AUTHOR KEYWORDS: Catalytic performance; Fischer–Tropsch synthesis; Inorganic precursor; Metal oxide promoter; Mixed metal catalyst INDEX KEYWORDS: Alumina; Aluminum oxide; Chemical reactors; Cobalt; Cobalt deposits; Crystal structure; Decomposition; Impregnation; Scanning electron microscopy; Silica; Single crystals; X ray diffraction, Catalytic performance; Inorganic precursor; Metal oxides; Mixed-metals; Tropsch synthesis, Catalyst activity PUBLISHER: Springer New York LLC
INDEX KEYWORDS: Cobalt; Ground state; Nanoparticles; Spin dynamics; X ray absorption spectroscopy, Co oxidation; Cobalt doping; High spin state; Oxidation state; Pre-edge features; Soft x-ray absorption spectroscopies; Spin evolution; Spin state evolution, Manganese PUBLISHER: American Chemical Society
Oxidative coupling of methane has been studied over (Mn+A+W)/SiO2 catalysts in a continuous-flow micro reactor, where A represents an alkali ion of Li, Na, K or Cs having different weight percents. The main aim of this study is to find the role of alkali ions in interaction between Mn and W species with SiO2 to make a proper structure for catalyzing oxidative coupling of methane (OCM) reaction. The catalysts were characterized by XRD, SEM, FTIR, TPR and also the electrical conductivity was measured in air and under OCM reaction. It was found that for the formation of crystallized catalyst, the amount of alkali ion should be such that the catalyst containing tungsten transforms into A2WO4. Using a smaller amount of alkali ions does not result in crystalline catalyst by calcination under the same condition of temperature and atmosphere. However, under the OCM reaction condition the catalyst gradually turns into a crystalline structure and its catalytic performance, i.e. conversion and selectivity, for the OCM reaction is almost similar to the (Mn+A2WO4)/SiO2 catalyst. The transformation of the catalyst containing alkali ions from amorphous to crystalline one indicates a kind of structural flexibility of the catalyst under OCM atmosphere. The structural flexibility of the catalyst under the OCM reaction is considered to be the main chemical role of the alkali ions.
AUTHOR KEYWORDS: Alkali ion; Electrical conductivity; Manganes oxide; Oxidative coupling of methane (OCM); TPR PUBLISHER: Shiraz University
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