Mo-based Catalysts Research Articles

Characteristics of integral plasma-fluidized bed and preparation of Mo-based catalysts for sulfur-resistant methanation

Characteristics of integral plasma-fluidized bed and preparation of Mo-based catalysts for sulfur-resistant methanation

In-Situ Dynamic Carburization of Mo Oxide with Unprecedented High CO Formation Rate in Reverse Water-Gas Shift Reaction.

In situ construction of active structure under reaction conditions is highly desired but still remains challenging in many important catalytic processes. Herein, we observe structural evolution of molybdenum oxide (MoOx) into highly active molybdenum carbide (MoCx) during reverse water-gas shift (RWGS) reaction. Surface oxygen atoms in various Mo-based catalysts are removed in H2-containing atmospheres and then carbon atoms can accumulate on surface to form MoCx phase with the RWGS reaction going on, both of which are enhanced by the presence of intercalated H species or Pt-dopants in MoOx. The structural evolution from MoOx to MoCx is accompanied by enhanced CO2 conversion, which is positively correlated with the surface C/Mo ratio but negatively with the surface O/Mo ratio. As a result, an unprecedented CO formation rate of 7544.6 mmol ⋅ gcatal -1 ⋅ h-1 at 600 °C has been achieved over in situ carbonized H-intercalated MoO3 catalyst, which is even higher than those from noble metal catalysts. During 100 h stability test only a minimal deactivation rate of 2.3 % is observed.

Regulation of Ir Dopant in Mo Oxides by Flame Spray Pyrolysis for Efficient CO2 Hydrogenation.

Mo carbide is recognized as one of the most promising catalyst for CO2 utilization via reverse water-gas shift (RWGS). However, it always suffered from low processing capacity, undesired products and deactivation. Herein, an Ir modified MoO3 synthesized by the flame spray pyrolysis (FSP) method exhibits higher reaction rate (63.0 gCO2·gcat-1·h-1) compared to the one made by traditional impregnation method (45.8 gCO2·gcat-1·h-1) over the RWGS reaction at 600°C. The distinguishing feature between the two catalysts lies in the chemical state and space distribution of Ir species. Ir species predominated in the bulk phase of MoO3 during the quenching process of the FSP method and were mainly in the metallic states, which revealed by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) characterizations. In contrast, the Ir introduced via impregnation method were mainly on the surface of MoO3 and in oxidized state. The regulation of Ir dopant in MoO3 catalyst by different methods determines the carbonization process to Mo carbides, and thus affects the catalytic performance. This work sheds light on the superiority of the FSP method in synthesizing Mo oxides with heteroatoms and further creating an efficient Mo-based catalyst for CO2 conversion.

Highly efficient nanosized MoS2/MoP heterocatalyst for enhancing hydrogen evolution reaction over a wide pH range

Energy consumption associated with the catalysts contributes partly to the high ohmic resistance arising from the low conductivity of the catalyst and poor charge transfer between nanoparticles, which has been difficult to study due to the complicated nanostructured framework of the catalysts. We constructed a novel heterostructure electrocatalyst (MoS2/MoP@NC) composed of nanosized MoS2/MoP heterostructures anchoring on hierarchical N-doped carbon for smoothing electron transfer in boosting hydrogen evolution reaction (HER). With the merits of large surface area, rapid charge transfer, and optimized electronic structure induced by charge transfer across the sufficient interface, the optimal MoS2/MoP@NC (MoSP) catalyst shows a competitive overpotential of 140 (0.5 M H2SO4), 76 (1.0 M KOH), and 103 mV (0.5 M NaCl &1.0 M KOH) at 10 mA cm−2, respectively. Raman experiment and Density functional theory (DFT) calculations reveal the formation of Mo-S-Mo bonds between MoS2 and MoP, which favor enhancing the Femi level to facilitate the electron transfer, therefore regulating the electronic structure for the optimization of adsorption energy of hydrogen intermediate. Based on the experimental results, we constructed an energy consumption model of catalysts, where energy consumption comes from three aspects. The heterostructure design decreases the energy consumption of the catalysts greatly compared to the single-phase Mo-based catalyst of MoS2 (78.0%) and MoP (45.2%) in alkaline electrolytes.

