Aqueous phase processes are expected to play a key role in the production of renewable chemicals and fuels from biomass. Facile separation makes heterogeneous catalysts an attractive option for achieving high efficiency in these processes. Unfortunately, little is known about the surface chemistry of biomass-derived oxygenates in an aqueous environment. However, this knowledge will be needed to improve the activity, selectivity, and stability of catalysts for aqueous phase processes to the level we are used to in vapor phase reactions. This presentation will focus on surface interactions of biomass-derived oxygenates with metal oxides such as Al₂O₃, TiO₂, ZrO₂, CeO₂, MgO, Nb₂O₅.

The surface chemistry of aqueous solutions of polyols on polar metal oxides is strongly affected by the competition between water and the polyols for adsorption sites. Directed interactions with specific surface sites dominate. Even in the presence of water, polyols with sufficient spatial separation between their alcohol groups (e.g. glycerol) can chemisorb on Lewis acid sites forming stable multidentate surface species. The frequencies of C-O stretching vibrations of participating groups scale linearly with the electronegativity of the metal atom providing an indication for reactivity trends in acid catalyzed reactions, such as dehydration. The surface species described here can also stabilize metal oxides like g-Al₂O₃ against hydrolysis in hot liquid water that would otherwise deteriorate the material.

When Brønsted acid sites are available on the surface or from dissociation of water dehydration of glycerol is observed. On Nb₂O₅, glycerol is selectively dehydrated in the primary position if it is coordinated to a Lewis acid site. Hydroxyacetone is formed as the main product of this reaction. If the dehydration reaction only involves a Brønsted acid site it occurs selectively in the secondary position, and acrolein is formed.