Catalytic Combustion of Methane over Cobalt–Magnesium Oxide Solid Solution Catalysts

A series of cobalt–magnesium oxide solid solution catalysts (CoMgO) have been prepared using urea combustion methods, and characterised by X-ray diffraction (XRD) and laser Raman (LR). The catalytic activities for methane combustion have been tested in a continuous-flow microreactor. The Co content has a significant effect on the activity of the cobalt–magnesium oxide solid solution catalysts. The catalysts containing 5 and 10% Co have the lowest light-off temperature in methane combustion. In the preparation of cobalt–magnesium oxide solid solution catalysts, higher urea to metal ratio favors the formation of the catalysts with smaller crystal particles and leads to a better catalytic performance for methane combustion. Addition of lanthanum nitrate to the solution of Co and Mg nitrate depressed the formation of the cobalt–magnesium oxide solid solution and decreased the activity of the catalysts for methane combustion. The cobalt–magnesium oxide solid solution catalysts are very stable when the calcination or reaction temperature is no more than 900°C. However, the catalytic activity decreases rapidly after high temperature (>1000°C) calcination, possibly due to sintering of the catalyst and thus decrease of the surface area.     

Oligomer-Rich Fraction from Polydisperse Sample of Poly(bis(β-phenoxyethoxy)phosphazene)

Poly[bis(-phenoxyethoxy)phosphazene] [PBPEP] had been shown in our previous paper to be a very useful polymer for investigating the crystallization mechanism of polymers, as the crystallization rate of PBPEP is extraordinarily small when isothermally crystallized from the melt. The crystallization of the low molecular weight oligomers of PBPEP was first studied in comparison to the high molecular weight polymers. The oligomer-rich fraction was obtained by fractionation of the as-polymerized sample, which had a broad molecular weight distribution. The fractions thus obtained were characterized by solution viscometry and size exclusion chromatography. The melting temperature and the growth rate of the spherulite from the melt were investigated by differential scanning calorimetry and optical microscopy. The growth rate was one or two orders of magnitude smaller in the oligomer-rich fraction than in the other high molecular weight fractions. A collapsed spherulite appeared in the oligomer-rich fraction at high crystallization temperatures. It is speculated that in the oligomer-rich fraction there is an excess free energy due to defects in the crystal phase. This defect is considerably larger in the oligomer-rich fraction than in the other fractions because a large quantity of short length chains is present.     

Kinetics of Ortho-nitrochlorobenzene Hydrogenation on Platinum/Carbon Catalyst

The kinetics of catalytic hydrogenation of ortho-nitrochlorobenzene to 2,2'-dichloroazoxybenzene on platinum/carbon catalyst is investigated in a slurry reactor with the temperature range of 313-343 K, and ortho-chloroaniline is formed as a byproduct. Models based on Rideal-Eley and Langmuir-Hinshelwood mechanism have been proposed based on the rate data and the kinetic regime. The former model can be used to fit the experimental data better. Reaction controlling steps are physical adsorption of hydrogen and adsorbed ortho-nitrochlorobenzene reacted on the surface of catalyst.     

Ozone Decomposition Reaction over α-Alumina-Supported Silver Catalyst: Comparative Study of Catalytic Surface Reactivity

An alumina-supported silver composite system has been investigated in the reaction of heterogeneous catalytic ozone decomposition. Perlite loaded with silver and silver modified zeolites have also been tested as catalysts for gas phase conversion of ozone to molecular oxygen. The catalysts have been activated by calcination and the changes occurring on the catalytic surface as a result of the reaction have been characterized in details using XPS. The SEM analysis has revealеd the role of surface morphology in the process of ozone decomposition on the surface of Ag/α-Al₂O₃ catalyst. A catalytic cycle is proposed that supports the hypothesis about the important role of the peroxide species as intermediates participating in the process and catalyzing the complete ozone conversion into molecular oxygen. It has been found out that the maximum conversion degree, achieved with the alumina-supported silver system, is up to 90%.     

Investigation of N-(Hydroxylethyl)pyrrolidone Dehydration over REO_x-doped Nano-ZrO_2 Catalyst

1 INTRODUCTION Poly-N-vinyl-pyrrolidone (PVP) is a non-ionic water-soluble chemical, which is widely used in many industrial fields such as pharmaceutical, cosmetic, foodstuff, electronics, printing, paper-making, deter- gent and adhesive etc.[1]. Traditional acetylene process is dangerous because of using acetylene under high temperature and pressure[2] Nowadays, it is usually produced by polymerization of N-vinyl-pyrrolidone (NVP), which is produced by cata- lytic dehydration of N-(h…     

Catalytic dehydration of methanol to dimethyl ether over modified γ-Al2O3 catalyst

A γ-Al₂O₃ catalyst was modified with metal oxide (Nb₂O₅) in order to improve its activity and stability for dimethyl ether (DME) synthesis from methanol. A series of modified γ-Al₂O₃ catalysts were prepared with Nb₂O₅ and characterized by X-ray diffraction and temperature programmed desorption of ammonia. Results showed that the γ-Al₂O₃ catalyst containing 10 wt.% of Nb₂O₅ exhibited the highest surface area among the modified ones. The number of acid sites of the modified catalysts was increased by the Nb₂O₅ modification. In the chemical reaction of DME synthesis, it was found that the Nb₂O₅ modified γ-Al₂O₃ catalyst exhibited a higher activity in the low temperature region (240 °C-260 °C) and a higher activity than did the untreated γ-Al₂O₃ catalyst.     

