CeO2-modified Au/TiO2catalysts with outstanding stability underharsh 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 (< 5 nm), was contacting the ceria phase. This evidences an important stabilizing effect of the proposed surface modification. Moreover, these results open up possibilities for gold catalysts in applications where high temperatures are reached under working conditions.