Carbide Catalysts Research Articles

In-situ synthesis of atomic Co-Nx sites in holey hollow carbon nanospheres for efficiency oxygen reduction reaction electrocatalyst

Recently, Metal-Organic Frameworks-derived carbide catalysts draw lots of attention because of their low price, abundant reserves and superior stability. However, the metal element tends to form particles at a high temperature still a challenge to achieving high Oxygen Reduction Reaction (ORR) activity. Herein, a kind of Zeolitic imidazolate frameworks (ZIFs) based carbon nanosphere with well-dispersed Co-Nx active sites (Co and N co-doped holey Hollow Carbon nanospheres, hHCS) are prepared by using Polyvinylpyrrolidone as the surfactant to realize the well dispersion of Cobalt. Then KOH activation is used to enlarge specific surfaces area (SSA). In an alkaline medium, the obtained sample shows excellent ORR catalytic performance with a half-ware potential of 0.80 V and a limiting current density of 6.53 mA cm−2, which are even comparable with that of commercial Pt/C. Further, the simple also exhibits remarkable stability during long-term working and better tolerance of methanol. According to the Density Functional Theory (DFT), the outstanding ORR activity can be ascribed to the favorable dispersed Co-Nx. It can be also attributed to the high SSA, hierarchically pore structure and N-base active sites.

In situ formation of multiple catalysts for enhancing the hydrogen storage of MgH2 by adding porous Ni3ZnC0.7/Ni loaded carbon nanotubes microspheres

MgH2 is considered one of the most promising hydrogen storage materials because of its safety, high efficiency, high hydrogen storage quantity and low cost characteristics. But some shortcomings are still existed: high operating temperature and poor hydrogen absorption dynamics, which limit its application. Porous Ni3ZnC0.7/Ni loaded carbon nanotubes microspheres (NZC/Ni@CNT) is prepared by facile filtration and calcination method. Then the different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%) is added to the MgH2 by ball milling. Among the three samples with different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%), the MgH2-5 wt% NZC/Ni@CNT composite exhibits the best hydrogen storage performances. After testing, the MgH2-5 wt% NZC/Ni@CNT begins to release hydrogen at around 110 °C and hydrogen absorption capacity reaches 2.34 wt% H2 at 80 °C within 60 min. Moreover, the composite can release about 5.36 wt% H2 at 300 °C. In addition, hydrogen absorption and desorption activation energies of the MgH2-5 wt% NZC/Ni@CNT composite are reduced to 37.28 and 84.22 KJ/mol H2, respectively. The in situ generated Mg2NiH4/Mg2Ni can serve as a "hydrogen pump" that plays the main role in providing more activation sites and hydrogen diffusion channels which promotes H2 dissociation during hydrogen absorption process. In addition, the evenly dispersed Zn and MgZn2 in Mg and MgH2 could provide sites for Mg/MgH2 nucleation and hydrogen diffusion channel. This attempt clearly proved that the bimetallic carbide Ni3ZnC0.7 is a effective additive for the hydrogen storage performances modification of MgH2, and the facile synthesis of the Ni3ZnC0.7/Ni@CNT can provide directions of better designing high performance carbide catalysts for improving MgH2.

Revealing the Real Role of Etching during Controlled Assembly of Nanocrystals Applied to Electrochemical Reduction of CO2.

In recent years, the use of inexpensive and efficient catalysts for the electrocatalytic CO2 reduction reaction (CO2RR) to regulate syngas ratios has become a hot research topic. Here, a series of nitrogen-doped iron carbide catalysts loaded onto reduced graphene oxide (N-Fe3C/rGO-H) were prepared by pyrolysis of iron oleate, etching, and nitrogen-doped carbonization. The main products of the N-Fe3C/rGO-H electrocatalytic reduction of CO2 are CO and H2, when tested in a 0.5 M KHCO3 electrolyte at room temperature and pressure. In the prepared catalysts, the high selectivity (the Faraday efficiency of CO was 40.8%, at −0.3 V), and the total current density reaches ~29.1 mA/cm2 at −1.0 V as demonstrated when the mass ratio of Fe3O4 NPs to rGO was equal to 100, the nitrogen doping temperature was 800 °C and the ratio of syngas during the reduction process was controlled by the applied potential (−0.2~−1.0 V) in the range of 1 to 20. This study provides an opportunity to develop nonprecious metals for the electrocatalytic CO2 reduction reaction preparation of synthesis and gas provides a good reference

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.

