Molybdenum Catalysts Research Articles

Molybdenum-Catalyzed Deoxygenation Coupling of Lignin-Derived Alcohols for Functionalized Bibenzyl Chemicals.

With the growing demand for sustainability and reducing CO2 footprint, lignocellulosic biomass has attracted much attention as a renewable, carbon-neutral and low-cost feedstock for the production of chemicals and fuels. To realize efficient utilization of biomass resource, it is essential to selectively alter the high degree of oxygen functionality of biomass-derivates. Herein, we introduced a novel procedure to transform renewable lignin-derived alcohols to various functionalized bibenzyl chemicals. This strategy relied on a short deoxygenation coupling pathway with economical molybdenum catalyst. A well-designed H-donor experiment was performed to investigate the mechanism of this Mo-catalyzed process. It was proven that benzyl carbon-radical was the most possible intermediate to form the bibenzyl products. It was also discovered that the para methoxy and phenolic hydroxyl groups could stabilize the corresponding radical intermediates and then facilitate to selectively obtain bibenzyl products. Our research provides a promising application to produce functionalized aromatics from biomass-derived materials.

Nickel–molybdenum catalysts for combined solid oxide fuel cell internal steam and dry reforming

A series of supported Ni-Mo catalysts were synthesised through a deposition-co-precipitation method (DcP) and investigated in combined steam and dry reforming. The prepared Ni-Mo catalysts supported by Yttria-Stabilised Zirconia (YSZ), Gadolinium-Doped Ceria (GDC) and Ceria Stabilised Zirconia (CSZ) with improved carbon tolerance have the potential to be used as anodes in Solid Oxide Fuel Cells (SOFC). These catalysts will be applied in the anode supporting layer where most of the internal reforming reaction takes place. The catalysts were compared to conventional reforming catalysts, where Al2O3 and TiO2 supports are typical for reforming catalysts. The catalytic performance of the Ni-Mo catalysts according to the support materials was observed in the sequence Al2O3 > YSZ > TiO2 > CSZ > GDC. Formation of Mo2C improved catalytic activity towards the steam reforming reaction. Increasing the Mo loading to Ni catalyst improved the coke resistance properties; however, it reduced the catalytic activity.

Direct conversion of ethylene to propylene based on molybdenum catalysts

The series of molybdenum catalysts prepared by the incipient wetness impregnation of porous alumina with a different impregnation order of the NiO (PdO) and MoO3 precursors was studied in the direct conversion of ethylene to propylene. The maximum propylene yield (28 wt.%) was achieved at 70 °C MoO3/PdO/Al2O3 catalyst obtained by sequential impregnation of the palladium precursor and then the molybdenum precursor. The samples containing stable oxidized forms of palladium or bonded to the surface of the support nickel cations exhibited a high activity in ethylene conversion. It was found that palladium-containing catalysts were more selective than nickel-containing, probably due to an easier formation of reduced active molybdenum sites in the presence of palladium.

Coordination Number Regulation of Molybdenum Single-Atom Nanozyme Peroxidase-like Specificity

Summary Nanozymes are promising alternatives to natural enzymes, but their use remains limited owing to poor specificity. Overcoming this and controlling the targeted enzyme-like performance of traditional nanozymes is extremely challenging due to the intrinsic structural complexity of these systems. We report theoretical design and experimental realization of a series of heterogeneous molybdenum single-atom nanozymes (named MoSA–Nx–C), wherein we find that the peroxidase-like specificity is well regulated by the coordination numbers of single Mo sites. The resulting MoSA–N3–C catalyst shows exclusive peroxidase-like behavior. It achieves this behavior via a homolytic pathway, whereas MoSA–N2–C and MoSA–N4–C catalysts have a different heterolytic pathway. The mechanism of this coordination-number-dependent enzymatic specificity is attributed to geometrical structure differences and orientation relationships of the frontier molecular orbitals toward these MoSA–Nx–C peroxidase mimics. This study demonstrates the rational design of peroxidase-specific nanozymes and precise regulation of their enzymatic properties.

Biobased Aldehydes from Fatty Epoxides through Thermal Cleavage of β-Hydroxy Hydroperoxides*.

The ring-opening of epoxidized methyl oleate by aqueous H2 O2 has been studied using tungsten and molybdenum catalysts to form the corresponding fatty β-hydroxy hydroperoxides. It was found that tungstic acid and phosphotungstic acid gave the highest selectivities (92-93 %) towards the formation of the desired products, thus limiting the formation of the corresponding fatty 1,2-diols. The optimized conditions were applied to a range of fatty epoxides to give the corresponding fatty β-hydroxy hydroperoxides with 30-80 % isolated yields (8 examples). These species were fully characterized by 1 H and 13 C NMR spectroscopy and HPLC-HRMS, and their stability was studied by differential scanning calorimetry. The thermal cleavage of the β-hydroxy hydroperoxide derived from methyl oleate was studied both in batch and flow conditions. It was found that the thermal cleavage in flow conditions gave the highest selectivity towards the formation of aldehydes with limited amounts of byproducts. The aldehydes were both formed with 68 % GC yield, and nonanal and methyl 9-oxononanoate were isolated with 57 and 55 % yield, respectively. Advantageously, the overall process does not require large excess of H2 O2 and only generates water as a byproduct.

