Furfural oxidation by hierarchical titanium silicate catalyst with NiO nanoparticles: Improved diacid yield and elucidation of reaction pathway

Oxidation of biomass-derived furfural with hydrogen peroxide provides a sustainable path to 1,4-diacids for polymer production. The state-of-the-art catalyst, titanium silicate (TS-1), suffers from drawbacks including deactivation and diffusion limitations, but its catalytic activity can be improved by introducing mesoporosity and metal species. Herein, hierarchical TS-1 (HTS-1) catalysts loaded with different metal oxides were prepared and examined for furfural oxidation with aqueous hydrogen peroxide. HTS-1 loaded with Ni (Ni/HTS-1) yielded 32% maleic acid from furfural under screening conditions, which was 28% higher relative yield than unloaded HTS-1 under the same conditions. Catalyst characterization and an in situ 13 C NMR study elucidated the promotional role of Ni and the pathway, by which the reaction proceeds. Surprisingly, the NMR study indicated that the reactions using both Ni/HTS-1 and unloaded HTS-1 proceed via formation of furfural peroxide followed by Baeyer-Villiger oxidation, and not via epoxidation as many other TS-1 catalyzed oxidations. • Effects of base metals in HTS-1 catalysts were studied for furfural oxidation • NiO loading on HTS-1 increased the maleic acid yields compared to unloaded HTS-1 • Promotional effect of NiO was attributed to enhanced electrophilicity of Ti sites • In situ 13 C NMR study confirmed Baeyer-Villiger oxidation by the HTS-1 catalyst