Mo Catalysts Research Articles

Surfactant PVA-Stabilized Co–Mo Nanocatalyst Supported by Graphene Oxide Sheets Toward the Hydrolytic Dehydrogenation of Ammonia Borane

By adding surfactant polyvinyl alcohol (PVA) and controlling the preparation process, we successfully synthesized Co–Mo catalysts. For further improving the dispersion, reduced graphene oxide sheets as catalyst carrier were introduced to synthesize Co–Mo@rGO composite catalyst as highly efficient catalysts for hydrolytic dehydrogenation of ammonia borane. The introduction of Mo for preparing Co–Mo@rGO catalyst helped to form alloy catalyst with better structure, better dispersity and smaller particle size. When the molar ratio of Co and Mo was 0.75:0.25, the bimetallic composite catalyst exhibited superior activity with TOF value of 16.29[Formula: see text]mol[Formula: see text]. The activation energy of the reaction was calculated to be 43.72[Formula: see text]kJ[Formula: see text][Formula: see text]. Furthermore, the reusability tests reveal that waxberry-like Co–Mo still show good catalytic activity with 80.3% of their initial activity in five successive runs. The enhanced catalytic activities were due to the synergistic interaction between graphene sheets and waxberry-like Co–Mo NPs, which was beneficial to improve the dispersion and stability of bimetallic NPs. Also, ligand effects on the formation of waxberry-like structure and amorphous state further promoted the catalytic activity.

High-resolution STEM-HAADF microscopy on a γ-Al2O3 supported MoS2 catalyst—proof of the changes in dispersion and morphology of the slabs with the addition of citric acid

Atomic-scale images of MoS2 slabs supported on γ-Al2O3 were obtained by high-resolution scanning transmission electron microscopy equipped with a high angular annular dark field detector (HR STEM-HAADF). These observations, obtained for sulfide catalysts prepared with or without citric acid as a chelating agent, evidenced variations in morphology (shape) and size of the MoS2 nanoslabs, as detected indirectly by the adsorption of CO followed by infrared spectroscopy. Quantitative dispersion values and a morphology index (S-edge/M-edge ratio) were determined from the slabs observed. In this way, HR STEM-HAADF underlines that the addition of citric acid to Mo catalysts decreases the size of the particles and modifies the shape of the MoS2 nanoslabs from slightly truncated triangles to particles with a higher ratio of S-edge/M-edge. These finding are of great significance since tayloring the morphology of the slabs is a way to increase their catalytic activity and selectivity. Furthermore, this work demonstrated that the IR/CO method is a relevant approach to describe the MoS2 morphology of supported catalysts used in hydrotreatment processes for clean fuel production.

Molybdenum hybrid – Nanocrystals supported on modified Laponite composite as superior catalyst for vapour phase hydrodeoxygenation of clove oil

Valorisation of bio-oil to sustainable energy through hydrodeoxygenation process has been attracted much attention in the development of bio-refineries. The present work emphasizes on the development of a highly active heterogeneous catalyst for hydrodeoxygenation reaction with modified Laponite-γ-alumina and SBA-15 – γ-alumina composites as support for Mo and NiMo catalysts using Mo–inorganic–organic hybrid nanocrystals (HNCs) prepared under hydrothermal condition. The synthesized catalysts were characterised using N2–physisorption, XRD, FT–IR, Raman, HRTEM, TPD/TPR, H2 pulse chemisorption and XPS techniques. The catalysts were evaluated for HDO of eugenol (Lignin model compound, Clove oil) at 400 °C under atmospheric pressure. The physicochemical characterization of the support composites revealed that Mo-HNC supported on modified Laponite exhibited extraordinary stability, metal-support interaction and metal dispersion over the support. The catalytic activity results revealed that the Laponite composite supported NiMo-HNC catalyst performed complete conversion of eugenol with enhanced % selectivity to 3- and 4-propyl phenol (mono-deoxygenated products) and to benzene and 4-propyl cyclohexene (complete deoxygenated products). Thereby, a new Mo-HNC supported modified Laponite composite catalyst has been successfully developed. The role of the HNC-Mo preparation method, textural properties, morphology of Laponite composite catalysts have been demonstrated for efficient HDO of clove oil.

