Selective conversion of microcrystalline cellulose into hexitols over a Ru/[Bmim]3PW12O40 catalyst under mild conditions

A catalyst consisting of dispersed Ru on an ionic liquid (BmimPF(6))-heteropolyacid (H3PW12O40 center dot nH(2)O) hybrid as a support, i.e. Ru/[Bmim](3)PW12O40, has been successfully synthesized. The catalyst, which combines the Ru sites for hydrogenation and both Lewis and Bronsted acidic sites for hydrolysis, exhibits a superior catalytic performance for selective conversion of the microcrystalline cellulose to hexitols over the catalyst of mixing [Bmim](3)PW12O40 and Ru/C. On the Ru/[Bmim](3)PW12O40 catalyst, a sorbitol selectivity of 70.3% with a microcrystalline cellulose conversion of 63.7% was achieved in 24 h at 433 K and 5 MPa H-2. The superior catalytic performance of Ru/[Bmim](3)PW12O40 has been characterized using the hydrogenolysis of cellobiose as a probe reaction and was attributed to the Bronsted acid sites generated from hydrogen spillover from the Ru sites to the O sites of the support. In situ generation of the Bronsted acidic sites through hydrogen spillover has been confirmed by FT-IR characterization of pyridine adsorption. Furthermore, pH changes after treating the catalyst in H-2 demonstrated that dissolution of the protons generated on the oxygen sites as a result of hydrogen spillover acidifies the liquid product. These Bronsted acids work synergistically with the supported Ru and contribute to the enhanced hydrogenolysis activity. (C) 2013 Elsevier B.V. All rights reserved.