First-principles study of single transition metal atoms on ZnO for the water gas shift reaction

Abstract

Supported single-atom catalysts have attracted increasing interest due to their high atomic efficiencies and simple structures used to establish the structure–activity relations in catalysis. In this contribution, we present a density functional theory study of ZnO supported single transition metal (TM: Mn, Fe, Co, and Ni) atoms for the water gas shift reaction (WGSR). We find that these single TM₁ atoms prefer to substitute in the surface Zn lattice and exhibit promising activity for stabilizing the intermediates (i.e. CO, OH, and COOH) involved in WGSR. Meanwhile, the surface lattice O coordinated with the TM₁ atoms is responsible for the hydrogen abstraction process. The formation of COOH via the association between CO and OH is the rate-limiting step in the catalytic cycle. Microkinetic modeling analysis is used to determine the activity trend, and a volcano-like plot between the calculated rates and the binding energies of COOH is obtained, suggesting that the COOH binding energy might be a good activity descriptor for catalyst screening. Among these single atoms, the single Ni₁ atom exhibits the highest activity and is promising for WGSR.