Nano-sized Ag rather than single-atom Ag determines CO oxidation activity and stability

Single-atom catalysis recently attracts great attentions, however, whether single atom or their nanoparticle (NP) has the advantage in its intrinsic activity remains under heated debate. Ag/Al2O3 is a widely used catalyst for many catalytic reactions, while the effect of Ag particle size on the activity is seldom investigated due to the great difficulty in synthesizing single atom Ag and Ag clusters/particles with different sizes. Herein, we firstly prepared an atomically dispersed Ag/Al2O3 catalyst using a nano-sized gamma-Al2O3 as the support, subsequently obtained a series of Ag-0/Al2O3 catalysts with different Ag particle sizes by H-2 reducing single-atom Ag/Al2O3 catalyst at various temperatures. The Ag-0/Al2O3 treated at 600 degrees C demonstrated superior CO oxidation performance over single-atom Ag/Al2O3 and the Ag/Al2O3 treated at 400 and 800 degrees C. Based on experimental data and density functional theory (DFT) calculation results, we reveal that the larger Ag-0 particle is beneficial to oxygen activation and improves the valence stability during oxidation reaction, while the aggregation of Ag-0 particle also accordingly decreases the concentration of surface active sites, hence, there is an optimum Ag-0 particle size. Our findings clearly confirm that Ag-0 nanoparticle has the advantage over single-atom Ag species in its intrinsic activity for CO oxidation.

Automated summary

This study demonstrates that Ag-0 nanoparticle has an advantage over single-atom Ag species in its intrinsic activity for CO oxidation. The larger Ag-0 particle benefits oxygen activation and improves valence stability during oxidation reactions, leading to superior performance in CO oxidation.