Carbide Catalysts Research Articles

A Highly Active Molybdenum Carbide Catalyst with Dynamic Carbon Flux for Reverse Water‐Gas Shift Reaction

Molybdenum carbide has been reported as an efficient and stable catalyst for reverse water‐gas shift reaction. The convention understanding of the mechanism suggests domination of the surface phenomena, with only surface or subsurface layers partaking in the catalytic cycle. In this study, we presented a highly active MoC catalyst from carburization process, which showed a mass‐specific reaction rate over 260 [[EQUATION]] with dynamic carbon flux in the bulk phase of the catalyst. Through Isotopic Temperature‐Programmed Reaction (ITPR) analysis and Environmental Transmission Electron Microscopy (ETEM), we discerned dynamic carbon flow circulating between the α‐MoC bulk phase and the gas phase reactants under the reverse water‐gas shift (RWGS) reaction atmosphere. This circulation, essential to maintaining the structural stability of the metastable α‐MoC and its ultra‐high reactivity, is accompanied by thorough carbon component exchange among the bulk, the surface and the gas‐phase reactants during the reaction process.

A Highly Active Molybdenum Carbide Catalyst with Dynamic Carbon Flux for Reverse Water-Gas Shift Reaction.

Molybdenum carbide has been reported as an efficient and stable catalyst for reverse water-gas shift reaction. The convention understanding of the mechanism suggests domination of the surface phenomena, with only surface or subsurface layers partaking in the catalytic cycle. In this study, we presented a highly active MoC catalyst from carburization process, which showed a mass-specific reaction rate over 260 [[EQUATION]] with dynamic carbon flux in the bulk phase of the catalyst. Through Isotopic Temperature-Programmed Reaction (ITPR) analysis and Environmental Transmission Electron Microscopy (ETEM), we discerned dynamic carbon flow circulating between the α-MoC bulk phase and the gas phase reactants under the reverse water-gas shift (RWGS) reaction atmosphere. This circulation, essential to maintaining the structural stability of the metastable α-MoC and its ultra-high reactivity, is accompanied by thorough carbon component exchange among the bulk, the surface and the gas-phase reactants during the reaction process.

Revealing the Potential of Bimetallic Carbide Catalysts for Upgrading Biomass‐Derived Bio‐Oil: A First Principles‐Based Investigation Using Representative Bio‐Oil Constituents

AbstractBimetallic carbides, especially based on molybdenum carbide, proved to be a promising hydrodeoxygenation (HDO) catalyst, with enhanced selectivity towards C─O bonds cleavage. However, catalysts are generally investigated using limited model components derived from only one of the biopolymers in biomass (either lignin or carbohydrates), therefore, HDO of raw biomass‐derived bio‐oil still remains a challenge, as it contains molecules of different functionalities. This paper presents a systematic comparison of the monometallic carbide, Mo2C, with the novel bimetallic carbide incorporating W using representative bio‐oil components of different functionalities and derived from different bio‐polymers components of biomass. We employed quantum mechanical investigation to reveal that the W‐doped Mo2C carbide (MoWC) catalyst with increased oxophilicity, owing to tungsten incorporation, can perform HDO of real bio‐oil more effectively in comparison to its monometallic counterpart (Mo2C) using six substrates representing different components of bio‐oil. We showed MoWC can selectively cleave both single/double (C─O/C═O) bonds with similar barriers in comparison to Mo2C which can only selectively cleave single C─O bonds. This observation was consistent for 5‐HMF, Acetic acid, and Methyl Glyoxal. We also showed that MoWC outperforms its metallic counterpart Mo2C in the HDO for aromatic and carbohydrates components.

Enhancing sulfamerazine degradation via peroxymonosulfate with Fe-doped Mo2C materials: Catalytic performance and mechanistic insights

