Photothermal Conversion of Biopolyols and Sugars into Syngas over Pd–PdO/TiO2

Abstract

Photocatalysis is promising for reforming biopolyols and sugars into syngas (CO+H₂), while the carbon is easily overoxidized to CO₂ due to the hydroxyl radical (•OH) under aqueous conditions. Targeting this problem, a temperature-controlled photo-reforming strategy is proposed and the Pd–PdO/TiO₂ is used as the catalyst. The photocatalytic reforming process effectively breaks the C–H and C–C bonds of biomass to produce radicals. The increased reaction temperature not only increases the photocatalytic reaction rate but also thermodynamically fine-tunes the radical reaction process, facilitating the decarbonylation of acyl radical intermediates and prohibiting its overoxidation to CO₂. With the reaction temperature increased from 40 to 180 °C, the CO selectivity from glycerol reforming over Pd–PdO/TiO₂ catalyst under aqueous conditions improves significantly from 1.6% to 66%. The unique Pd–PdO/TiO₂ structure plays an important role in syngas production. On one hand, the decorated Pd species significantly promote light adsorption and the separation of photogenerated charge carriers. On the other hand, the PdO nanoparticles effectively facilitate the adsorption and decarbonylation process of acyl radical intermediates. A CO yield of over 60% for glycerol reforming under photothermal conditions can be obtained over Pd–PdO/TiO₂, which is 3 times that of pristine TiO₂ (20%). A wide range of biopolyols and sugars can also be converted into syngas through this photothermal system with a CO yield of 20–66%, along with 0.17–2.13 mmol·g^–1·h^–1 H₂ evolution.