One-Pot Conversion of Furfural to Gamma-Valerolactone over Zr-SBA-15: Cooperation of Lewis and Brønsted Acidic Sites

A series of bifunctional Zr-SBA-15_x of varying molar Si/Zr ratio x (15–730) with isolated Lewis and Brønsted acid sites were prepared by an in situ synthesis procedure and applied to the one-pot conversion of furfural (FUR) to gamma-valerolactone (GVL). These catalysts were detailed and characterized by XRF, XRD, N2 physisorption, FTIR, SEM, TEM, NH3-TPD, and pyridine-DRIFT techniques. On all these Zr-SBA-15_x catalysts, the conversion of FUR was higher than 99%, while the GVL selectivity first increased and then decreased with decreasing x. A Zr-SBA-15_25 was identified as the best-performing catalyst, offering a 93.3% selectivity of GVL under optimized reaction conditions. The effects of reaction temperature, time, and solvent on catalytic performance were also investigated. Correlating the catalyst performance with the Brønsted acid site (BAS)/Lewis acid site (LAS) ratio uncovers that the balance between the LAS and the BAS would be the key to the higher catalytic performance. The possible reaction mechanism for the cascade conversion of FUR to GVL was proposed. Moreover, basic (lutidine and pyridine) additives were added, respectively, to the reaction solution to investigate their effects on catalytic performance, which provide a piece of evidence in support of the cooperative LAS–BAS bifunctional catalytic mechanism.