Key words: amorphous silica, crystallization, phase composition, cristobalite, NaWMn/SiO2-catalyst, support, oxidative coupling of methane
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.
doi:10.1134/S1990793120070167