(488c) Surface Chemistry of Oxygenates On Pt(111) Modified By Mo and Re

Biomass-derived compounds are highly functionalized, making them difficult to selectively process into a desired product because they can interact with the surface in multiple, often uncontrolled ways. Addition of metals including rhenium and molybdenum to supported catalysts has been shown to facilitate C-O bond activation and influence selectivity for a number of deoxygenation reactions. However, the mechanism for the improvements is not known, hampering efforts to design better catalysts. Surface science techniques using single crystals can provide a fundamental understanding of the role of oxophilic metals (Re, Mo) as promoters to Pt group catalysts for deoxygenation reactions.

Our initial investigations have focused on how oxophilic modifiers interact with water and related surface species such as O, H, and CO. The majority of deoxygenation reactions using biomass-derived feedstocks are performed in the aqueous phase; it has been proposed that oxophilic modifiers allow water to dissociate and create acidic sites that alter the catalyst’s behavior. Temperature programmed desorption (TPD) and Auger electron spectroscopy (AES) have been used to investigate this chemistry on unmodified and Mo-coated Pt(111) surfaces. The Mo-coated catalysts form surface oxides following even low-temperature exposure to oxygen.  Preliminary results suggest that these surface oxides primarily influence reactivity of small molecules (water, CO) by blocking surface sites.  On the reduced surface, Mo appears to have a more pronounced effect on surface adsorption energies.  Possible mechanisms by which Mo influences reactions of small oxygenates on Pt will be discussed.