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.

Figure optionsDownload high-quality image (168 K)Download as PowerPoint slide