Selective synthesis of tungsten carbide phases W2C and WC as hydrogenation catalysts

Tungsten carbides are possible low-cost replacements for noble metal catalysts, but the role of different carbide stoichiometries (W2C, WC) and their polymorphs for catalytic behavior is poorly understood. We develop a "dynamic, isothermal" carburization of WO3 in a mixture of CH4 and H-2 to control phase composition and catalytic properties. A design-of-experiments approach reveals that the key parameters are synthesis temperature (670 to 775 degrees C) and addition of silica as stabilizer (0 or 70 mol%). X-ray diffraction shows that the composition can be adjusted from 14 to 99 wt% W2C, complemented by WC and a small fraction of W metal. Crystalline domain sizes for W2C are smaller than those of WC (>= 10 nm), affording thermodynamic stabilization of W2C in agreement with computational predictions (Shrestha et al., Chem. Mater. 2021, 33, 4606-4620). The amount of CO adsorbed scales with W2C content, and so does the performance in butyraldehyde or toluene hydrogenation. (C) 2021 Elsevier Inc. All rights reserved.