Reaction-induced unsaturated Mo oxycarbides afford highly active CO conversion catalysts.

Sustainable CO conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (MoO) shows a high activity for the reverse water-gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of MoO and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoOC) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO conversion.