LnxPdyTi1−x−yO₆ Catalysts: Formation of Oxygen Vacancy and Identification of the Active Site for CO Oxidation

The catalytic activities for CO oxidation at low temperature on various Ln x Pd 1− x − y TiO 6 catalysts have been investigated. The results showed that the catalytic activities of Pd y Ti 1− y O 6 catalysts could be promoted significantly by the addition of rare earth elements. Ce x Pd y Ti 1− x − y O 6 showed the highest activity among these catalysts. Evidence from characterization by XRD, XPS, TPR, and BET indicated that the synergistic interaction between Pd and Ce in the Ce x Pd y Ti 1− x − y O 6 catalyst was stronger than that of any other rare earth element dopant. The doping resulted in the formation of oxygen vacancies and the higher ionization of Pd species. Three kinds of structure have been proposed according to the distribution of Pd and oxygen vacancies in TiO 2 . Results of computer simulations show that the structure with an oxygen vacancy adjacent to each Pd atom is predicted to be favored, which might be due to the high stability of Pd 2+ in a square-planar environment. A possible reaction mechanism for CO oxidation over these Ln-doped Ln x Pd y Ti 1− x − y O 6 catalysts is discussed.