Mo Catalysts Research Articles

Mass-Mediated Phase Modulation of Thin Molybdenum Nitride Crystals on a Liquid Cu-Mo Alloy

The high-quality and controllable preparation of molybdenum nitrides (MoxNy) will significantly advance the fields of heterogeneous catalysis, energy storage, and superconductivity. However, the complex structure of MoxNy, which contains multiple phases, makes exploring the structure-property relationship challenging. The selective preparation of MoxNy with distinct phases is undoubtedly an effective method for addressing this issue, but it is lacking experimental cases and theoretical reports. Here we demonstrate a feasible chemical vapor deposition (CVD) strategy for selectively producing γ-Mo2N or δ-MoN through modulating the mass quantity of N precursors. A liquid Cu-Mo alloy was used as a Mo precursor and catalyst in this system. The resulting γ-Mo2N was systematically characterized and found to be of high quality. Furthermore, the morphology evolutions of γ-Mo2N and δ-MoN with growth time were summarized in detail, as a result of growth and etching dynamics. This work promotes the phase modulation of MoxNy and provides a framework for future research on the structure-property relationship.

Sulfidation of Supported Ni, Mo and NiMo Catalysts Studied by In Situ XAFS

Active sites in Mo-based hydrotreating catalysts are produced by sulfidation. To achieve insights that may enable optimization of the catalysts, this process should be studied in situ. Herein we present a comparative XAFS study where the in situ sulfidation of Mo/δ-Al2O3 and Ni/δ-Al2O3 is compared to that of δ-Al2O3 supported NiMo catalysts with different NiMo ratios. The study also covers the comparison of sulfidation of Ni and Mo using different oxide supports as well as the sulfidation conditions applied in the reactor. The XAFS spectra confirms the oxide phase for all catalysts at the beginning of the sulfidation reaction and their conversion to a sulfidized phase is followed with in situ measurements. Furthermore, it is found that the monometallic catalysts are less readily sulfidized than bimetallic ones, indicating the importance of Ni-Mo interactions for catalyst activation. Mo K-edge XAFS spectra did not show any difference related to the support of the catalyst or the pressure applied during the reaction. Ni K-edge XAFS spectra, however, show a more complete sulfidation of the Ni species in the catalyst when SiO2 is used as a support as compared to the Al2O3. Nevertheless, it is believed that stronger interactions with Al2O3 support prevent sintering of the catalyst which leads to its stabilization. The results contribute to a better understanding of how different parameters affect the formation of the active phase of the NiMo catalysts used in the production of biofuel.

Synergism between hierarchical MFI zeolites and alumina in alkene cross-metathesis reactions as a function of composition.

Synergism between hierarchical zeolites and alumina in the preparation of active Mo catalysts, as a function of composition ratios, has been demonstrated in the cross-metathesis reaction between ethene and 2-butene. The metathesis reaction activity, reflected by ethene conversion, increases from 24.1% to 49.2% with the increase in the alumina content in composites from 10 wt% to 30 wt%. A further increase in the alumina content leads to the reduction in the metathesis activity, in which the ethene conversion decreases from 30.3% to 4.8% upon the enhanced alumina content from 50 wt% to 90 wt%. The impact of alumina content on the metathesis activity is closely associated with the interaction mode between the hierarchical ZSM-5 zeolite and alumina. TEM observation as well as EDS analysis and XPS results prove the progressive coating of alumina phase on the surface of zeolites along with the progressive enhancement of alumina content. The moderate alumina content in the composite enables the desired interaction between hierarchical zeolites and alumina, which is beneficial for the preparation of active catalysts for the alkene cross-metathesis reaction.

Reversible alkaline hydrogen evolution and oxidation reactions using Ni–Mo catalysts supported on carbon

Carbon-supported Ni–Mo composites catalyze alkaline hydrogen evolution and oxidation with negligible onset overpotential. Electrolyzers using Ni–Mo cathodes perform comparably to Pt–Ru cathodes, but oxidative instability limits fuel cell operation.