Compositional and Fabrication Cycle Optimization of Ceria-Zirconia-Supported Mo-Based Catalysts for NH3-SCR NOx Reduction

The reduction of nitrogen oxides (NOx), critical pollutants from stationary to mobile sources, mainly relies on the selective catalytic reduction (NH3-SCR) method, employing ammonia to reduce NOx into nitrogen and water. However, conventional catalysts, while effective, pose both environmental and operational challenges. This study investigates ceria-zirconia-supported molybdenum-based catalysts, exploring the effects of zirconium doping and different catalyst synthesis techniques, i.e., co-precipitation and impregnation. The catalytic performance of the differently prepared samples was significantly influenced by the molybdenum incorporation method and the zirconium content within the ceria-zirconia support. Co-precipitation at higher temperatures resulted in catalysts with better structural attributes but slightly lower catalytic activity compared to those prepared via impregnation. Optimal NOx reduction (close to 100%) was observed at a 15 mol% zirconium doping level when using the impregnation method.

Biphasic Mo-based catalysts with abundant pores and rich heterostructures for high-efficient production of hydrogen in both alkaline and acidic media

Electrolysis of water to produce H2 demands high-efficient catalysts. Herein, biphasic γ-MoC/MoS2/C electrocatalyst with heterostructures was prepared using methyl orange as the low-cost C and S resource. The γ-MoC/MoS2/C presented convoluted nanosheets with abundant pores and rich heterostructures, which owed it excellent catalytic performance in both of 1 M KOH and 0.5 M H2SO4 solutions. The overpotentials required to reach 10 mA·cm−2 were 58 mV and 81 mV, respectively, under alkaline and acidic conditions. γ-MoC/MoS2/C also exhibited satisfactory long-term stability, that negligible decrease of the LSV curves was observed after 3000 CV cycles. The current density was maintained at approximately 95 % and 91 % in 1 M KOH and 0.5 M H2SO4 solutions, respectively, over 36 h. DFT results showed that the ΔGHads* value of γ-MoC/MoS2/C is −0.12 eV, approaching to zero, which is conducive to the adsorption and desorption of Hads* and thus promotes the hydrogen evolution reactions (HER). The synthesis of γ-MoC/MoS2/C was quite facile and flexible, which avoid stepwise carbonization and sulfuration. It is expected to provide a fresh reference for the synthesis of high-efficient, low-cost and susceptible Mo-based catalysts.

Pt atomic clusters/MoS2 nanosheets/Co-doped hollow carbon nanofibers for high-current–density alkaline hydrogen production

The application of layered molybdenum disulfide (MoS2) in catalytic hydrogen production has attracted great interest, while their catalytic properties are limited by poor electron conductivity and a few catalytically active sites. In this work, we demonstrated a highly active electrocatalyst for large-scale hydrogen production, consisting of two-dimensional (2D) Pt-MoS2 nanosheets along one-dimensional (1D) cobalt nanoparticle integrated carbon hollow nanofibers (Co@CHNF). The as-prepared Pt-MoS2-Co@CHNF had a large specific surface area (44.5 m2 g−1). X-ray photoelectron spectrometer (XPS) and spherical aberration corrected transmission electron microscope (AC-STEM) demonstrated that Pt atomic clusters (Pt ACs) were doped on MoS2 nanosheets by thermodynamically induced spontaneous interfacial redox between MoS2 and H₂PtCl₆. The Pt-MoS2-Co@CHNF based catalysts exhibited an overpotential as low as 91 mV for 10 mA cm−2 and 258 mV for 200 mA cm−2 in 1 M KOH electrolyte, and there is no significant floating for catalytic active with 14 h continuous operation, which demonstrates its excellent long-term operation durability, significantly superior to the previously reported state-of-the-art Co-based or Mo-based catalysts. In particular, the self-supporting binder-free Pt-MoS2-Co@CHNF catalyst-based electrode showed an ultra-high current density of 500 mA cm−2 at a low overpotential of 301 mV, without any decrease after 24 h operation at 500 mA cm−2 in 1 M KOH seawater electrolyte, representing a great potential for large-scale seawater hydrogen production.

