Molybdenum Carbide Catalysts Research Articles

Molybdenum Carbide Catalyst Enables Efficient Conversion of Chlorinated Volatile Organic Waste into Syngas through Catalytic Steam Reforming

Molybdenum Carbide Catalyst Enables Efficient Conversion of Chlorinated Volatile Organic Waste into Syngas through Catalytic Steam Reforming

Reaction-induced unsaturated Mo oxycarbides afford highly active CO2 conversion catalysts.

Sustainable CO2 conversion is crucial in curbing excess emissions. Molybdenum carbide catalysts have demonstrated excellent performances for catalytic CO2 conversion, but harsh carburization syntheses and poor stabilities make studies challenging. Here an unsaturated Mo oxide (Mo17O47) shows a high activity for the reverse water-gas shift reaction, without carburization pretreatments, and remains stable for 2,000 h at 600 °C. Flame spray pyrolysis synthesis and Ir promoter facilitate the formation of Mo17O47 and its in situ carburization during reaction. The reaction-induced cubic α-MoC with unsaturated Mo oxycarbide (MoOxCy) on the surface serves as the active sites that are crucial for catalysis. Mechanistic studies indicate that the C atom in CO2 inserts itself in the vacancy between two Mo atoms, and releases CO by taking another C atom from the oxycarbide to regenerate the vacancy, following a carbon cycle pathway. The design of Mo catalysts with unsaturated oxycarbide active sites affords new territory for high-temperature applications and provides alternative pathways for CO2 conversion.

Catalytic Hydrogenolysis of HMF to DMF over N-doped Molybdenum Carbide Catalyst

Catalytic Hydrogenolysis of HMF to DMF over N-doped Molybdenum Carbide Catalyst

Eugenol Hydrodeoxygenation Over Mixed Mo-W Carbides.

The modification of molybdenum carbide catalysts by another transition metal has raised an increasing research interest due to the significant improvement of catalyst activity in hydrodeoxygenation of lignin derivatives. At par with the commonly used Co and Ni that add a strong hydrogenation functionality, it was found that the addition of the more oxophilic W restricts ring hydrogenation while allowing the deoxygenation of oxygenated compounds and thus yielding higher selectivity toward the formation of non-oxygenated aromatic compounds. The coexistence of Mo2C with W2C along with metallic W altered the electronic properties of Mo2C which resulted in an increase of catalyst active site density and facilitated further total eugenol deoxygenation. Propyl-benzene selectivity of up to 83 % was reached at close to 100 % eugenol conversion. These findings will allow a better overview of the effect of different metal phases of mixed carbides on the catalyst performance and raise the prospect of optimizing catalyst design for a hydrodeoxygenation processing of lignin depolymerization products.

Novel phosphorus-doped molybdenum carbide catalyst for the reverse water-gas shift reaction

The effect of phosphorus on the catalytic performance of molybdenum carbide for the reverse water-gas shift (RWGS) reaction was studied for the first time. It was found that the catalytic activity and selectivity of the P-doped molybdenum carbide catalysts were greatly related to their P/Mo molar ratios within a narrow range (0–0.1). It was obvious that increasing P/Mo molar ratio led to a decreased activity, but can effectively enhance selectivity. The P-doped molybdenum carbide with a P/Mo molar ratio of 0.05 was proposed to be more excellent than other P-doped molybdenum carbides in terms of both activity and selectivity, which was attributed to its higher oxophilicity and weaker affinity toward CO.

H2 production through aqueous phase reforming of ethanol over molybdenum carbide catalysts supported on zirconium oxide.

Molybdenum carbide catalysts supported on monoclinic and tetragonal zirconium oxide were studied for hydrogen production through aqueous phase reforming of ethanol. Catalysts were characterized by N2 physisorption, XRD, TPR and XPS. Results showed that 10%Mo2C/m-ZrO2 was less carburized and had a lower surface area than 10%Mo2C/t-ZrO2 and 10%MoC/t-ZrO2. Mo oxide was identified on the surface as well as two types of Mo oxycarbide and Mo oxynitride. The α crystalline phase of the carbide was more active than β phase and was ascribed to its higher relative superficial distribution. However, the α phase generated less H2 probably because there was less oxycarbide presence. 10%Mo2C/m-ZrO2 produced significantly more H2 and was stable for five consecutive reactions. This catalyst showed higher carburization degree after the reaction, which greatly enhanced the generation of H2, suggesting that carbides species improved H2 production compared to oxycarbides.

