Catalytic routes and oxidation mechanisms in photoreforming of polyols

Photocatalytic reforming of biomass-derived oxygenates leads to H-2 generation and evolution of CO2 via parallel formation of organic intermediates through anodic oxidations on a RhiTiO(2) photocatalyst. The reaction pathways and kinetics in the photoreforming of C-3-C-6 polyols were explored. Polyols are converted via direct and indirect hole transfer pathways resulting in (i) oxidative rupture of C-C bonds, (ii) oxidation to alpha-oxygen functionalized aldoses and ketoses (carbonyl group formation) and (iii) light-driven dehydration. Direct hole transfer to chemisorbed oxygenates on terminal Ti(IV)-OH groups, generating alkoxy-radicals that undergo beta-C-C-cleavage, is proposed for the oxidative C-C rupture. Carbonyl group formation and dehydration are attributed to indirect hole transfer at surface lattice oxygen sites [Ti center dot center dot O center dot center dot center dot Ti] followed by the generation of carbon-centered radicals. Polyol chain length impacts the contribution of the oxidation mechanisms favoring the C-C bond cleavage (internal preferred over terminal) as the dominant pathway with higher polyol carbon number. (C) 2016 Elsevier Inc. All rights reserved.