Effect of silicon content on active catalytic phase for hydrocracking of heavy crude oils

The silicon composition effect on acidic properties of Ni[sbond]Mo catalysts was investigated for hydrocracking reaction, where an optimal Si and Al ratio is required for the formation of Brønsted acid sites and as well as of Al3+ (IV) tetrahedral coordinated sites. The support composition affects the Si[sbond]OH[sbond]Al network, where cations (Al3+ or Si4+) have a coordination number of IV generating higher Brønsted acidity and macro-pores. The supports and fresh catalysts were characterized by atomic absorption, nitrogen physisorption, FT-IR of CO and pyridine adsorption and 27Al MAS NMR.

Molybdenum (VI)‐functionalized UiO‐66 provides an efficient heterogeneous nanocatalyst in oxidation reactions

A novel heterogeneous nanocatalyst was established by supporting molybdenum (VI) on Zr6 nodes in the structure of the well‐known UiO‐66 metal–organic framework (MOF). The structure of the UiO‐66 before and after Mo (VI) immobilization was confirmed with XRD, DR‐FTIR and UV–vis spectroscopy, and the presence and amount of Mo (VI) was identified by X‐ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy. TEM imaging confirmed the absence of Mo clusters on the MOF surface, while SEM confirmed that the appearance of the MOF has not changed upon immobilizing the Mo (VI) catalyst. BET adsorption measurements were used to confirm the porosity of the catalyst. The catalytic activity of this heterogeneous catalyst was investigated in oxidation of sulfides with H2O2 in acetonitrile and oxidative desulfurization of dibenzothiophene. Easy work up, convenient and steady reuse and high activity and selectivity are prominent properties of this new hybrid material.

Hydroconversion of methyl laurate over beta-zeolite-supported Ni–Mo catalysts: Effect of acid and base treatments of beta zeolite

Beta-zeolite-supported Ni–Mo catalysts, NiMo/HBeta, were developed and applied to the hydroconversion of methyl laurate under a hydrogen pressure of 0.4 MPa. Compared with the Ni–Mo catalyst supported on a zeolite with no Al content, NiMo/HBeta exhibited high catalytic activity and selectivity for n-dodecane produced through the hydrodeoxygenation (HDO) process. Furthermore, prior to Ni–Mo particle loading, beta zeolite was acid-treated with HNO3 solution or base-treated with tetraethylammonium hydroxide (TEAOH) or NaOH solutions. The acid and base treatments influenced the Ni–Mo particles, with large Ni–Mo particles formed on the acid-treated beta zeolite and small, highly dispersed Ni–Mo particles formed on the base-treated beta zeolites. Both the acid- and TEAOH-treated beta zeolites improved the catalytic activity and enhanced the HDO process, whereas the NaOH-treated beta zeolite slightly depressed the catalytic activity. An increased ratio of Brønsted acid sites in beta zeolite played an important role in improving both the catalytic activity and the HDO process. The combination of the TEAOH treatment of beta zeolite with subsequent acid treatment was effective for further improving the catalytic activity while maintaining high n-dodecane selectivity.

Mo Thio Molecular Complexes As Water-Soluble Catalysts for the Photocatalytic Hydrogen Evolution Reaction on 2D Materials

