at 400 °C. Structural and surface properties of materials were studied by means of transmission electron microscopy, X-ray diffraction and low-temperature nitrogen adsorption methods. Temperature-programmed reduction methods were used for investigation of the influence of chromium on the redox properties of zinc oxides. The nature of surface sites and the course of surface reactions occurred during methanol decomposition were determined by the temperature-programmed desorption of methanol with detection of evolved gasses by mass spectrometry and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have found that modification of ZnO with chromium led to the increase of the specific surface area of oxides and decrease of mean crystallite size of ZnO. Partial incorporation of chromium ions to the hexagonal ZnO structure, formation of strongly dispersed spinel (ZnCrO) and chromium zinc oxide species (ZnO·CrO) was observed. We have stated that methanol was adsorbed on the surface of ZnO at 100 °C mainly via formation of methoxy species, and the main products of methanol desorption were carbon monoxide and hydrogen. The presence of chromium facilitated direct oxidation of methoxy groups to formate species at low temperatures (~100 °C) and their transformation to hydrogen and carbon dioxide during temperature-programmed desorption. The enhanced transformation of methoxy to formate species was attributed to the labile oxygen in chromium-modified zinc oxides. [ABSTRACT FROM AUTHOR]

A low-temperature vapor phase catalytic oxidation of dimethyl sulfide (DMS) with ozone over nano-sized Fe 2 O 3 –ZrO 2 catalyst is carried out at temperatures of 50–200 °C. Nanostructured Fe 2 O 3 –ZrO 2 catalyst (FZN) is prepared by modified sol–gel method using citric acid as a chelating agent and conventional FZ catalyst is prepared with co-precipitation method. The catalysts are characterized using N 2 -BET surface area and pore size distributions, X-ray diffraction, TPR, TPD of DMS and NH 3 , SEM and TEM. The effects of operating temperature, ozone/DMS concentration and gas hourly space velocity (GHSV) on DMS removal efficiencies via catalytic ozonation are investigated. Relatively higher amount of ozone decomposition is observed on nanocatalyst compared to the co-precipitate catalyst from 50 °C to 150 °C. In contrast, at 200 °C irrespective of the particle size, both catalysts performed similar activity. It clearly demonstrates that under ozone assisted catalytic oxidation over nanocatalyst offers the 100% of DMS conversion at lower temperature. The synthesized nanocatalyst and ozone are observed highly efficient for low temperature catalytic oxidation of DMS. The stability test shows that the nanocatalyst have relatively high activity and stability under the reaction conditions. A plausible reaction mechanism has been proposed for the oxidation of DMS based on the possible reaction products. [ABSTRACT FROM AUTHOR]

The CeTbOX/La2O3-Al2O3, CeO2/La2O3-Al2O3, CeTbOX/SiO2 and CeO2/SiO2 catalysts were prepared by incipient wetness impregnation technique from aqueous solutions of cerium, terbium and lanthanum chlorides. The catalysts were characterized by X-ray fluorescence (XRF), Surface area, Temperature- programmed reduction (TPR), Temperature-programmed desorption of hydrogen (TPD-H2), Oxygen storage capacity (OSC). The catalytic behavior was studied using methane oxidation reaction after different thermal treatments. The TPR study showed that the addition of Tb ion improves the reduction properties of cerium oxide. TPR profiles showed appreciable changes in the nature of the superficial phases in surface after the different thermal treatments, and that the oxides supported on silica reduce in a temperature range lower than those corresponding to the modified alumina-supported catalysts; this effect is advantageous but it does not correlate with the low values of OSC and catalytic activity. The higher OSC and the higher conversions were obtained with CeTbOX/La2O3-Al2O3 catalyst. The methane oxidation reaction is not favored with the increase of the oxygen partial pressure.

A series of CuO/CZ catalysts with different amounts of copper oxide were synthesized from copper nitrates by incipient wetness impregnation of the ceria-zirconia support. The structural, redox, acidic and adsorption properties were investigated using X-ray diffraction (XRD), BET, H temperature programmed reduction (H-TPR), temperature programmed desorption of NO in the presence of oxygen (NO-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results have shown good catalytic activity for CuO/CeZrO in NO oxidation to NO. Species such as nitrites and nitrates were formed on the surface. The transformation of nitrite compounds into nitrate was observed above 200 °C. From 300 up to 400 °C, decomposition of the surface nitrate to nitrite was discerned. Ammonia was adsorbed on the Lewis and Brønsted acid sites on Cu/CZ catalyst surface during temperature programmed reactions. The evolution of adsorbed NH species to NH surface group was confirmed by formation specific band of absorption at 1528 cm. [ABSTRACT FROM AUTHOR]

Exothermic reactions between metals and fluorinated polymers are found in a variety of energetic materials, including reactive binder systems and the Magnesium-Teflon-Viton incendiary composition. This paper describes the reactions between a high molecular weight perfluoropolyether, Fomblin Y 140/13, and magnesium in a variety of morphologies including μm-scale powders and nano-scale layered films. Using Temperature Programmed Desorption and Temperature Programmed Reaction we have found that the magnesium-perfluoropolyether interaction is characterized by: (1) competition between Fomblin decomposition and desorption, and (2) magnesium passivation by the formation of magnesium fluoride. Differential Scanning Calorimetry measurements establish a lower-bound estimate of the specific reaction energy of 9.2 kJ g−1. High molecular weight Fomblin (6500 amu) undergoes a competitive reaction/desorption process with desorption occurring at 550 K and decomposition at 610 K. Decomposition becomes more favorable relative to desorption for higher heating rates and thicker films. Perfluoropolyethers produce several characteristic ions in the 70 eV election ionization mass spectra, with the CF3+ ion being the most abundant ion observed during both the molecular desorption and decomposition. Larger fragment ions with masses of 235 and 285 amu are observed in relatively high concentrations during desorption and low concentrations during decomposition. The reaction between magnesium and Fomblin begins at 400 K, producing CF3+, CO+, and C2F5+ in the electron ionization mass spectrum. We propose that these reactions form a passivating layer of magnesium fluoride that protects the remaining metal as it approaches the magnesium melting point. Most of the reaction takes place at 800 K and above when the magnesium fluoride film ruptures. [ABSTRACT FROM AUTHOR]

