Enhanced hydrothermal stability by a semi-embedded structure: An efficient Ru catalyst for levulinic acid conversion in the aqueous phase

Catalyst stability is believed to be one of the greatest challenges faced for the supported metal catalysts in the catalytic conversion of biomass and its derivatives because many biomass transformations are conducted in the aqueous phase. In this work, we report a simple yet efficient coating-impregnation-pyrolysis (CIP) strategy to fabricate Al₂O₃ supported Ru catalyst (Ru-Al₂O₃@CN) with Ru NPs (nanoparticles) semi-embedded into N-doped carbon (CN) layer for the efficient hydrogenation of levulinic acid (LA) to γ-valerolactone in the aqueous phase. Benefit from the special structure of Ru-Al₂O₃@CN catalyst, it possesses both high catalytic activity and stability, giving a TOF of 28,099 h^-1 for LA hydrogenation at 120 °C and 2 MPa H₂, which is superior to the most of reported Ru-based catalysts. More importantly, compared with conventional impregnated Ru/Al₂O₃ catalyst, the Ru-Al₂O₃@CN catalyst exhibits a remarkably improved hydrothermal stability. Based on series of catalyst characterizations and control experiments, it was found that the presence of CN can weak the interaction between Ru and Al₂O₃, as well as protect the Al₂O₃ and Ru NPs from hydrolysis and aggregation, respectively. We anticipate that such a novel strategy may provide some valuable insights into the synthesis of oxides-supported metal catalyst with high hydrothermal stability.