(701f) Supercritical Fluid Deposition of Dispersed Platinum On Supported Ceria

Catalysts composed of noble metals and reducible metal oxides are of great significance for modern energy applications, including key reactions in downstream hydrogen production such as water-gas shift and preferential oxidation as well as fuel cell electrodes.  An important example of such a catalyst/promoter pair is platinum dispersed on supported ceria.  The degree of promotion is dependent upon interfacial area between platinum active sites and ceria, and thus methods of synthesizing supported catalysts with intimate contact between the two are essential.  In this work we investigate the supercritical fluid deposition of platinum on ceria supported on alumina.  Supercritical fluid deposition offers an alternative to wet methods of catalytic metal deposition that may provide greater control over deposition rates and reduce particle agglomeration.  The solvent properties of supercritical fluids can be tuned by varying temperature and pressure, allowing control of precursor solubility and sorption kinetics.  Futhermore, the solvent can be removed without heating and leaves no residue on the catalyst material.  Variation of ligands may provide opportunities for the manipulation of particle shape and size essential to synthesis of rationally designed catalysts.  This study employs the precursor platinum acetylacetonate in supercritical carbon dioxide.  The dispersion of platinum metal and surface crystallite size are evaluated by chemisorption analysis via pulse titration, and the interaction of platinum and surface ceria is characterized using temperature programmed reduction.  The effect of pretreatment of the supported ceria in a reducing atmosphere on both platinum dispersion and Pt/ceria interaction is explored.  Additional investigation includes the influence of calcination temperature and metal reduction by thermal or chemical means.