Zr Oxo Cluster for Cascade Conversion of Furfural to Alkyl Levulinates

Graphical Zr oxo cluster bifunctional catalyst : The Zr oxo cluster [Zr 6 O 4 (OH) 4 (HSCH 2 CH 2 COO) 12 ] 2 has been developed, and then the molecular catalyst with Lewis acid and Brönsted acid sites were attained by the oxidation of the sulfhydryl group of the Zr oxo cluster with H 2 O 2 . The resulting bifunctional catalyst showed a superior catalytic activity for alcoholysis of furfural to alkyl levulinates. A novel dodecanuclear Zr oxo cluster [Zr 6 O 4 (OH) 4 (HSCH 2 CH 2 COO) 12 ] 2 (ZrO-SH-10) has been constructed under the room temperature, followed by oxidation of the sulfhydryl group with H 2 O 2 to achieve a bifunctional catalyst with Lewis acid and Brönsted acid sites. The characterization of catalysts indicated that {Zr 6 O 4 } cluster core can be stabilized with a shell of carboxylate ligands, and the resulting ZrO-SO 3 H was formed as a discrete molecular catalyst, exhibiting superior activity and recyclability for the cascade conversion of furfural to alkyl levulinate by the integration of transfer hydrogenation and alcoholysis in n-butanol. The yield of n-butyl levulinate can achieve as high as 91 % under the optimum conditions. Meanwhile, no leaching of the active species was found, which confirmed the structure of the Zr oxo cluster was air and moisture-stable. On the basis of the studies on the reaction kinetics and isotope tracking, the reaction mechanism was proposed accordingly.