Unveiling the structure-performance of MoO3/La2O2CO3 for ultra-deep aerobic oxidative desulfurization of diesel

The production of clean fuel via the aerobic oxidative desulfurization (ODS) technique is a potential substitute due to its moderate reaction conditions and outstanding catalytic efficiency. However, the relationship between the catalyst structure and the catalytic performance for sulfur-containing compounds with high steric hindrance effect in this process remains unclear hitherto. Herein, a series of MoO3/La2O2CO3 catalysts with various MoO3 particle sizes were carefully designed and prepared through a facile citric acid-assisted hydrothermal strategy. The structures of the loaded Mo-based catalysts were analyzed by series characterization methods, and their structure-performance relationships were investigated for catalytic ODS of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The results revealed that the particle size of MoO3 significantly influenced the redox properties, reactive oxygen species, and ODS performances of MoO3/La2O2CO3 catalysts. With the decrease of MoO3 crystal size from 15.8 nm to 5.3 nm, the ODS performances of MoO3/La2O2CO3 catalysts considerably increased. Among them, MoO3/La2O2CO3-3 exhibited the best ODS activity with complete 4,6-DMDBT conversion within 2.5 h at 130 °C because of its appropriate MoO3 size and the lowest apparent activation energy (Ea). Nevertheless, further downsizing the crystal size of MoO3 to 2.8 nm resulted in a significant increase in the Ea, which dramatically suppressed the catalytic ODS performance of the corresponding MoO3/La2O2CO3-4 catalyst instead. It therefore reveals for the first time that there is a balance between the geometry and the catalytic efficiency of MoO3/La2O2CO3 catalysts for catalytic ODS of 4,6-DMDBT with high steric hindrance effect, which could provide insight for developing advanced ODS catalysts in the future.

Enhancing perhydrobenzyltoluene dehydrogenation performance with Co, Mo and Mn metal oxides: A comparative study with Pt/Al2O3 catalyst

In this study, the influence of incorporating Co, Mo and Mn oxides into Pt/Al2O3 catalyst on the dehydrogenation performance of Liquid organic Hydrogen Carrier (LOHCs) is investigated. A notable positive impact on the dehydrogenation process was observed, resulting in enhanced catalytic performance. This effect is associated with improved product desorption and a significant reduction in the by-product formation like methylfluorene. Particularly, the electron-acceptor effect exhibited by molybdenum, emerge as the key factor in enhancing catalytic performance. This effect allowed for the reduction of platinum content without compromising the productivity and selectivity and representing a significant advancement in catalyst design. These findings highlight the potential for Mo-based catalysts to serve as a promising alternatives to Pt-based catalysts in LOHC dehydrogenation processes.

Molybdenum nitride thin films coated cobalt-metal-organic framework nanocolumns for high-efficiency alkaline hydrogen evolution

The sustainable development of catalysts with Pt-like catalytic activity to produce hydrogen economically from water electrolysis is essential and challenging. Herein, we have prepared a novel catalyst with the combined virtues of nanocolumn structures and heterojunctions by magnetron sputtering molybdenum nitride (Mo2N) thin films over cobalt-metal-organic framework (Co-MOF) nanocolumns on carbon paper (CP), and explored the catalytic activities in hydrogen evolution reaction (HER). By optimizing the preparation process, the heterostructured Co-MOF@Mo2N/CP catalysts can exhibit an excellent HER performance with an overpotential of only 72.8 mV at 10 mA cm−2 and cycling durability over 24 h and 5000 cycles, achieving one of the best performances among state-of-the-art Mo-based catalysts. This work guides and accelerates the design of low-cost and high-performance transition metal nitrides HER catalysts for industrial applications.

Atomic Molybdenum Nanomaterials for Electrocatalysis.

As a sustainable energy technology, electrocatalytic energy conversion requires electrocatalysts, which greatly motivates the exploitation of high-performance electrocatalysts based on nonprecious metals. Molybdenum-based nanomaterials have demonstrated promise as electrocatalysts because of their unique physiochemical and electronic properties. Among them, atomic Mo catalysts, also called Mo-based single-atom catalysts (Mo-SACs), have the most accessible active sites and tunable microenvironments and are thrivingly explored in various electrochemical conversion reactions. A timely review of such rapidly developing topics is necessary to provide guidance for further exploration of optimized Mo-SACs toward electrochemical energy technologies. In this review, recent advances in the synthetic strategies for Mo-SACs are highlighted, focusing on the microenvironment engineering of Mo atoms. Then, the representative achievements of their applications in various electrocatalytic reactions involving the N2, H2O, and CO2 cycles are summarized by combining experimental and computational results. Finally, prospects for the future development of Mo-SACs in electrocatalysis are provided and the key challenges that require further investigation and optimization are highlighted.

Mo-based bimetallic oxide catalysts for the reverse water gas shift reaction

The reverse water gas shift (RWGS) is of great significance to the resource utilization of CO2. In this paper, based on the features of MoO3, the Mo-based catalysts doped with Ga, Ti and Ce were prepared, and the effects of oxygen vacancies and basic sites on the RWGS reaction were studied. When the volume ratio of H2 and CO2 is 1 : 1, the yield of CO can reach 26.66%. Because it exposes higher concentration of Ce sites and moderate alkaline active sites on the surface. When the proportion of H2 in the reaction gas increases, the highest yield of CO can reach 54.53%, which is mainly attributed to a large number of oxygen vacancies on the surface of MoTi. This study can be used as a reference for the design of catalysts for RWGS reaction under different reaction conditions.

