M supported on Al-defective Al 2- δ O 3 (M = Fe, Co, Ni, Cu, Ag, Au) as catalysts for acetylene semi-hydrogenation: a theoretical perspective.

Semi-hydrogenation of acetylene is of great importance for both industry and academia. High prices and limited supplements of noble metals leave room for developing base metal catalysts. Experiments revealed the atomically dispersed Cu supported by Al 2 O 3 with excellent long-term stability and high ethylene selectivity, but the physical nature has rarely been investigated theoretically. DFT calculations and microkinetic modeling revealed that the surface OH species could stabilize Cu 1 /Al 2- δ O 3 and enhance its catalytic performance. The selectivity of ethylene formation decreases with increasing copper clusters ( e.g. , Cu 1 /Al 2- δ O 3 > Cu 4 /Al 2- δ O 3 > Cu 8 /Al 2- δ O 3 ), meaning that the atomically dispersed copper may be a potential candidate for acetylene semi-hydrogenation. The structures of a series of single site catalysts M 1 /Al 2- δ O 3 (M = Fe, Co, Ni, Ag, Au) are similar to that of Cu 1 /Al 2- δ O 3 , but their performances in catalyzing acetylene semi-hydrogenation are different. M 1 /Al 2- δ O 3 (M = Ag, Au) shows higher selectivity than Cu 1 /Al 2- δ O 3 , while M 1 /Al 2- δ O 3 (M = Fe, Co, Ni) demonstrates a higher turnover frequency (TOF) of ethylene than Cu 1 /Al 2- δ O 3 . Moreover, our results indicate that the Ni 1 -Cu 1 /Al 2- δ O 3 alloy shows both high activity and ethylene selectivity. The present results show a compensation between the reactivity and the selectivity, suggesting that alloys of VIIIB metals with IB metals like Ni 1 -Cu 1 /Al 2- δ O 3 may be efficient candidate catalysts in acetylene selective hydrogenation.