Unsaturated Fe–Ov–Ti5c Structure with Enhanced C–H and C–C Bond Activation Ability for Selective Oxidation of Glycerol to Glycolic Acid

The development of efficient catalytic structure for selective cleavage of thermodynamically stable C–C and C–H bonds is a challenging research field for renewable polyol oxidation, which is largely unexplored. Herein, we constructed an unsaturated coordination Fe–Ov–Ti5c structure for glycerol oxidation to glycolic acid via tuning the crystal forms of TiO2. Compared with Fe/TiO2-rutile dominated with Fe–O–Ti6c sites, Fe/TiO2-anatase exhibits rich Fe–Ov–Ti5c sites with strong electron transfer and abundant surface oxygen vacancies originating from the chemical nature of the (101) facet. Specifically, the synergistic effect between unsaturated Ti5c sites and Fe5c (five-coordination) sites promotes the adsorption of glycerol via strong electron transfer from the TiO2-anatase (101) to Fe species. Moreover, the abundant surface oxygen vacancies enhance the activation of the C–H bond and the cleavage of the C–C bond over the interfacial unsaturated coordination Fe–Ov–Ti5c structure. Consequently, the Fe/TiO2-anatase catalyst exhibits record high catalytic activity (TOF: 54.4 h–1) and glycolic acid selectivity (59.1%). The outcome of this work may provide some meaningful suggestions for the rational design of catalysts in biopolyol oxidation systems.