Enhanced Effect of the Mesoporous Carbon on Iron Carbide Catalyst for Hydrogenation of Dimethyl Oxalate to Ethanol

AbstractDue to the low activity of bulk Fe5C2 catalyst in the hydrogenation of dimethyl oxalate to ethanol, a supported Fe5C2 catalyst was designed and prepared with mesoporous carbon as the carrier. For a comparison, two iron carbide catalysts supported on activated carbon and microporous carbon were also prepared. Based on the characterization results of IR, XRD, H2‐TPR, CO‐TPD, XPS and MES, the oxygen‐containing functional groups (especially COOH group) on the surface of the carbon supports inhibit the formation of iron carbides, which are regarded as the active sites and play the key role in the hydrogenation of dimethyl oxalate to ethanol. However, the mesoporous carbon exhibits a more positive effect on the dispersion of iron particles than the other two carbon supports. As a result, the as‐prepared mesoporous catalyst presents an excellent activity (the ethanol yield of 85.8 %) and stability in the hydrogenation of dimethyl oxalate. This work suggests a practical strategy in fabricating a supported iron carbides catalyst for the chemosynthesis of ethanol via DMO hydrogenation from syngas.

Fischer-Tropsch synthesis to olefins boosted by MFI zeolite nanosheets.

Catalytic reactions are severely restricted by the strong adsorption of product molecules on the catalyst surface, where promoting desorption of the product and hindering its re-adsorption benefit the formation of free sites on the catalyst surface for continuous substrate conversion1,2. A solution to this issue is constructing a robust nanochannel for the rapid escape of products. We demonstrate here that MFI zeolite crystals with a short b-axis of 90-110 nm and a finely controllable microporous environment can effectively boost the Fischer-Tropsch synthesis to olefins by shipping the olefin molecules. The ferric carbide catalyst (Na-FeCx) physically mixed with a zeolite promoter exhibited a CO conversion of 82.5% with an olefin selectivity of 72.0% at the low temperature of 260 °C. By contrast, Na-FeCx alone without the zeolite promoter is poorly active under equivalent conditions, and shows the significantly improved olefin productivity achieved through the zeolite promoter. These results show that the well-designed zeolite, as a promising promoter, significantly boosts Fischer-Tropsch synthesis to olefins by accelerating escape of the product from the catalyst surface.

Boosting the Production of Higher Alcohols from CO2and H2over Mn- and K-Modified Iron Carbide

The catalytic conversion of CO2 to higher alcohols (HAs, representing ethanol and alcohols with more than two carbon atoms) has been of great interest to mitigating the greenhouse effect and effectively utilizing CO2. However, most present catalysts have disadvantages of poor activity (conversion less than 30%) and selectivity (less than 10%) and high price. Herein, we report a Mn- and K-modified iron carbide catalyst that offers a CO2 conversion higher than 40% and a selectivity of higher alcohols exceeding 10%, and the proportion of propanol and butanol in alcohol products is more than 30%. Unpromoted iron carbide has a strong ability of hydrocarbon chain growth, leading to the fast formation of hydrocarbon products rather than HAs. However, on the Mn- and K-modified iron carbide catalyst, K is used to increase the surface C/H ratio of the catalyst by enhancing the adsorption of CO2 on the catalytic surface. The increased C/H ratio is indispensable to the formation of HAs, and the addition of Mn promoter dramatically improves the production of HAs, especially the formation of propanol and butanol. The synergistic effect between Mn and K on iron carbide is the key to produce HAs. In addition, the Mn- and K-modified iron carbide is of low cost, which can potentially provide an alternative for the hydrogenation of CO2 to produce valuable chemicals.

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.

Kinetic Conversion of Carbon Dioxide in Supported Tungsten Carbide Catalysts and Oxide Catalysts for the Reverse Water Gas Shift Reaction

The reverse water-gas shift reaction (RWGS) had a critical stage in the conversion of abundant carbon dioxide into chemicals or hydrocarbon fuels and has attracted widespread interest as a renewable fuel assembly system in unconventional ways. Interest has been in industrial applications such as the catalytic activity, carbon dioxide conversion, kinetics, and efficacy levels of tungsten carbide-supported catalysts and carbide oxide catalysts for the production of RWGS reaction. Additionally, carbide oxides have the ability to enhance RWGS and develop high-performance catalysts in RWGS. The RWGS reaction was (CO2 + H2 ↔ CO + H2O; ΔG°=27.94kJ/mol) an exothermic reaction that exhibits equilibrium conversion with temperature.

