Single-phase mixed molybdenum-tungsten carbides: Synthesis, characterization and catalytic activity for toluene conversion

Synthesis and Characterization of Supported Mixed MoW Carbide Catalysts

For mixed MoW carbide catalysts, the relationship between synthesis conditions, evolution of (mixed) phases, extent of mixing, and catalytic performance of supported Mo/W carbides remains unclear. In this study, we prepared a series of carbon nanofiber-supported mixed Mo/W-carbide catalysts with varying Mo and W compositions using either temperature-programmed reduction (TPR) or carbothermal reduction (CR). Regardless of the synthesis method, all bimetallic catalysts (Mo:W bulk ratios of 1:3, 1:1, and 3:1) were mixed at the nanoscale, although the Mo/W ratio in individual nanoparticles varied from the expected bulk values. Moreover, the crystal structures of the produced phases and nanoparticle sizes differed depending on the synthesis method. When using the TPR method, a cubic carbide (MeC_1-x ) phase with 3-4 nm nanoparticles was obtained, while a hexagonal phase (Me₂C) with 4-5 nm nanoparticles was found when using the CR method. The TPR-synthesized carbides exhibited higher activity for the hydrodeoxygenation of fatty acids, tentatively attributed to a combination of crystal structure and particle size.

Molybdenum-Tungsten Blue Nanoparticles as a Precursor for Ultrafine Binary Carbides

Herein, we demonstrate a promising method for the synthesis of ultrafine carbide particles using dispersions of molybdenum–tungsten nanoparticles. Dispersions of molybdenum–tungsten blue nanoparticles with different initial molar ratios of molybdenum/tungsten were synthesized through the reduction of molybdate and tungstate ions by ascorbic acid in an acidic medium (pH = 1.0–2.5). Molybdenum–tungsten blue nanoparticles were characterized by ultraviolet–visual (UV–VIS), infrared (FTIR), and X-ray photoelectron (XPS) spectroscopies; transmission electronic microscopy (TEM); and dynamic light scattering (DLS). We demonstrated that molybdenum–tungsten blue nanoparticles belong to toroidal polyoxometalate clusters (λ_max = 680–750 nm) with a predominant particle size of 4.0 nm. Molybdenum–tungsten blue dispersions were shown to be monodispersed systems with a small particle size and long-term stability (>30 days) and are suitable for further catalytic applications.

Synthesis of Microporous Mo2C-W2C Binary Carbides by Thermal Decomposition of Molybdenum-Tungsten Blues

Molybdenum and tungsten carbides are perspective catalytic systems. Their activity in many reactions is comparable to the activity of platinum group metals. The development of the synthesis method for of highly dispersed binary molybdenum and tungsten carbides is an important task. Dispersions of molybdenum-tungsten blue were used as a precursor for synthesis of binary molybdenum and tungsten carbides. The synthesis of carbides was carried out by thermal decomposition of molybdenum-tungsten blue xerogels in an inert atmosphere. The binary carbides were characterized by XRD, TGA, SEM and nitrogen adsorption. The influence of the molar ratio reducing agent/Me [R]/[ΣMe], molar ratio molybdenum/tungsten [Mo]/[W] on phase composition, and morphology and porous structure of binary carbides was investigated. Samples of binary molybdenum and tungsten carbides with a highly developed porous structure and a specific surface area were synthesized.

Synergistic effect of Mo–W carbides on selective hydrodeoxygenation of guaiacol to oxygen-free aromatic hydrocarbons

Mo–W carbide was synthesized via temperature-programmed reduction to generate a β-Mo₂C phase with bulk morphology.