Construction of electron-deficient zirconium sites for the efficient catalytic transfer hydrogenation of levulinic acid

Abstract

Zirconium-derived catalyst with abundant Lewis acid-base pairs has earned it a place of prominence for the catalytic upgrade of bio-based carbonyls to valuable chemicals and fuels through catalytic transfer hydrogenation (CTH) reaction. However, the low catalytic efficiency of Zr-based catalysts urgently needs to be improved to meet the criterion for their industrial deployment. In this contribution, tungstophosphoric acid (HPW) was demonstrated as an effective modifier to the electronic structure of the pristine polyacrylonitrile and lignin-supported Zr nanofiber (Zr-Lig@PAN) to boost the CTH of levulinic acid (LA) into γ-valerolactone (GVL). Especially, an impressive GVL formation rate of 32.5 mmol·g−1·h−1 was implemented over Zr/HPW0.75g-Lig@PAN, significantly prevailing over the previous reported Zr-based catalysts for the CTH of LA or its ester to GVL. Mechanistic investigations well demonstrated that the superior electron-accept ability of HPW allowed the construction of electron-deficient Zr sites, which is beneficial to the adsorption and activation of LA and isopropanol, thus boosting the CTH reaction. These findings open up a new avenue to design efficient Zr-based catalysts for the CTH reaction by elaborately tuning the electronic structure of the catalyst in the presence of a second metal.