Temperature-programmed reduction (TPR) and temperature-programmed desorption (TPD) were used to study the effects of Cu and Ca promotion on Fe-Zn-based Fischer-Tropsch catalysts. The reduction temperature for FeO → FeO was unaffected by Ca addition but decreased when promoted with Cu. Fe-Zn promoted with Cu and Ca showed even much lower reduction temperature for FeO → FeO. Ca promotion enhances carburization and increases surface acidity and basicity of the Fe-Zn oxide precursor. While Cu inhibits carburization and decreases the surface acidity and basicity of the Fe-Zn oxide precursor. The implications of these effects on the application of catalysts for FT are discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The influence of Pd on a Co-Pd/γ-Al2O3 heavy oil upgrading catalyst is investigated using different physicochemical and reactive Characterization techniques. Nitrogen adsorption isotherm analysis shows that the specific surface area and porosity of the support alumina is significantly decreased due to the blockage of the pores by the loaded cobalt species. The estimated activation energy of NH3 desorption is found to be less for Co-Pd/γ-Al2O3 sample, which confirms improved acidity due to Pd. TPR experiments show that the reducibility of the catalyst is significantly improved with the presence of Pd. Higher metal dispersion and hydrogen spillover effects are the main reasons for the enhanced reducibility of the Pd promoted catalyst as revealed by the H2-pulse chemisorptions study. When evaluated using VGO as feed stock, the Co-Pd/γ-Al2O3 displayed superiority both in hydrodesulphurisation (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co/γ-Al2O3 catalyst. The coke deposition on the spent catalyst is also found to be low due to the Pd promotional effects. This is an encouraging result, given that higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity and sustained activity of the catalyst. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the work described here is to evaluate the catalytic performance in the tri-reforming process of Ni/CeO2 and Ni/β-SiC catalysts prepared by using four different nickel salts (nitrate, acetate, chloride and citrate). Metal particles supported over ceria had bigger particle sizes (leading to lower metal-support interactions) than those supported on β-SiC. It was also demonstrated that the metal salt used in the preparation of Ni-based catalysts had a marked influence on the size of the nickel particles. Larger particles with a worse catalytic behaviour were obtained when nickel chloride and nickel citrate were used as the precursors of Ni supported species. Methane consumption rate and H2/CO ratio in the effluents were influenced by the type of support and salt precursor used in the preparation of the catalysts. CO2-TPD proved that catalysts based on ceria as the support presented more basic sites, which was related to a decrease of the H2/CO molar ratio in the effluents coming from the reactor. High methane consumption rate and good catalytic stability were obtained when nickel nitrate and nickel acetate were used to prepare Ni/β-SiC catalysts. The results showed that these latter catalysts can be considered as promising ones for the tri-reforming process. [Copyright &y& Elsevier]

Abstract: A series of copper-ion exchanged titania pillared clays (Cu-Ti-PILC) with different Ti/clay rates were used for the selective catalytic reduction (SCR) of NO by propylene to examine the role of titania pillar in these catalysts. Among the catalysts tested, the sample with Ti/clay=10 provided the best performance with 55.4% yield on N2. XRD coupled with N2 adsorption confirmed that the interlay spacing and surface area of the studied catalysts increased with a rise in Ti/clay rate. The TPR study showed that the Cu2+ amount reached a maximum of 0.69μmol/g-cat at Ti/clay=10. The NO+O2-TPD study indicated that the decomposition amount of the adsorbed nitrate species increased remarkably after the introduction of titania into clay as support. Moreover, the largest decomposition amount was obtained for the sample with Ti/clay=10. It is concluded that the titania pillar provides the Cu-Ti-PILC samples with the increased interlay spacing, surface area and Cu2+ amount formed in the adjacent layers. These features make NO adsorbed more easily by copper species to form the intermediate of nitrate species, which enhances the conversion of NO into N2. [Copyright &y& Elsevier]

Abstract: The catalytic oxidation of toluene has been investigated over binary mixtures of copper, manganese and cerium oxides supported on high surface area γ-Al2O3 in comparison with the corresponding single metal oxide components. Catalysts were synthesized with the impregnation method and were characterized with respect to their specific surface area (BET method), phase composition and mean crystallite size (XRD technique), reducibility (H2-TPR) and adsorption/desorption characteristics toward toluene (TPD followed by TPO). Results obtained using a feed composition consisting of 1000ppm toluene in air showed that the catalytic performance of mixed oxide catalysts can be improved significantly by proper selection of metal oxide (M x O y ) loading and composition. The intrinsic activity of optimized catalysts, measured under differential reaction conditions, was found to be significantly higher compared to that of their single-component counterparts. This has been attributed to the better dispersion of the active M x O y phases, their increased reducibility (reactivity of surface oxygen), and their lower tendency to form coke deposits under reaction conditions. Addition of a second VOC (propane) or water vapor in the feed affected differently the activity of optimized-mixed oxide catalysts. As a general trend, inhibition by the presence of propane was more pronounced for CeO2-containing samples whereas the presence of H2O affected mainly the CuO x -containing catalysts. It is concluded that the VOC oxidation activity of Al2O3-supported mixed oxide catalysts is determined by the reducibility of the dispersed active phases, which may be controlled by proper selection of M x O y nature, loading and composition. [Copyright &y& Elsevier]

commercial Pd/activated carbon catalyst (10%) was treated using several redox processes: reduction with gaseous hydrogen at 140 °C, reduction by negative electrochemical polarization in acidic and basic environments, oxidation with aqueous hydrogen peroxide, and positive electrochemical polarization in acidic and basic environments. To establish the electrochemical reduction/oxidation conditions, the potentials of hydrogen and oxygen evolution at Pd/AC powder electrodes were determined from cyclic voltammetric (CV) measurements. The samples were examined for the presence of palladium oxide phases on dispersed metal particles using XRD, TPR, and TPD. The metal oxide phase disappeared following hydrogen and electrochemical reduction. Oxidative treatment of the commercial catalyst differentiated the palladium oxide layers on the metal particle surface. Changes in the surface chemistry of the Pd/PdO/AC system were confirmed by the electrochemical behavior of electrodes prepared from the carbon samples. [ABSTRACT FROM AUTHOR]

