Room temperature continuous flow synthesis of γ-valerolactone and N-containing heterocycles over Ru supported bimodal N,S-doped cubic mesoporous carbon

Abstract

One of the key steps in producing value-added chemicals from biomass-derived compounds is the conversion of levulinic acid (LA) into useful products. In the present work, a novel catalyst was prepared by immobilizing ruthenium nanoparticles on bimodal N,S-doped ordered mesoporous carbon (IBOMC). Various analytical methods, including TEM, XRD, XPS and N₂ adsorption–desorption, were used to characterize both IBOMC and the synthesized catalyst (Ru@IBOMC). Ru@IBOMC was then successfully utilized in the continuous flow catalytic hydrogenation of LA to γ-valerolactone and N-containing heterocycles at room temperature. The effects of different reaction variables (such as temperature, H₂ gas pressure, solvent, LA concentration, and flow rate) were examined. This catalytic protocol exclusively affords quantitative yields of γ-valerolactone at room temperature under continuous flow conditions under 30 bar H₂ pressure. The catalyst also exhibits excellent activity for producing N-containing heterocycles at room temperature by using either aniline or acetonitrile as the amine source. The catalyst shows consistent performance for at least 72 hours without significant loss of activity and selectivity in a wide range of solvents, giving an excellent weight hourly space velocity (WHSV) of 48 h⁻¹. These results confirmed that nitrogen and sulfur active centres in IBOMC can effectively stabilize ruthenium nanoparticles and synergistically enhance the performance of Ru active centers in the hydrogenation of LA.