Study of the feasibility of obtaining the compound Bi2Si3O9 via annealing from the amorphous state and investigation of the catalytic properties of bismuth germanate and silicate Bi2O3—GeO2 and Bi2O3—SiO2 (25: 75, mol.%) in the oxidative dimerization of methane

Abstract

Partially crystallized amorphous samples with the compositions Bi₂O₃—GeO₂ and Bi₂O₃—SiO₂ (25: 75, mol.%) were obtained in this study; their catalytic properties in the reaction of oxidative dimerization of methane (ODM) were investigated. The annealing of bismuth silicate at various temperatures and holding times did not result in the formation of a compound with the benitoite structure (Bi₂Si₃O₉). The analysis of the phase composition and microstructure of the obtained samples revealed the presence of compounds such as Bi₂SiO₅, Bi₄Si₃O₁₂, Bi₁₂SiO₂₀, and SiO₂ in three different modifications (cristobalite, tridymite, and quartz), depending on the annealing conditions. The annealing of bismuth germanate leads to the rapid and reliable formation of a compound with the benitoite structure (Bi₂Ge₃O₉). Monolithic samples of bismuth germanate and silicate exhibit low activity in the ODM reaction. The bismuth germanate sample exhibits exclusively deep oxidation of CH₄. In contrast, in the presence of the bismuth silicate sample the ODM reaction proceeds with a selectivity of up to 71% for the total C₂ hydrocarbons at 820 °C.