Сверхкритические флюиды. Теория и практика
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2019, N3, pp. 45-55

M.Yu. Sinev, Yu.D. Ivakin, D.P. Shashkin, Z.T. Fattakhova, E.A. Ponomareva, Yu.A. Gordienko, V.Yu. Bychkov

Formation of the Phase Composition of Crystalline Silica in the Processing of Amorphous Precursors in Superand Subcritical Aqueous Media

The regularities of the formation of the phase composition of crystalline silica during the processing of amorphous precursors in the aqueous fluid media below and above the critical point of water aimed at the formation of optimal support for the methane oxidative coupling (OCM) catalyst are studied. It is shown that the phase composition of SiO2 and the rate of phase formation strongly depend on the processing conditions (temperature, time, phase state of the aqueous fluid) and the presence of microimpurities in the initial amorphous material. Nevertheless, for different precursors, the phase formation occurs, apparently, through the formation of the same bulk-hydrated structures. Optimization of the processing in the aqueous fluid and subsequent heat treatment made it possible to obtain an OCM catalyst that is significantly more efficient than the one obtained by the conventional procedure using an amorphous support. It was concluded that the catalytic properties are entirely determined by chemical and phase transformations occurring in the active component (Na2WO4—Mn2O3) on the surface of the support, and do not depend on the doping of the latter.

Key words: amorphous silica, crystallization, phase composition, cristobalite, NaWMn/SiO2-catalyst, support, oxidative coupling of methane

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