M supported on Al-defective Al2−δO3 (M = Fe, Co, Ni, Cu, Ag, Au) as catalysts for acetylene semi-hydrogenation: a theoretical perspective

Abstract

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 Al₂O₃ 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 Cu₁/Al_2−δO₃ and enhance its catalytic performance. The selectivity of ethylene formation decreases with increasing copper clusters (e.g., Cu₁/Al_2−δO₃> Cu₄/Al_2−δO₃> Cu₈/Al_2−δO₃), meaning that the atomically dispersed copper may be a potential candidate for acetylene semi-hydrogenation. The structures of a series of single site catalysts M₁/Al_2−δO₃ (M = Fe, Co, Ni, Ag, Au) are similar to that of Cu₁/Al_2−δO₃, but their performances in catalyzing acetylene semi-hydrogenation are different. M₁/Al_2−δO₃ (M = Ag, Au) shows higher selectivity than Cu₁/Al_2−δO₃, while M₁/Al_2−δO₃ (M = Fe, Co, Ni) demonstrates a higher turnover frequency (TOF) of ethylene than Cu₁/Al_2−δO₃. Moreover, our results indicate that the Ni₁–Cu₁/Al_2−δO₃ 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 Ni₁–Cu₁/Al_2−δO₃ may be efficient candidate catalysts in acetylene selective hydrogenation.