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 nitrides from structures to industrial applications

Owing to their remarkable characteristics, refractory molybdenum nitride (MoN x )-based compounds have been deployed in a wide range of strategic industrial applications. This review reports the electronic and structural properties that render MoN x materials as potent catalytic surfaces for numerous chemical reactions and surveys the syntheses, procedures, and catalytic applications in pertinent industries such as the petroleum industry. In particular, hydrogenation, hydrodesulfurization, and hydrodeoxygenation are essential processes in the refinement of oil segments and their conversions into commodity fuels and platform chemicals. N-vacant sites over a catalyst’s surface are a significant driver of diverse chemical phenomena. Studies on various reaction routes have emphasized that the transfer of adsorbed hydrogen atoms from the N-vacant sites reduces the activation barriers for bond breaking at key structural linkages. Density functional theory has recently provided an atomic-level understanding of Mo–N systems as active ingredients in hydrotreating processes. These Mo–N systems are potentially extendible to the hydrogenation of more complex molecules, most notably, oxygenated aromatic compounds.

On Catalytic Behavior of Bulk Mo2C in the Hydrodenitrogenation of Indole over a Wide Range of Conversion Thereof

The catalytic activity of bulk molybdenum carbide (Mo2C) in the hydrodenitrogenation (HDN) of indole was studied. The catalyst was synthesized using a temperature-programmed reaction of the respective oxide precursor (MoO3) with the carburizing gas mixture of 10 vol.\% CH4/H2. The resultant material was characterized using X-ray diffraction, CO chemisorption, and nitrogen adsorption. The catalytic activity was studied in the HDN of indole over a wide range of conversion thereof and in the presence of a low amount of sulfur (50 ppm), which was used to simulate the processing of real petroleum intermediates. The molybdenum carbide has shown high activity under the tested operating conditions. Apparently, the bulk molybdenum carbide turned out to be selective towards the formation of aromatic products such as ethylbenzene, toluene, and benzene. The main products of HDN were ethylbenzene and ethylcyclohexane. After 99% conversion of indole HDN was reached (i.e., lack of N-containing compounds in the products was observed), the hydrogenation of ethylbenzene to ethylcyclohexane took place. Thus, the catalytic behavior of bulk molybdenum carbide for the HDN of indole is completely different compared to previously studied sulfide-based systems.

Molybdenum and tungsten carbides can shine too

In this perspective, we argue that transition metal carbides such as molybdenum and tungsten hold great potential for the catalytic conversions of future feedstocks due to their ability to remain active in the presence of impurities in the feedstock.

Key Role of Precursor Nature in Phase Composition of Supported Molybdenum Carbides and Nitrides

In this work, we studied the effect of molybdenum precursors and the synthesis conditions on the final phase composition of bulk and supported molybdenum carbides and nitrides. Ammonium heptamolybdate, its mixture with hexamethylenetetramine, and their complex were used as the precursors at different temperatures. It was investigated that the synthesis of the target molybdenum nitrides strongly depended on the structure of the precursor and temperature conditions, while the synthesis of carbide samples always led to the target phase composition. Unlike the carbide samples, where the α-Mo₂C phase was predominant, the mixture of β-Mo₂N, MoO₂ with a small amount of metal molybdenum was generally formed during the nitridation. All supported samples showed a very good dispersion of the carbide or nitride phases.

Highly dispersed molybdenum carbide nanoparticles supported on activated carbon as an efficient catalyst for the hydrodeoxygenation of vanillin

Characterized by XRD and TEM, highly dispersed molybdenum carbide (Mo₂C) nanoparticles with a diameter of 1–4 nm were effectively synthesized on activated carbon at 700 °C.

First Principles Calculations of the Relative Stability, Structure and Electronic Properties of Two Dimensional Metal Carbides and Nitrides

Recently, a number of graphene-like early transition metal carbides and nitrides named as MXenes were fabricated by exfoliating MAX phases in hydrofluoric acid at room temperature. From experiments results and theory calculations, MXenes are promising anode materials in batteries as well as in metal-ion capacitors. To the best of our knowledge, experimental or calculated evidence has been supported the existence of more than 70 MAX phases members. Therefore, many counterparts MXene may be exist. Herein, employing density functional theory (DFT) computations, we have systematically examined the relative stability, structure and electronic properties of a series of two-dimensional metal carbides and nitrides including M2C (M=Sc, Ti, V, Cr, Zr, Nb, Hf, Mo and Ta), M2N (M=Ti, V, Cr, Zr, Hf), M3C2(M=Ti, V, Nb, Ta), Ti3N2, M4C3(M=Ti, V, Nb, Ta) and Ti4N3. The results demonstrate that all MXenes are metallic and have the similarly electronic structure with bulk transition metal carbides and nitrides, indicating that MXene may have superior catalysis and adsorption instead of expensive pure transition metal.

Preparation of supported Mo(2)C-based catalysts from organic-inorganic hybrid precursor for hydrogen production from methanol decomposition

An effective and safe route is proposed to prepare supported Mo(2)C-based catalysts from organic-inorganic hybrids, which exhibit high activity and stability for producing H(2) from methanol catalytic decomposition.