Oxidation of CO over gold supported on Zn-modified ceria catalysts

A series of Zn-modified ceria solids were prepared by thermal decomposition of the corresponding metal propionates. The formation of segregated ZnO particles on the ceria surface is evidenced for these solids using X-ray diffraction; in addition to this the characterization data may allow discarding the formation of a ZnO–CeO2 solid solution. On modifying with Zn, the reducibility of the ceria support is enhanced, being the highest reducibility the one obtained for the ZnO–CeO2 solid having a 1:9 Zn:Ce atomic ratio (CeZn10). The activity of this solid in the CO oxidation reaction was the highest among the tested Zn-modified ceria solids. Therefore, catalysts containing 1 wt.% gold, supported on pure ceria and CeZn solids, were prepared, characterized and their catalytic activities tested. The Zn-modified gold catalyst is more active than the un-modified Au/CeO2 catalyst in the oxidation of CO; this behavior is related to the higher metallic dispersion of gold on the CeZn support surface. However, the number of oxygen vacancies acting as nucleation sites for gold, is hardly modified in the Zn-modified ceria support and, therefore, the higher gold dispersion must be related to high electron density sites on the catalyst surface as a result of Au–Ce–Zn interaction, this improved gold dispersion results in higher activities for CO oxidation.

There is formation of a monolayer of ZnO growing epitaxially on the CeO2 (1 1 1) surface. At higher ZnO loadings, ZnO islands start to grow on top of the distorted ZnO monolayer being bigger the size of the islands; these becoming a physical barrier for the reduction of CeO2.Figure optionsDownload high-quality image (155 K)Download as PowerPoint slideResearch highlights
► Zn-doped ceria solids evidenced the formation of segregated ZnO islands.
► The reducibility of ceria is enhanced, especially for the lowest Zn content.
► The Au/CeZn10 catalyst shows better catalytic performances that the Au/CeO2.
► Higher gold metallic dispersion on the CeZn support surface.