The DFT study of Si-doped Pd6Si clusters for selective acetylene hydrogenation reaction

Abstract

Recently, it has been demonstrated that Si-modified Pd catalyst shows excellent selectivity and produces less amount of green oil than the unmodified Pd catalyst in acetylene hydrogenation. Motivated by experiment works, we systematically investigate the mechanism of the selective acetylene hydrogenation reactions over pristine Pd7 and Si-doped Pd6Si clusters by using the B3LYP method of density functional theory. Our result confirms that both the Pd7 and Pd6Si clusters catalytic hydrogenation of acetylene are mainly through two different pathways and a series of intermediates can be transformed into each other by proton transfer, which link the two independent reaction paths into a network path. Among these reaction paths, activation energies for all steps of the reaction have been calculated and it is illustrated that the lowest activation energy in the process of ethylene generation are 22.59 kcal/mol for Pd7 cluster and 11.25 kcal/mol for Pd6Si cluster, which indicate that the Pd6Si cluster perform better than Pd7 cluster in the aspect of catalytic activity. Besides, it has also been demonstrated that the selectivity for the reaction is enhanced after doping a Si atom.