Unimolecular and bimolecular reactions of organic intermediates on metal oxide catalysts: an update

The surface chemistry of metal oxides and their catalytic roles in activating and transforming oxygenate and hydrocarbon feedstocks is rich. This review provides an update on mechanisms of such reactions, as well as modern promising concepts for selective catalytic conversions on metal oxide catalysts, including those occurring in molecularly confining reaction environments. Case examples built upon electronic structure modeling of transition states are emphasized, as well as on contemporary ideas to enable low free energies of activation. The chemistry covered is broad, and includes examples of Lewis acid–base chemistry, Brønsted acid–base chemistry, and oxygen vacancy-based redox chemistry. The reactions covered include C-H activation of alkanes, C–C coupling of aldehydes, C–C coupling of carboxylic acids (ketonization), dehydration of alcohols over confined sites, C–C bond formation between aldehydes over confined sites, and C–C bond formation between carboxylic acids over confined sites. For each reaction type, molecular-level knowledge of elementary reaction steps is critically reviewed.