Biomass to aviation-fuel-range hydrocarbon conversion over Pd-Mo/γ-Al₂O₃ catalysts: Revealing synergistic active sites and reaction pathways

Biomass hydropyrolysis (HP) vapor upgrading (VU) is highly promising for producing sustainable aviation fuel, yet challenges remain. This study focused on PdMo/γ-Al 2 O 3 and Mo/γ-Al 2 O 3 catalyzed HP-VU of biomass in a pressurized continuous fixed-bed and the reaction mechanism. The results demonstrated that the introduction of Pd enhanced the hydrodeoxygenation activity through multiple effects, including the generation of surface acidic sites, the formation of oxygen vacancies, and the effect of hydrogen spillover. Beyond this, the effects of upgrading temperature and pressure on the catalytic performance of PdMo/γ-Al 2 O 3 were also investigated. Under optimal conditions of 400 °C and 1.0 MPa, the organic phase achieved a mass yield of 12.03 wt%, with the selectivity of C4+ aliphatic hydrocarbons and monocyclic aromatic hydrocarbons reaching 77.01 %, leading to an HHV of 42.41 MJ/kg and high mass balance (98.71 %). Density functional theory calculations further provided insights into the role of defect sites in facilitating C–O/C=O bond cleavage and the contribution of Pd sites to C C bond activation. By integrating theoretical calculations with model compound experiments, the study revealed the potential reaction pathways including hydrodeoxygenation, hydrogenation, and C C coupling. This study provides practical and theoretical insights into the bimetallic-catalyzed HP-VU process of biomass.