Producing hydrogen fuel through solar-driven photoelectrochemical (PEC) water splitting represents an attractive approach for the development of sustainable energy. 2D semiconducting Transition Metal dichalcogenide (TMDC) nanosheets are attractive materials for solar energy conversion and have been applied as photocathodes for the Hydrogen Evolution Reaction (HER). To improve the performances of the photocathodes, optimized TMDC film microstructure was proposed involving a self-assembly at a liquid-liquid interface. In addition, in combination with a hexyl-tri-silane surfactant treatment, molecularly thin 2D WSe2 nanosheets films were coated by a Pt-Cu catalyst. In this process, the increase of photocurrent resulting from the surfactant treatment was attributed to edge site passivation of the 2D nanosheets drastically decreasing the charge carrier recombination site density. Indeed, for a large scale development of these photocathodes, replacement of Pt-Cu by a precious metal-free catalyst is highly desirable. In this talk, we will present our recent results concerning Mo thio complexes as catalysts anchored on WSe2 nanosheets for efficient water splitting under visible light irradiation. We used WSe2 films prepared by a simple film forming process, i.e. drop casting, and an aqueous environmentally friendly process for the catalyst preparation. Active molecular Mo catalysts including (Mo2S12)2- were deposited via a selection process from a solution allowing the deposition of the most interactive Mo complexes towards the WSe2 nanosheets thus improving their anchorage and durability. Our ultrathin films showed a current density up to -2 mA/cm² at 0 V vs NHE without any passivation additive such as HTS surfactant. The respective contributions namely in electro-catalysis and site passivation observed experimentally for the various molecular Mo complexes involved were supported by DFT calculations of i) Adsorption energies of the Mo thio complexes on the WSe2 substrates and ii) Free energies changes for the hydrogen Evolution Reaction on the various adsorbed molecular Mo complexes. These results will greatly help to better design molecular photo-catalysts for photo-electrodes displaying high surface recombination site density.

Promotional Effect of Cr in Sulfated Zirconia‐Based Mo Catalyst for Methane Dehydroaromatization

The need for valuable hydrocarbons is now at its peak. Methane is an abundant source of natural gas, and is well‐studied as a feedstock for producing heavier hydrocarbons of higher value. A number of processes are well‐studied, including methane dehydroaromatization (MDHA). This is a direct methane conversion process, eliminating the need for a syngas step while producing both benzene and hydrogen.

Plasma‐activated methane partial oxidation reaction to oxygenate platform chemicals over Fe, Mo, Pd and zeolite catalysts

Natural gas from stranded sources is being predominantly flared, and there is a growing demand for new technologies for its utilisation, where electrification, flexibility, and modularity play an important role. Plasma-activated methane partial oxidation reaction was studied in a designed dielectric barrier discharge ionisation reactor unit, producing value-added platform chemicals, namely, methanol, formaldehyde, intermediate formic acid, acetic acid, and paraformaldehyde at ambient temperature and atmospheric pressure. The effects of various process parameters, such as voltage, total convertible gas flow rate, and reagent ratio relationship, were considered. In addition, coupling of the following catalytic materials with plasma was examined: alumina (Al2O3), chabazite, ferrierite, microporous beta zeolite, silica (SiO2) glass beads, ZSM-5 (MFI), Fe on H-ZSM-5 and Al2O3, Mo on H-ZSM-5, TiO2 and SiO2, and Pd on Al2O3. In the liquid product, 21.5% CH3OH, 20.4% CH2O, 0.3% HCOOH, and 2.4% CH3COOH were measured when using pure plasma, and a maximum aggregate yield of the organic oxygenate compounds of 5.21 mol.% was achieved. The usage of shaped silicate surface increased the selectivity towards synthesised oxygen-containing structures, while the application of alumino-silicate mixture constituents reduced it. It was determined that elementary covalently bonded carbon was formed inside pores when pure zeolites were used. Fe- and Pd-based heterogeneous catalysts favoured the complete exothermic combustion of CH4 feedstock reactant species, and the liquid product consisted only of water in the Pd- case. The utilisation of Mo/H-ZSM-5 resulted in a 46% increased yield of formalin. A mechanism for the role of Mo was proposed, where Mo oxidises methanol to formaldehyde and the metal is reoxidised in plasma.

