(425f) Enhancement in the Bio-Oil Hydrodeoxygenation Performance of Mo2c Due to Tungsten Doping: A DFT Study Using Lignin and Carbohydrates Derived Model Compounds

Transition metal carbide catalysts (Mo₂C, W₂C, TiC, VC) have emerged as promising alternatives to precious-metal-based catalysts (Ru, Pt, Pd) for hydrodeoxygenation (HDO) of biomass-derived species, including the HDO of pyrolysis derived bio-oil. However, low selectivity towards deoxygenation, high hydrogen partial pressure requirement, and excessive hydrogenation are major limitations of monometallic carbide catalysts. As a result, doping of mono-metallic carbides with another transition metal is suggested. In our previous work, we elucidated the microstructure of Tungsten (W) – doped molybdenum carbide (MoWC)sing experimental characterization and first-principles simulations. This study examines the HDO performance of the MoWC catalyst and compares it to that of its monometallic counterpart using six model compounds derived from the cellulose, hemicellulose, and lignin components of biomass: 5-HMF, Acetic acid, Eugenol, Levoglucosan, Methylglyoxal, and Vanillin. These moieties also make up for a significant portion of bio-oil. Furthermore, they encompass the vast majority of oxygen-containing function groups that constitute bio-oil. The generally accepted mechanism for HDO includes two major pathways: i) direct deoxygenation (DDO) and ii) hydrogenation–dehydration (HYD). Computational results in this work suggest that the presence of oxophilic tungsten in MoWC significantly brings down the direct deoxygenation barrier as compared to the corresponding monometallic catalyst Mo₂C. This trend of relatively lower deoxygenation energy barriers on MoWC is consistent across all model compounds, implying that MoWC would prefer direct deoxygenation pathways that reduce the H₂ consumption. Further, we also investigated the alternate pathway (HYD), and the comparison of reaction energetics revealed that kinetic barriers on both catalysts are identical. This suggests that MoWC has a higher relative preference for DDO over HYD, as compared to Mo₂C. As a result of its superior HDO performance for all oxygenated compounds, MoWC could be an effective and efficient catalyst for the real bio-oil mixture.