A Cp‐based Molybdenum Catalyst for the Deoxydehydration of Biomass‐derived Diols

AbstractDioxo‐molybdenum complexes have been reported as catalysts for the deoxydehydration (DODH) of diols and polyols. Here, we report on the DODH of diols using [Cp*MoO2]2O as catalyst (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of [Cp*MoO2]2O, 1.1 equiv. of PPh3 as reductant, and anisole as solvent. Aliphatic vicinal diols are converted to the corresponding olefins by [Cp*MoO2]2O in up to 65 % yield (representing over 30 turnovers per catalyst) and 91 % olefin selectivity, which rivals the performance of other Mo‐based DODH catalysts. Remarkably, cis‐1,2‐cyclohexanediol, which is known as quite a challenging substrate for DODH catalysis, is converted to 30 % of 1‐cyclohexene under optimized reaction conditions. Overall, the mass balances (up to 79 %) and TONs per Mo achievable with [Cp*MoO2]2O are amongst the highest reported for molecular Mo‐based DODH catalysts. A number of experiments aimed at providing insight in the reaction mechanism of [Cp*MoO2]2O have led to the proposal of a catalytic pathway in which the [Cp*MoO2]2O catalyst reacts with the diol substrate to form a putative nonsymmetric dimeric diolate species, which is reduced in the next step at only one of its Mo‐centers before extrusion of the olefin product.

활성탄 담지 몰리브덴 촉매를 이용한 합성가스 직접 메탄화 반응

활성탄 담지 몰리브덴 촉매를 이용한 합성가스 직접 메탄화 반응

Effect of Silica, Activated Carbon, and Alumina Supports on NiMo Catalysts for Residue Upgrading

The effect of different supports such as silica (SBA-15), activated carbon (AC), and mesoporous alumina (Al2O3) on catalytic activities of hydrotreating nickel molybdenum (NiMo) catalysts was demonstrated for upgrading vacuum residue. Nitrogen adsorption-desorption analysis showed that SBA-15 and the AC-supported NiMo catalyst possessed a very high surface area compared to the alumina-supported catalyst. However, NiMo/Al2O3 catalyst possesses a higher pore diameter and pore volume with an appropriate surface area. X-ray diffraction (XRD) analysis showed that active metals were dispersed in the catalytic supports. Transmission electron microscopy (TEM) analysis revealed the presence of type II active MoS2 sites in the NiMo/Al2O3 catalyst, which showed weak metal-support interactions having a high intrinsic activity. Catalyst activities such as hydrodesulfurization (HDS), hydrodemetallization (HDM) and asphaltene conversion (HDAs), and hydrocracking conversions of a vacuum residue were evaluated. The highest hydrotreating and hydrocracking conversions were observed with the NiMo catalyst supported on mesoporous alumina. The results also supported that the catalyst that has a large pore diameter, high pore volume, and better active metals dispersion is highly desirable for the upgrading of a vacuum residue.

Cyclohexene Epoxidation Catalysts Based on Porous Aromatic Frameworks

Molybdenum and tungsten catalysts, PAF-30-Mo and PAF-30-W, synthesized based on a porous aromatic framework PAF-30 have been tested in the epoxidation of cyclohexene with tert-butyl hydroperoxide. The influence of the temperature and the substrate to oxidant ratio on the characteristic features of the process has been studied. It has been shown that the catalysts exhibit high activity and make it possible to obtain cyclohexene epoxide in a high yield; however, they lose their activity over time due to the leaching of the metal from the pores of the polymer.

Chemoselective Hydrogenation of Functionalized Nitroarenes into Anilines by Supported Molybdenum Catalysts

AbstractAnilines are the most important fine chemicals that have been widely used as the intermediates of industrial products. Herein, a new series of nanostructured Mo‐based catalysts were reported, such as MoOx/ZSM‐5(25), MoOx/ZSM‐5(50) and MoOx/SBA‐15, which can serve as efficient catalysts in the hydrogenation of nitroarenes by using hydrogen as the reducing reagent to afford functionalized anilines. Those catalysts showed both excellent activity and high chemoselectivity of the nitro group even though other reducible groups (C−X, C=C, C=O and C≡N) were exiting. This protocol constitutes an economically responsible pathway for the synthesis of anilines in high yields, good functional group compatibility and high chemselectivity.

