Elements Of X Ray Diffraction

Thermal decomposition of ammonium perchlorate

(1990). Conversion of Methane by Oxidative Coupling. Catalysis Reviews: Vol. 32, No. 3, pp. 163-227.

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Conversion of Methane by Oxidative Coupling

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Analysis Synthesis And Design Of Chemical Processes

Natural gas is an abundant resource in various parts of the world. Methane is the major component of natural gas, often comprising over 90 mol% of the hydrocarbon fraction of the gas. Methane itself is primarily used as a fuel, while the nonmethane components can be separated and used as feedstocks for the production of chemicals or liquid fuels. In many cases, however, natural gas reserves are found in locations distant from their place of utilization. Since it is not generally economical to transport liquefied natural gas, efficient methods are needed to convert methane into transportable liquid products. A possible route is oxidative dimerization of methane followed by oligomer-ization of the C2 products.

Oxidative Coupling of Methane to Higher Hydrocarbons

The thermal decomposition of ammonium chromate (AC) in dynamic air, CO2 and N2 and in static atmospheres and in the presence of MoO3, V2O5, Fe2O3, CuO, MnO2 and Nd2O3 additives was studied by means of TG, DTA, IR spectroscopy and electrical conductivity measurements. It was found that AC decomposes in four stages, forming unstable intermediates which produce Cr2O3 as a final product. The presence of the different atmospheres and the oxide additives affected the decompositions of these intermediates and the oxidation state of the chromium ions. Finally, the mechanisms associated with the different decomposition stages are discussed.

Effects of various atmospheres and some metal oxide additives on the thermal decomposition on ammonium chromate

The contribution of lattice oxygen atoms of Sm2O3 catalysts in the oxidative coupling of methane has been examined by comparing the distributions of products and reactivities of the catalysts observed in the presence and absence of oxygen in the gas phase. The products of the reaction of CH4 with lattice oxygen atoms (without oxygen in the gas phase) at 873–998 K were H2, CO, C2H4 and H2O without a trace of C2H6. The main products H2 and CO were speculated to be produced from HCHO as the reaction intermediate. The amount of C2H4 did not depend on the reaction temperatures. Direct formation of C2H4 from CH4 suggested the formation of CH2=groups on special active sites on the surface. In contrast, the reation of CH4 with the adsorbed oxygens (in the presence of gaseous oxygen) gave C2H6, C2H4, CO2, CO and H2O. The selectivity to C2-compounds (C2H6 + C2H4) was remarkably high compared to that observed for the lattice oxygen atoms. Thus the adsorbed oxygens are better oxidants for oxidative coupling of CH4. The main products observed in the reactions of C2H6 and C2H4 with lattice oxygen atoms were CO, H2 and CH4. CO2 was not produced at temperatures below 973 K. In contrast, the reactions with adsorbed oxygens in the presence of gaseous oxygen produced only CO2, CO and H2O without any H2 or CH4. The reactivity of the adsorbed oxygen for converting CH4 was more than three orders of magnitude greater than that of the lattice oxygen atoms. Thus, oxidative coupling of CH4 in the presence of gaseous oxygen can be ascribed to the role of adsorbed oxygens.

Role of Lattice Oxygen Atoms in Partial Oxidations of Methane, Ethane and Ethylene Over Samarium Oxides.

Fe3O4@CMC-Cu magnetic nanocomposite as an efficient catalyst for reduction of toxic pollutants in water

Decomposition of hydrogen peroxide in aqueous solution was used for testing the effect of gamma radiation on the catalytic activity of CoxFe3−xO4, with O≤x≤3.0. The activity variation was interpreted in terms of the catalysts electronic structure. The presence of Co2+ on octahedral sites is superior to Fe2+ in the catalytic process. However, γ-irradiation can produce a considerable effect on the catalytic activity due to its influence on the active site concentration and cation distribution.

Gamma‐Irradiation Effect on the Catalytic Behavior of Binary Oxide Catalysts.

Selective production of dimethyl ether (DME), as a second-generation biofuel, under mild green conditions is still a challenge. Herein, FexMn1-xWO4 wolframite-type materials were proposed for the first time as efficient, selective, and stable catalysts towards methanol dehydration into DME. A simple one-step co-precipitation approach was used to fabricate the nanocomposites, and their catalytic performances were evaluated in comparison to earlier studies and to the commercial γ-Al2O3 in terms of activity. The catalysts’ structure, morphology, and porosity were identified by XRD, XPS, FTIR, TEM, and N2-sorption analyses. Results of XRD and XPS confirmed the successful synthesis of FexMn1-xWO4 catalysts. Acidity of these nanocomposites were greatly influenced with the variation in x-value, calcination temperature, and doping with SO42−. The Brønsted characters of the acid sites and their weak and medium strength were investigated from PY-FTIR, chemisorption of basic probes and pyridine-TPD. The variation of the catalytic activities of these nanocomposites was strongly correlated to the variation in the catalyst acidity. The catalytic activity results indicated that Fe0.5Mn0.5WO4 catalyst calcined at 500 °C and modified with 5 wt.% of SO42- is the most effective nanocomposite with conversion values of 86 and 90% at reaction temperatures of 250 and 275 °C, respectively and all of 100% DME selectivity. The remarkable enhancement in the catalytic activity due to the doping with SO42- is attributed to the inductive effect of S = O group created on the catalyst surface. This nanocomposite could be regenerated many times with nearly the same efficiency and selectivity. Moreover, it offered a long-term stability (∼120 h) towards DME production. 

Abd El-Aziz A. Said

Papers

Effects of various atmospheres and some metal oxide additives on the thermal decomposition on ammonium chromate

Role of Lattice Oxygen Atoms in Partial Oxidations of Methane, Ethane and Ethylene Over Samarium Oxides.

Fe3O4@CMC-Cu magnetic nanocomposite as an efficient catalyst for reduction of toxic pollutants in water

Gamma‐Irradiation Effect on the Catalytic Behavior of Binary Oxide Catalysts.

The catalytic performance of FexMn1-xWO4 as novel wolframite-type nanocatalysts for the selective dehydration of methanol into dimethyl ether