Mo_xC nanoparticles confined in carbon nanotubes for selective hydrodeoxygenation of guaiacol to value-added phenol

Transition metal carbides have emerged as promising non-precious heterogeneous catalysts for lignin hydrodeoxygenation, but achieving high selectivity toward a specific product remains a significant challenge. In this work, we precisely control guaiacol conversion and phenol selectivity by tailoring the spatial distribution of molybdenum carbide (Mo_xC) nanoparticles on carbon nanotubes (CNT). The nanoparticles encapsulated within the CNT interior channels exhibit a coexistence of α-MoC and β-Mo₂C phases (Mo_xC@CNT), while the Mo_xC supported on CNT outside surfaces, which displays a single-phase β-Mo₂C structure (Mo₂C/CNT). The confined Mo_xC@CNT exhibits superior catalytic performance, delivering a phenol space-time yield of 131.5 μmol g_Mo^–1 s^–1 and an outstanding selectivity of 91.7%. In contrast, Mo₂C/CNT with nanoparticles dispersed on the outer CNT surface shows a poor guaiacol conversion. Furthermore, bulk Mo₂C achieves high guaiacol conversion but yields considerable amounts of benzene alongside phenol. Characterizations by means of HRTEM, CO–TPD, and H₂–TPD reveal that the confinement effects within the Mo_xC@CNT channels enriches H₂ and reactants, in addition to the synergy effects of α-MoC and β-Mo₂C phases, thereby boosting catalytic performance. However, bulk Mo₂C facilitates C_aryl–OH removal from phenol, resulting in benzene formation.