Superhydrophilic and superaerophobic Ni–Mo alloy grown on 3D Ni foam with heterogeneous structure as self-standing electrocatalysts toward efficient alkaline HER

Hydrogen energy is the most promising clean energy at present and hydrogen production by electrocatalytic water splitting is the frontier technology of alternative energy in the future. Herein, the Ni–Mo alloy supported with nickel foam (NF) was prepared by hydrogen reduction strategy at high temperature. The catalytic activity and stability of NiMo@NF-x catalyst (x stands for temperature) with multistage (sheet/particle) array structure were studied under different temperatures. The performance of the catalyst was evaluated by contact angle and related electrochemical characterization. It was found that the surface of NiMo@NF-550 catalyst prepared at 550 °C had superhydrophilic and superaerophobic properties, which contributed to the deactivation of bubbles from the surface of the electrode and improved the efficiency of the catalytic reaction. Moreover, the multi-stage array structure of sheet/particle will form a greater specific surface area than the plain sheet structure, offering more reaction sites. These results indicate that the self-supported superhydrophilic and superaerophobic Ni–Mo catalysts have excellent electrocatalytic hydrogen evolution ability.

C2H2 selective hydrogenation over transition metal carbide (MxCy): Probing into the influences of crystal facet, M type and M: C ratio on C2H4 activity, selectivity and catalyst stability

Aiming at probing into the structure and composition sensitivity of transition metal carbides (MxCy) to catalytic performance of C2H2 selective hydrogenation, twenty-three kinds of MxCy (M = Ti, Zr, Hf, Mo, W and Co) catalysts with different M types, crystal facets and M: C ratios are investigated using DFT calculations and microkinetic modeling. The results show that C2H4 activity and selectivity depend on surface composition and structure due to the ensemble and/or ligand effects. Charge transfer number from M to C atoms and d-band center can be used as the descriptors to efficiently evaluate C2H4 selectivity and activity over MxCy catalysts, respectively. α-MoC(101) is screened out to exhibit Pt-like electronic properties with better C2H4 activity, selectivity, and catalyst stability to resist green oil formation compared to Pt and other MxCy catalysts when the temperature is ≤425 K and H2: C2H2 ratio is ≥1: 1, which is superior to the industrial PdAg/Al2O3 catalyst.

Catalytic Activity and Coke Resistance of Gasification Slag-Supported Ni Catalysts during Steam Reforming of Plastic Pyrolysis Gas

Pyrolysis gas from polyolefinic plastic waste is a hydrocarbon-rich feedstock for sustainable syngas production. The effect of Cr, Mo, and W promoters on the activity of gasification slag-supported Ni catalysts during the reforming of plastic pyrolysis gas was investigated (polyethylene and polypropylene mixed feedstock, Ni:promoter molar ratio = 4.5, 800 °C, steam-to-carbon molar ratio of 7). Based on 3 h reforming tests, all catalysts showed stable conversion efficiency, suggesting that gasification slag from municipal solid waste is a promising replacement material for traditionally used alumina supports. Moreover, the slag demonstrated good thermal stability and potential for catalyst recycling, justifying the economic benefit of valorizing the material. Interestingly, interaction between slags and promoters is evidenced by the formation of CaWO4 and CaMoO4 phases, which may have an impact on the reforming activity of bimetallic catalysts. Among the studied catalysts, the highest conversion efficiency of hydrocarbon compounds (76%), highest H2 (122.65 mmol Lfeed–1) and CO (49.34 mmol Lfeed–1) yields, and lowest coke deposition (0.06 wt %) were demonstrated by the Ni–Mo catalyst. The superior performance of Ni–Mo was accompanied by the growth of carbon nanotubes via a tip-growth mechanism, which was not observed in other catalysts. Spherical carbon nanocages and filamentous carbon nanofibers predominated in coke deposits of Ni, Ni–W, and Ni–Cr. The high syngas production efficiency of Ni–Mo could be attributed to the dispersion of metal by the growing carbon nanotubes providing the reaction sites for reforming and coke gasification reactions. Owing to these properties, Ni catalyst promoted by Mo and loaded on a gasification support has high potential for the syngas production from plastic pyrolysis gas.