Sulfonamide antibiotics are a common group of drugs that have the potential to induce the generation of resistance genes even at low concentrations. Herein, a novel Fe3Mo3C/Mo2C/Mo composite (Fe-Mo2C-1.0) was prepared by modifying the synthesis process of Fe-doped Mo2C and used to activate peroxymonosulfate (PMS) to degrade sulfamerazine (SMR). The optimal performance catalyst was obtained at Fe/Mo = 1.0 and a calcination temperature of 900 ℃. Fe-Mo2C-1.0 achieved 98.8 % SMR removal in 20 min, which was 4.5 and 44.3 times higher than that of Fe-Mo2C-0.5/PMS and Mo2C/PMS systems, respectively. In Fe-Mo2C-1.0, multiple low-valent forms of the element Mo, including Mo, Mo(II) and Mo(IV), which are highly reductive, participated in and contributed to the regeneration of Fe(II). The proportion of Fe(II) on the surface of Fe-Mo2C-1.0 before and after the reaction was maintained at a stable level. In addition, the high Fe content and sp2 hybridized carbon in Fe-Mo2C-1.0 promoted the role of mediated electron transfer during catalysis process. Electrochemical characterization indicated that Fe-Mo2C-1.0 had better redox properties, smaller electron transfer resistance and a faster corrosion rate than Fe-Mo2C-0.5 and Mo2C. Other SMR oxidation mechanisms included SO4∙-, O2∙- and 1O2, with 1O2 contributing the most. Finally, three possible degradation pathways of SMR were proposed. This work provided thoughts on the synthesis of Fe/Mo bimetallic carbide catalysts as well as reference for the removal of SMR by PMS activation.

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

Catalytic steam reforming offers a groundbreaking approach for converting industrial chlorinated volatile organic compound (CVOC) waste into valuable syngas (H2 and CO) and recovering HCl. However, the lack of C-Cl bond activation ability in traditional transition metal catalysts results in their insufficient reforming activity toward CVOCs. Herein, a novel molybdenum carbide (β-Mo2C) catalyst is developed and loaded onto a γ-Al2O3 support synthesized through a self-assembly method. The γ-Al2O3 support provides abundant unsaturated coordinated Al3+ ions, which effectively anchor and disperse β-Mo2C nanoparticles. In the catalytic steam reforming reaction at 600 °C, the β-Mo2C/γ-Al2O3 catalyst achieves a conversion efficiency higher than 95% and syngas yields of 82.4-92.3% for various typical industrial CVOCs. The mechanistic research reveals that the coordination between C and Mo atoms in β-Mo2C leads to a slightly electron-deficient state of the Mo sites, accompanied by a high density of unoccupied 4d orbitals. These characteristics are highly advantageous for the adsorption and dechlorination of CVOC molecules. The produced nonchlorinated intermediates can subsequently be oxidized to CO and H2 by hydroxyl radicals on adjacent Mo sites.

W-based carbide derived from PW12@ZIF-8 as Pt-free catalyst on counter electrode of dye-sensitized solar cells for triiodide reduction

The preparation of counter electrodes (CEs) catalysts at different pyrolysis temperatures will directly affect the composition, morphology, and performance of the catalysts in dye-sensitized solar cells (DSSCs) applications. Herein, four W-based carbides catalysts were derived from H3PW12O40-based ZIF-8 metal–organic frameworks (PW12@ZIF-8) by in-situ pyrolysis at 600, 700, 800, and 900 ℃ under N2 atmosphere. The pyrolysis mechanism and structure characteristics of the prepared W-based carbides with temperature variation were confirmed by TG-DTG-DSC simultaneous, XRD, XPS, TEM, SEM and N2 adsorption/desorption, which exhibits the gradual transformation of PW12@ZIF–8 → WC-C→WC→W1-xC→W2C. Furthermore, the photovoltaic performance of four different W-based carbides as CEs catalysts for regenerating I3−/I− shuttles in DSSCs were identified by photocurrent-voltage (J-V) measurement, which achieved PCEs of 4.63, 4.91, 5.05 and 5.78 %, respectively. As a result, W2C (900 ℃) provide more vacancies and defects on the catalyst surface as abundant catalytic active sites, as well as promote the appearance of more pores and voids in the morphology to diffuse and permeate electrolyte due to the highest specific surface area, and the PCE value of 5.78 % was also superior to 5.51 % of Pt CE.

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.

High-Performance Bimetallic Electrocatalysts for Hydrogen Evolution Reaction Using N-Doped Graphene-Supported N-Co6Mo6C.

Hydrogen has garnered considerable attention as a promising energy source for addressing contemporary environmental degradation and energy scarcity challenges. Electrocatalytic water splitting for hydrogen production has emerged as an environmentally friendly and versatile method, offering high purity. However, the development of cost-effective electrocatalytic catalysts using abundant and inexpensive materials is crucial. In this study, we successfully synthesized nitrogen-doped Co6Mo6C supported on nitrogen-doped graphene (N-Co6Mo6C/NC). The catalyst exhibited high performance and durability in alkaline electrolytes (1.0 M KOH) for hydrogen evolution, showcasing an overpotential of 185 mV at a current density of 100 mA cm-2 and a Tafel slope of 80 mV dec-1. These findings present a novel avenue for the fabrication of efficient bimetallic carbide catalysts.

