Aqueous-phase hydrodeoxygenation of sorbitol with Pt/SiO2-Al2O3: Identification of reaction intermediates

Aqueous-phase hydrodeoxygenation of sugar and sugar-derived molecules can be used to produce a range of alkanes and oxygenates. In this paper, we have identified the reaction intermediates and reaction chemistry for the aqueous-phase hydrodeoxygenation of sorbitol over a bifunctional catalyst (Pt/SiO2-Al2O3) that contains both metal (Pt) and acid (SiO2-Al2O3) sites. A wide variety of reactions occur in this process including C C bond cleavage, C-O bond cleavage, and hydrogenation reactions. The key C C bond cleavage reactions include: retro-aldol condensation and decarbonylation, which both occur on metal catalytic sites. Dehydration is the key C-O bond cleavage reaction and occurs on acid catalytic sites. Sorbitol initially undergoes dehydration and ring closure to produce cyclic C6 molecules or retro-aldol condensation reactions to produce primarily C3 polyols. Isosorbide is the major final product from sorbitol dehydration. Isosorbide then undergoes ring opening hydrogenation reactions and a dehydration/hydrogenation step to form 1,2,6-hexanetriol. The hexanetriol is then converted into hexanol and hexane by dehydration/hydrogenation. Smaller oxygenates are produced by C C bond cleavage. These smaller oxygenates undergo dehydration/hydrogenation reactions to produce alkanes from C1-C5. The results from this paper suggest that hydrodeoxygenation chemistry can be tuned to make a wide variety of products from biomass-derived oxygenates. (C) 2009 Elsevier Inc. All rights reserved.