Preparation and effect of Mo-V-Cr-Bi-Si oxide catalysts on controlled oxidation of methane to methanol and formaldehyde

Mo-Cr-V-Bi-Si multi-component oxide catalysts were synthesized by three different coprecipitation methods and used in the controlled oxidation of methane to methanol and formaldehyde. It was shown that Mo content in Mo-V-Cr-Bi-Si oxides and the performance of these catalysts were strongly influenced by different coprecipitation methods. The highest methanol and formaldehyde selectivity of 80.2% could be achieved at a methane conversion of 10 % for the catalyst prepared by a particular method. The results of XRD indicated that the crystalline phase structures of catalysts were sensitive to Mo, V and Bi loadings. Bi(III) could combine with V(V) and Mo(VI) to form BiVO₄ and γ-Bi₂MoO₆, whereas Cr seemed to form a single Cr₂O₂ crystalline phase in the presence of Bi. The effects of Mo and Cr loading on controlled methane oxidation were also investigated. Mo(VI) oxide appears to favor the formation of partial oxidation products and Cr(III) oxide seems to enhance the conversion of methane.