Abstract: Perovskite-like LaBO3 catalysts (B=Co, Mn, Fe), prepared by flame pyrolysis, and doped with Ce, Sr or with small amounts of Pd or Pt were used for the flameless combustion of methane. The effect of the dopants on the reducibility of the B metal ion has been analysed comparatively, trying to correlate this parameter with catalytic activity. The higher the B3+ ion reducibility, the lower was the light off temperature of the reaction. However, the correlation with the temperature of half conversion revealed that a too high reducibility of the catalyst depressed the second step of the Mars–van Krevelen reaction mechanism, i.e. the reoxidation of active site. The quantitative elaboration of the TPR pattern allowed to determine oxygen non-stoichiometry, at least for the LaCoO3 based samples. Furthermore, the available oxygen amount was correlated to catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: This study is a continuation of the research reported recently that showed La and V doubly promoted Rh/SiO2 catalysts to be active and selective for the synthesis of ethanol from syngas. In this work, the effect of Fe on Rh–La–V/SiO2 was examined and the role of each individual promoter was further scrutinized. Several series of promoted Rh/SiO2 catalysts were prepared by incipient wetness and characterized by BET, XRD, TEM, FTIR, TPR, and H2-TPD. The catalytic activity was tested using a fixed-bed differential reactor at 230°C and 1.8atm. It was found that the addition of 0.8wt% Fe, 2.6wt% La, and 1.5wt%V to 1.5wt% Rh/SiO2 resulted in the highest selectivity to ethanol (34.6%) and a moderate activity compared to other promoted catalysts. The investigation based on the catalytic performance and other characterizations of Rh/SiO2 promoted by different promoters suggests that the primary promoting effects of La, V, and Fe are different. The main effects of the addition of different promoters in this study appear to be increasing CO adsorption and insertion for La, decreasing CO adsorption but enhancing CO dissociation and chain growth for V, and decreasing CO adsorption but enhancing hydrogenation for Fe. The synergistic effects of the multiple promoters indicate that the key in catalyst design for ethanol synthesis from syngas is to optimize CO dissociation, hydrogenation, and CO insertion in a balanced way. [Copyright &y& Elsevier]

Formaldehyde (HCHO) emitted from buildings, furnishing materials and consumer products is one of the most dominant volatile organic compounds (VOCs) in an indoor environment. In this work, a Pt/TiO2/Al2O3 catalyst was prepared on an anodic alumite plate and was employed in the catalytic decomposition of formaldehyde at ambient temperature. Firstly, TiO2 was deposited on the anodic alumite plate with electro-deposition technology. Then, platinum was supported on the anodic alumite plate with wet impregnation method. The developed catalyst exhibits good activity towards the decomposition of HCHO at ambient temperature. TPR (temperature programmed reduction) and TPD (temperature programmed desorption) analysis results indicate that oxygen adsorbed on the Pt/TiO2/Al2O3 catalyst can be activated and generated to O:Ptsurface species quickly at ambient temperature. Hence, the developed catalyst experiences the high activity towards the catalytic decomposition of formaldehyde at ambient temperature. Moreover, in accordance with the process requirements, the developed catalyst can be formed into various shapes such as a mesh, plate, fin, serrate etc., because aluminum can be formed into any shapes. The serrate type catalyst was prepared in this work and it also exhibits fine activity towards the decomposition of HCHO. [Copyright &y& Elsevier]

In the present work we have evaluated the oxidation of toluene over different lanthanum perovskites with a general composition of LaNi1− yCo yO3−δ. These catalysts, prepared by a spray pyrolysis method, have been characterised by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O2, reduction in H2 and X-ray absorption spectroscopy were also performed in order to identify the main surface oxygen species and the reducibility of the different perovskites. The catalytic behaviour toward the oxidation of toluene (as a model for VOCs compounds) was evaluated in the range 100–600 °C, detecting a total conversion for all the samples below 400 °C and higher activities for the cobalt-containing perovskites. The catalytic behaviour of these samples is consistent with a suprafacial mechanism, with the α-type oxygen playing an active role in the oxidation reaction. [ABSTRACT FROM AUTHOR]

Abstract: The harmful nature of nitrogen oxides (NO x ) to environmental systems necessitates sensors to detect their presence. One effective means is the use of solid state sensors. These sensors are compact, rugged, and can be inexpensively fashioned, making them a viable option for measuring gas concentration. A non-Nernstian potentiometric sensor can be used to detect low concentrations of NO x gas in multiple regions of oxygen concentration. Understanding the mechanism for this behavior can assist in optimizing the sensor couple for a given application. Previous studies using Temperature Programmed Reaction and Desorption (TPR/TPD), along with IR and XPS analysis, have identified the formation of charge-building compounds that establish voltage on the sensing electrode when exposed to NO x gas. To further elucidate the mechanism, TPR and TPD were performed using isotopically labeled oxygen with simultaneous exposure to NO x . The material was examined under multiple gas conditions of NO x and 16O2/18O2 atmospheres, as well as varied levels of 18O enrichment in the lattice itself. Through these studies, it was determined that the formation of charged surface complexes occurs solely through the use of lattice oxygen (vs. gas phase O2) with adsorbed NO x . [Copyright &y& Elsevier]

