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A facile strategy was developed for the preparation of Ru nanoparticles supported on reduced graphene oxide (Ru/rGO) and its following functionalization with benzenesulfonic acid groups (Ru/rGO-S). The formation of a C–C bond between p-sulfophenyl and sp2 carbon of graphene can be unambiguously confirmed by XPS quantitative analysis. The two catalysts were used to catalyze the conversion of levulinic acid in aqueous phase, which is an important reaction during biorefinery. Not GC but HPLC was found to be the reliable analysis method for this reaction. Both of the catalysts exhibited high hydrogenation activities under mild reaction conditions (50 °C, 2 MPa), although their selectivities were different. The hydrogenated intermediate 4-hydroxyvaleric acid could be accumulated over Ru/rGO with a yield of 82% in 40 min, but the main product over Ru/rGO-S was γ-valerolactone (a yield of 82% within the same time) due to the accelerated dehydration process by strong acid sites. After being reused several times, the hydrogenation activities of Ru in each catalyst and dehydration ability of SO3H could be well kept. This effective method could be a general way to prepare graphene-based bifunctional catalysts, which are expected to have broad application prospects in biomass conversion.

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