Atomic-level insight into the carburization process of iron-based catalysts: A ReaxFF molecular dynamics study

Transition metal carbide catalysts have garnered widespread attention due to their outstanding catalytic performance. The carbide catalysts, such as FexC and MoxC are typically obtained from their oxide carburization. The reduction and carburization processes are key steps during the activation of oxide precursors, which determine the activity and stability. An understanding of the carburization process mechanism is very important for the optimization of carbide catalysts. Iron-based catalysts are widely used in the large-scale coal-to-liquid industry because of their low price and high activity. In this paper, the carburization process of iron oxide nanoparticles was simulated by the Reactive force field (ReaxFF) molecular dynamics method. The results illustrate that the competition between CO dissociation and reduction of oxides occurs at the 100 ps time scale, which can be tuned by particle size and oxygen vacancy. We have explained the counter-intuitive finding that small oxide particles are more difficult to achieve fully carburization than larger ones; this is because rapid carbon accumulation on the surface blocks the oxygen diffusion channels from bulk to surface. The atomic distribution heat map was carried out to demonstrate the carbon and oxygen penetration processes. Meanwhile, the volumetric strain analysis reveals the driving force comes from the strong tendency to form Fe-C bonds. The dependence on surface orientation was further systematically investigated. This work provides microscopic insights into the carburization process of iron-based materials and the fundamental knowledge for the optimization of catalyst synthesis procedures.

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.

Practice of Ecological Aesthetics in Green Production of Bimetallic Carbide Catalyst for Oxygen Reduction Reaction: Integrating Technological Development with Ecological Protection

This work summarizes the disciplinary connotation of ecological aesthetics, discusses the social and philosophical background of the origination of ecological aesthetics, and applies ecological aesthetics to the research on the production processes of catalytic materials. It is found that compared with conventional chemical processes, catalytic materials synthesized using green chemical processes that conform to ecological aesthetics have advantages in raw material cost, energy consumption, environmental protection, operational complexity, and product performance. Based on this, it is proposed that, as green chemical processes develop to a certain extent, they will unify anthropocentrism and ecocentrism, and meet both human needs and ecological protection requirements. The mentioned green chemical processes adopt biomass lotus leaf stems as a carbon source to produce non-noble metal bimetallic carbide (C19Cr7Mo24)-based catalysts for oxygen reduction reaction (ORR). Its initial half-wave potential (E1/2) for catalyzing ORR in an alkaline medium is 0.903 V, the E1/2 retention rate after 50,000 cycles is 98.9%, and its peak power density in H2/O2 fuel cell reaches 1.47 W cm−2, making it one of the most active non-noble metal catalysts for ORR reported so far; its stability is unparalleled.

Enhanced Catalytic Hydrogenation of Olefins in Sulfur-Rich Naphtha Using Molybdenum Carbide Supported on γ-Al2O3 Spheres under Steam Conditions: Simulating the Hot Separator Stream Process.

Spheres comprising 10 wt.% Mo2C/γ-Al2O3, synthesized through the sucrose route, exhibited unprecedented catalytic activity for olefin hydrogenation within an industrial naphtha feedstock that contained 23 wt.% olefins, as determined by supercritical fluid chromatography (SFC). The catalyst demonstrated resilience to sulfur, exhibiting no discernible deactivation signs over a tested 96 h operational period. The resultant hydrogenated naphtha from the catalytic process contained only 2.5 wt.% olefins when the reaction was conducted at 280 °C and 3.44 × 106 Pa H2, subsequently blended with Athabasca bitumen to meet pipeline specifications for oil transportation. Additionally, the carbide catalyst spheres effectively hydrogenated olefins under steam conditions without experiencing any notable hydrogenation in the aromatics. We propose the supported carbide catalyst as a viable alternative to noble metals, serving as a selective agent for olefin elimination from light petroleum distillates in the presence of steam and sulfur, mitigating the formation of gums and deposits during the transportation of diluted bitumen (dilbit) through pipelines.

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.