Boosting CO2 Hydrogenation to Methanol over Monolayer MoS2 Nanotubes by Creating More Strained Basal Planes.

The controlled creation, selective exposure, and activation of more basal planes while simultaneously minimizing the generation and exposure of edge sites are crucial for accelerating methanol synthesis from CO2 hydrogenation over MoS2 catalysts but remain a bottleneck. Here, we report a facile method to fabricate heteronanotube catalysts with single-layer MoS2 coaxially encapsulating the carbon nanotubes (CNTs@MoS2) through host-guest chemistry. Inheriting the long tubular structure of CNTs, the grown MoS2 nanotubes exhibit significantly more basal planes than bulk MoS2 crystals. More importantly, the tubular curvature not only promotes strain and sulfur vacancy (Sv) generation but also preferentially exposes more in-plane Sv while limiting edge Sv exposure, which is conducive to methanol synthesis. Both the strain and layer number of MoS2 can be easily and finely adjusted by altering CNT diameter and quantity of precursors. Remarkably, CNTs@MoS2 with monolayer MoS2 and maximum strain displayed methanol selectivity of 78.1% and methanol space time yield of 1.6 g gMoS2-1 h-1 at 260 °C and GHSV of 24000 mL gcat.-1 h-1, representing the best results to date among Mo-based catalysts. This study provides prospects for novel catalyst design by synthesizing coaxial tubular heterostructure to create additional catalytic sites and ultimately enhance conversion and selectivity.

Effect of DBD Plasma Treatment on Activity of Mo-Based Sulfur-Resistant Methanation Catalyst.

By combining the advantages of dielectric barrier discharge (DBD) low temperature plasma and fluidized bed, the effect of plasma on the performance of supported Mo-based catalyst was studied in this paper. The performance of the catalyst obtained by plasma treatment, calcined, plasma+calcined was compared, and the appropriate catalyst preparation scheme was explored. Comparing with the three catalysts, it was concluded that the catalyst average conversion after 30 W plasma treatment is 33.40 %, which was 8.94 % and 12.75 % higher than the other two, respectively. The structure and properties of the catalyst were characterized by N2-Physisorption, H2-chemisorption, XRD, TEM, XPS, Raman and NO-pulse adsorption. Then, by analyzing the characterization results, it can be seen that plasma can make the catalyst have a higher specific surface area and a more dispersed active metal with smaller grain size. Through the surface species identification characterization, it was found that plasma can produce more defective structures and expose more active sites, which is the main reason for the difference in conversion.

The Influence of Sulfurization and Carbonization on Mo-Based Catalysts for CH3SH Synthesis

Sulfur-resistant Mo-based catalysts have become promising for the one-step synthesis of methanethiol (CH3SH) from CO/H2/H2S, but the low reactant conversion and poor product selectivity have constrained its development. Herein, we synthesized K-MoS2/Al2O3 and K-Mo2C/Al2O3 catalysts via the sulfurization and carbonization of K-Mo-based catalysts in the oxidized state, respectively. During the synthesis of CH3SH, both K-Mo2C/Al2O3 and K-MoS2/Al2O3 showed excellent catalytic performance, and the activity of the former is superior to that of the latter. The effect of different treatments on the catalytic performance of Mo-based catalysts was investigated by XRD, BET, Raman spectroscopy, H2-TPR, and reactants-TPD characterization. The results showed that the sulfide-treated sample showed stronger metal-support interactions and contributed to the formation of K2S, which exposed more active sites and stabilized the formation of C-S bonds. Carbonized samples enhanced the activation of H2, which promoted the hydrogenation of the intermediate species of carbonyl sulfide (COS) and thus improved the selectivity of CH3SH.

