Self-assembly of Atomically Dispersed Ag Catalysts on Polyhedral Co3O4 at Elevated Temperatures: A Top-Down Nanofabrication of High-Loading Atomically Dispersed Catalysts

摘要

Catalysts based on atomically dispersed noble metal catalysts have attracted considerable attention due to their enhanced reactivity and selectivity. However, to prevent the formation of metal nanoparticles and to keep the dispersity of isolated single atoms on surface, the loading concentration of the noble metal must be kept low (usually below 0.5 %). Here, we report a self-assembly approach for synthesizing a stable atomically dispersed silver-cobalt oxide catalyst on polyhedral Co3O4 nanoparticles containing Ag up to 10 wt % at elevated temperature. The sample-averaged extended X-ray absorption fine structure (EXAFS) analysis revealed the presence of highly dispersed Ag species along with small Ag clusters. The coordinatively unsaturated Co3+ centers present on the {110} facets of the Co3O4 surface were shown to be crucial for anchoring catalytically active single Ag atoms. Control experiments showed that polyhedral Co3O4 was more effective than Co3O4-cube and Co3O4-octahedron at anchoring Ag atoms. The oxidized nature of the atomically dispersed Ag sites was revealed by X-ray absorption near-edge structure (XANES) Ag-L-3-edge spectra. From the H-2-temperature programmed reduction and CO oxidation test, it was discovered that downsizing catalytically active components from nanocrystals to single atoms not only enhanced the catalytic activity, but also endowed single-atom catalysts with exceptional oxygen activation ability at low temperature.