Partial Oxidation of Methane on Silica-Supported Different Alkali Metal Molybdates

The partial oxidation of methane was studied on silica-supported alkali metal molybdate catalysts in a fixed-bed continuous-flow reactor at 860–923 K using O2 as oxidant. The catalysts were characterized by Raman and XP spectroscopy. It was found that the surface structure and composition of molybdates deposited by impregnation depend on the cation. From lithium to potassium monomolybdate was formed with the original structure, Rb2MoO4/SiO2 contains distorted [MoO4] tetrahedra, and in the case of cesium dimolybdate was obtained. The main products of the oxidation reaction were formaldehyde, ethane, CO, and CO2. The activity of the catalysts and the product distribution were markedly influenced by the structure of the catalysts. The highest catalytic activity was measured on Rb2MoO4/SiO2. Formaldehyde in a larger quantity was produced on MoO3/SiO2, but when the rate was related to the amount of surface molybdenum atoms Rb2MoO4/SiO2 had the highest activity. A possible mechanism for the oxidation of methane is discussed.