Engineering oxygen vacancy and crystal surfaces for TiO2-based photocatalysts for enhanced photocatalytic hydrogenation of bio-based carbonyls to biofuels

Photocatalytic reductive conversion of bio-derivatives to biofuels and fine chemicals is an eco-friendly and energy-saving way for biomass valorization. Herein, we developed a new and high-performance protocol for control of activity/selectivity in photocatalytic reductive upgrading of biomass to biofuels at room temperature via engineering oxygen vacancy (Ov) and manipulating the exposed crystal surfaces of the TiO2-based catalysts, such as efficient cascade photocatalytic hydrogenation-cyclization of ethyl levulinate to gamma-valerolactone in water (up to 96% yield, TOF: 112.1 h-1), and the selective conversion of 5-methylfurfural to 5-methylfurfuryl alcohol (90% yield) or long carbon-chain coupling products (86% yield) in methanol, respectively. The {101} crystal plane is prone to produce more Ov in situ than the {001} and {110} crystal planes. The formation of Ov was not only beneficial to the adsorption and activation of the bio-based carbonyls, but also could enhance the migration efficiency of the photo-generated carriers and effectively adjust the semiconductor band structure of the TiO2- based photocatalyst to promote the visible-light absorption, thus enhancing the overall reductive conversion process, as elucidated by DFT calculations. Also, the charge distribution and adsorption intensity of different exposed crystal surfaces of the photocatalyst were able to control the selectivity of the bioproducts. In addition, the optimal Ov-TiO2_x{101} catalyst had excellent reusability and could be reused at least five times with no obvious decrease in photocatalytic performance. The strategy of selectivity control via engineering the catalyst exposed crystal surfaces and loaded Ov provides an opportunity for multi-catalytic biomass conversion to biofuels.