Selective, Room-Temperature Transformation of Methane to C1 Oxygenates by Deep UV Photolysis over Zeolites

摘要

Methane can directly be transformed into liquid C_I oxygenated products with selectivities above 95% at 13% conversion by deep UV photocatalysis, in the presence of H_2O and air. Pure silica zeolites, and more specifically, beta zeolite with a large number of internal silanol groups is active and selective, while amorphous silica with no micropores is much less efficient. Irradiation produces the homolytic cleavage of surface hydroxyl groups, leading to silyloxyl radicals that will generate methyl radicals from methane. The selectivity arises from the occurrence of the reaction in a confined space restricting the mobility of the radical intermediates that will be mostly attached to the solid surface. Energy consumption of the process is in the order of 7.2 Gcal × mol~(-1) that compares very favorably with the energy required for transforming methane to synthesis gas (15.96 Gcal × mol~(-1)).