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Keywords:

  • cerium;
  • metal-support interaction;
  • oxidation;
  • platinum;
  • supported catalysts;
  • structure–activity relationships

Abstract

Pt/CeO2 catalysts with various Pt loadings were prepared by a conventional incipient wetness impregnation method that employed CeO2 cubes (c-CeO2), rods (r-CeO2), and octahedra (o-CeO2) as the support and Pt(NH3)4(NO3)2 as the metal precursor. Their structures and catalytic activities in CO oxidation in excess O2 and the preferential oxidation of CO in a H2-rich gas (CO-PROX) were studied, and strong morphology effects were observed. The impregnated Pt precursor interacts more strongly with CeO2 rods and cubes than with CeO2 octahedra, and the reduction/decomposition of the Pt precursor impregnated on CeO2 octahedra is easier than that on CeO2 rods and cubes. With the same Pt loading, the Pt/o-CeO2 catalyst contains the largest fraction of metallic Pt, whereas the Pt/c-CeO2 catalyst contains the largest fraction of Pt2+ species. The reducibility of pure CeO2 and CeO2 in the Pt/CeO2 catalysts follows the order r-CeO2>c-CeO2>o-CeO2, and the reducibility of CeO2 depends on the Pt loading for the Pt/c-CeO2 catalysts but not much for the Pt/r-CeO2 and Pt/o-CeO2 catalysts. The catalytic performance of Pt/CeO2 catalysts in both CO oxidation and the CO-PROX reaction follows the order Pt/r-CeO2>Pt/c-CeO2> Pt/o-CeO2. The Pt0-CeO2 ensemble is more active than the Pt2+-CeO2 ensemble in the catalysis of CO oxidation in excess O2. H2-assisted CO oxidation catalyzed by the Pt/CeO2 catalysts was observed in the CO-PROX reaction, and the Pt2+ species and CeO2 with a large concentration of oxygen vacancies constitute the active structure of the Pt/CeO2 catalyst for the CO-PROX reaction. The effect of the morphology of the CeO2 support in the preparation, metal–support interaction, and catalytic performance of Pt/CeO2 catalysts can be correlated the exposed crystal planes and surface composition/structure of the CeO2 support with different morphologies. These results not only demonstrate that the structure and catalytic performance of oxide-supported catalysts can be tuned by controlling the morphology of the oxide support but also deepens the fundamental understanding of CO oxidation reactions catalyzed by Pt/CeO2 catalysts.