Hydrothermal liquefaction of biomass with molybdenum, aluminum, cobalt metal powder catalysts and evaluation of wastewater by fungus cultivation

In this study, the Ammi visnaga plant was liquefied in the presence of Mo, Al and Co metal powder catalysts and without catalyst. Liquefaction trials were carried out at 225, 250, 275 and 300 °C reaction temperatures and reaction times of 0, 15, 30 and 45 min. The highest liquid product yield was determined as 42.31% in the experiment without catalyst and 39.42% with Mo catalyst at 300 °C. GC-MS, XRD, TOC, SEM-EDX and Elemental analysis methods were used to characterization of solid and liquid product. The highest energy values were determined as 25.34 MJ/kg for light oil and 29.69 MJ/kg for heavy oil with Co catalyst. In order to investigate the agricultural application potential, the effects of the wastewater obtained at the end of the trials on Trichoderma harzianum, Clonostachys rose and Rhizoctonia solani fungi were investigated. It was determined the bioagent fungi developed and pathogen growth was inhibited.

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN 3 P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN ³ P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

Bimetallic NiM/C (M = Cu and Mo) Catalysts for the Hydrogen Oxidation Reaction: Deciphering the Role of Unintentional Surface Oxides in the Activity Enhancement

Bimetallic NiM/C (M = Cu and Mo) Catalysts for the Hydrogen Oxidation Reaction: Deciphering the Role of Unintentional Surface Oxides in the Activity Enhancement

Hydrodesulphurization of Bonny light crude oil using nano Co–Mo supported on zeolite synthesized from Akoko clay

At present, petroleum remains the single largest global source of nearly all transportation fuel and the main source of industrial chemicals. But the legislative demand for cleaner fuel in automobile worldwide has forced scientists to develop and adopt new technologies to reduce the amount of sulphur in fuel. In this study, a Co–Mo catalyst supported on zeolite synthesized from local clay was developed and tested in hydrodesulphurization reactions, using Bonny light crude oil feed. The Co–Mo was incorporated into the zeolite by wet impregnation method and its activity was evaluated in a batch reactor. The catalyst was characterized and the efficiency was investigated in terms of product distribution and reaction conditions. With a rise in the temperature, the sulphur in the crude oil gets released into the liquid and gas effluents. In the case of gas effluents, the removal of sulphur depends on the reaction temperature, while in the liquid products, the removal of sulphur lies on the reaction time rather than the reaction temperature. The use of this catalyst results in significant upgraded and enhanced oil production with an environmentally friendly fuel, which therefore recommended as an alternative to conventional industrial catalysts.

Efficient and economic transesterification of waste cooking soybean oil to biodiesel catalyzed by outer surface of ZSM-22 supported different Mo catalyst

With the aim of developing efficient heterogeneous catalysts for production of clean biodiesel through the transesterification process, a novel Mo catalyst supported on the outer surface of ZSM-22 (xMo/ZSM-22) was developed and synthesized successfully with the wet impregnation method. The characterization results showed that the Mo(VI) oxide species were highly dispersed on the surface of catalysts under the Mo-loading not higher than 5%, and the aggregation of the MoO3 nanoparticles were detected above the Mo-loading of 5%. Meanwhile, the maximum acid intensity was also exhibited in the 5Mo/ZSM-22 catalyst. As a result, the catalytic performance of Mo/ZSM-22 catalysts in the transesterification of waste cooking soybean oil (WCSO) was significantly improved compared with the untreated ZSM-22 catalyst. Especially, the 5Mo/ZSM-22 showed the good activity (XWCSO of 59.29%, SBiodiesel of 99.86%), which was mainly due to the well dispersed Mo species and the larger acidity. Additionally, the 5Mo/ZSM-22 catalyst exhibits good stability and the high biodiesel selectivity, and the fuel properties of the as-synthesized biodiesel meet ASTM D6751 standards. This work provides a useful synthesis strategy of transesterification catalysts for the preparation of biodiesel.