Synthesis and characterization of molybdenum carbide catalysts on different carbon supports

Molybdenum carbide is a noble-metal-like material, which shows great potential in many applications. The conventional Temperature-Programmed-Reduction (TPRe) method uses carbonaceous gases to carburize with molybdenum precursors, which has made a significant progress but still hard to scale up. In this work, molybdenum carbides were prepared by carburization of ammonium molybdenum molybdate on cellulose, g-C3N4, MWCNTs and sodium lignosulfonate without using any gaseous carbon source. Moreover, the formation of molybdenum carbide was subjected to in-depth investigation by using an in situ Simultaneous Thermal Analyzer – Quadrupole Mass Spectrometry coupling System. The technique revealed that the solid carbon carriers do have a great effect on the formation of molybdenum carbides. Furthermore, various characterization methods such as XRD, SEM, CO-TPD, FTIR and organic element analysis (OEA) were also applied to investigate the property of prepared molybdenum carbides. The results suggested that the prepared molybdenum carbides with CEL, MWCNTs and SLF as carbon supports could retain the skeleton and porous structure of a solid carbon carrier, and the prepared molybdenum carbides with g-C3N4 as a carbon support could generate a new three-dimensional (3D) structure support, and the composition of carriers would also have an impact on the adsorption and physicochemical properties of molybdenum carbides.

Molybdenum carbide nanocatalyst for activation of water and hydrogen towards upgrading of low-quality hydrocarbons

Molybdenum carbide catalyst is proposed to be used in a novel downhole upgrading method, called in-situ upgrading technology (ISUT). In this work, this catalyst is assessed for its activity and stability for this process. In an attempt to partially replace hydrogen with steam, as a carbon free source of hydrogen, several experiments under hybrid environments of steam and hydrogen were carried out. A systematic approach was also followed to replace either of the two gases with an inert gas like nitrogen. The presence of steam and its potential impact on the activity and stability of the catalyst is essential to be studied as water is often present in downhole heavy oil producing environments. Molybdenum carbide shows great activity and selectivity under different environments including co-presence of hydrogen and water. As well, this catalyst shows capability of water activation towards upgrading of products. Compared to the hybrid case of co-presence of hydrogen and nitrogen, co-incorporation of water with hydrogen improved the H/C ratio, tendency to form coke, asphaltene removal and desulphurization. In addition, the hydrogenation capability of the catalyst in a reservoir simulated environment was confirmed to be stable by quantifying hydrogenation of two polyaromatic model molecules under the co-presence of steam and hydrogen. Upon removal of steam and switching back to hydrogen-only environment, the activity of the catalyst was restored, highlighting its tolerance to water in terms of hydrogenation and hydroprocessing activities, making molybdenum carbide a promising catalyst for in-reservoir upgrading methods to partially replace hydrogen that in turn may improve the economics of the process.

Selective hydrogenolysis of lignin for phenolic monomers with a focus on β-O-4 cleavage and C = O hydrodeoxygenation

Catalytic hydrogenolysis of lignin for the production of phenolic monomers has received a lot of attentions. During the hydrogenolysis process, the cleavage of β-O-4 is important for high conversion and the hydrodeoxygenation of C = O is favor for high selectivity of monophenols. Herein, multiple functional metal modified molybdenum carbide catalyst was designed for β-O-4 cleavage and C = O hydrodeoxygenation in lignin and model compound. Experiments coupled with various characterization methods (X-ray diffraction, chemisorption-desorption, X-ray photoelectron spectroscopy) showed that the combined acidity and hydrogenation performance of molybdenum carbide was modified by Ni metal, and was beneficial for the complete cleavage of β-O-4. Meanwhile, due to the synergistic effects between Ni and Cu/Fe, the totally hydrodeoxygenation of C = O was also obtained without excessive hydrogenation of benzene rings. Moreover, by using Ni7Fe3-Mo2C/AC as the catalyst, maximally 35.42% of phenolic monomers and 85.11% of ethyl acetate soluble products from corn straw lignin hydrogenolysis were obtained.

Computational identification of facet-dependent CO2 initial activation and hydrogenation over iron carbide catalyst

χ-Fe5C2 is a promising candidate catalyst for hydrocarbons synthesis through CO2 hydrogenation, however, surface structure reconstruction of the catalyst occurs under reaction conditions which impacts the catalytic performance. In this work, the facet-dependent catalytic behavior of χ-Fe5C2 toward CO2 initial activation and hydrogenation was revealed by density functional theory calculations. Among the six studied facets of χ-Fe5C2, the (510) surface was found to be more active for CO2 activation via direct dissociation to CO* +O* (barrier of 0.24 eV) whereas on the (111) surface, CO2 hydrogenation to HCOO* intermediate was kinetically most favorable with a small barrier of 0.25 eV. Both (510) and (111) facets are good candidates for CO2 initial activation and transformation although the conversion pathways are different. The (110) facet of χ-Fe5C2 is inactive toward CO2 initial activation and conversion due to large barriers. As identified in the literature that the (111) facet of χ-Fe5C2 is more active toward C2 formation via C-C coupling in Fischer-Tropsch synthesis, this surface should also be a good candidate for hydrocarbons synthesis from CO2 hydrogenation as demonstrated in this work. This study fills in gaps in the understanding of facet and surface structure effect of single-phase iron carbide catalysts on CO2 activation and transformation, and offers important insight into the design of improved CO2 hydrogenation catalysts.