Selective hydrogenation of 5-hydroxymethylfurfural triggered bya high Lewis acidic Ni-based transition metal carbide catalyst

The high-efficiency conversion of biomass resources to biofuels has attracted widespread attention, and the active sites and synergistic effect of catalysts significantly impact their surface arrangement and electronic structure. Here, a nickel-based transition metal carbide catalyst (Ni/TMC) with high Lewis acidity was prepared by self-assembly of transition metal carbide (TMC) and nickel, which exhibited excellent performance on synergistic hydrogenation and hydrogenolysis of 5-hydroxymethylfurfural (HMF) into liquid biofuel 2,5-dimethylfuran (DMF). Notably, Ni/WC with the highest Lewis acidity (4728.3 μmol/g) can achieve 100% conversion of HMF to 97.6% yield of DMF, with a turn-over frequency of up to 46.5 h−1. The characterization results demonstrate that the rich Lewis acid sites yielded by the synergistic effect between Ni species and TMC are beneficial for the CO hydrogenation and C–O cleavage, thereby accelerating the process of hydrodeoxygenation (HDO). Besides, a kinetic model for the HDO of HMF to DMF process has been established based on the experimental results, which elucidated a significant correlation between the measured and the predicted data (R2 > 0.97). Corresponding to the adsorption configuration of Ni/WC and substrate determined by in-situ FTIR characterization, this study provides a novel insight into the selective conversion of HMF process for functional biofuel and bio-chemicals.

CO hydrogenation conversion driven by micro-environments of active sites over iron carbide catalysts

Essentially clearing the structure–activity relationship between iron carbide catalysts involving multiple active centers to understand the reaction mechanism of CO hydrogenation conversion process is still a great challenge. Here, two main micro-environment factors, namely electronic properties and geometrical effects were found to have an integrated effect on the mechanism of CO hydrogenation conversion, involving active sites on multiple crystal phases. The Bader charge of the surface Fe atoms on the active sites had a guiding effect on the CO activation pathway, while the spatial configuration of the active sites greatly affected the energy barriers of CO activation. Although the defective surfaces were more conducive to CO activation, the defective sites were not the only sites to dissociate CO, as CO always tended to dissociate in a wider area. This synergistic effect of the micro-environment also occurred during the CO conversion process. Surface C atoms on relatively flat configurations were more likely to form methane, while the electronic properties of the active sites could effectively describe the C–C coupling process, as well as distinguish the coupling mechanisms.

Lignin carbon-initiated Ni/K/Mo2C catalyst for efficient synthesis of higher alcohols from syngas

Bamboo lignin, the principal constituent of non-wood pulping black liquor, is ecologically and environmentally harmful due to its complex molecular structure and stability. Additionally, the syngas-based synthesis of higher alcohols is a desired industrial application, alleviating the dependency on petroleum resources. However, developing highly efficient catalysts with high space–time yield and selectivity towards higher alcohols remains challenging. Herein, for the first time, taking into account the permeable structure of bamboo lignin in paper-making black liquid resulting from cellulose and hemicellulose extraction, porous nano molybdenum carbide was manufactured by designed pretreatment and activation processes of the lignin, which was further doped by the K and Ni additive to create a highly efficient catalyst (Ni/K/Mo2C@LC) for the high alcohols synthesis reaction, yielding a surprising space–time yield of 0.455 g/gcat/h) to alcohol products under the optimal reaction conditions. Control experiments and characterizations were conducted over relevant catalysts, revealing that Ni and K could be integrated to regulate the adsorption property, acidity/basicity, and carbon chain growth ability of the catalysts. Also, the open mesoporous lignin carbon provided larger metal particles, enhancing the hydrogenation ability and better balancing the non-dissociative and dissociative active sites for the high alcohol synthesis reaction. These results provide insights into the structure design of carbide catalysts toward efficiently utilizing industrial lignin and other biomass-derived feedstocks, and the development of an efficient Mo-based catalyst for syngas conversion.

Photoelectrocatalytic CO2 conversion over carbon @ silicon carbide composites

Artificial photosynthesis, which utilizes sunlight to produce value-added chemicals and fuels from CO2, is a promising strategy to storage fluctuating solar energy and to realize zero carbon cycle simultaneously. While selective C2+ production via CO2 photoelectrocatalytic conversion remains a challenge due to the sluggish C-C coupling kinetics over current artificial photosynthesis catalysts. Herein, we present a carbon @ silicon carbide (C@SiC) catalyst for ambient CO2 photoelectric reduction under simulated solar irradiation, giving a CO2 conversion rate of 487 μmol∙gcat−1∙h−1 with an ethanol selectivity of 87.8%. The optimal sp2/sp3 carbon ratio of carbon layer not only facilitates the photo-generated electrons transfer from SiC to carbon layer, but also favors the C-C coupling kinetics of key intermediates for efficient CO2 to ethanol conversion.

Recent progress in bimetallic carbide-based electrocatalysts for water splitting

This review provides recent progresses in bimetallic carbides (Bi-TMCs) catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting.

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.