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

• Published in: Journal of catalysis Vol. 293; pp. 195 - 204
• Main Authors: Chang, Sujie, Li, Mo, Hua, Qing, Zhang, Lijuan, Ma, Yunsheng, Ye, Bangjiao, Huang, Weixin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-09-2012; Elsevier; Elsevier BV
• Subjects: Active structure; Ag/CeO2 catalysts; air; carbon monoxide; Catalysis; Catalysts; catalytic activity; ceric oxide; Chemistry; CO oxidation; Colloidal state and disperse state; engineering; Exact sciences and technology; General and physical chemistry; Metal–support interaction; nanocrystals; nanorods; nanosilver; oxidation; Oxygen; Oxygen vacancy; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Shape dependence; silver; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Metal–support interaction; Active structure; Shape dependence; CO oxidation; Ag/CeO2 catalysts; Oxygen vacancy; Metal support interaction; Binary compound; Shape; Support; Nanoparticle; Cerium oxide; Lanthanide compound; Design; Chemical reduction; catalysts; Oxidation; Metal-support interaction; Chemical reactivity; Structure; Nanorod; Nanocrystal; Oxygen; Catalytic reaction; Vacancy; Ag/CeO; Transition metal; Air; Charge density; Silver; Heterogeneous catalysis; Impregnation; Catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.06.025

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. [Display omitted]
► 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.
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.