Nonoxidative methane activation, coupling, and conversion to ethane, ethylene, and hydrogen over Fe/HZSM‐5, Mo/HZSM‐5, and Fe–Mo/HZSM‐5 catalysts in packed bed reactor

A high abundance of methane and its relatively low price make it an attractive raw feedstock for the production of ethylene, which is in the consumer demand in recent years. Direct catalytic nonoxidative conversion is interesting, because it could be utilized on natural gas well sites. Monometallic and bimetallic Fe and Mo catalysts were prepared for the purpose of the coupling to ethane and ethene. Three supported materials were synthesized with the following loading of metal: 2.5-wt% Fe, 5.0-wt% Fe, and 2.5-wt% Mo on HZSM-5. Process' chemical reactions were also catalyzed with a constant 2.5-wt% Mo/HZSM-5, which had different amounts of Fe, namely, 0.5, 1.0, and 2.5 wt%. Fourier transform infrared (FTIR), N2 adsorption/desorption, NH3 temperature-programmed desorption (TPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were applied for characterization. Coke, accumulated on spent solids, was determined by thermogravimetric analysis (TGA). Activity was evaluated in quartz-packed bed reactor. All surfaces suffered from deactivation due to carbon formation. The addition of Fe to Mo increased CH4 reacted. The highest selectivity for alkenes was achieved over 1.0-wt% Fe to 2.5-wt% Mo/HZSM-5. At the peak of performance, the C-based reactivity was 52% for olefins and 2% for alkanes. Stability was accomplished over 2.5-wt% Fe/HZSM-5, where the rate of C2 synthesis was comparatively stable for 20 hours of the time on stream. The selective C-basis yield for C2H4 and C2H6 was 36% and 23%, respectively. The lowest measured quantity of (carbonaceous) by-products was deposited on 2.5-wt% Fe/HZSM-5 after 26 hours. Propylene was detected very limitedly.

Highly Site-Selective Formation of Perfluoroalkylated Anilids via a Protecting Strategy by Molybdenum Hexacarbonyl Catalyst.

Introducing a perfluoroalkyl group on the aromatic ring with high site selectivity remains a challenging area in organofluorine chemistry. We herein report a highly para-selective C-H perfluoroalkylation of aniline substrates using the molybdenum hexacarbonyl catalyst. Various substituted anilids derived from anilids were well-tolerated, affording the corresponding products in moderate to good yields. Preliminary mechanism studies and density functional theory calculations revealed the coordination of Mo catalyst with amides as the key factor to realize para selectivity.

Silica‐Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis

AbstractGrafting a molybdenum oxo alkylidene on silica (partially dehydroxylated at 700 °C) affords the first example of a well‐defined silica‐supported Mo oxo alkylidene, which is an analogue of the putative active sites in heterogeneous Mo‐based metathesis catalysts. In contrast to its tungsten analogue, which shows poor activity towards terminal olefins because of the formation of a stable off‐cycle metallacyclobutane intermediate, the Mo catalyst shows high metathesis activity for both terminal and internal olefins that is consistent with the lower stability of Mo metallacyclobutane intermediates. This Mo oxo metathesis catalyst also outperforms its corresponding neutral silica‐supported Mo and W imido analogues.

Silica-Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis.

Grafting a molybdenum oxo alkylidene on silica (partially dehydroxylated at 700 °C) affords the first example of a well-defined silica-supported Mo oxo alkylidene, which is an analogue of the putative active sites in heterogeneous Mo-based metathesis catalysts. In contrast to its tungsten analogue, which shows poor activity towards terminal olefins because of the formation of a stable off-cycle metallacyclobutane intermediate, the Mo catalyst shows high metathesis activity for both terminal and internal olefins that is consistent with the lower stability of Mo metallacyclobutane intermediates. This Mo oxo metathesis catalyst also outperforms its corresponding neutral silica-supported Mo and W imido analogues.

What Is the Effect of Promoter Loading on Alkalized Bimetallic Co–Mo Catalyst for Higher Alcohols Synthesis from Syngas?

