Hydrogenation of Furfural to Furfuryl Alcohol over Magnetic and Porous FeAl (Hydr)oxide Composites

In this work, a porous, magnetic, and high specific surface area FeAl (hydr)oxide composite was synthesized via prolonged low-temperature crystallization of FeAl precipitates at 80 °C. The material exhibited significantly higher contents of acidic and basic sites compared to samples prepared under high-temperature or short-duration low-temperature conditions. Furthermore, comparative analysis demonstrates that the introduction of Al facilitates both increased electron deficiency in Fe species and the formation of α-FeOOH crystalline phase while simultaneously enhancing specific surface area, thereby significantly improving catalytic performance. During the transfer hydrogenation of furfural to furfuryl alcohol using 2-propanol as the hydrogen donor, the composite demonstrated superior performance, achieving a furfuryl alcohol yield of 95.1% after 8 h at 140 °C, with approximately 89.1% yield maintained even after eight catalytic cycles. Catalytic site poisoning experiments reveal that the coexistence of abundant acidic and basic sites is a crucial factor for achieving high catalytic transfer hydrogenation (CTH) activity, and that equivalent-level depletion of basic sites induces markedly stronger suppression of reaction efficiency than corresponding acid site poisoning. The introduction of exogenous Brønsted acids, such as benzoic acid, not only passivated active basic sites but also induced the etherification of furfuryl alcohol with 2-propanol. Isotopic labeling studies confirmed that the hydroxyl H in furfuryl alcohol was specifically transferred from the hydroxyl H of 2-propanol, while the α-H in furfuryl alcohol originated from nonhydroxyl H, most likely from the α-H of 2-propanol. These findings provide strong evidence for the proposed catalytic mechanism.