Thermodynamic analysis of carbon dioxide reforming of methane in view of solid carbon formation

The development of nonprecious metal based electrocatalysts for hydrogen evolution reaction (HER) has received increasing attention over recent years. Previous studies have established Mo2C as a promising candidate. Nevertheless, its preparation requires high reaction temperature, which more than often causes particle sintering and results in low surface areas. In this study, we show supporting Mo2C nanoparticles on the three-dimensional scaffold as a possible solution to this challenge and develop a facile two-step preparation method for ∼3 nm Mo2C nanoparticles uniformly dispersed on carbon microflowers (Mo2C/NCF) via the self-polymerization of dopamine. The resulting hybrid material possesses large surface areas and a fully open and accessible structure with hierarchical order at different levels. MoO42– was found to play an important role in inducing the formation of this morphology presumably via its strong chelating interaction with the catechol groups of dopamine. Our electrochemical evaluation dem...

Mo2C Nanoparticles Dispersed on Hierarchical Carbon Microflowers for Efficient Electrocatalytic Hydrogen Evolution

The carbides and nitrides of Mo and W can adsorb and activate hydrogen. The effects of particle size and surface area on the total amount of adsorbed hydrogen differ from those observed for transition metal sulfides. In the former case, this amount increases with increasing particle size and/or decreasing surface area. This is consistent with the involvement of the sub-surface regions of the crystallites during hydrogen adsorption. The activity for hydrogenation, hydrodesulfurization and hydrodenitrogenation exhibits similar trends. The high HDN activity of the Mo(W) carbide and nitride based catalysts has been noted. These catalysts are stable under typical hydroprocessing conditions although a partial sulfidation of their surface during HDS cannot be avoided.

Metal carbides and nitrides as potential catalysts for hydroprocessing

As a new member of the MXene group, 2D Mo2 C has attracted considerable interest due to its potential application as electrodes for energy storage and catalysis. The large-area synthesis of Mo2 C film is needed for such applications. Here, the one-step direct synthesis of 2D Mo2 C-on-graphene film by molten copper-catalyzed chemical vapor deposition (CVD) is reported. High-quality and uniform Mo2 C film in the centimeter range can be grown on graphene using a Mo-Cu alloy catalyst. Within the vertical heterostructure, graphene acts as a diffusion barrier to the phase-segregated Mo and allows nanometer-thin Mo2 C to be grown. Graphene-templated growth of Mo2 C produces well-faceted, large-sized single crystals with low defect density, as confirmed by scanning transmission electron microscopy (STEM) measurements. Due to its more efficient graphene-mediated charge-transfer kinetics, the as-grown Mo2 C-on-graphene heterostructure shows a much lower onset voltage for hydrogen evolution reactions as compared to Mo2 C-only electrodes.

Direct Synthesis of Large-Area 2D Mo 2 C on In Situ Grown Graphene.

A high level of hydrodenitrogenation (HDN) is required to achieve a desirable conversion of other hydroprocessing reactions. This results from a strong adsorption of nitrogen‐containing compounds on catalytic sites that slows down the hydrogen activation process and hinders the adsorption of other reactants. Studies on model compounds and real feeds indicate that less than 50 ppm of nitrogen in the feed can poison catalytic sites. Kinetic studies determined adsorption constants of various nitrogen‐containing compounds and concluded that at least four different catalytic sites are required to interpret experimental observations in contrast with a dual site site≅concept, which only considered two sites. The advancements in experimental techniques allowed identification of products formed during very early stages of hydrodenitrogenation. These results confirmed that the removal of the amino group from saturated amines, as the last step in hydrodenitrogenation, is governed by the type of carbon to which the a...

Hydrodenitrogenation of Petroleum

The synthesis of high surface area molybdenum carbides from molybdenum oxide and butane has been studied via temperature-programmed reaction (TPRe), X-ray diffraction (XRD), scanning electron microscopy (SEM), 13C solid-state NMR, infrared (IR), and Raman spectroscopy (LR) The molybdenum oxygen/carbon system passes through four phase transitions before transforming into the pure Mo2C carbide Carbon exists in two forms within high surface area molybdenum carbide The initially produced molybdenum carbide has a face-centered-cubic (fcc) structure but is gradually converted into the hexagonal-close-packed (hcp) structure with increasing carburization temperature, and eventually at high temperature coke is deposited During the early stages, MoO3 is reduced by H2, but at higher temperatures, butane also takes part in the reduction and, besides being consumed in the formation of carbide, is catalytically converted into methane, ethane, propane, and benzene The high surface area of the molybdenum carbide mat

Preparation of Molybdenum Carbides Using Butane and Their Catalytic Performance

Preparation and Characterisation of Bimetallic Cobalt and Molybdenum Carbides

The utilisation of high CO2 content natural gas, such as that found at Natuna island in Indonesia, using methane dry reforming with carbon dioxide to synthesis gas is demonstrated. Highly active catalysts employed for coke-free, stable dry reforming include alumina-supported nickel, either as-prepared or doped with tungsten oxide or calcium oxide, and the supported group VIII metals. No deactivation was observed for the duration of any of the experiments (>70 h), and the methane conversion and product distributions were close to those predicted from thermodynamic equilibrium calculations. It is calculated that the application of dry reforming to the Natuna field alone, combined with known gas-to-liquids (GTL) technology, could provide liquid fuel to Indonesia for almost 18 years.

Potential utilisation of Indonesia's Natuna natural gas field via methane dry reforming to synthesis gas

Bimetallic cobalt–molybdenum oxide (CoMoO x ) has been prepared and converted into CoMoN x , CoMoC x and CoMoS x materials by temperature-programmed reactions with ammonia, ethane or hydrogen sulfide, respectively. These new bimetallic materials have been characterised using X-ray diffraction (XRD) and solid state NMR and tested for pyridine hydrodenitrogenation (HDN) at various temperatures. The initial HDN activity of the catalysts decreases in order CoMoC x  ∼ CoMoN x  ∼ CoMoO x  > CoMoS x . The stability order of the first three of catalysts is CoMoC x  > CoMoN x  > CoMoO x , and their activities decrease with the time on stream. In contrast the pyridine conversion over CoMoS x is more stable and activity increases with the time on stream, from 30 to over 50%, this is accompanied by the formation of CoMoSC x material. The high catalytic activity of the CoMoC x catalyst may reflect the ability to hydrocrack pyridine to yield methane. The CoMoS x catalyst system has the highest selectivity to the products cyclopentane (35%) and pentane (27%).

Comparison of bulk CoMo bimetallic carbide, oxide, nitride and sulfide catalysts for pyridine hydrodenitrogenation

The synthesis of molybdenum and tungsten carbide from their oxides using the temperature programmed reaction method with methane and ethane is presented. Lower reaction temperatures are required for metal carbide formation with ethane, and the highest surface areas materials are also prepared by this method. In addition, the use of the different hydrocarbons enables synthesis of various phases of molybdenum or tungsten carbide. Thermogravimetric analysis studies demonstrate that the carbide formation mechanisms for the two transition metal carbides in ethane differ. Finally, a similar technique has been employed for the synthesis of uranium monocarbide with moderately high surface area.

Hamid Al-Megren

Papers

Preparation of Molybdenum Carbides Using Butane and Their Catalytic Performance

Preparation and Characterisation of Bimetallic Cobalt and Molybdenum Carbides

Potential utilisation of Indonesia's Natuna natural gas field via methane dry reforming to synthesis gas

Comparison of bulk CoMo bimetallic carbide, oxide, nitride and sulfide catalysts for pyridine hydrodenitrogenation

Synthesis of high surface area transition metal carbide catalysts