ZrOCl2 as bifunctional and in-situ precusor materials for catalytic hydrogen transfer of bio-based carboxides
The effective and economically feasible tandem synthesis of γ-valerolactone (GVL), a renowned bio-based platform molecule with great promising applications in the production of drop-in chemicals, liquid fuels and polymers, is significantly vital and challengeable. Herein, we for the first time describe a direct and effective catalytic system based on ZrOCl2•8H2O capable of facilitating one-pot one-step tandem synthesis of GVL from bio-based furfural or furfuryl alcohol in 2-propanol by integrating sequential transfer hydrogenation, ring-opening, and transfer hydrogenation-cyclization reactions. A maximum GVL yield of 63.3% or 52.1% was achieved from furfuryl alcohol or furfural at 200 °C, respectively. The synergistic effect of [ZrO(OH)2]n•xH2O species and Brønsted acid species H+, derived from in-situ hydrolysis of ZrOCl2•8H2O, is accountable for its remarkable catalytic performance. Moreover, calcinations of leftover solid after tandem synthesis of GVL could fabricate hollow microrod ZrO2 material, in which the formation of microrod morphology and hollow structure were probably attributed to the electrostatic repulsion forces among particles in alcohol solution and removal of generated humins/coke during the reactions within collected solids via calcinations, respectively. Importantly, hollow microrod ZrO2 innovatively featured with high BET surface area, a large amount of acid-base sites and facile active-sites accessibility, and thereby exhibited a superior performance in the catalytic transfer hydrogenation of biomass-derived aldehydes or ketones than ZrO2 prepared by precipitation method.