Solid Br�nsted acid catalyses the deoxygenation of aldehydes and ketones from biomass pyrolysis stream at ambient pressures and moderate temperatures (< 673 K) to form C6-C15 aromatics, C2-C9 olefins, larger, unsaturated oxygenates, and a small amount of diene. We report the reaction pathways and their catalytic requirements for aldehyde and ketone deoxygenation on Br�nsted acid sites contained within microporous crystalline structures (H-MFI) and on H4SiW12O40 polyoxometalate clusters (POM), based on rate assessments, acid site titrations, and temperature programmed techniques. We specifically address the influences of reactant structures and the local environment of Br�nsted acid sites on rates and selectivities. Aldehyde reactions on Br�nsted acid sites occur via an initial aldol condensation step to create the inter-molecular C=C bond, which lengthens the carbon chain, followed by intra-molecular ring closure to form the aromatic ring. Sequential steps involve the inter-molecular transfer of H atoms to promote the deoxygenation of aldehydes, by removal of the oxygen atom and forming intra-molecular C=C bond to evolve alkenes. The aldol type condensation reaction occurs at much higher rates and the sequential ring closure, H transfer, and direct deoxygenation reactions at much lower rates on POM clusters than on H-MFI. As the ring closure and H transfer occur less effectively, a separate isomerization pathway followed by dehydration occurs on POM clusters and leads to diene formation. Br�nsted acid sites at POM cluster surfaces maintain much higher deoxygenation reactivities than those confined within microporous structures, apparently because they do not promote the sequential ring closure step that forms larger species, which occupy sites and cause deactivation. Deoxygenation of ketones on Br�nsted acid sites, in contrast, forms predominantly alkenes, acids, and a small amount of aromatics, because sequential reactions of the primary condensation product occur much more effectively than the initial condensation reactions to produce alkenes and acids. These catalytic effects of reactant structures and site confinement provide mechanistic guidance for tuning the relative rates and thus selectivities for the formation of larger oxygenates, alkenes, and aromatics.

Catalytic requirements for the deoxygenation of aldehydes and ketones on solid Br�nsted acid catalysts

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.