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

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.