Revealing the effect of Ag coverage on the performance of oxide supported Ag single atom catalyst: A first principles study

Singly dispersed Ag atoms on CeO₂(110) show great promise for oxidation reactions. Experimental evidence [1] indicates that their catalytic activity for NH₃ oxidation is strongly influenced by the density/coverage of Ag atoms. Using density functional theory, we find that the NH₃-oxidation reaction pathway is bottlenecked by H₂O desorption. At low Ag density (Ag-Ag distance ~ 15.49 Å), surface geometry and charge-density-difference map reveal a dual-site stabilization for the H₂O molecule, i.e., the O of H₂O (O_w) binds and donates electron to a surface Ce while interacts strongly with a subsurface Ce via electrostatic interaction, strengthening the adsorption of H₂O and thus making desorption less facile (with a desorption energy of 1.27 eV). At high Ag density (Ag-Ag distance ~ 5.47 Å), charge-density-difference map shows that the interaction of H₂O with the subsurface Ce disappears, leading to a single-site interaction that weakens adsorption and leads to a lower desorption energy (of 0.74 eV) than that for the low Ag density. In addition, electronic-structure analysis indicates that increasing Ag density drives the surface from semiconducting toward metallic. Our work suggests that the catalytic activity of Ag single atom catalyst supported on CeO₂(110) for NH₃ oxidation can be finetuned by controlling the Ag density during the synthesis of the catalyst.

[1] F. Liu et al (Private communication)