SSZ-39 zeolite-based Ru catalysts for selective hydrogenation of levulinic acid to γ-valerolactone: Influence of synthesis method and zeolite acidity

Novel SSZ-39 zeolite-based Ru catalysts were synthesized by impregnation on as-synthesized metallic and protonated SSZ-39 and a one-pot synthesis strategy. The study focused on the influence of the SSZ-39 zeolite characteristics and catalyst preparation method type toward levulinic acid (LA) selective conversion to γ-valerolactone (GVL) under relatively mild reaction conditions (150 °C, 4 h and 2 MPa of H2 with H2O and THF as solvents). Catalysts exhibited excellent catalytic efficiency (100 % LA conversion and 98.3 % GVL selectivity) and remarkable hydrothermal stability. The results revealed a correlation between excellent catalytic activity and the structural features of the synthesized catalysts, predominantly dependent on their appropriate surface acidity (strong Lewis acid sites) and enhanced electronic interaction between Ru species and SSZ-39. The one-pot method promoted the formation of mesopores besides the zeolitic micropores present in SSZ-39; therefore, the catalyst prepared by the one-pot method (Ru/SSZ-39) showed purer SSZ-39 crystallites and a slightly larger catalytic surface area of 439 m2/g than the original zeolite surface area of 424 m2/g. In addition, the original zeolite crystals retained their morphology as spherical aggregates and remained unaffected by Ru impregnation on the metallic or protonated support during the synthesis of Ru/Na-SSZ-39 and Ru/H-SSZ-39 catalysts, respectively. Notably, it has been demonstrated that SSZ-39 zeolite effectively acts as a support for the preparation of Ru catalyst in biomass conversion reactions. Moreover, the reused catalyst exhibited consistent activity over six cycles, maintaining its structural framework without significant loss in activity. [Display omitted] •Ru/SSZ-39 zeolite catalysts were achieved using impregnation and one-pot method synthesis methods.•The one-pot synthesis yielded purer SSZ-39 crystallites and a larger catalytic surface area.•The addition of Ru generates intermediate acidic sites, enhancing catalytic performance toward hydrogenating LA to GVL.•SSZ-39 zeolite effectively acts as a Ru catalyst support in biomass conversion reactions.