Abstract: The effects of alkali additives on the physicochemical and chemisorptive properties of 0.5% Pt/TiO2 have been investigated over catalysts promoted with variable amounts of Na (0–0.2 wt%) or Cs (0–0.68 wt%) with the use of diffuse reflectance infrared spectroscopy (DRIFTS) and temperature-programmed (TPD, TPR) techniques. It has been found that addition of alkalis does not affect adsorption of CO and H2 on the surface of Pt crystallites, indicating the absence of strong electronic-type interactions between these sites and the promoters. However, the presence of alkalis results in the creation and population of new sites with increased electron density, proposed to be located at perimetric sites of Pt crystallites, which are in contact with the support. The adsorption strength of these sites toward CO increases with increasing alkali content, which is evidenced by the development of new, low-frequency IR bands in the ν(CO) region. In contrast, addition of alkali results in weakening of hydrogen adsorption on sites located at the metal/support interface, which is reflected to a significant shift of the corresponding TPD peak toward lower temperatures. Results of CO-TPD experiments indicate that CO adsorbed on Pt interacts with hydroxyl groups associated with the support to yield formate, which decomposes during TPD to CO2 and H2. Thermal decomposition of formate is accomplished at lower temperatures in the presence of alkali. Finally, CO-TPR experiments indicate that the reducibility of TiO2 is enhanced in the presence of alkali, which can be related to the creation of the new sites at the metal/support interface. [Copyright &y& Elsevier]

The promoting effect of Pt and Pd in bimetallic Ni–Pt and Ni–Pd catalysts supported on alumina nano-fibre (Alnf) were tested for the liquid phase reforming of sorbitol to produce hydrogen. The mono- and bimetallic catalysts were studied by different characterisation techniques such as: temperature programmed reduction, oxidation, CO desorption, microcalorimetry, TEM and STEM/EDX. Although bimetallic catalysts have long been the subject of great interest because of their exceptional properties compared to the monometallic catalysts, the reason behind their improved activity is still a question of debate. Experimental evidence showed that the addition of both Pt and Pd—even in a very small fraction—to the Ni catalyst increases its reducibility significantly. The TEM and STEM/EDX analysis confirmed that Pt and Ni are present as alloys in nano-sized rod shaped particles. At the same time it was found that the CO differential heat of adsorption is appreciably lowered in the bimetallic catalysts. This is substantial because reducing the CO binding strength can avoid the poisoning of the active metal sites. As a result, we demonstrate that the rate of H2 formation from sorbitol reforming was 3 to 5 times higher for bimetallic catalysts when compared to the monometallic catalysts. [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]

The role of Ag in simultaneously catalyzing NO reduction and C3H6 oxidation was shown to be strongly dependent on the redox properties of its local environment. Under an atmosphere of 1,000 ppm NO, 3,000 ppm C3H6, and 1% O2 and a GHSV of 30,000 h−1, a perovskite La0.88Ag0.12FeO3 prepared by reactive grinding is active giving a complete NO conversion and 92% C3H6 conversion at 500 °C. These values are much higher than the NO conversion of 55% and C3H6 conversion of 45% obtained over a 3 wt.% Ag/Al2O3 catalyst under the same conditions. Under an excess of oxygen (10% O2) a good SCR performance with a plateau of N2 yield above 97% over a wide temperature window of 350–500 °C along with C3H6 conversion of 90% at 500 °C was observed over Ag/Al2O3, while minor N2 yields (∼10% at 250–350 °C) and high C3H6 conversions (reaching ∼100% at 450 °C) were obtained over La0.88Ag0.12FeO3. Abundant molecular oxygen is desorbed from Ag substituted perovskite after 10% O2 adsorption as verified by O2- temperature programmed desorption (TPD). This reflects the strongly oxidative properties of La0.88Ag0.12FeO3, which lead to a satisfactory NO reduction at 1% O2 due to the ease of nitrate formation but to a significant C3H6 combustion above that value. The formation of nitrate species over the less oxidizing Ag/Al2O3 was accelerated under an excess of oxygen resulting in an excellent lean NO reduction behavior. The redox properties of silver catalysts could be adjusted via mixing perovskite with alumina for an optimal elimination of both NO and C3H6 over the whole range of oxygen concentration between 0 to 10%. [ABSTRACT FROM AUTHOR]

Abstract: A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400°C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4. [Copyright &y& Elsevier]

Abstract: The oxidation states and reducibility of γ-alumina-supported vanadium oxide catalysts with V loadings between 1.7 and 15.7 wt% were studied by means of temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) for fresh as well as used catalysts. As additional experimental techniques, X-ray diffraction (XRD), diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), and temperature-programmed desorption (TPD) were applied. For V loadings up to 6.1 wt%, the surface was found to be covered only by vanadate, while at higher loadings the formation of V2O5 crystallites was observed. The XPS and TPR data showed that under moderate oxidizing conditions, only of V in the vanadate catalysts was in the oxidation state +5, while in the catalysts containing V2O5 crystallites it was about 80%, with the remainder being present as V(IV) in both cases. In the ambient pressure TPR experiments, all catalysts were completely reduced by hydrogen to V(III), although the vanadate catalysts were found to be more easily reducible than those containing V2O5. The V dispersion changed during redox cycles, as they appeared under working conditions. These changes were different for the exposure to ethane or hydrogen, but did not influence the maximum oxidation states. In the catalytic oxidation of ethane used as a model reaction, all catalysts were found to be in their oxidized state under steady-state conditions. Significant catalyst reduction occurred only if the surrounding gas-phase oxygen was completely consumed, leading to the loss of catalytic activity due to the disappearance of V(V) species. A novel structure for γ-alumina-supported vanadia catalysts is proposed on the basis of the experimental data. [Copyright &y& Elsevier]