Molybdenum Carbide for Catalytic De/hydrogenation Process: Synthesis, Modulation and Applications

AbstractThe catalytic de/hydrogenation process is important in the fields of petrochemical refining, fuel synthesis, drug synthesis, CO2 conversion, and hydrogen synthesis, where the construction of low‐cost and high‐efficiency de/hydrogenation catalysts attracting significant attentions. Molybdenum carbide (MoxC), as a non‐noble transition metal carbide catalyst, has been widely investigated for hydrogen activation. Herein, research progress and achievements of molybdenum carbide for catalytic de/hydrogenation are reviewed. Additional attention is paid to the structure and crystal phase of molybdenum carbide, and various modification strategies related to the catalytic activity regulation are summarized. Finally, the application prospect of molybdenum carbide catalysts is also discussed. This review provides a framework reference for further understanding the design and utilization of molybdenum carbide catalysts for catalytic de/hydrogenation and the key research problems to be addressed.

Influence of Carbonization Conditions on Structural and Surface Properties of K-Doped Mo2C Catalysts for the Synthesis of Methyl Mercaptan from CO/H2/H2S.

The cooperative transition of sulfur-containing pollutants of H2S/CO/H2 to the high-value chemical methyl mercaptan (CH3SH) is catalyzed by Mo-based catalysts and has good application prospects. Herein, a series of Al2O3-supported molybdenum carbide catalysts with K doping (denoted herein as K-Mo2C/Al2O3) are fabricated by the impregnation method, with the carbonization process occurring under different atmospheres and different temperatures between 400 and 600 °C. The CH4-K-Mo2C/Al2O3 catalyst carbonized by CH4/H2 at 500 °C displays unprecedented performance in the synthesis of CH3SH from CO/H2S/H2, with 66.1% selectivity and a 0.2990 g·gcat-1·h-1 formation rate of CH3SH at 325 °C. H2 temperature-programmed reduction, temperature-programmed desorption, X-ray diffraction and Raman and BET analyses reveal that the CH4-K-Mo2C/Al2O3 catalyst contains more Mo coordinatively unsaturated surface sites that are responsible for promoting the adsorption of reactants and the desorption of intermediate products, thereby improving the selectivity towards and production of CH3SH. This study systematically investigates the effects of catalyst carbonization and passivation conditions on catalyst activity, conclusively demonstrating that Mo2C-based catalyst systems can be highly selective for producing CH3SH from CO/H2S/H2.

Introducing trace Co to molybdenum carbide catalyst for efficient ammonia synthesis

AbstractDevelopment of the cost‐effective catalysts with excellent catalytic performance is highly demanded for ammonia synthesis, and the strong adsorption of ammonia greatly hinders the design of cost‐effective and high‐performance ammonia synthesis catalysts. Herein, we report that the addition of a small amount of Co species (0.1 wt%) into Mo2C catalyst, which can provide electrons to Mo2C, not only leads to improvement of the adsorption and migration of hydrogen, but also facilitates the adsorption and desorption of ammonia. Consequently, Mo2C catalyst with 0.1 wt%Co offers a 40% higher ammonia synthesis activity and a lower negative reaction order with respect to NH3 in comparison to Mo2C. This work stresses the importance of the minor components in improving the ammonia synthesis activity by accelerating the migration of reactants over the catalyst surface and the escape of products from the catalyst.

Dual-Doping Strategy for Enhancing Hydrogen Evolution on Molybdenum Carbide Catalysts

Hydrogen evolution reaction (HER) is a topic of great interest due to its efficient hydrogen production properties, which can address the increasing demand for clean and sustainable energy sources. On the other hand, molybdenum carbide (MoC) has been widely studied due to its noble metal-like surface electronic properties. In the HER process, it is crucial to regulate the Mo−H bonding energy effectively and increase the electron transfer rate on the MoC catalyst surface in a rational manner. In this study, we introduce highly electronegative nitrogen and non-noble transition metal atoms (Cu or Co) into the molybdenum carbide crystal lattice (N−M−MoC, M: Cu, or Co), which leads to a dual—doping effect. This effect results in the rearrangement of the electronic configuration on the catalyst surface and the enrichment of electrons around Mo atom, leading to an optimization in the Mo−H bonding energy. Moreover, the unique two-dimensional nano-sheet structure of the N−M−MoC materials further promotes the electron transfer and exposure of active sites. Benefiting from the above, the HER performance of the N−M−MoC is significantly improved. Among them, N−Cu−MoC exhibits the lowest overpotential (η10 = 158 mV) and highest stability (about 30 h) in alkaline solutions.

