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

•The bifunctional Ru/[Bmim]3PW12O40 catalyst has a high hexitol selectivity in cellulose conversion.•Brønsted acid sites were generated in situ via hydrogen spillover from Ru to the support.•The Brønsted acids work synergistically with Ru to catalyze the hydrogenolysis of cellulose.

A catalyst consisting of dispersed Ru on an ionic liquid (BmimPF6)–heteropolyacid (H3PW12O40·nH2O) hybrid as a support, i.e. Ru/[Bmim]3PW12O40, has been successfully synthesized. The catalyst, which combines the Ru sites for hydrogenation and both Lewis and Brønsted acidic sites for hydrolysis, exhibits a superior catalytic performance for selective conversion of the microcrystalline cellulose to hexitols over the catalyst of mixing [Bmim]3PW12O40 and Ru/C. On the Ru/[Bmim]3PW12O40 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 H2. The superior catalytic performance of Ru/[Bmim]3PW12O40 has been characterized using the hydrogenolysis of cellobiose as a probe reaction and was attributed to the Brønsted acid sites generated from hydrogen spillover from the Ru sites to the O sites of the support. In situ generation of the Brønsted acidic sites through hydrogen spillover has been confirmed by FT-IR characterization of pyridine adsorption. Furthermore, pH changes after treating the catalyst in H2 demonstrated that dissolution of the protons generated on the oxygen sites as a result of hydrogen spillover acidifies the liquid product. These Brønsted acids work synergistically with the supported Ru and contribute to the enhanced hydrogenolysis activity.

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