Microkinetic Modeling\nwith Intermediate Density Effects\nIdentify the Key Factors in Selective Acetylene Hydrogenation on PdAg(111)

Selective acetylene hydrogenation, a crucial industrial\nreaction,\nhas been extensively studied for decades yet continues to present\nunresolved challenges. This work presents a comprehensive microkinetic\nmodel, derived from density functional theory calculations, aimed\nat providing a detailed understanding of the key impact of acetylene\nhydrogenation on the PdAg(111) surface. This with intermediate density(coverage)\neffects kinetic simulation, which considers both self-and cross-interactions\namong adsorbates and the influence of intermediate density on the\ntransition states of each elementary step, is contrasted with a nonintermediate\ndensity effects kinetic calculation derived from energies determined\nat low density. Kinetic results reveal that the key intermediate CH<sub>2</sub>CH<sub>3</sub> in the formation of ethane is generated via\nCHCH<sub>2</sub>* + H* → CHCH<sub>3</sub>* + * and CHCH<sub>3</sub>* + H* → CH<sub>2</sub>CH<sub>3</sub>* + * rather than\nthe hydrogenation of CH<sub>2</sub>CH<sub>2</sub>*. We demonstrate\nthat the intermediate density effect kinetic model yields a turnover\nfrequency (TOF) that is roughly 28 orders of magnitude greater than\nthe TOF obtained from the nonintermediate density effect kinetic model.\nThe microkinetic outcomes, including activity and selectivity, align\nsatisfactorily with experimental. Extensive kinetic analyses have\nbeen performed, revealing that the introduction of Ag makes the rate\ncontrolling step of the reaction activity shift to hydrogen dissociation.