Theoretical insights into the selective oxidation of methane to methanol on single-atom alloy catalysts

The direct conversion of methane into value-added fuels and chemicals such as methanol has attracted increasing interest, but remains a great challenge due to the chemical inertness of methane. Herein, twelve single-atom alloys (SAAs) were designed for the activation of methane initially, and then the ones owning superior catalytic activity for C-H bond dissociation were screened out for further investigation of selective oxidation of methane to methanol by using density functional theory (DFT) calculations and microkinetic modeling. The results indicate that doping of Ir metal-atom into inert coinage hosts (Ag, Au and Cu) leads to a higher activity for methane dissociation, primarily deriving from the interaction between the C-H bond of methane and the unique projected d-band density of states of the Ir atom. With the introduction of molecular oxygen, three possible reaction mechanisms for selective oxidation of methane to methanol were proposed. Through DFT calculations, the complete reaction networks of three pathways were determined, and microkinetics revealed the changes of surface coverage of reactive species on each SAA under actual reaction conditions. The sophisticated analysis showed oxidation reactions were in favor on Ir-1/Ag surface over all temperature ranges while favorable for Ir-1/Au and Ir-1/Cu within a limited interval, indicating that Ir-1/Ag SAA is the most efficient for selective oxidation of methane to methanol. The insights in this work provide important guidelines for the design of highly active and efficient catalysts for direct conversion of methane in future.