Catalytic combustion of chlorobenzene over Mn–Ce/Al2O3 catalyst promoted by Mg

Mn–Ce–Mg/Al₂O₃ catalyst prepared by a wet impregnation method was investigated in the catalytic combustion of chlorobenzene. The addition of Mg decreased the interaction of Mn and Ce species with Al₂O₃ and promotes the dispersion of Mn and Ce species and the formation of Ce–Mn–O solid solution. High activity, good selectivity and desired stability of Mn–Ce–Mg/Al₂O₃ catalyst were observed.     

Kinetics of Acetylene Hydrochlorination over Bimetallic Au–Cu/C Catalyst

A kinetic model of the acetylene hydrochlorination over the bimetallic Au–Cu/C catalyst was obtained on the basis of kinetic data. DFT theoretical calculation and the kinetic model indicated the reaction probably proceeds via the Eley-Rideal mechanism in which gas phase HCl reacts with the adsorbed C₂H₂ to produce vinyl chloride. Reaction conditions were optimized according to kinetics analyses. Under the optimized reaction conditions obtained, the bimetallic Au–Cu/C showed excellent performances with more than 99.5% conversion and selectivity and did not deactivate in 200 h on stream.     

Kinetics of the Steady-State Acetylene Oxidation by Oxygen over a Pt/Rh/CeO2/γ-Al2O3 Three-Way Catalyst

The steady-state kinetics of acetylene oxidation has been studied in the framework of automotive exhaust gas catalysis over a commercially available three-way catalyst. Experiments under cold-start conditions have been carried out in a laboratory fixed-bed reactor, which can adequately be described by the developed elementary step model and rate parameters.     

Carbon Deposition and Catalytic Deactivation during CO2 Reforming of CH4 over Co/γ-Al2O3 Catalysts

The reaction behavior and carbon deposition during the CO₂/CH₄ reforming reaction have been investigated over the γ-Al₂O₃-supported Co catalysts as a function of Co loading (between 2 and 20 wt%) and calcination temperature (T_c=500 or 1000°C). It was found that the stability of Co/γ-Al₂O₃ catalysts was strongly dependent on the Co loading and calcination temperature. For some loadings (6 wt% for T_c=500°C and 9 wt% for T_c=1000°C), stable activities have been achieved. However, over the catalysts with high Co loadings (>12 wt%), notable amounts of carbon were accumulated during reforming, and deactivation was observed. Moreover, severe deactivation was also noted over the 2 wt% catalysts, both when carbon deposition occurred (T_c=500°C) or was absent (T_c=1000°C). In the latter case, the oxidation of the metallic sites was responsible for the deactivation. Hence, there are two different deactivation mechanisms, namely, carbon deposition and oxidation of metallic sites. The activities were stable when a balance between carbon formation and its oxidation could be achieved.     

Spherical clusters of β-Ni(OH)2 nanosheets supported on nickel foam for nickel metal hydride battery

Spherical clusters of Ni(OH)₂ nanosheets are directly grown on skeletons of nickel foam via a facile template-free spontaneous growth method. The obtained electrode (β-Ni(OH)₂/Ni-foam) is characterized by X-ray diffractometry, scanning and transmission electron microscopy and thermal analysis. Results show that Ni(OH)₂ has a β-phase structure and presents on the nickel foam skeleton mostly as spherical clusters with a diameter of ∼10 μm. The spheres are composed of nanosheets with thickness of ∼60 nm, width of ∼230 nm and length up to ∼2 μm, and the nanosheets are assembled by nanoparticles with diameter of ∼20 nm. The electrochemical performance of the β-Ni(OH)₂/Ni-foam electrode is evaluated by cyclic voltammetry and galvanostatic charge–discharge tests. The difference between the oxygen evolution reaction onset potential and the anodic peak potential for this electrode (∼100 mV) is larger than that for β-Ni(OH)₂ nanosheets and nanotubes powder electrode (∼65–77 mV) and much larger than that for commercial spherical β-Ni(OH)₂ powder electrode (∼25–47 mV), indicating that the β-Ni(OH)₂/Ni-foam electrode can be fully charged. The specific discharge capacity of β-Ni(OH)₂ in the β-Ni(OH)₂/Ni-foam electrode reaches 275 mAh g⁻¹, which is close to the theoretical value, lower than that of β-Ni(OH)₂ nanotubes (315 mAh g⁻¹), but higher than that of nanosheets (219.5 mAh g⁻¹), commercial micrometer grade spherical powders (265 mAh g⁻¹) and microtubes (232.4 mAh g⁻¹).     

