Catalytic Transfer Hydrodeoxygenation of Lignin-Derived Phenolic Compounds over RuMo/NC with Isopropanol as <i>In Situ</i> Hydrogen Source

Using isopropanol as an in situ hydrogen source, lignin-derived phenolics were effectively hydrodeoxygenated to cyclohexanol and cyclohexane over RuMo/NC bimetallic catalysts, which were prepared via a facile in situ pyrolysis strategy. Catalyst screening showed that Ru0.75Mo0.25/NC achieved complete conversion of 4-propylguaiacol at 240 °C, producing 70.4% 4-propylcyclohexanol and 20.4% propylcyclohexane as the major products. Physicochemical characterizations, including N2 sorption, high-resolution transmission electron microscopy, X-ray diffraction, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy, revealed that the uniform dispersion of nanoscale, electron-deficient Ru species and electron-enriched Mo species, anchored on a micromesoporous N-doped carbon matrix, is responsible for the excellent catalytic transfer hydrodeoxygenation (CTHDO) activity of Ru0.75Mo0.25/NC. Isopropanol, as a secondary alcohol, demonstrated significantly superior in situ hydrogen-donating capabilities than primary alcohols, effectively promoting the CTHDO of phenolic compounds. The CTHDO of 4-propylguaiacol followed a sequential reaction pathway consisting of dehydroxylation to form 4-propylphenol, aromatic hydrogenation to yield 4-propylcyclohexanol, and further dehydroxylation to generate propylcyclohexane. CTHDO of other phenolic compounds confirmed the general applicability of Ru0.75Mo0.25/NC. Moreover, the catalyst exhibited high stability and retained its activity after five cycles, highlighting its potential for sustainable applications in green fuel production.