Phase-dependent selectivity control over TiO₂ in the photocatalytic oxidation of bio-polyols

Photocatalytic oxidation shows great potential in the valorization of biomass under mild conditions, while the selectivity control is particularly challenging for the complex and reactive bio-polyols. Herein, we report a selective photocatalytic process to convert bio-polyols into formic acid (FA) or carbon monoxide (CO) by controlling the phase of TiO₂. The bio-polyols are facially oxidized to formic acid (FA) which is stable over rutile and could be dehydrated to CO over anatase TiO₂. Through controlling the phase, FA or CO could be obtained from a wide range of bio-polyols with selectivity up to 63% or 52%. Our studies elucidate that the phase-dependent selectivity is essentially derived from the difference in the adsorption configuration of FA. In situ Fourier transform infrared spectroscopy (FTIR) and density functional (DFT) calculations were used to study the FA decomposition process on the surface of TiO₂. The phase-dependent FA decomposition is mainly derived from the different surface geometry, which affects the configuration of FA adsorption. Molecular adsorbed FA on anatase favors the dehydration of FA to CO while bidentate dissociated adsorption of FA on the rutile phase is inert to be further converted. This work provides a new horizon to the design of photocatalytic systems for biomass conversion.