Graphene-Based Metal/Acid Bifunctional Catalyst for the Conversion of Levulinic Acid to γ-Valerolactone

Abstract

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.

Functionalised heterogeneous catalysts for sustainable biomass valorisation

“…Compared to metal oxides, carbon supports show a stronger ability to stabilise both acid and metal sites because of their high hydrothermal stability and rich surface chemistry. Wang et al 79 developed a facile synthesis procedure for developing a graphene-supported Ru/SO 3 H bi-functional catalyst. In this process, Ru NPs are initially deposited on graphene, followed by its functionalisation with benzenesulfonic acid groups (Fig.…”

Cascade catalytic hydrogenation–cyclization of methyl levulinate to form γ-valerolactone over Ru nanoparticles supported on a sulfonic acid-functionalized UiO-66 catalyst

“…[5][6][7][8][9] Indeed, many reports exist into the catalytic conversion of LA using both homogeneous and heterogeneous noble and non-noble metal catalysts in liquid and vapor phase systems. [5][6][7][8][9][11][12][13][14][15][16][17][18] Among the various metals investigated, ruthenium appears to be the most active and selective metal for the conversion of LA to GVL, mainly due to its selective hydrogenation of carbonyl groups without altering other unsaturated functionalities. [11][12][13][14][15][16][17][18] However, traditional catalysts, such as commercial Ru/C, oen exhibit leaching of the ruthenium species through the formation of metal-carboxylate complexes with LA, which is likely caused by the weak acidity of LA (pK a ¼ 4.59), [19][20][21] results in a low catalytic activity and poor catalyst reusability.…”

“…Therefore, the prerequisite for establishing an efficient ML to GVL conversion process is to develop high performance dual-functional solid catalysts containing metal nanoparticles and acidic sites to enhance the process efficiency (i.e., catalytic activity and selectivity) and process simplicity. 14,15 As a relative new class of crystalline ordered materials, metal-organic frameworks (MOFs), have attached signicant attention in several areas, in particular in the eld of catalysis, because of their controllable pores characteristics, large internal surface areas, and tunable chemical properties. [25][26][27] For example, the typical Zr-based MOF, UiO-66, is comprised of 12coordinated Zr 6 O 4 (OH) 4 clusters that are connected threedimensionally with terephthalic acid (BDC) linkers.…”

Transformation of Levulinic Acid to Valeric Biofuels: A Review on Heterogeneous Bifunctional Catalytic Systems

“…The satisfactory catalytic performance was proven to be attributed to the synergistic effect of acid sites on the SPES support and metal sites of the Ru nanoparticles. Reduced sulfonated graphene oxide supported Ru (Ru/rGO‐S) and reduced graphene oxide supported Ru (Ru/rGO) were fabricated to promote the hydrogenation of LA in aqueous solution by Wang et al . Contrasting experiments indicated that, although high hydrogenation performance was achieved at 50 °C under 2 MPa H 2 , the two catalysts exhibited different product selectivity.…”