(143e) Effects of Component Segregation in Bimetallic Alloy Catalysis

Upgrading biomass-derived oxygenates to fuels and chemicals often requires a chemical reaction step that takes place over heterogeneous catalysts. Due to the complex nature of biomass, and the multitude of functional groups present therein, bimetallic catalysts are used to modulate the surface reactivity of the heterogeneous catalysts. More specifically, selective oxidation and reduction of oxygenates, such as dehydrogenation of butanol or hydrodeoxygenation of furfuryl alcohol, respectively, requires the suppression of decarbonylation and ring opening reactions that take place over the most commonly used catalysts, such as Pt and Pd.

This may be achieved by destabilizing strongly bound carbonaceous surface intermediates. In this study, we use butyraldehyde and its isomers as probe molecules to interrogate the surface reactivity of Pd-Cu, Pd-Ag and other alloys. Operando X-ray absorption spectroscopy reveals that, in alloys with identical bulk composition, the segregation of the more weakly binding component to the surface (e.g. Cu) and the blockage of strongly binding active sites (e.g. Pt or Pd) selectively suppress undesired reactions. We further investigate the effect of atomic size mismatch on the segregation and the effects of the adsorbate and the reactive environment on the geometry and electronics of the metal components and discover general trends connecting structure and reactivity. We use the knowledge obtained from these studies to propose novel catalysts, not only for the upgrading of biomass but for a broad range of reactions in diverse fields such as automotive catalysis and hydrogen storage.