Bioinspired Oxidation of Methane: From Academic Models of Methane Monooxygenases to Direct Conversion of Methane to Methanol

A study of methane monooxygenase (MMO) mechanisms in enzymology and the problem of selective methane oxidation in chemistry are two parallel related fundamental directions that attract the attention of many scientists all over the world. For a long time, selective methane oxidation is considered as the strongest challenge in catalysis from the standpoint of practical applications. In spite of great efforts, no process acceptable for use in industry has yet been found for the direct conversion of methane to methanol and this problem still remains highly relevant. There are high expectations connected with MMOs, which are capable of transforming methane into methanol with a selectivity of up to 100% under natural environmental conditions. This review discusses the results of long and dramatic studies that have made it possible to elucidate structures of active sites and puzzling mechanisms of the two most studied MMOs: iron-containing soluble methane monooxygenase (sMMO) and copper-containing membrane-bound particulate methane monooxygenase (pMMO). Main attention is paid to various bioinspired models of these MMOs, both homogeneous and heterogeneous ones. The recent improvement of heterogeneous chemical analogues of MMOs, which effectively catalyze the direct selective oxidation of methane to methanol by hydrogen peroxide or O-2, undoubtedly opens up new horizons for the chemical industry and has been actively discussed in recent years with regard to adaptation to modern technological requirements.