Photocatalytic selective oxidation of glycerol to formic acid and formaldehyde over surface cobalt-doped titanium dioxide.

Glycerol is one of the most important biomass platform compounds that is a by-product of biodiesel production, and the selective cleavage of the CC bond of glycerol to produce liquid hydrogen carriers (i.e., formic acid and formaldehyde) offers a viable strategy to alleviate the currently faced energy shortages. However, the harsh reaction conditions, long reaction times, poor yields of liquid hydrogen carriers, and the tendency of peroxidation to carbon dioxide (CO2) make the selective CC bond cleavage of glycerol more challenging. Herein, we report the selective CC bond cleavage of glycerol to formic acid and formaldehyde using surface cobalt (Co)-doped titanium dioxide (TiO2) under light irradiation and ambient conditions. The optimized system exhibits a high conversion of glycerol (95 %) and the yield of liquid hydrogen carriers reaches 78 % (formic acid, 57 %; formaldehyde, 21 %) in 8 h, effectively preventing their peroxidation to CO2. The outstanding photocatalytic performance is mainly attributed to the introduction of Co species and oxygen vacancies that promote the separation of photogenerated charges and holes and provide more adsorption sites for oxygen which are electron acceptors, respectively. In-depth investigations have shown that photogenerated holes and superoxide radicals are the main active species in this reaction. This work presents an effective and promising strategy for the efficient utilization of biomass resources.