Shape-dependent interplay between oxygen vacancies and Ag–CeO2 interaction in Ag/CeO2 catalysts and their influence on the catalytic activity

Ag/CeO2 catalysts employing CeO2 nanocubes (c-CeO2) and nanorods (r-CeO2) as the support were prepared by conventional incipient wetness impregnation followed by calcination at 500 °C in air. Their structures have been characterized in detail and their catalytic activities in CO oxidation have also been tested. c-CeO2 and r-CeO2 nanocrystals exhibit different concentrations and structures of oxygen vacancies. The silver-r-CeO2 interaction is stronger than the silver-c-CeO2 interaction. Fine Ag nanoparticles form in 1%-Ag/c-CeO2 and grow in size in 3%-Ag/c-CeO2; however, positively charged Agn+ clusters dominate in 1%-Ag/r-CeO2, and fine Ag nanoparticles dominate in 3%-Ag/r-CeO2. Supported Ag nanoparticles are much more capable of creating oxygen vacancies in CeO2 than supported positively charged Agn+ clusters. More oxygen vacancies form in Ag/c-CeO2 than in Ag/r-CeO2. The average charge density of oxygen vacancies and the ratio between large oxygen vacancy clusters and small vacancies in CeO2 nanocrystals are enhanced when loaded with positively charged Agn+ clusters but reduced when loaded with Ag nanoparticles. Ag nanoparticles greatly promote the reduction and catalytic activity in CO oxidation of CeO2 nanocrystals but positively charged Agn+ clusters do not. These results demonstrate the concept that the interplay between oxygen vacancies and Ag–CeO2 interaction controls the structures of silver and CeO2 in Ag/CeO2 catalysts and thus their surface reactivity and catalytic activity, deepening the fundamental understanding of metal/CeO2 catalysts. These results also reveal that the interplay between oxygen vacancies and Ag–CeO2 interaction in Ag/CeO2 catalysts depends on the shape of CeO2 support, opening up a new strategy for the design of efficient and economic metal/CeO2 catalysts by engineering the shape of CeO2 support.

The structure and activity in CO oxidation of Ag/CeO2 employing CeO2 nanorods and nanocubes as the support have been studied. The experimental results reveal the shape-dependent interplay between oxygen vacancies and Ag-CeO2 interaction and their influence on the catalytic activity. Silver supported on CeO2 nanocubes with a loading of 1% shows the highest specific catalytic activity.Figure optionsDownload high-quality image (310 K)Download as PowerPoint slideHighlights
► The interplay between oxygen vacancies and Ag–CeO2 interaction depends on the shape of CeO2.
► Such an interplay controls the structures and catalytic activity of Ag/CeO2 catalysts.
► CeO2 nanorods stabilize cationic Ag species.
► CeO2 nanocubes facilitate the formation of metallic Ag nanoparticles.
► The Ag nanoparticle–CeO2 interface is the active structure in catalyzing CO oxidation.