Hydrogen Evolution Reaction of γ-Mo0.5W0.5 C Achieved by High Pressure High Temperature Synthesis

Synthesis of Electrocatalytic Tungsten Carbide Nanoparticles by High-Pressure and High-Temperature Treatment of Organotungsten Compounds

Metal-organic framework (MOF)-derived carbon, which contains metal nanoparticles embedded in a carbon matrix, is becoming an important group of catalysts. We report the synthesis of tungsten carbide-carbon nanocomposites using a similar concept, i.e., by pyrolysis of organotungsten compounds under high-temperature and high-pressure conditions. We characterized the product using various analytical techniques and examined its electrocatalytic activity. Two precursors, Bis(cyclopentadienyl)tungsten (IV) dichloride (Cp2WCl2) and Bis(cyclopentadienyl)tungsten (IV) dihydride (Cp2WH2) were pyrolyzed at 4.5 GPa and 600 °C. Tungsten carbide (β-WC1-x) crystals with a size of 2 nm embedded in graphitic carbon were formed from Cp2WH2-derived samples. Electrochemical measurements showed that all samples were active in the oxygen reduction reaction (ORR), with the Cp2WH2-derived sample having the best catalytic performance.

Synthesis and Characterization of Mechanically Alloyed, Nanostructured Cubic MoW Carbide

Carbides are used extensively as cutting tools, forming dies, and recently in catalysis applications, among other industrial applications. In this work, the synthesis and characterization of a nanostructured MoW bimetallic carbide were carried out by mechanical alloying with a mixture of elemental powders with a nominal composition of W1.5Mo6C2.5 at different grinding times as follows: 25, 50, and 75 h in a low-energy ball mill at a speed of 500 rpm and 125 and 150 h in a high-energy ball mill at a speed of 1500 rpm. The formation of a solid solution was observed at 150 h of milling; the nanostructured bcc MoW carbide corresponded to the main phase in the sample, besides the presence of the nanostructured MoW alloy as a secondary phase with an average crystal size of 40.8 nm. The phases and morphology at every stage of milling were studied by: X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Vickers hardness. As the milling time increased, the hardness of these particles increased from 10.5 to 31.48 GPa for the powder particles milled for 150 h. The samples obtained at 125 and 150 h of milling were evaluated during catalytic aqua-thermolysis of heavy oil to analyze fuel desulfurization properties by Fourier transform infrared (FTIR) techniques. The results showed the breaking of S-S bonds, indicating the existence of a desulfurization reaction of heavy oil.

The shape-dependent surface oxidation of 2D ultrathin Mo2C crystals

2D atomic crystals have been widely explored, usually owing to their numerous shapes, of which the typical hexagon has drawn the most interest. However, the relationship between shape and properties has not been fully probed, owing to the lack of a proper system. Here, we demonstrate for the first time the shape-dependent surface oxidation of 2D Mo₂C crystals, where the elongated flakes are preferentially oxidized under ambient conditions when compared with regular ones, showing higher chemical activity. The gradual surface oxidation of elongated Mo₂C crystals as a function of time is clearly observable. Structural determinations reveal that a discrepancy in the arrangement of Mo and C atoms between elongated and regular crystals accounts for the selective oxidation behavior. The identification of the shape-dependent surface oxidization of Mo₂C crystals provides significant possibilities for tuning the properties of 2D materials via shape-control.