DFT study on mechanism for size-dependence of Pt catalysts for propane dehydrogenation

Abstract

Pt-based catalysts for propane dehydrogenation (PDH) are known to exhibit size-dependent activity, selectivity and stability, but the nature of the active Pt species responsible for size-dependent behavior remains unknown. In this paper, by employing density functional theory, microkinetic modeling as well as kinetic Monte Carlo simulations, we investigate PDH over (i) single Pt atom supported on the Al₂O₃(1 1 0), (ii) cluster of 13 Pt atoms adsorbed on Al₂O₃(1 1 0) and (iii) Pt(1 1 1) crystal surface. With decreasing size of Pt species, PDH activity increase, while both propene selectivity and stability against coking precursors exhibit an inverted volcano trend, which indicate the superiority of Pt single-atom catalyst and align closely with relevant experiment. Electronic structure analysis revealed that Pt species transfer electrons to the alumina, resulting in Pt positively charged. The valence electrons of Pt exhibit an inverted volcano relationship with adsorption energies of C₃H₇—H (activity index), while a volcano relationship with energy difference between propylene desorption and deep dehydrogenation (selectivity and stability index). The size reduction affects the number of electrons transferring, and the loss of relative moderate electrons of supported Pt single-atom, compared with Pt nanocluster and Pt large particle, leads to enhanced PDH activity, selectivity and stability against carbon deposition.