Porous MoP2/MoS2 hierarchical nanowires for efficient hydrogen evolution reaction in full pH range

Rational designing Mo-based heterojunction catalysts as hydrogen evolution catalysts is seriously significant for the widespread utilization of hydrogen energy. Here, the ingenious hierarchical construction of MoP2/MoS2 nanowires was delivered with high conductivity of porous MoP2 and abundant active sites of defect-rich MoS2. Under synergistic effect of two materials, this catalyst achieves a dramatically optimized electronic structure to boost hydrogen evolution in all-pH range. The optimal MoP2/MoS2/CC nanoreactor showed overpotentials of 47.11, 60.16, and 89.83 mV to drive −10 mA cm−2 and Tafel slopes of 51.69, 52.04, and 73.79 mV dec−1 in acidic, alkaline, and neutral media, respectively. This finding may provide an effective approach for elevating the pH-universal electrocatalytic performance in order to achieve industrial hydrogen evolution.

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.

Interfacial MoO2 nanograins assembled over graphitic carbon nanofibers boosting efficient electrocatalytic reduction of nitrate to ammonia

Electrocatalytic nitrate reduction reaction (NO3-RR) for sustainable carbon-free hydrogen carrier (NH3) production from polluted NO3- sources of industrial wastewater is very promising. Mo-based catalysts are defined as popular electrocatalytic materials, but the rational performance achievement of Mo-based catalysts in the NO3-RR remains limited. In this study, to overcome the NO3-RR activity limitation, the interfacial MoO2 nanograins assembled on the N-functional carbon nanofibers (defined as MoO2/C) were constructed by electrospun and controlled graphitizing process. The comparative catalysts dominated by molybdenum oxides namely MoO2/MoO3 were synthesized by controlled calcination in air atmosphere. The MoO2 nanograins anchored in situ on carbon nanofibres could afford more interfacial active regions and accelerate the electron transfer efficiency of the electrocatalytic process by graphitic carbon fiber network. More importantly, MoO2/C was endowed with more oxygen vacancy sites which can trap the free NO3- ions over the reactive sites to enhance the surface interaction of NO3- with catalytic sites during the reaction process. The experimental results showed that the electrocatalytic nitrate reduction performance of the catalyst MoO2/C obviously outperformed that of MoO2/MoO3 in the light of the atomic activity efficiency with a near 7.5 folds enhancement. The MoO2/C affords the highest NH3 yield of 4838.5 µg h−1 mgcat−1 and Faraday efficiency of 30 % at –0.9 V vs.RHE and was endowed with 50 h of continuous reaction stability, proving the potential in practical electrochemical water treatment involving nitrate contamination.

An in-situ combo Mo-based ionic liquid and SAPO-11 catalyst for efficient biolipids hydrodeoxygenation and isomerization

The design of novel practical catalysts is critical for the blossoming of biodiesel green-energy, in which Mo-based catalysts are of particular interest. In this work, an in-situ synthesis method was proposed to obtain a combo Mo-based ionic liquid and SAPO-11 catalyst. The catalyst presents both highly dispersed MoS2 as hydrodeoxygenation active sites and acidic sites for isomerization. MoS2 with a few fine layers can be identified based on TEM images and the Brønsted acid sites are dominant based on Pyridine-IR analysis. A great performance of MoS2/C8min-15 %SA can be obtained under optimized reaction conditions with 100 % conversion of methyl palmitate, 75.0 mol% hydrodeoxygenation to n-C15-C16, and 20.5 mol % isomerization to i-C15-C16. The structure and activity of the catalyst can be retained at least for 4 cycles. Thin layers and high sulfurization, large amount of Brønsted acid sites, and suitable reaction conditions are key points to achieve a significant performance and avoid over cracking and deactivation. On basis of detected intermediates and kinetic data simulations, a complex reaction pathway was proposed and the specific k values for each elementary reaction were provided for the hydrodeoxygenation and isomerization of methyl palmitate.

Carbon dioxide resource recycling technology: Analysis and prospects of Mo-based catalyst performance in low-carbon alcohol synthesis

This study addresses the escalating issue of atmospheric CO2 emissions and climate change, exacerbated by the increased use of fossil fuels. It explores the synthesis of low-carbon alcohols as a viable method to utilize excess atmospheric CO2, meeting the growing demand for sustainable fuel alternatives. The research focuses on the challenges of activating CO2, often requiring conversion to CO via a reverse water gas shift reaction (RWGS) prior to alcohol synthesis. Through detailed case studies, this review investigates the factors influencing the catalytic efficiency of molybdenum-based (Mo-based) catalysts in alcohol synthesis from CO. Key aspects such as the addition of additives, support types, preparation methods, and the catalyst’s composition are analyzed for their impact on catalyst selectivity and activity. This comprehensive review not only highlights the critical conditions for optimizing catalytic reactions but also contributes to the development of effective strategies for reducing greenhouse gases through innovative catalytic technologies.