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 efficiency of catalysts for aqueous phase processes to the level we are used to in vapor phase reactions.In-situ NMR studies showed that polyols compete with water for adsorption sites on polar metal oxide surfaces. Directed interactions with specific surface sites dominate. In-situ IR spectroscopy showed that even in the presence of water, polyols with sufficient spatial separation of their alcohol groups (e.g. glycerol) can chemisorb on Lewis acid sites forming stable multidentate surface species. These polyols are adsorbed via a bridging alkoxy bond coordinatively unsaturated metal atoms while another alcohol group coordinates to the same sites without dissociation. 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 oxide like ?-Al2O3 against hydrolysis in hot liquid water that would otherwise deteriorate the material.The conversion of glycerol over Pt/Al2O3 was also studied by operando ATR-IR spectroscopy. Surface bound CO on the Pt particles was identified as key intermediate. The number of available surface sites is increased when Pt/?-Al2O3 is cleaned by hydrogen and oxygen saturated water. After this pretreatment, some of the Pt sites that bind bridging CO show activity for the water-gas-shift reaction even at room temperature.

In-situ and operando studies on the surface chemistry of polyols

248th National Meeting (2014)

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