Molybdenum Carbide-Reduced Graphene Oxide Composites as Electrocatalysts for Hydrogen Evolution

The development of cost-effective, highly efficient, and stable electrocatalysts to replace expensive platinum-like metal catalysts remains a great challenge for the hydrogen evolution reaction (HER). In this study, we report a facile, microwave-assisted solvothermal (MWSV) synthesis of molybdenum carbide (Mo2C) nanoparticles and molybdenum carbide-reduced graphene oxide (Mo2C-RGO) nanocomposites at elevated temperatures. The optimized Mo2C-RGO nanocomposite catalysts show excellent HER performance in acidic media. When GO is added, the onset potential and Tafel slope of the nanocomposite catalyst are 120 mV and 85 mV/dec, respectively. The catalysts also exhibit good stability in an acidic environment. This improvement of the carbide catalyst is attributed to highly accessible active reaction sites, efficient mass/charge transportation, and enhanced conductivity of the hybrid structure.

Integrating bio-oil and carbohydrate valorization on the fractionation of sugarcane bagasse via Organosolv process using Mo2C-based catalysts

This work studied the fractionation of sugarcane bagasse via Organosolv treatment using isopropanol/water in the presence of Raney-Ni and molybdenum carbide catalysts (Bulk Mo2C and Mo2C supported on activated carbon (AC) or Al2O3). The degree of delignification, the bio-oil and solid residue composition depended on the type of catalyst. A partial extraction of hemicellulose occurred followed by depolymerization, resulting in a product distribution that depended on the catalyst. Raney-Ni catalyst promoted the formation of diols and triols, while xylose, furfural, and furan were mainly produced by Mo2C based-catalysts. The Organosolv treatment without catalyst and in the presence of bulk Mo2C produced a bio-oil containing mainly 2,3-dihydrobenzofuran. Mo2C/AC and Mo2C/Al2O3 are promising catalysts for the fractionation of sugarcane bagasse that produced a bio-oil with higher yield to substituted methoxyphenols and a solid residue more easily hydrolyzed by cellulases, producing higher yield to glucose than Raney-Ni catalyst.

Co-processing of Atmospheric Gas Oil with Rapeseed Oil Over Sulfur-Free Supported and Phosphorus-Modified Co-Mo and Ni-Mo Carbide Catalysts

Co-processing of Atmospheric Gas Oil with Rapeseed Oil Over Sulfur-Free Supported and Phosphorus-Modified Co-Mo and Ni-Mo Carbide Catalysts

Theoretical insight into the interaction between hydrogen and Hägg carbide (χ-Fe5C2) surfaces

In heterogeneous catalysis, the interaction between adsorbates and substrate surface plays an important role on surface structure evolution and even the reaction mechanism. Herein, unified DFT calculation and ab initio atomistic thermodynamics were adopted to explore the interaction between hydrogen and multiple Fe5C2 surfaces. The computation indicates that the dissociation of hydrogen molecule is both thermodynamically and kinetically favorable on Fe5C2 surfaces. The adsorption energy of hydrogen atoms is related to the summed H bond valance (SBVH), a higher SBVH corresponding to a more stable adsorption strength. Based on calculated surface free energy with different hydrogen coverage, the equilibrium crystalline morphology evolution of Fe5C2 under dynamic conditions was constructed with Wulff theorem. C-rich facets expose more area in Wulff construction with decreasing hydrogen chemical potential. The generation of carbon vacancy through reducing to methane has also been investigated, and the reduction of (111) and (11-1) facets is more facile than other facets. We anticipate this work could complement some knowledge to help understanding the surface structure and performance of iron carbide catalysts under experimental conditions.

Microwave modification of cobalt supported on beta silicon carbide catalyst for Fischer–Tropsch synthesis

Microwave modification of cobalt supported on beta silicon carbide catalyst for Fischer–Tropsch synthesis

Cinnamaldehyde hydrogenation over carbon supported molybdenum and tungsten carbide catalysts.

The potential of carbon supported Mo and W carbides to replace Pt is shown for the hydrogenation of cinnamaldehyde. Although the carbide catalysts are 4-6 times less active, both the carbides and Pt are selective towards CC hydrogenation. Unlike Pt, the carbides additionally form β-methylstyrene.

Evidence of water dissociation and hydrogenation on molybdenum carbide nanocatalyst for hydroprocessing reactions

The cubic molybdenum carbide catalyst showed great activity and stability for water dissociation and hydrogenation in hydroprocessing reactions. Isotopic labelling of hydrogen and oxygen atoms allowed explicit verification of water dissociation.