Mechanistic insights into benzene oxidation over CuMn2O4 catalyst

Abstract

The spinel-type CuMn2O4 catalyst exhibits good catalytic activity towards benzene oxidation, but the catalytic oxidation mechanism is not established. Theoretical calculations were implemented to unearth the reaction mechanism of benzene catalytic oxidation over CuMn2O4 catalyst through density functional theory (DFT). The results indicate that benzene adsorption on both Cu-terminated and Mn-terminated surfaces are controlled by the chemisorption mechanism. The Cu-terminated surface is more active for benzene adsorption than the Mn-terminated surface. Cu atom is regarded as the primary active site. During benzene catalytic oxidation, benzene firstly undergoes dehydrooxidation reaction to generate phenoxy group (C6H6* → C6H5* → C6H5O*). Two reaction channels are responsible for the ring-opening and oxidation reactions of phenoxy group, including benzoquinone- and cyclopentadienyl-dominated channels. In the benzoquinone-dominated channel, C6H4O2* is produced from phenoxy dehydrogenation and oxidation, and then decomposes into acetylene via the ring-opening reaction (C6H4O2* → C4H2O2* → C4H2O4* → C2H2*). Compared with the benzoquinone-dominated channel, the cyclopentadienyl-dominated channel is dominant for phenoxy group oxidation. Phenoxy group decomposes to generate cyclopentadienyl. C5H5* is dehydrogenated and oxidized to form cyclopentadienone. Finally, C5H4O* is oxidized to form carbon dioxide through a nine-step reaction pathway. The ring-opening reaction (C5H4O* → C3H2O*) has the highest energy barrier of 283.45 kJ/mol, and is identified as the rate-determining step of benzene catalytic oxidation.