(180c) Effect of W Dopant on the Hydrodeoxygenation Performance of Mo2c: Investigating the Microstructure of the Catalyst and Reaction Pathways Using Guaiacol As a Model Compound

Pyrolysis of lignocellulosic biomass is a promising method to convert it to fuels. However, the intermediate product i.e., bio-oil exhibits undesired properties like low heating value and high oxygen content, making catalytic hydrodeoxygenation (HDO) essential to improve the quality of biofuels. Transition metal carbide catalysts (Mo₂C, W₂C) have emerged as promising alternatives to precious-metal-based catalysts (Pt, Pd) for HDO. However, low selectivity and high hydrogen consumption are major limitations of catalysts based on monometallic carbides. To enhance the HDO performance, monometallic carbides should be systematically modified with suitable dopants, and this requires fundamental understanding of catalyst microstructure (and its stability), reaction mechanisms and energetics. Hence, this work focuses on developing bimetallic carbides by doping with tungsten (W), an oxophilic metal, in the monometallic molybdenum carbide (MoWC). Firstly, the thermodynamically most stable microstructure of the bimetallic carbide is suggested. Using the experimentally determined stoichiometric ratio in the bimetallic carbide, calculations revealed that bulk alloy of mixed metal carbide (MoWC) along with a monolayer of metallic tungsten is the most stable microstructure. We also computed core-level shifts in binding energy of Mo and W, validating the experimentally observed XPS shifts of +0.3 eV and -0.1 eV in W 4f and Mo 3d spectra respectively, which corresponds to a decrease in the electron density of W atom. Secondly, the HDO reaction mechanisms of guaiacol, a model compound, are explored on Mo₂C and MoWC. Two competitive pathways, Direct Deoxygenation (DDO) and Hydrogenation – dehydration (HYD), are observed on Mo₂C with relatively similar free energy barriers. The former is to directly break the –OH bond of phenol to form benzene, while the latter is to hydrogenate the aromatic ring of phenol leading to undesirable ring saturated products. Conversely, the modified MoWC catalyst facilitates the DDO pathway over the HYD pathway, potentially reducing the hydrogen requirements.