Carbon Nitride-Modified Zr/SBA-15: A Highly Efficient Catalyst for Reductive Etherification of Furfural to Isopropyl Furfuryl Ether

Abstract The direct conversion of biomass-derived furfural (FUR) into isopropyl furfuryl ether (IPFE) via one-pot reductive etherification is a sustainable and economical route. However, this process remains challenging due to the need for bifunctional catalysts with balanced Lewis and Brønsted acid sites. In this work, a series of carbon nitride (CN)-modified Zr/SBA-15 catalysts (ZrxCNy/SBA-15) were synthesized by a simple impregnation method and evaluated for the reductive etherification of FUR using isopropanol as both the solvent and the hydrogen donor. The introduction of CN significantly enhanced the catalytic performance by increasing the dispersion of Zr species, enriching Lewis acid sites (LAS), and introducing Lewis base sites (LBS) from nitrogen functionalities. The optimized Zr4.4CN3.6/SBA-15 catalyst achieved a remarkable IPFE yield of 91.6% under mild conditions, substantially outperforming the CN-free counterpart (14.9% IPFE yield). By optimizing the reaction conditions, a 94.2% FUR conversion and a 92.7% selectivity to IPFE were achieved at 150 °C within only 20 min, corresponding to a productivity of 52.5 mmol·g–1·h–1, which was significantly superior to the results reported in the literature. XPS and Py-FTIR characterization revealed that the synergistic acid–base bifunctional mechanism, together with enhanced Lewis acidity via electronic interaction between CN and Zr, is responsible for the high activity and selectivity. Poisoning experiments confirmed that LBS, LAS, and BAS are all essential for the cascade conversion of FUR to IPFE, and a plausible reaction mechanism was accordingly proposed. The catalyst also exhibited excellent reusability and structural stability over five consecutive cycles.