Reactivity of Lattice Oxygen in Ti-Site-Substituted SrTiO3 Perovskite Catalysts

An environmental catalyst in which a transition metal (Mn, Fe, or Co) was substituted into the Ti site of the host material, SrTiO3, was synthesized, and the reactivity of lattice oxygen was evaluated. For CO oxidation, Mn-and Co-doped SrTiO3 catalysts, which provided high thermal stabilities, exhibited higher activities than Pt/Al2O3 catalysts despite their low surface areas. Temperature-programmed reduction experiments using Xray 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 18O2 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 SrTiO3.