(708c) Density Functional Theory (DFT) Exploration of Cs & Re Promoter Effects on Ag Catalysts for Ethylene Oxidation

In optimizing the ethylene oxidation (EO) reaction system, the addition of promoters has been pivotal; The introduction of multiple different promoters has increased the selectivity towards the desired product from ~50% on an unpromoted silver (Ag) catalyst, up to ~90% for a heavily promoted counterpart. However, among the many aspects of the EO reaction system, one of the least understood is the effect of the many catalyst promoters of the catalyst. Beyond the complexities of understanding the effect of a single promoter on catalyst, in a realistic industrial catalyst, a large number (sometimes 5 or more) of different promoters are present. While it may be more feasible to study the effects of any individual promoter in isolation, the effects of a multi-promoter complex during reaction condition involves a more challenging elucidation process.

In an earlier study, we highlighted the importance of a closer study of the EO reaction system on partially oxidized Ag surfaces such as the p(4x4)-O-Ag(111) partial reconstruction of the Ag(111) surface. Moving away from idealized single crystal models of the catalyst, the study of these complicated surfaces introduces, among other challenges, various distinct adsorption sites and the presence of sub-surface oxygen atoms in the catalyst. The latter being especially important for promoters like rhenium (Re), cesium (Cs) and the combination thereof, which tend to form oxygen complexes on the catalyst. This study presents a primarily Density Functional Theory (DFT) based approach in 1) Exploring the possible stable configurations of Re, Cs, and Re-Cs promoters on the model catalyst, and 2) Studying the effects of these promoter complexes on key elementary reactions in the EO reaction system. This talk will highlight the findings of the aforementioned study, the workflow of which can be extended to study the remaining common promoters on Ag catalysts in the EO reaction system.