Au/M_xO_y/TiO₂ catalysts for CO oxidation: Promotional effect of main-group, transition, and rare-earth metal oxide additives

Au/TiO₂ catalysts are active for CO oxidation, but they suffer from high-temperature sintering of the gold particles, and few attempts have been made to promote or stabilize Au/TiO₂. Our recent communication addressed these issues by loading gold onto Al₂O₃/TiO₂ prepared via surface-sol-gel processing of Al(sec-OC₄H₉)₃ on TiO₂ [W.F. Yan, S.M. Mahurin, Z.W. Pan, S.H. Overbury, S. Dai, J. Am. Chem. Soc. 127 (2005) 10480-10481]. In our current full paper, Au/Al₂O₃/TiO₂ catalysts were prepared alternatively by thermal decomposition of Al(NO₃)₃ on TiO₂ followed by loading gold, and the influences of the decomposition temperature and Al₂O₃ content were systematically surveyed. This facile method was subsequently extended to the preparation of a battery of metal oxide-modified Au/TiO₂ catalysts virtually not reported. It was found that Au/TiO₂ modified by CaO, NiO, ZnO, Ga₂O₃, Y₂O₃, ZrO₂, La₂O₃, Pr₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, or Yb₂O₃ could retain significant activity at ambient temperature even after aging in O₂-He at 500 °C, whereas unmodified Au/TiO₂ lost its activity. Moreover, some 200 °C-calcined promoted catalysts showed high activity even at about -100 °C. The deactivation and regeneration of some of these new catalysts were studied. This work furnished novel catalysts for further fundamental and applied research.