What size of Cun clusters loaded on poly(heptazine imide) have better catalytic performance for acetylene semi-hydrogenation?

Development of earth-abundant, low-cost and easily synthesizable catalysts for the semi-hydrogenation of acetylene is urgently needed. Here, we have systematically investigated the structure, electronic properties, hydrogen dissociation, and acetylene semi-hydrogenation activity and selectivity of poly(heptazine imide) (PHI) loaded with different sizes of Cu_n (n = 1,2,4,13) clusters (Cu_n/PHI) by density functional theory calculations. The results show that Cu₄/PHI with tetrahedral configuration has a better hydrogenation activity in the acetylene semi-hydrogenation reaction with H adsorbed in the vicinity of acetylene and subsequent intermediates in a non-bridge position, resulting in a smaller hydrogenation energy barrier. In addition, the top Cu atom transfers a large number of electrons to the bottom Cu atoms and PHI, and only a small number of electrons transfer to ethylene, resulting in weak adsorption of ethylene and easy desorption, which makes it good selectivity and therefore it can be used as a candidate catalyst for the semi-hydrogenation of acetylene. This study provides insights into the design of catalysts with suitable size clusters loaded on carbon nitride materials for efficient acetylene semi-hydrogenation reactions.