Synergistic effect of Pd and Mo catalysts on the biomass hydropyrolysis vapor upgrading for aromatic hydrocarbons

Biomass hydropyrolysis vapor upgrading (HPVU) is a promising approach for biofuel production, where metallic catalysts play a key role in oxygen removal and aromatic hydrocarbon formation. In this study, Pd/HZSM-5 and Mo/γAl 2 O 3 catalysts were prepared and utilized individually or in combination to investigate their effects on poplar HPVU in a continuous-flow reactor. Meanwhile, the influence of upgrading temperature on hydrodeoxygenation (HDO) reactions was studied. At an upgrading temperature of 400 ℃, combination of Pd/HZSM-5 and Mo/γAl₂O₃ resulted in an organic phase yield of 9.19 wt%. The mass yield and selectivity of aromatic hydrocarbons reached 8.13 wt% and 93.4 %, respectively, with selectivity of C8 + monocyclic aromatic hydrocarbons accounting for 56.7 %. The overall mass balance was 96.2 %. The presence of Pd promotes hydrogenation and hydroalkylation reactions, while Mo/γAl₂O₃ enhances deoxygenation. Additionally, its mesoporous structure facilitates reactant diffusion. The density functional theory calculations confirmed that Pd could efficiently activate H 2 and thus provide hydrogen radicals for HDO on Mo/γAl₂O₃ surface, which revealed the synergistic effect of these two catalysts. This study highlights that noble-metal catalyst aided by oxophilic metal catalyst can make a significant contribution to biomass HPVU.