Modeling the Surface Chemistry of Sugars: Glycolaldehyde on Rhodium (100)

It is important to understand the interaction of C-OH and C=O functional groups of sugar with a catalytically active metal surface for selectively converting of biomass-derived molecules into useful chemicals. Glycolaldehyde (HOCH2CHO), with its C-OH and C=O functional groups, is the smallest molecule to model aspects of the chemistry of sugars on metal surfaces. Rhodium catalysts are candidates for activation of biomass-derived molecules. We have investigated the decomposition of glycolaldehyde on the Rh(100) surface using a combination of experimental surface science techniques (temperature-programmed reaction spectroscopy (TPRS), reflection absorption infrared spectroscopy (RAIRS)) and a computational method (density functional theory (DFT)). At low coverage, glycolaldehyde decomposition commences with O-H bond breaking upon adsorption at 100 K and proceeds via dehydrogenation and C-C bond breaking below room temperature, ultimately producing CO and hydrogen (synthesis gas). At high coverage a side reaction becomes apparent, involving C-O bond breaking. As a result, some methane and carbon formation are observed as well. Our findings on the decomposition of glycolaldehyde on Rh(100) suggest that sugars can be converted into synthesis gas on Rh surfaces, and, depending on the surface coverage, small hydrocarbons can be produced from sugar molecules, leaving the surface covered by surface carbon.