Oxygenated groups enriched polyolefin-Zr(IV) complexes catalyzing low-temperature transfer hydrogenation of biomass-derived furfural with 2-propanol

Zr4+-O2- pairs in MOFs and macromolecule - Zr(IV) complexes have proved one of the ideal catalytic components for catalytic transfer hydrogenation of biomass-derived furfural. However, restricted by limited adjustability of Zr4+-O2- coordination environment and the complex design and creation of ligand defects, currently, there are only a few efficient low-temperature (<100 degrees C) catalytic systems. In this work, oxygenated groups enriched polyolefin - Zr(IV) complexes were prepared and fixed on/in mesoporous silica aerogel support. The complexes possessed a stable structure with CC bonds as the connecting skeleton of each oxygenated group, and the types and densities of oxygenated groups (COOH, SO3H, and OH) could be easily adjusted by using different monomers. In the catalytic transfer hydrogenation reaction of furfural and 2-propanol, the catalyst synthesized using dicarboxylic maleic acid as a monomer of polyolefin exhibited the best catalytic performance in low temperatures, the main product furfuryl alcohol with a high yield of 96.0 % and a high selectivity of 98.2 % was obtained at 85 degrees C for 8 h. In 6 cycles of reactions at 85 degrees C, the furfuryl alcohol yield decreased gradually from 96 % in the 1st cycle to 84.0 % in the 4th cycle and further restored to 90.9 % and 89.3 % in the 5th and 6th cycles, respectively, by refreshing the used catalyst with methanol washing, and there was almost no leaching of Zr4+ species in the reaction medium. The catalyst poisoning experiment with acidic and basic sites shielded by pyridine and boric acid, respectively, showed that the catalytic activity was more sensitive to the shielding of basic sites, and the isotope experiments revealed that two H of the product furfuryl alcohol are transferred from 2-propanol. Hereby, the oxygenated group-bearing polyolefin - Zr(IV) complexes with stable structure, variable functional groups and the corresponding various Zr4+-O2- coordination pairs, are ideal catalyst candidates for the selective transfer hydrogenation of furfural to furfuryl alcohol.