Reactivity of Lattice Oxygen in Ti-Site-Substituted SrTiO 3 Perovskite Catalysts.

An environmental catalyst in which a transition metal (Mn, Fe, or Co) was substituted into the Ti site of the host material, SrTiO 3 , was synthesized, and the reactivity of lattice oxygen was evaluated. For CO oxidation, Mn- and Co-doped SrTiO 3 catalysts, which provided high thermal stabilities, exhibited higher activities than Pt/Al 2 O 3 catalysts despite their low surface areas. Temperature-programmed reduction experiments using X-ray absorption fine structure (XAFS) measurements showed that the lattice oxygen of Co-doped catalyst was released at the lowest temperature. Isotopic experiments with CO and 18 O 2 revealed that the lattice oxygen was involved in CO oxidation on Fe- and Co-doped catalysts; that is, CO oxidation on these catalysts proceeded via the Mars-van Krevelen mechanism. On the other hand, for Mn-doped catalyst, the contribution of lattice oxygen to CO oxidation was relatively negligible, indicating that the reaction proceeded according to the Langmuir-Hinshelwood mechanism. This paper clearly demonstrates that the catalytic mechanism can be adjusted by substituting transition metals into SrTiO 3 .