Selective Reduction of Biomass-Derived Carbonyl-Containing Compounds over a Zirconium-Methylimidazole Coordination Catalyst

Abstract Meerwein–Ponndorf–Verley (MPV) reduction is an extremely important strategy for the effective hydrogenation of biomass-derived carbonyl compounds. In this strategy, developing the proper Lewis acid–base catalysts is the core mission. At present, considerable concerns are mainly focused on zirconium-organic acid coordination catalysts, but the majority of them contain a certain number of Brønsted acid sites (BASs), which can trigger some secondary reactions and then influence the yield and selectivity of objective products. Herein, a zirconium-methylimidazole coordination catalyst (Zr-MIZ) was fabricated in methanol at room temperature via a straightforward self-assembly process, in which 2-methylimidazole (MIZ) was directly adopted as an inexpensive organic base ligand. Interestingly, Zr-MIZ successfully introduced abundant and strong Lewis acid–base sites (LABSs); meanwhile, it was short of BASs. These unique features could not only ensure the propitious procession of MPV reduction but also suppress the emergence of secondary reactions; hence, Zr-MIZ demonstrated excellent catalytic performance. When it was employed for the hydrogenation of furfural in isopropanol, the yield and selectivity of furfuryl alcohol could be achieved at 99.2% at 130 °C for 4 h. More notably, Zr-MIZ could also be reused for five cycles with steady activity and for catalyzing the selective hydrogenation of many other carbonyl compounds (such as 5-methylfurfural, 5-hydroxymethylfurfural, benzaldehyde, terephthalaldehyde, cyclopentanone, cyclohexanone, levulinic acid, and methyl levulinate) via the MPV reduction under the appropriate reaction conditions, which further indicated good catalytic stability and universality. All in all, this work highlighted the immense potential of BAS-free zirconium-based coordination catalysts in isopropanol-based endogenous hydrogen systems.