Correlating the Surface Chemistry of C2 and C3 Aldoses with a C6 Sugar: Reaction of Glucose, Glyceraldehyde, and Glycolaldehyde on Pd(111)

Abstract

The catalytic conversion of biomass into fuels and chemicals requires an understanding of the adsorption and reaction of C5 and C6 sugars on catalytically active metals. In this investigation glycolaldehyde and glyceraldehyde were used as model compounds in a density functional theory (DFT) and experimental surface science study of the reaction of sugars on Pd(111). For the first time the stable intermediates formed by glucose on a single crystal metal surface were identified, allowing for comparisons with the surrogate molecules. Adsorption was governed by aldehyde group–surface interactions forming η1(C═O) intermediates, which, upon heating, transformed into more stable di-σ η2(C–O) species followed by α-O–H bond scission to produce an α-oxo-η2 intermediate. A consequence of the surface–carbonyl group interaction is that it precludes using simple alcohols or polyols as model compounds for biomass-derived sugars in mechanistic studies of heterogeneously catalyzed biomass reforming on metal surfaces and s...