Selective Oxidation of Methane to Methanol at Low Temperatures with Molecular Inspired Solid Catalysts

Methane is an abundant material found world-wide, particularly in form of natural gas. The ability to directly convert methane to methanol in economically satisfactory yields is an important goal of the oil and gas industry. Current technologies or catalytic systems for a direct utilization suffer from low selectivities owing to overoxidation to carbon dioxide. These systems typically involve high temperatures and high energy intermediates like radicals leading to unselective methane conversion. A highly promising alternative is the low-temperature oxidation of methane to methanol via C-H activation mediated by late transition metal complexes. The catalytic system developed by the group of R. Periana involving a molecular Pt(bpym)Cl2 complex and fuming sulfuric acid is considered to be the most active one. Under reaction conditions methane is converted to methylbisulfate wherein hydrogen sulfate is acting as a protecting group against further oxidation. This intermediate can be hydrolyzed in a subsequent step resulting in a high overall selectivity to methanol. An industrial application was ruled out due to drawbacks like e.g. product and catalyst separation [1].