Abstract: In this work, a series of NiMo/Al2O3 catalyst was prepared using different Al2O3 supports modified by titania (0–9wt%). All modified supports and fresh catalysts were characterized by BET surface area, pore volume and pore diameter measurement, TPR, TPD, XRD, FTIR and Raman spectroscopy analyses. The initial activity of these catalysts were tested in a trickle-bed reactor using three different gas oils such as light gas oil (LGO), blended gas oil (blended: 50% LGO and 50% HGO) and heavy gas oil (HGO), all derived from Athabasca bitumen. Little structural change in alumina was observed with the incorporation of titania. XRD analysis showed the well dispersion of Ni and Mo on the support. Titania in alumina increased the formation of polymolybdenum oxide on the catalyst as evident from TPR and Raman analyses. Weak–intermediate–strong acid sites on the catalyst were observed at all titania concentrations. The Lewis and Bronsted acidity on the catalyst surface increased with the increase in titania concentration from 0 to 9wt%. Nitrogen conversion increased from 57 to 71wt%, from 83 to 93wt% and from 75 to 80wt% for LGO, blended and HGO, respectively and also sulfur conversion of LGO increased from 86 to 92wt% when titania concentration was increased from 0 to 9wt%. For blended and HGO, sulfur conversion was in the range 96–99wt% at all titania concentrations. [Copyright &y& Elsevier]

Abstract: Cu x Ce1−x O2−y mixed oxide catalysts were prepared by different preparation procedures: co-precipitation, the sol–gel peroxide route, and the sol–gel citric acid-assisted route. The resulting solids were investigated by means of XRD, BET, H2 and CO temperature-programmed reduction (TPR), oxidation (TPO) and desorption (TPD) analyses, and N2O pulse selective reaction. It was confirmed that H2 (CO) consumed for complete reduction of well-dispersed and bulk-like CuO phases to Cu0, reduction of surface ceria and H2 (CO) adsorption on the catalyst surface contribute to the total H2 (CO) consumption. Among catalysts examined, the Cu0.15Ce0.85O2−y mixed oxide sample prepared by means of co-precipitation method exhibits the highest activity and stability for water–gas shift (WGS) pulse reaction in the range of employed operating conditions. WGS activity of copper–ceria mixed oxide catalysts is determined by the extent of surface ceria reduction and dispersion of copper species. [Copyright &y& Elsevier]

The aim of this work is to study the effect of Sr substitution on the redox properties and catalytic activity of La2− x Sr x NiO4 ( x = 0.0–1.2) for NO decomposition. Results suggest that the x = 0.6 sample shows the highest activity. The characterization (TPD, TPR, etc.) of samples indicates that the x = 0.6 sample possesses suitable abilities in both oxidation and reduction, which facilitates the proceeding of oxygen desorption and NO adsorption. At temperature below 700°C, the oxygen desorption is difficult, and is the rate-determining step of NO decomposition. With the increase of reaction temperature ( T > 700°C), the oxygen desorption is favorable and, the active adsorption of NO on the active site (NO + V o + Ni2+ → NO−-Ni3+) turns out to be the rate-determining step. The existence of oxygen vacancy is the prerequisite condition for NO decomposition, but its quantity does not relate much to the activity. [ABSTRACT FROM AUTHOR]

Abstract: The promotional effects of trace amount of noble metal (Rh, Pd, Pt) on Co-saponite (high surface area) catalysts were studied by different characterization and evaluation techniques. BET experiments showed that the specific surface area and the pore volume of the noble metal promoted catalysts remained almost unchanged. The reduction/adsorption characteristics of the catalysts were significantly influenced by the presence of the noble metals as revealed by the temperature programmed studies. The main reduction peak was shifted remarkably to the lower temperature due to the noble metal effects. It also increased the amount of cobalt oxide phase reduction. Pulse chemisorptions and H2–TPD kinetics studies revealed that the improved metal dispersion and the lower desorption activation energy have combined effects on the enhanced reducibility of the modified Co-saponite catalysts. The reactivity experiments showed that all of the noble metal promoted catalysts exhibited higher hydrodesulfurization (HDS) and hydrocracking (HC) activities as compared to the unpromoted Co-saponite and among those the Rh promoted catalyst provides superior performances. The coke deposition on the catalyst was also considerably decreased due to the noble metals. These superior activities were attributed to enhanced reducibility and metal dispersion of cobalt due to the influence of the noble metals. [Copyright &y& Elsevier]

Abstract: A fixed bed reactor was used to assess the catalytic incineration of toluene by various transition-metal oxide species supported on γ-Al2O3. CuO/γ-Al2O3 was found to be the most active of seven catalysts investigated. The CuO species, with a Cu content of 5% (wt), was hence used with four different supports (CeO2, γ-Al2O3, TiO2 and V2O5) in order to define the optimal combination. Results of the catalytic incineration of toluene, X-ray diffraction (XRD) analysis, oxygen-temperature programmed desorption (O2-TPD), toluene-temperature programmed desorption (toluene-TPD) and hydrogen-temperature programmed reduction (H2-TPR) showed that CuO/CeO2 was the most active catalyst, followed by CuO/γ-Al2O3. The activity of CuO/CeO2 with respect to the VOC molecule was observed to follow this sequence: toluen> p-xylene>benzene. The addition of water vapor or CO2 significantly inhibited the activity of the CuO/CeO2 and CuO/γ-Al2O3 catalysts. The inhibiting effect of both was reversible for CuO/γ-Al2O3. For CuO/CeO2, the inhibiting effect of CO2 was reversible and even insignificant at a higher temperature (220°C), but the effect of H2O vapor was somewhat irreversible at lower incineration temperatures (⩽220°C). For complete oxidation of toluene, the required reaction temperature increased with gas hourly space velocity (GHSV) and toluene inlet concentration. [Copyright &y& Elsevier]

