Revealing the Active Site Local Atomic Environment of Oxide-supported Ag Single Atom Catalyst

Single atom catalyst (SAC) supported on a metal oxide surface is a promising candidate for various reactions. Determining the relationship between the active site’s local atomic coordination and its catalytic performance is important for designing SAC. Here, we apply the ab initio thermodynamics approach to investigate the local coordination of Ag atoms that stabilize on CeO₂(ııo), ZrO₂(īıı), and Al₂O₃(ııı) through calculated phase diagrams and examine NH₃ dissociation on so determined Ag SAC. We find that for the CeO₂(ııo)-supported Ag SAC structure, one surface oxygen vacancy nearby is the most thermodynamically favorable, while with the ZrO₂(īıı) and Al₂O₃(ııı)-supported ones, no oxygen vacancy nearby is the most thermodynamically favorable. Our results also show that oxygen vacancy formation is spontaneous near the Ag atom when supported by CeO₂(ııo), while non-spontaneous when supported by ZrO₂(īıı) and Al₂O₃(ııı). We compare the energetics of NH₃ adsorption and dissociation on Ag/CeO₂(ııo) with those on Ag/ZrO₂(īıı) and Ag/Al₂O₃(ııı), finding that the first hydrogen abstraction is the most facile on Ag/CeO₂(ııo). We trace the catalytic behavior of these oxide-supported Ag SACs to the differences in coordination, charge states and the availability of unoccupied density of states of Ag atoms, as well as the distance from a H atom of the adsorbed NH₃ to nearby surface O atoms. We will discuss the good qualitative agreement of the above results with experimental data that we have obtained.