Greener and Efficient Epoxidation of 1,5-Hexadiene with tert-Butyl Hydroperoxide (TBHP) as an Oxidising Reagent in the Presence of Polybenzimidazole Supported Mo(VI) Catalyst

Alkene epoxidation with TBHP as an oxidising reagent using heterogeneous Mo(VI) catalyst is an environmentally friendly process since it eliminates acid waste and chlorinated by-products often associated with the conventional industrial method that uses stoichiometric peracid such as peracetic acid and m-chloroperbenzoic acid. Polybenzimidazole supported Mo(VI) complex, i.e., PBI.Mo has been successfully prepared, characterised and assessed for the epoxidation of 1,5-hexadiene in the presence of tert-butyl hydroperoxide (TBHP) as an oxidising reagent. A quadratic polynomial model has been developed, demonstrating the yield of 1,2-epoxy-5-hexene in four independent variables. The effects of different parameters such as reaction temperature, feed mole ratio of 1,5-hexadiene to TBHP, catalyst loading, and reaction time were studied. Response surface methodology (RSM) using Box-Behnken Design (BBD) was employed to study the interaction effect of different variables on the reaction response. This study presents the optimization of 1,5-hexadiene epoxidation in a batch reactor using TBHP as an oxidant and a polymer-supported Mo(VI) catalyst.

Biodiesel production by transesterification of waste cooking oil in the presence of graphitic carbon nitride supported molybdenum catalyst

Development of the active metal species with high utilization and accessibility of oil macromoleculars is one of the critical factors affecting heterogeneous metal-based catalysts for production of biodiesel. Here, we synthesized two-dimensional graphitic carbon nitride supported molybdenum (xMo/g-C3N4) catalysts for the facile transesterification of waste cooking soybean oil. Various characterization results of these catalysts show the crystal structure of g-C3N4 is not destroyed, however, Mo oxides phase, containing Mo6+ and Mo5+ state, is detected on the surface of the Mo/g-C3N4 with much Mo-loading, and the ratio of Mo6+/Mo5+ increases significantly with the increasing Mo loading. As expected, compared with the neat g-C3N4 catalyst, the g-C3N4 supported Mo catalyst exhibits a better catalytic performance; especially the 10%Mo/g-C3N4 catalyst has the optimal waste cooking soybean oil conversion of 71.1% and biodiesel selectivity of 99.5%. Furthermore, the experimental parameters and catalytic reusability for the transesterification reaction over 10%Mo/g-C3N4 catalyst are investigated. Moreover, the possible deactivation mechanism and regeneration method of as-prepared catalyst are also proposed. This work provides a valuable tactics for the production of clean and low-cost biodiesel from waste cooking soybean oil in the presence of efficient solid catalyst.

Hydrothermal co-liquefaction of biomass and plastic wastes into biofuel: Study on catalyst property, product distribution and synergistic effects

This study reports an efficient conversion route for prosopis juliflora (PJ) biomass into high-quality bio-oil through catalytic hydrothermal liquefaction (HTL) process with systematically substituted hydrogen-rich plastic waste ‘polypropylene (PP)’, and using alumina supported metal oxide (Mo, Ni, W, and Nb) catalysts. The HTL treatments of PJ with PP (0-75 wt.%) were investigated in both sub and supercritical water conditions. An excellent synergy between PP and PJ was observed even in subcritical conditions (97.6% synergy at 340 °C at 25% PP to PJ), while efficient liquefaction of PP alone was observed only in the supercritical conditions. The optimum temperature, and PP substitution were found to be 420 °C and 25% respectively, with 46.5% bio-oil yield, high deoxygenation (65.1%), and carbon recovery (78.9%) when using Nb/Al2O3 as the catalyst. An in-depth analysis of physicochemical properties and the bio-oil product distribution with respect to each catalyst and PP/PJ substitution ratio are discussed in detail. Among all, the Nb/Al2O3 catalyst performed well with remarkable recyclability up to 10 cycles. The produced bio-oil mixture due to its low oxygen content is very promising to be upgraded to precursors for chemicals and transportation biofuels.

