Nitrogen doped carbon supported ruthenium catalyst from chitosan: a sustainable approach for efficient hydrogenation of Levulinic acid to γ-valerolactone

Fossil fuels have long powered industries and transportation, but their depletion and environmental impact have driven the search for renewable alternatives like biomass. Levulinic acid (LA), derived from lignocellulosic biomass, can be converted into valuable products such as gamma valerolactone (GVL). GVL which can be used as solvent and for synthesis of sustainable fuels and polymers. Ruthenium-based catalysts, particularly Ru/C, are effective in hydrogenating LA to GVL but face challenges like metal leaching and catalyst degradation. To address this, researchers are improving catalyst stability through nitrogen-doped carbon supports and embedding strategies, however most of them involves tedious synthesis and expensive and non-renewable chemicals. In this work, we synthesized a stable, efficient ruthenium catalyst supported on carbon from biomass-derived chitosan without using additional nitrogen dopants, aiming to enhance its performance in LA hydrogenation. The Ru catalyst supported on N-doped carbon from chitosan pyrolysis at 700 °C, exhibited superior activity, stability, and recyclability for LA hydrogenation to GVL, outperforming conventional Ru/C and shows comparable activity with other reported Ru catalysts. Characterization by XPS and H₂-TPR revealed strong metal-support interactions facilitated by nitrogen functionalities, which stabilized ruthenium species in both reduced and oxidized states. Graphitic nitrogen species in the catalyst were decisive in the controlling the catalytic activity also maintaining a fine balnace between different nitrogen species and N-content was the key to synthesize suitable supports from chitosan. A proposed reaction mechanism highlights the role of Ru-N centers in facilitating hydrogen and LA activation and hydrogenation step, with basic nitrogen sites (pyridinic and pyrrolic nitrogen) aiding in the dehydration step to form GVL. Overall, this work features the potential of chitosan derived carbon as a sustainable and tunable support for designing efficient catalysts for biomass hydrogenation and the findings provide fundamental insights into the role of nitrogen doping in enhancing catalytic performance.