Methane selective oxidation to methanol by metal-exchanged zeolites: A review of active sites and their reactivity

Over the past decade, zeolites (microporous aluminosilicate minerals) have been gaining significant popularity due to their broad applications in catalysis including the dream reaction of selective oxidation (hydroxylation) of methane to methanol at low temperature. In this review, we outline the current main challenges in the development of Fe-, Cu-, Co- and Ni-exchanged zeolites for methane hydroxylation and summarize key findings that have been reported in both spectroscopy and computational studies. Also, using density functional theory (DFT) calculations, we calculate energy diagrams of methane hydroxylation over various structures of metal-oxo active sites in zeolites and discuss some key points that can be improved for achieving higher reactivity. Short outlooks on the future research opportunities are also discussed.