Noble Metal-Substituted Complex Oxides as Highly Robust Catalysts for Extreme Conditions

1. Noble Metal-Substituted Complex Oxides as Highly Robust Catalysts for Extreme Conditions Xiaoying Ouyang and Susannah L. Scott Department of Chemistry and Biochemistry University of California, Santa Barbara, CA, 93106-5080 Noble metal-containing catalysts suffer from severe sintering at high temperatures, losing activity as their surface area declines. Complex oxides are compositionally flexible and thermodynamically stable, resisting phase changes at elevated temperatures. When noble metals are introduced into a host whose cation sites are tailored to accommodate them, very robust catalysts may result. Due to their crystalline nature of the hosts, the local environments of the noble metal cation are highly uniform. However, it was possible that the low surface areas of these materials would present a significant limitation to their use as catalysts. The image above shows BaCeO3 with Pd(II) (blue) substituted for Ce(IV) (yellow) on the perovskite’s B-sites. Its solid-state synthesis is conducted at 1000 oC, and its B.E.T. surface area is very low (ca. 1 m2/g). Nevertheless, the activity of the catalyst for CO oxidation is very high. Its thermodynamic stability enables the catalyst to recover its activity fully even after exposure to temperature extremes. The isotope switching experiment shown on the left demonstrates the participation of lattice oxygen from the bulk, presumably due to the introduction of vacancies caused by the Pd(II) substitution. Deactivation by SO2 and spontaneous recovery of the catalytic activity have also been studied.