Abstract: Nanoscale LaMn1−x Cu x O3 perovskites with high specific surface areas were prepared by reactive grinding and characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-temperature programmed reduction (TPR), O2-, NO+O2- and C3H6-temperature programmed desorption (TPD) and NO+O2-temperature programmed surface reduction (TPSR) under C3H6/He flow. The samples were then submitted to activity tests in the selective catalytic reduction (SCR) of NO by C3H6 with or without O2. The catalytic performances over unsubstituted LaMnO3 is observed with maximum N2 yield of 62% and a C3H6 conversion of 80% at 550°C at a space velocity of 50,000h−1 (3000ppm NO, 3000ppm C3H6, 1% O2 in helium). The N2 yield is however significantly improved by Cu incorporation into the lattice, achieving a remarkable N2 yield of 86% at 500°C at 20% Mn substitution by Cu. The content of α-oxygen over lanthanum manganite is enhanced by Cu substitution, but the opposite occurs for excess oxygen. The better performance of Cu-substituted samples is likely to correspond to the facility in the formation of adsorbed nitrate species via the oxidation of NO by α-oxygen in addition to the intrinsic effect of Cu in NO transformation. However, the excessive α-oxygen content observed over LaCo0.8Cu0.2O3 accelerated the unselective hydrocarbon oxidation and suppressed the formation of organo nitrogen compounds, which led to a poor N2 yield with respect to Mn-based perovskites. A mechanism involving the formation of an organic nitrogen intermediate, which further converts into N2, CO2 and H2O via isocyanate, was proposed. The gas phase oxygen acts as a promoter when its concentration is lower than 1000ppm because of the promotion of nitrate formation and organo nitrogen compounds transformation. O2 acts however as an inhibitor when its concentration is higher than 5000ppm due to the heavily unselective combustion of C3H6 by O2, in the reaction of NO and C3H6 over LaMn0.8Cu0.2O3 at 400°C. [Copyright &y& Elsevier]

Abstract: One series of LaCo1−x Cu x O3 perovskites with high specific surface area was prepared by the new method designated as reactive grinding. These solids were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-temperature programmed reduction (TPR), O2-temperature programmed desorption (TPD), NO+O2-TPD, C3H6-TPD, NO+O2-temperature programmed surface reaction (TPSR) under C3H6/He flow as well as catalytic reduction of NO activity tests. The catalytic performance of unsubstituted sample is poor with a maximum conversion to N2 of 19% at 500°C at a space velocity of 55,000h−1 (3000ppm NO, 3000ppm C3H6, 1% O2 in helium) but it is improved by incorporation of Cu into the lattice. A maximal N2 yield of 46% was observed over LaCo0.8Cu0.2O3 under the same conditions. Not only the abundance of α-oxygen but also the mobility of β-oxygen of lanthanum cobaltite was remarkably enhanced by Cu substitution according to O2-TPD and H2-TPR studies. The better performance of Cu-substituted samples is likely to correspond to the essential nature of Cu and facility to form nitrate species in NO transformation conditions. In the absence of O2, the reduction of NO by C3H6 was performed over LaCo0.8Cu0.2O3, leading to a maximal conversion to N2 of 73% accompanied with the appearance of some organo nitrogen compounds (identified as mainly C3H7NO2). Subsequently, a mechanism involving the formation of an organic nitro intermediate, which further converts into N2, CO2 and H2O via isocyanate, was proposed. Gaseous oxygen acts rather as an inhibitor in the reaction of NO and C3H6 over highly oxidative LaCo0.8Cu0.2O3 due to the heavily unselective combustion of C3H6 by O2. [Copyright &y& Elsevier]

Abstract: (A=La, Pr; B=Mn, Co), (A=La, Pr; B=Mn, Co; Co, Pd), and (A=La, Pr; B=Fe, Mn) (, 0.37; ) perovskites were synthesized via malic acid complexation. O2-TPD, O2-TPO, and H2-TPR treatments were carried out to study the oxidation and reduction behavior of the synthesized perovskites. LaCo0.95Pd0.05O3, PrCo0.95Pd0.05O3, and PrCoO3 perovskites had the highest desorption, oxidation, and reduction activity within the studied perovskite series. Powder XRD studies revealed structural transformation of the cubic structure of all synthesized perovskites except LaFe0.57Co0.38Pd0.05O3 in H2/Ar atmosphere when the temperature was over 400 °C. The decomposed structure reverted to the original perovskite structure under oxidizing atmosphere. This reversion was accompanied by increased oxygen desorption activity. It was noticed that the Co and Mn combinations in the B-site of the perovskites structure decreased the thermal stability of the synthesized perovskites. [Copyright &y& Elsevier]

Abstract: A series of Fe-based perovskites with high specific surface area was prepared by a new method, reactive grinding, and characterized by N2 adsorption, XRD, SEM, H2-TPR, TPD of O2, TPD of NO+O2, TPD of C3H6, and TPSR of NO+O2 under C3H6/He flow. These materials were then subjected to activity tests in the selective catalytic reduction of NO by propene. The catalytic performance over LaFeO3 is poor but can be improved significantly by incorporating Cu into its lattice, resulting in N2 yields over LaFe0.8Cu0.2O3 of 81% at 450 °C and 97% at 700 °C with a reactant mixture containing 3000 ppm NO, 3000 ppm C3H6, and 1% O2 in helium at a space velocity of 50,000 h−1. The enhanced NO reduction after Cu substitution is attributed to the easy formation of nitrate species, which have high reactivity toward C3H6. A mechanism was proposed with the formation of nitrate species as the first step and organo nitrogen compounds as important intermediates. Great catalytic performance at low temperature was also achieved over LaFe0.97Pd0.03O3 with a N2 yield of 67% and C3H6 conversion of 68% at 350 °C corresponding to the outstanding redox properties of this catalyst. O2 can act as a promoter to oxidize NO into strongly adsorbed nitrate species, and also can accelerate the transformation of organo nitrogen compounds and isocyanate to get the desired products. In contrast, at higher concentrations O2 has a detrimental effect, leading to consumption of the reducing agent by the complete oxidation of C3H6. [Copyright &y& Elsevier]