Monte Carlo Simulation of Kinetics of Ammonia Oxidative Decomposition over the Commercial Propylene Ammoxidation Catalyst (Mo-Bi)

Monte Carlo method is applied to investigate the kinetics of ammonia oxidative decomposition over the commercial propylene ammoxidation catalyst(Mo-Bi). The simulation is quite in agreement with experimental results. Monte Carlo simulation proves that the process of ammonia oxidation decomposition is a two-step reaction.     

Kinetic study of propane dehydrogenation and side reactions over Pt–Sn/Al2O3 catalyst

The kinetics of reactions involved in dehydrogenation of propane to propylene over Pt–Sn/Al₂O₃ catalyst was studied. The simultaneous deactivation of individual dehydrogenation, hydrogenolysis and cracking sites was also studied. A model was developed to obtain the transient conversion of propane, product selectivity and catalytic site activity. The dehydrogenation reaction was considered as the main reaction governing propane and hydrogen concentrations along the reactor. Catalytic test runs were performed in a fixed-bed quartz reactor. The kinetic expressions developed for the main and side reactions were verified by integral and a combination of integral–differential analysis of reactor data, respectively, and the kinetic parameters were obtained. The deactivation of the active sites for the three reactions was found to follow a first-order independent decay law. The rate constants of deactivation were found to decrease in the order of dehydrogenation, hydrogenolysis and cracking. Noncatalytic thermal cracking was found to be comparable to the catalytic route resulting in a very low apparent deactivation rate constant for cracking reaction.     

Catalytic oxidation of gas-phase mercury over Co/TiO2 catalysts prepared by sol–gel method

Co/TiO₂ catalysts prepared by sol–gel method were studied for gas-phase mercury oxidation in this paper. Experimental results revealed that the optimal loading of Co was 7.5%, which yielded more than 90% oxidation efficiency within the temperature range of 120–330 °C. The high activity was mainly attributed to the enrichment of well dispersed Co₃O₄. We also found that oxygen performed a key role in mercury oxidation process, while HCl could corrode the oxidized mercury and release it to gas phase. Thereafter, a modified Mars–Maessen mechanism was proposed and the possible simultaneous oxidization of NO and mercury was studied.     

Effect of V2O5 Loading on Propane Combustion over Pt/V2O5–Al2O3 Catalysts

Propane combustion was studied on Pt(0.4%)/V₂O₅–Al₂O₃ catalysts containing up to 20% V₂O₅. The density, strength and nature of surface acid sites were determined by TPD of NH₃ and FTIR spectra of adsorbed pyridine. The sample acidity increased with the vanadium content, essentially because the addition of vanadium oxide generated Brønsted acid sites. The Pt dispersion as determined by H₂ chemisorption increased with increasing V₂O₅ loading. The sample activity for propane combustion was evaluated through both conversion versus temperature (light-off curves) and kinetically-controlled conversion versus time catalytic tests. The propane combustion turnover rate on Pt/V₂O₅–Al₂O₃ increased with the amount of vanadium, probably because the intrinsic Pt oxidation activity increases with the sample acidity.     

Oxidative Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide over Fe2O3/TiO2–ZrO2 Catalyst: Influence of Chloride

This study was undertaken to know the influence of chloride ions in TiO₂–ZrO₂ mixed oxide and to explore chloride containing Fe₂O₃/TiO₂–ZrO₂ catalyst for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The TiO₂–ZrO₂ mixed oxide was synthesized by a co-precipitation method. Over the calcined support, a nominal 15 wt.% Fe₂O₃ was deposited by a wet impregnation method. The prepared catalysts were characterized using X-ray diffraction, temperature programmed desorption of NH₃ and CO₂, scanning electron microscopy and BET surface area methods. The catalytic activity measurements were made in a fixed-bed microreactor under normal atmospheric pressure. Characterization studies reveal that chloride ions exhibit a strong influence on the physicochemical and catalytic properties of the titania–zirconia composite oxides. The impregnated iron oxide was found to be in a highly dispersed form over the TiO₂–ZrO₂ support and influenced greatly on its acid–base properties. The chloride containing Fe₂O₃/TiO₂–ZrO₂ catalyst exhibited better activity and selectivity. The order of activity on various samples was found to be Fe₂O₃/TiO₂–ZrO₂ (chloride) > TiO₂–ZrO₂ (chloride) > TiO₂–ZrO₂.