Partial Oxidation of Methane on Supported Potassium Molybdate

The partial oxidation of methane to formaldehyde was studied on K2MoO4, deposited on various supports, in a fixed-bed continuous-flow reactor at 860–923 K using O2as oxidant. The catalysts were characterized by Raman and XPS spectroscopies. It was found that the composition of molybdates deposited by impregnation depended sensitively on the pH value of the slurry containing the support. At low pH values a significant amount of K2Mo2O7was formed. The product distribution of the oxidation reaction was markedly influenced by the nature of the support. The highest activity was measured for magnesia-supported catalyst. In this case, however, only the complete oxidation of methane occurred. Formaldehyde, in a larger quantity, was produced on silica-supported catalyst containing a greater amount of K2Mo2O7and on K2MoO4/ZSM-5. It was observed that at very low oxygen content, ∼0.1%, the reaction pathway of methane conversion was basically different: in this case the main hydrocarbon products were ethylene, ethane, and benzene. Formaldehyde was not detected. A possible mechanism for the reaction of methane is discussed.