A Highly Active NiMoAl Catalyst Prepared by a Solvothermal Method for the Hydrogenation of Methyl Acrylate

In this study, a series of Ni10MoxAl composite metal oxide (Ni10MoxAl, NiO = 10 wt.%, x = 2.5, 5, 10, 15, 20 wt.%) catalysts with different Mo content were prepared by a solvothermal method using a water—ethanol system. By employing various characterization technologies, it was confirmed that the suitable amount of the Mo element can not only promote the dispersion of the Ni species but also inhibit the formation of the inactive NiAl2O4 phase. Consequently, the hydrogenation activity of the Ni10MoxAl catalysts was affected by the particle size of the active components and the amount of the NiAl2O4 phase. As a result, the Ni10Mo10Al catalyst showed the best catalytic performance on methyl acrylate hydrogenation, and the yield of methyl propionate can be increased from 53.7% to 89.5% at 100 °C and 1 MP H2, compared with the Ni10Mo10/γ–Al2O3 catalyst prepared by a traditional impregnation method. The stability of the Ni10Mo10Al catalyst was also investigated, and the catalyst can run stably for 23 h. The novel strategy adopted in this article provides a new direction for the preparation of high activity Ni–Mo catalysts.

A comprehensive theoretical investigation on the thiophene hydrodesulphurisation mechanism over sulphided Co–Mo catalysts supported by ZSM-5, FAU, Beta and MCM-22 zeolites

ABSTRACT We have theoretically studied the hydrodesulphurisation (HDS) mechanism of thiophene and its hydrogenated derivatives over sulphided Co–Mo catalysts supported by four zeolites (ZSM-5, FAU, Beta, MCM-22) by a two-layer ONIOM (our Own N-layered Integrated molecular Orbital and molecular Mechanics) method. Due to low energy barriers, the thiophene can be hydrogenated to 2,3-dihydrothiophene (2,3-DHT), 2,5-dihydrothiophene (2,5-DHT) and tetrahydrothiophene (THT). Direct desulphurisation (DDS) and hydrogenolysis desulphurisation (HYD) pathways were investigated in detail. The calculated results show that in DDS mechanism of thiophene, the rate-determining step is the C–S bond cleavage. In HYD mechanisms of 2,5-DHT, 2,3-DHT and THT, the rate-determining step is hydrogen transfer on ZSM-5, FAU and Beta zeolites except MCM-22 zeolite. The HYD of 2,3-DHT and THT should occur by the stepwise pathway. But for the 2,5-DHT, the concerted pathway is probably more favourable than the stepwise pathway. The reduced density gradient (RDG), differential charge density (DCD), and local orbital locator (LOL) maps show that for all transition states (TSs), there are complicated van der Waals (VDW) and electrostatic interactions between the organic fragment and the catalytic centre.

Effect of oxidant on the epoxidation of methyl oleate over transition metal-based Al2O3 catalysts

Various transition metal-based Al2O3 catalysts are employed for the epoxidation of methyl oleate (MO) as a representative compound of fatty acid methyl ester (FAME). Two different oxidants, H2O2 and O2, are used for the oxidative epoxidation reaction and resulted in significantly different activities according to the catalytic properties of the Al2O3 catalysts. The reactivity for H2O2-based epoxidation of methyl oleate is proportional to the acidity of the catalysts. On the other hand, in O2-based epoxidation, the reactivity is strongly dependent on the redox properties of the catalysts and O2 behavior on the catalyst surface. Mo and Cu-based catalysts show outstanding catalytic performance with H2O2 and O2 via different reaction pathways. These results provide valuable information on the promising combination between catalysts and oxidants, which will be a useful guide for designing catalyst reaction processes according to the kind of oxidizing agent.

The Features of the CCVD of Trichloroethylene Over Microdispersed Ni and Ni–Mo Catalysts

The Features of the CCVD of Trichloroethylene Over Microdispersed Ni and Ni–Mo Catalysts

Low-Temperature Efficient Hydrogen Production from Raw Biomass on the Ni–Mo Catalyst

Low-Temperature Efficient Hydrogen Production from Raw Biomass on the Ni–Mo Catalyst