Manganese and nickel co-modified K/Co/MoS2 catalysts supported on graphene were prepared by incipient wetness impregnation method for application in higher alcohol synthesis (HAS). All catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The effect of promoters, as well as supports on higher alcohol synthesis production from syngas, was investigated in a fixed bed reactor. The process was performed with an molar ratio H2 : CO = 1 : 1, operating pressure and temperature of 4 MPa and 330°C, respectively, and gas hourly space velocity (GHSV) 3.84 m3(STP)/(kgcat h) as reaction conditions (STP— standard temperature and pressure). Results originated from practical works showed that the addition of Ni to the graphene-based catalyst increased HAS production and decreased methanol formation. The total alcohols space-time yield (STY) and alcohol selectivity on Ni/Mn/Co/Mo/K/graphene catalyst reached a maximum at 0.41 galc/(gcat h) and 63.51%, respectively, which is higher than the same composition over alumina supported catalyst.

Catalytic Decomposition of Ammonia for Hydrogen Production over Carbon Nanofiber Supported Fe and Mo Catalysts in a Microwave Heated Reactor

Abstract Microwave heated reactor which was loaded with carbon fiber supported iron and molybdenum incorporated monometallic catalysts was used to produce COx free hydrogen from ammonia. Impregnation procedure was applied to synthesize the catalysts at different metal loading (4–14 wt % according to ICP-OES) using iron nitrate or ammonium molybdate and reaction tests were carried out under the flow of pure ammonia (GHSV: 36,000 ml/hgcat). Activities of molybdenum incorporated carbon fiber catalyts are found to be lower than that of the iron loaded ones in the conventional reaction system. The effect of metal loading was clealy seen in the activity of molybdenum incorporated catalyst, unlike iron incorporated catalyts, especially under high reaction temperature conditions. Catalysts showed greatly enhanced activities in microwave heated system in comparison to conventionally heated reactor system. Complete conversion of ammonia was achieved at 500 °C by using molybdenum incorporated catalysts and at 450 °C by using iron incorporated catalysts (with GHSV of 36,000 ml/hgcat) in microwave heated reactor system. Transfer of energy directly to the active species and formation of carbide species, Fe2C or Mo2C, during the reaction under microwave application could be considered as the major factors leading to a better ammonia conversion. Structural properties of carbon support materials, such as the surface area, could be effective on the activity of the catalysts via the distribution of active species, however, this would be more pronounced effect in conventional system.

Activity and selectivity of Co(Ni)Mo sulfides supported on MgO, Al2O3, ZrO2, TiO2, MCM-41 and activated carbon in parallel hydrodeoxygenation of octanoic acid and hydrodesulfurization of 1-benzothiophene

Mo, CoMo and NiMo sulfide catalysts were prepared using MgO, Al2O3, ZrO2, TiO2, MCM-41 and activated carbon supports. The catalysts were tested in parallel hydrodeoxygenation (HDO) of octanoic acid and hydrodesulfurization (HDS) of 1-benzothiophene. For all supports, NiMo catalysts were more active in both HDO and HDS than Mo and CoMo catalysts. HDO activity of NiMo catalysts decreased with type of support in the following order TiO2 > C > ZrO2 > Al2O3 > MCM-41 > MgO. The products of HDO were linear C7 and C8 hydrocarbons. Some isomerization and cracking activity was observed only with MCM-41 support. HDS activity of NiMo catalysts decreased in the following order C > ZrO2 > TiO2 > Al2O3 > MgO > MCM-41. HDO/HDS selectivity was influenced by the active phase and the support type and it was the highest over the NiMo/TiO2 catalyst.

Boosting Electrochemical Nitrogen Reduction Performance over Binuclear Mo Atoms on N-Doped Nanoporous Graphene: A Theoretical Investigation.

