CeO2 modified Au/TiO2 catalysts with outstanding stability under harsh CO oxidation conditions
Abstract The 1.5 wt% Au/TiO2 World Gold Council catalyst (WGC) was modified by depositing on its surface a 5.4 wt% CeO2 loading by incipient wetness impregnation. Calcination at 673 K of the resulting, surface modified, catalyst yielded a material in which the system of gold particles was not significantly modified with respect to that of the starting 1.5% Au/TiO2 WGC catalyst, neither in terms of its size distribution or metallic dispersion. The latter parameter remained, as in the catalyst prior to CeO2 deposition, in a value about 36% Both catalysts, Au(1.5%/TiO2 WGC and CeO2(5.4%/Au(1.5%/TiO2, were tested in consecutive CO oxidation reaction loops at increasing final temperatures. In these cycles, the ceria modified catalyst showed not only a higher activity but, more importantly, a largely enhanced stability against deactivation. Scanning Transmission Electron Microscopy (STEM) studies clearly revealed the presence of nanometer sized ceria rafts, less than 1 nm thick, on the surface of the fresh CeO2(5.4%/Au(1.5%/TiO2 catalysts. After the CO oxidation test at the highest temperature, 1223 K, the WGC catalyst suffered from a very severe Au nanoparticle sintering whereas Au nanoparticle growth was very much limited in the ceria modified catalyst after the same aging test. STEM results reveal that a major fraction of the Au nanoparticles (75% comprising all the smaller ones