Effect of Lewis and Brønsted acidity in Ni/ZSM-5 on catalytic reductive etherification of furfural and alcohols

Reductive etherification is an attractive and practical strategy to convert bio-platform compounds into valuable chemicals. In directed synthesis of furfuryl ethers, reductive etherification of bioderived furfurals is still challenging due to the complexity of catalytic reaction. Herein, reductive etherification of furfural with alcohol was investigated over Ni/ZSM-5 catalyst, which found that Si/Al ratios in ZSM-5 played an important role on the catalytic performance. For Ni/ZSM-5 with Si/Al ratio of 50, 80.9% yield of furfuryl ether at 90.8% conversion of furfural was achieved under the condition of 2 MPa H2 and 180 °C for 3 h in isopropanol. The catalyst exhibited superior stability and recyclability during the consecutive cycle run. Catalysts characterization demonstrated that both acidic properties and furfural adsorption were influenced by the Si/Al ratios in Ni/ZSM-5, which correlated to the reaction route and catalytic performance. Lewis acid sites enhanced furfural hydrogenation into furfuryl alcohol, while Brønsted acid sites on ZSM-5 effectively catalyzed sequential etherification of furfuryl alcohol to furfuryl ether. Under optimization conditions, various furfuryl ethers could be obtained with yields above 80% over Ni/ZSM-5 catalyst in different primary alcohols, demonstrating the general versatility of the approach. Our findings offered opportunities to develop an efficient furfuryl ethers synthesis method.