Facile synthesis of ordered mesoporous molybdenum carbide electrocatalysts for high‐performance hydrogen evolution reaction

AbstractIn this study, a simple method was designed to prepare ordered mesoporous carbons embedded with molybdenum without any extreme conditions. We prepared three different ordered molybdenum carbide materials with mesoporous structures to explore the influence of the structure of molybdenum‐based materials on the HER catalytic efficiency. The ordered mesoporous molybdenum carbide catalysts (CMK‐3‐MoCx, fCMK‐3‐MoCx, CMK‐8‐MoCx) were characterized by SEM, TEM, XRD, nitrogen adsorption‐desorption and XPS. The HER is catalyzed efficiently on the three electrocatalysts, fCMK‐3‐MoCx shows the best HER electro‐catalytic performance with a small onset potential of −0.06 V vs. RHE, a low tafel slope of 66 mV dec−1 and a small over‐potential value of 89 mV at 10 mA cm−2. This excellent performance on HER is due to its high specific surface area and highly ordered mesoporous structure that resulted in excellent proton transport efficiency and high electron transfer rate. Our results provide a new research direction for the application of flat ordered mesoporous structures in catalysis.

First comparison of catalytic CO2 reduction to CO over molybdenum carbide, nitride and phosphide catalysts

The nitrided Mo/CNT catalyst can show comparable reverse water gas shift (RWGS) performance to the bimetallic Cu/β-Mo2C catalyst under similar conditions.

Accelerating the evaluation of crucial descriptors for catalyst screening via message passing neural network

Graph neural networks developed for adsorption energy prediction on molybdenum carbide catalysts provide a significant acceleration over density functional theory calculations.

Zeolitic Imidazolate Framework Decorated Molybdenum Carbide Catalysts for Hydrodeoxygenation of Guaiacol to Phenol

Bimetallic zeolitic imidazolate framework (BMZIF)-decorated Mo carbide catalysts were designed for the catalytic hydrodeoxygenation of guaiacol to produce phenol with high selectivity. A uniform layer of BMZIF was systematically coated onto the surface of the MoO3 nanorods. During carbonization at 700 °C for 4 h, BMZIF generated active species (ZnO, CoO) on highly dispersed N-doped carbons, creating a porous shell structure. Simultaneously, the MoO3 nanorod was transformed into the Mo2C phase. The resulting core@shell type Mo2C@BMZIF-700 °C (4 h) catalyst promoted a 97% guaiacol conversion and 70% phenol selectivity under 4 MPa of H2 at 330 °C for 4 h, which was not achieved by other supported catalysts. The catalyst also showed excellent selective cleavage of the methoxy group of lignin derivatives (syringol and vanillin), which makes it suitable for selective demethoxylation in future biomass catalysis. Moreover, it exhibits excellent recyclability and stability without changing the structure or active species.

H2 Production from Methane Reforming over Molybdenum Carbide Catalysts: From Surface Properties and Reaction Mechanism to Catalyst Development

Hydrogen, with its high energy content and environmental-friendly properties, is considered an effective energy carrier in addition to fossil fuels. Methane reforming represents a major method of hydrogen production, although the applied catalysts often suffer from coke deposition and metal sintering at high operating temperatures. Transition-metal carbides (TMCs), particularly molybdenum carbides (MoxC), possess features such as Pt-like behaviors, affinity with oxidants such as CO2 and H2O, and a strong metal–support interaction for metal dispersion and stabilization, rendering them great prospective candidates for catalyzing the methane reforming reactions (MRRs). This review focuses on the recent applications and challenges of TMCs in MRRs, with an emphasis on the strategies to improve their performance by (1) engineering the operational conditions, (2) designing a dual M–MoxC (M = Ni or Co etc.) active site, (3) dispersing M–MoxC on supports, and (4) generating a M–MoxC/MoOxCy interface in situ. The present review will provide guidance for the future design of efficient catalysts for H2 production from MRRs.

Computational study of CO2 methanation over two-dimensional molybdenum carbide catalysts

Two-dimensional molybdenum carbide (2D-Mo2C) is thought to be promising for catalytic hydrogenation of CO2 to CH4, but little is known about its catalytic reaction mechanism. In this work, we investigate the hydrogenation of CO2 to CH4 on 2D-Mo2C using density functional theory. Our calculations show that Mo on the surface can efficiently decompose CO2 to CO and O, and also H2 to H. The hydrogenation of CO produces CHO that is readily deoxygenated to CH, and CH is selectively hydrogenated to produce CH4. Interestingly, the embedded Ir1 on 2D-Mo2C can act as a single-atom promoter to improve the performance of CO2 methanation, while on the other hand maintaining its high selectivity for CH4. This work provides insight into the mechanism of 2D-Mo2C-catalyzed CO2 methanation reactions and suggests a strategy to improve the performance of such catalysts through single-atom promoters.