Exploration of efficient catalysts is a priority for the electrochemical nitrogen reduction reaction (NRR) in order to receive a high product yield rate and faradaic efficiency of NH3, under ambient conditions. In the present contribution, the binding free energy of N2, NNH, and NH2 were used as descriptors to screen the potential NRR electrocatalyst among different single or binuclear transition metal atoms on N-doped nanoporous graphene. Results showed that the binuclear Mo catalyst might exhibit the highest catalytic activity. Further free energy profiles confirmed that binuclear Mo catalysts possess the lowest potential determining step (hydrogenation of NH2* to NH3). The improved activities could be ascribed to a down-shift of the density of states for Mo atoms. This investigation could contribute to the design of a highly active NRR electrocatalyst.

Growth of multi-layered graphene on molybdenum catalyst by solid phase reaction with amorphous carbon

A method to grow multi layers graphene (MLG) just by thermal annealing in an inert atmosphere is reported. A molybdenum (Mo) catalyst layer is used in combination with a solid amorphous carbon (a-C) source on top or below the Mo layer.The formation of MLG directly on top of the catalyst substrate surface is confirmed by Raman spectroscopy, atomic force microscopy, cross-section transmission electron microscopy, electron energy loss spectroscopy and x-ray photoelectron spectroscopy. Growth of MLG on top of the Mo catalyst is demonstrated both with a-C below and above the Mo layer. The growth mechanism is attributed to the diffusion of a-C through the Mo layer and precipitation into the graphene at the surface, similar to the growth by chemical vapour deposition (CVD) on a Ni catalyst. The role of the inert Ar/H2 atmosphere, carbon thickness, catalyst thickness, anneal time and anneal temperature are reported. Fast growth of MLG (5 min) at 915 °C is demonstrated. The quality of MLG prepared by thermal annealing is at least as good as that of MLG synthesized by CVD. The relevant achievements presented in this study make the proposed technique a promising alternative to CVD based MLG.

Steam reforming of toluene as model of tar compound over Mo catalysts derived from hydrotalcites

This study evaluated the catalytic activity of Mo catalysts derived from hydrotalcite-like compounds for steam reforming of toluene as a model compound for tar. The catalysts with 1.5, 3 and 4.5 Mo loadings (wt%), denoted as Mo1.5MgAl, Mo3MgAl and Mo4.5MgAl respectively, were prepared by coprecipitation and characterized by BET, XRD, SEM, TEM, FT-IR and UV–VIS. The results showed that toluene conversion increased with increasing molybdenum content. The hydrogen amount depended on two factors: the presence of molybdate species on the surface and the presence of aluminum cations in tetrahedral sites (Mo3MgAl), with molybdenum influence being more pronounced. The H2/CO ratio decreased at increasing temperature while, the H2/CO2 ratio increased proportionally with temperature. Mo1.5MgAl catalyst was more selective for CO2 and H2, while, Mo3MgAl and Mo4.5MgAl were more selective for CO and H2.

Hydrodeoxygenation of Octanoic Acid over Supported Ni and Mo Catalysts: Effect of Ni/Mo Ratio and Catalyst Recycling

AbstractHydrodeoxygenation of octanoic acid over supported NiMo bimetallic catalysts was investigated as a representative of carboxylic acid compounds in bio‐oils. A series of MCM‐41supported Ni and Mo bimetal catalysts were prepared with the wetness impregnation method. The microstructural and physicochemical properties of the fresh and recovered bimetal catalysts were characterized by various methods such as X‐ray diffraction (XRD), Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS), etc.. The results show that the bulk NiO particles were well‐uniformly dispersed on the surface of the bimetal catalyst, and Mo4+ was founded as the main valence of Mo inside solid. Under the optimal conditions, i. e. the reaction temperature of 270 °C, reaction pressure of 3 MPa, and reaction time of 7 h, the 3Ni7Mo/MCM‐41 sample exhibits selectivity to octane 72.6% with a high conversion of octanoic acid 96.1%. Only a slight decrease in catalytic activity was observed after reused for three times. Moreover, the recovered sample was easily regenerated only with simple calcination and deoxidization, but has the similar microstructure compared with the fresh one.