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. This fundamental work is complimented by supported catalyst studies focusing on understanding how to improve selective deoxygenation of biomass-derived compounds.<br/><br/>Our recent studies have focused on how oxophilic modifiers influence oxygenate chemistry. Temperature programmed desorption (TPD), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS) have been used to investigate surface chemistry of simple probe molecules (hydrogen, oxygen, CO, water) as well as model compounds for biorefinery streams (2-methoxyethanol, m-cresol) on unmodified and Mo-coated Pt(111) surfaces. The results indicate that modifier sites influence the adsorption energies of both oxygenates and their decomposition intermediates. XPS and computational results indicate that the active sites responsible for these interesting TPD findings involve reduced molybdenum interacting with neighboring platinum atoms.<br/>These UHV results have been used to help explain observed trends from complementary investigations on supported bimetallic PtMo catalysts that show improved hydrodeoxygenation (HDO) selectivity. GC-MS data from m-cresol HDO indicates that the bimetallic catalysts are more selective than monometallic platinum to formation of deoxygenated products.

Surface chemistry of oxygenates on molybdenum-modified platinum

249th National Meeting (2015)

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