Optimization of Potassium Promoted Molybdenum Carbide Catalyst for the Low Temperature Reverse Water Gas Shift Reaction

The reduction of CO2 to CO through the reverse water gas shift (RWGS) reaction is an important catalytic step in the overall strategy of CO2 utilization. The product CO can be subsequently used as a feedstock for a variety of useful reactions, including the synthesis of fuels through the Fischer–Tropsch process. Recent works have demonstrated that potassium-promoted molybdenum carbide (K-Mo2C) is a highly selective catalyst for low-temperature RWGS. In this work, we describe the systematic investigation of key parameters in the synthesis of K-Mo2C, and their influence on the overall activity and selectivity for the low-temperature RWGS reaction. Specifically, we demonstrate how catalyst support, precursor calcination, catalyst loading, and long-term ambient storage influence performance of the K-Mo2C catalyst.

Cobalt promoted molybdenum carbide supported on γ-alumina as an efficient catalyst for hydrodesulfurization of dibenzothiophene

The development of new hydrodesulfurization (HDS) catalysts with suitable electronic structure and metal-support interaction are critical for the efficient removal of sulfur from oil. In this work, cobalt-promoted molybdenum carbide supported on mesoporous alumina (CoxMo2C/MA) catalysts were prepared by a simple one-step hydrolysis method combined with a temperature programmed carbonization process, and the effects of Co on the physicochemical properties and HDS performance of the catalysts were systematically investigated. The results show that the appropriate Co addition can reduce the interaction between Mo species and alumina support, which is beneficial for the carbonization of Mo. Besides, the introduction of Co makes Mo species electron-rich, causing the C–S bond is vulnerable to attack. Taking dibenzothiophene (DBT) as a probe, Co0.3Mo2C/MA shows significant high sulfur removal efficiency (about 100%) and effective direct desulfurization selectivity. Furthermore, the density functional theory calculations further prove that the activation energy barrier of DBT HDS at the Co–Mo2C site is lower than that of Mo2C, confirming its reaction is easier to proceed. This work may provide a strategy for accessing new efficient modified molybdenum carbide catalysts for the HDS field.

Upgrading of benzofuran to hydrocarbons by hydrodeoxygenation over nickel–molybdenum carbide catalysts supported inside multi-wall carbon nanotubes

This work proposed a controllable synthesis of Ni-Mo catalyst supported inside multi-wall carbon nanotubes (CNTs). The results indicate that Ni improved the β-Mo2C formation and markedly promoted the benzofuran (BF) hydrogenation and hydrodeoxygenation activity of the catalysts. The synergistic interaction between Ni and Mo reached the maximum at a Ni/Mo molar ratio of 0.3, which could be favored by the proximity between the Ni and β-Mo2C particles inside the CNTs reaching a 99.5% of BF conversion to hydrogenated and deoxygenated products as 2,3-dihydrobenzofuran, octahydrobenzofuran, and ethylcyclohexane; in contrast, BF conversion on unsupported Ni-Mo2C-0.3 was only 0.7%. Deoxygenated products are favored under different conditions, such as the time, and mainly with the temperature achieving 93.8% of yield toward deoxygenated products with 100% of BF conversion at 320 °C. However, the catalyst activity is lost through reuse cycles, likely due to the deposition of high molecular weight compounds (coke) on the catalyst surface.

B/N co-doped carbon supported molybdenum carbide catalysts with oxygen vacancies for facile synthesis of flavones through oxidative dehydrogenation

Flavonoids are a type of naturally bioactive molecules, but their chemical producing methods are challenging. Herein, a simple and effective one-step pyrolysis method was developed to successfully prepare a series of molybdenum carbide catalysts dispersed on B and N-codoped carbon materials (Mo2C@BNC-x). Under a calcination temperature of 1000 °C, the as-prepared Mo2C@BNC-1000 served as a highly efficient heterogeneous catalyst for oxidative dehydrogenation of flavanones into flavones, and the conversion and yield were both 99%. Moreover, several characterizations and density functional theory calculations showed the excellent catalytic performance of Mo2C@BNC-1000 catalyst originated from the synergistic effect between Mo2C and the B/N co-doped carbon support with rich oxygen vacancies. In addition, the Mo2C@BNC-1000 catalyst showed good applicability and reusability, with no significant reduction in catalytic activity at least five runs. The prepared Mo2C@BNC catalyst thus triggers facile synthesis of flavones through oxidative dehydrogenation of flavanone with green economy and high efficiency.