Abstract: Temperature-programmed reduction (TPR), oxidation (TPO), and desorption (TPD) studies were performed on three copper–ceria mixed oxide samples having the same nominal composition, Cu0.15Ce0.85O2-y, but prepared in three different ways: by co-precipitation, the sol–gel peroxide route, and the sol–gel citric acid route. The obtained results reveal that despite a drastic initial drop in specific surface area after consecutive redox cycles, the hydrogen consumption remains constant. This is because CuO is highly dispersed over the surface of CeO2 nanocrystallites and remains highly dispersed even after the agglomeration of CeO2 nanocrystallites in a denser secondary structure. The dispersed CuO is reduced to Cu0 during the TPR, forming agglomerated metal particles on the surface of partially reduced CeO2. However, after subsequent temperature-programmed oxidation all the Cu0 is oxidized back into CuO and redispersed over the CeO2 crystallites. [Copyright &y& Elsevier]

Abstract: Development and evaluation of novel catalysts capable of activating CO2 especially in CO2 hydrogenation have been investigated. Several catalysts have been prepared, and characterized by CO2 TPD. Their performance has been evaluated at 300°C and 10bar. All catalysts were active in CO2 hydrogenation reaction with conversions of approximately 15–30% at 24h time on stream. Potassium was found to enhance chain growth and to decrease the formation of methane. Ru promoter did not provide any benefit in activity or selectivity. Zr-promoted catalyst materials exhibited enhanced CO2 adsorption and improved hydrocarbon yields. [Copyright &y& Elsevier]

Temperature-programmed desorption (TPD), temperature-programmed reaction (TPR), temperature-programmed surface reaction (TPSR) and stop flow-TPD techniques as well as FT-IR spectroscopy of pre-adsorbed NH3 and NO were applied to characterize surface sites present on the titania or alumina pillared montmorillonites modified with Cu or Co cations. For all the catalysts the surface concentration of ammonia was at least twice higher than the amount of chemisorbed NO. Formation of surface NO3- anions was found for all the studied samples, however, thermal stability of nitrates and products of their decomposition depended on a kind of pillars introduced to the clay material. Weakly chemisorbed NO molecules are easy replaced by ammonia under reaction conditions. The reactivity of NH3 and NO pre-adsorbed on the titania pillared montmorillonite modified with copper was significantly higher than that measured for the other studied catalysts. The mechanism of DeNOx process over modified pillared clay (PILC) catalysts depends on the reaction temperature. At the lower temperatures conversion of NO from the gas phase by chemisorbed ammonia dominates, while at higher temperatures also surface NO3- anions can react with chemisorbed NH3 molecules. [Copyright &y& Elsevier]

A vanadium–antimony mixed oxide catalyst has been prepared via slurry method. The precursors obtained were calcined in different calcination temperatures, i.e. 673, 773 and 873 K and compared its effect on the physicochemical properties of the oxide. These catalysts were characterised by X-ray diffraction (XRD), FTIR spectroscopy, BET surface area measurements and scanning electron microscopy (SEM). Calcination at high temperature was found to promote the formation of ≈VSbO4 and α-Sb2O4 phase, while the formation of Sb6O13 phase was inhibited. The nature of the oxidizing species in the VSbO catalysts were studied by temperature programmed desorption (TPD) of oxygen and temperature programmed reduction (TPR) of hydrogen. Results revealed that two types of kinetically different oxygen states exist in the catalysts and calcination at high temperature, i.e. 873 K produced a more reducible sample. [Copyright &y& Elsevier]

We report in this paper on the H2-reduction and catalytic behavior of uranyl groups and nano-size crystallites of uranium oxide, co-encapsulated in the pore system of MCM-41 host matrix by employing the two alternative methods of incipient wet impregnation and the exchange of template cations. Based on the results of activity measurements, in situ IR spectroscopy and thermal programmed reduction/desorption studies we conclude that both the uranyl groups and the highly dispersed crystallites of uranium oxide in UOx/MCM samples may independently contribute to the catalytic oxidation of organic molecules, such as methanol, the uranyl groups playing a more important role at lower reaction temperatures. We also observed that the lattice oxygen and the size of uranium oxide crystallites play a vital role, not only in the lowering of reaction onset temperature but also in deciding the nature and the reactivity of transient surface species formed during the decomposition/oxidation of methanol. Furthermore, whereas the larger size U3O8 crystallites helped in the growth of certain oxymethylene (&z.sbnd;OCH2) and polymerized oxymethylene ((&z.sbnd;OCH2)n) species, additional formation of formate-type complexes was observed during the adsorption of methanol on smaller size particles. The formation of these distinct transient species accounted for the lowering of reaction temperature and the enhanced conversion of methanol to CO2, CO and methane as a function of the decrease in uranium oxide crystallite size. [Copyright &y& Elsevier]

This contribution concerns the surface characterisation of the Pd–Ag/Al2O3 catalyst for the selective hydrogenation of acetylene. It is shown that, by means of the temperature programmed reduction (TPR) and temperature programmed desorption (TPD), it is possible to view the surface Pd sites of the catalyst prior to pretreatment with NO or N2O, as well as seeing the effect of Ag addition. It is shown that hydrogen adsorption on the palladium is effectively inhibited by the presence of Ag. The role of pretreatment on the activity and ethylene gain enhancement reported in our previous communication is investigated by employing transmission infrared spectroscopy. Strong adsorption of nitrate or nitrite species on Pd surface was observed from NO and N2O pretreatment, resulting in the blockage of Pd sites responsible for direct ethane formation. Accordingly, higher ethylene gain from NOx-treated catalysts was seen over the untreated catalyst. [Copyright &y& Elsevier]

