Chapter 10 - Gas-Phase Synthesis of Nonstoichiometric Nanocrystalline Catalysts

Abstract

This chapter demonstrates the uniqueness and applications of gas-phase nanocrystalline synthesis in advanced catalyst preparation. Modified magnetron sputtering and inert gas condensation are combined as a new technique to produce nanocrystalline and nanocomposite catalysts. Via controlled postoxidation, nonstoichiometric CeO2-x-based catalysts are generated for SO2 reduction by CO and CO oxidation by O2 . These new materials exhibited outstanding catalytic activities in both reactions compared with the conventional catalysts. The findings could be explained by assuming that the active state of the catalyst involved a partially reduced surface. The higher activity might be attributed to a change in the nature of surface oxygen species for the nonstoichiometric CeO2-x. Superoxide species could be formed easily on bulk-reduced CeO2-x and were readily available for catalytic reactions. This difference translated into easy partial surface reduction, absence of hysteresis, and CO2 poisoning resistance for the nonstoichiometric nanocrystalline materials. The oxidation catalytic activity could be further improved by doping CeO2-x with Cu. A thermally stable dispersion of Cu on CeO2-x could be achieved by the gas-phase synthesis and controlled posttreatment, and it provided synergistic chemical and electronic effects in this nanocomposite catalyst.