Mechanism investigation and product selectivity control on CO-assisted direct conversion of methane into C1 and C2 oxygenates catalyzed by zeolite-supported Rh

Methane has emerged as an important energy source and chemical feedstock, and thus breakthrough strategies for the direct partial oxidation of CH 4 into small oxygenates have been desired. Here, CO-assisted CH 4 conversion towards C1 and C2 oxygenates over zeolite-supported single-atom Rh catalysts was demonstrated, and the key role of CO, as an indispensable additive, and the reaction mechanism were experimentally investigated. Step-by-step introduction of the reactants resulted in the formation of stoichiometric amounts of product. Replacement of O 2 by H 2 O 2 revealed that gaseous O 2 acts as a true oxidant, and CO enhanced the reaction as a ligand. The critical effect of acid sites in the formation of the C 2 product was also confirmed. Based on these results, a plausible reaction mechanism was proposed. Finally, a small-pore zeolite, SSZ-13, was found to be superior for the selective production of methanol. • CO-assisted partial oxidation of methane was conducted over Rh supported zeolites. • CO worked as role of a reductant, a ligand, and a reactant. • A small pore zeolite catalyst showed superior selectivity towards methanol.