In this work, a series of nickel–molybdenum, nickel–molybdenum–boron and one nickel–molybdenum–phosphorus catalysts were prepared by incipient wetness impregnation method. Calcination temperature, nickel, molybdenum and boron concentrations in γ-Al2O3 were varied from 450 to 600 °C, 1.8 to 3.1 wt.%, 10.6 to 13.2 wt.% and 0.5 to 1.7 wt.%, respectively. Nickel–molybdenum–phosphorus catalyst was prepared using 2.7 wt.% phosphorus. All catalysts were thoroughly characterized. The catalyst containing 10.6 wt.% Mo and 2.4 wt.% Ni in γ-Al2O3 gave maximum BET area of 211 m2/g. In these catalysts, the molybdenum oxides were present predominantly as polymolybdate and tetrahedral form. Addition of boron to NiMo/Al2O3 caused an increase in weak acid centers, whereas phosphorus caused the formation of acid centers with intermediate strength. Also, addition of boron caused the formation of crystalline B2O3 and MoO3 on the catalyst surface, evident from both XRD and SEM analyses. Whereas addition of phosphorus caused the formation of irregular particle size and agglomeration on the catalyst surface, evident from SEM-EDS analysis. New Lewis and Bro¨nsted acid sites on the catalyst surface were observed from FTIR analysis because of the addition of boron and phosphorus to NiMo/Al2O3. [Copyright &y& Elsevier]

The gas-phase catalytic hydrodechlorination (HDC) of 1,3-dichlorobenzene (1,3-DCB) and hydrodebromination (HDB) of 1,3-dibromobenzene (1,3-DBB) have been studied (T=573 K) over Ni/SiO2. The catalyst was 100% selective in terms of hydrodehalogenation where HDC far exceeded HDB, an effect that is attributed to substituent inductive effects. Catalytic activity declined with time on stream with a concomitant increase in partial dehalogenation (to the mono-haloarene). A precontact of the catalyst with the haloarene resulted in a complete loss of any hydrogenation activity. The pre- and postreaction catalyst samples have been characterized by TPR, TEM, H2 chemisorption, TPD, XRD, and XANES/EXAFS. Appreciable Ni particle growth during catalysis (particularly HDB) has been observed with Ni particle faceting, which is attributed to a halide-induced metal agglomeration/reconstruction; there was no evidence of any bulk nickel halide formation. The possible effect of nickel sintering on hydrodehalogenation was considered by inducing particle growth by thermal means where the resultant sintering did not result in any significant loss of catalytic activity. Catalyst deactivation is linked to a restructuring of the Ni sites during reaction that serves to disrupt H2 chemisorption/desorption dynamics: the used samples exhibit a lower H2 uptake with weaker surface interactions. [Copyright &y& Elsevier]

The effect of addition of alkali metals was investigated on the catalytic activity of cobalt oxide (Co3O4) for the direct decomposition of NO. Although Co3O4 was totally inactive, NO decomposition over Co3O4 was significantly promoted by the addition of alkali metals (Li, Na, K, Rb and Cs). Potassium was found to be the most effective additive. The addition of alkali metals increased not only the surface area but also the specific activity per unit surface area. This suggests that catalytically active sites are created on the Co3O4 surface as a result of interaction with alkali metals. The interface between alkali metals and Co3O4 is clearly essential in the NO decomposition reaction. Characterization of the catalyst using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and desorption of O2 (O2-TPD) revealed that traces of added alkali metals weaken the Co&z.sbnd;O bond strength and promote oxygen desorption from Co3O4, resulting in the formation of cobalt species with a slightly lower valence state. We conclude that these effects, caused by addition of alkali metals, are responsible for the activity enhancement of Co3O4. [Copyright &y& Elsevier]

Li–Fe,Al oxide system has been proposed as the effective catalysts for ethylbenzene (EB) dehydrogenation with CO2 used as an oxidant. All the samples were characterised by chemical and phase analysis. TPR-H2 as well as TPD-NH3 and -CO2 were used to determine redox and acid/base properties of the samples. The best catalytic performance was found for the catalysts containing 15–45 wt.% of Fe. Reduction of iron in such materials occurred at higher temperatures. Moreover, the most active catalysts showed higher fraction of the strong acid/base sites, though their total number was diminished with increasing of Fe content. The activity and selectivity of the catalysts in the standard dehydrogenation of EB in the presence of water steam were much worse than those obtained with CO2 as an oxidant. Using CO2 instead of H2O results in decrease of acidic Brønsted centres concentration formed in the course of oxidative dehydrogenation of EB. [Copyright &y& Elsevier]

Meso-porous Al2O3-supported Ni catalysts exhibited the highest activity, stability and excellent coke-resistance ability for CH4 reforming with CO2 among several oxide-supported Ni catalysts (meso-porous Al2O3 (Yas1-2, Yas3-8), γ-Al2O3, α-Al2O3, SiO2, MgO, La2O3, CeO2 and ZrO2). The properties of deposited carbons depended on the properties of the supports, and on the meso-porous Al2O3-supported Ni catalyst, only the intermediate carbon of the reforming reaction formed. XRD and H2-TPR analysis found that mainly spinel NiAl2O4 formed in meso-porous Al2O3 and γ-Al2O3-supported catalysts, while only NiO was detected in α-Al2O3, SiO2, CeO2, La2O3 and ZrO2 supports. The strong interaction between Ni and meso-porous Al2O3 improved the dispersion of Ni, retarded its sintering and improved the activated adsorption of CO2. The coking reaction via CH4 temperature-programed decomposition indicated that meso-porous Al2O3-supported Ni catalysts were less active for carbon formation by CH4 decomposition than Ni/γ-Al2O3 and Ni/α-Al2O3. [ABSTRACT FROM AUTHOR]

Thermal characterization of Pd/TiO2-Al2O3 catalysts under oxygen or hydrogen atmosphere was investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). Further, the effects of titania on the catalytic property of Pd/Al2O3 towards methane combustion were also examined. A TG–DSC studies revealed that the heat evolved during oxygen adsorption at 25 °C depended on the crystallite diameter. TPR and TPD studies of oxidized samples also demonstrated that the coating of Pd/Al2O3 catalysts with titania can weaken the strength of the Pd&z.sbnd;O bonds. Apparently the effect of coating Pd/Al2O3 catalyst with TiO2 is the improvement of the methane combustion at lower temperatures. This is probably due to the decrease of the strength of the Pd&z.sbnd;O bonds. [Copyright &y& Elsevier]