Highly efficient Zr-based coordination polymer for catalytic transfer hydrogenation of 5-hydroxymethylfurfural: Tuning acid strength and enhancing stability

Abstract

In this study, Zr-based coordination polymers were synthesized via solvothermal method for the Meerwein-Ponndorf-Verley reduction of biomass-derived aldehydes and ketones. The morphology and strength of Lewis acid sites could be tuned by using different solvent during catalyst preparation. A 98.5 % yield of 2,5-bis(hydroxymethyl)furan (BHMF) was achieved at 100 °C using Zr-PDC/DMF-DCB, which was synthesized with pyridine-2,6-dicarboxylic acid (PDC) as ligand in a mixed solvent of N, N-dimethylformamide (DMF) and 1,2-dichlorobenzeneisopropanol (DCB) and exhibited moderate Lewis acid sites. Conversely, while Zr-PDC synthesized in alcohols (Zr-PDC/MeOH and Zr-PDC/EtOH) were used as catalysts, etherification products formed instead of BHMF. Further investigation into the role of solvents during catalyst preparation revealed that coordination between Zr sites and DMF increased the electron cloud density of Zr sites, thus weakening Lewis acidity. In addition, the inclusion of hydrophobic DCB resulted in the formation of spherical morphology, which improved resistance to carbon deposition and enhanced anti-agglomeration properties. This work presents a strategy for controlling acid strength and improving catalytic stability of coordination polymers.