Ethylene Epoxidation on Ag(100), Ag(110), and Ag(111): A Joint Ab Initio and Kinetic Monte Carlo Study and Comparison with Experiments
Journal article, 2019
Ethylene epoxidation is commercially one of the most important selective oxidation reactions. Despite extensive research into different catalytic materials, silver catalysts remain unrivaled in industrial applications, albeit with significant doping. Experiments have already shown that different silver facets exhibit different catalytic performance in terms of turnover frequencies as well as selectivity. In this work, we present extensive first-principles simulations and kinetic Monte Carlo (KMC) modeling of the reaction on the three pristine silver surfaces Ag(100), Ag(110), and Ag(111) and on the missing-row reconstructed Ag(110). To better understand the kinetics on different surfaces and veraciously describe the surface coverages, we explicitly take into account the lateral interactions between the adsorbates and their effect on the activation barriers. We show that the most stable Ag(111) surface maintains very low oxygen coverage while being the least active surface and only moderately selective. Ag(100) at high oxygen coverage is, on the other hand, shown to exhibit the highest selectivity. Both pristine and reconstructed Ag(110) surfaces lack any substantial selectivity but are the most active. A comparison with the bulk experimental data shows a good agreement with the modeling data for Ag(111), as this is the most stable facet and thus is expected to be prevalent in catalysts without special treatment. Experimental results on silver nanowires are, however, more consistent with the modeling on Ag(100), which is the main facet therein.