CeO2@N/C@TiO2 Core‐shell Nanosphere Catalyst for the Aerobic Oxidation of 5‐Hydroxymethylfurfural to 5‐Hydroxymethyl‐2‐Furancarboxylic Acid.

Defective D‐CeO2@N/C@TiO2 nanospheres, each comprising a spherical CeO2 core coated with shells of N‐doped carbon and TiO2, were successfully synthesized then evaluated for the aerobic oxidation of 5‐hydroxymethylfurfural (HMF) to 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA). Detailed catalyst characterization studies using XRD, SEM, TEM, TG‐DTA, XPS, N2 physisorption confirmed the hierarchical core‐shell structure of the D‐CeO2@N/C@TiO2 nanospheres, with the defective surface structures created through a thermal hydrogenation process using NaBH4 promoting HMF conversion. The effect of various reaction parameters, including the reaction time, temperature, oxygen pressure, type of alkali co‐reactant and the amount of catalyst, on HMF oxidation to HMFCA over the D‐CeO2@N/C@TiO2 nanospheres were studied. Under the optimized reaction conditions (temperature 80 °C, reaction time 30 min, O2 pressure 1 MPa), a high HMF conversion of 87.8 % and a remarkable HMFCA selectivity of 100 % were obtained. In addition, the D‐CeO2@N/C@TiO2 nanosphere catalyst showed great stability over four consecutive HMF oxidation tests, implying good catalyst stability. Experimental findings were used to develop a plausible reaction mechanism for the selective oxidation of HMF on the D‐CeO2@N/C@TiO2 nanospheres. [ABSTRACT FROM AUTHOR]