Particular kinetic patterns of heavy oil feedstock hydroconversion in the presence of dispersed nanosize MoS2

Abstract A kinetic model of the heavy oil feedstock hydroconversion performed in continuous flow reactor in the presence of in-situ synthesized dispersed nanosize catalyst Molybdenum disulfide (MoS2) has been proposed. The kinetic parameters of heavy oil feedstock with different properties have been determined for the two process versions: with coke formation and without appreciable coke formation. It has been stated that hydroconversion in the presence of in-situ synthesized dispersed MoS2 (C(Mo) = 0.05% wt. (per feed)) corresponds to a first-order reaction for all studied feedstock samples. The rate and activation energy constants have been determined. It has been shown that the conditions of polycondensation products (coke) formation result in increasing process rate and decreasing activation energy.

Catalytic performance stability of Mo, W and Re-based sour water–gas shift catalysts

It has been shown in our previous findings that Mo-, W- and Re-based catalysts promoted with Ni, Co, and K are considered as a promising tri-component catalyst for sour WGS reaction. In order to evaluate the stability of the formed active sulfide and oxysulfidic species at sulfided Mo-, W- and Re-based catalysts at the same surface density of the main component, namely 2 atoms metal/nm2 γ-Al2O3 support, under influence of oxidizing agents as H2O steam and CO2, the WGS reaction was proceeded in absence of sulfur in gas feed. With the intent to enable a quick check, the applied approach was to perform the WGS reaction at high reaction temperature, 400 °C, in H2S-free syngas and varying the gas hourly space velocity (GHSV). This study gave information about the behaviour of sour molybdenum, tungsten and rhenium WGS catalysts during operation accident. It was found that the active sulfide and oxysulfidic species are more stable in absence of sulfur in feed at tri-component KCoMo and KCoRe catalysts. These catalysts possess lowest sulfur dependence of WGS activity and stability of the deactivation, which is an indication of the applicability of these two systems as optimal sour water–gas shift catalysts.

Molybdenum (VI)-catalyzed dehydrative construction of C[sbnd]O and C[sbnd]S bonds formation via etherification and thioetherification of alcohols and thiols

An inexpensive, easily available, environmentally benign, and efficient catalyst molybdenum(VI) dioxo (acetylacetonate)2 was used for the direct oxo- and thioetherification of alcohol. This method endures selective molybdenum catalyzed dehydrative synthesis of symmetrical ethers from benzylic secondary alcohols as well as unsymmetrical ethers from the reaction of benzylic secondary alcohols with primary alcohol. Furthermore, we have been also successful in the synthesis of Aryl thioether by using alcohol and thiols.

Process for using iron and molybdenum catalyst for slurry hydrocracking

Process for using iron and molybdenum catalyst for slurry hydrocracking

Influence of titanium oxide on the performance of molybdenum catalysts loaded on zeolite toward hydrodesulfurization reactions

In this work, molybdenum, cobalt, and vanadium (MCV) based catalysts were loaded on zeolite Y (Z) and modified with different ratios of titanium oxide (0, 5 and 10%) as co-support (ZT). The catalysts were characterized using a scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), electron dispersive x-ray spectroscopy (EDX), powder x-ray diffraction (XRD), N 2 adsorption-desorption isotherm, Fourier-transform infrared spectroscopy (FTIR), and temperature-programmed desorption (TPD). The prepared catalysts were evaluated for the hydrodesulfurization (HDS) reactions of dibenzothiophene (DBT). The incorporation of titania within the Z support was used to enhance the interaction between the active phases and the support surface through better distribution of the catalyst nanoparticles on the composite support. From the BET measurements, all of the catalysts exhibited the type IV isotherm with micro/mesoporous contributions. TPD was applied to illustrate the calcined catalyst acidity, which confirmed the positive role of titania in increasing the acidic strength of the catalyst. The XRD demonstrated the introduction of titania to the support which is clear from the characteristic peaks of titania. The elemental compositions of the catalyst and dispersion on the support surface were confirmed by EDX and x-ray mapping. The catalytic performance of 5% and 10% titania (ZT5-MCV and ZT5-MCV) showed higher activity compared to the control catalyst without titania (Z-MCV). A comparison of this catalyst with those reported in the literature points out that it is a promising candidate for fuel HDS. • MoCo-Zeolite/titania showed excellent hydrodesulphurization of dibenzothiophene. • Direct desulfurization mechanism was dominant based on characterization results and GC-SM. • The work is offering a convenient approach to prepare an effective HDS catalyst.

Multiwall carbon nanotube-supported molybdenum catalysts for ammonia decomposition reaction under microwave effect.

In this study, microwave-assisted ammonia decomposition reaction was investigated over molybdenum incorporated catalysts. Due to the selective, volumetric, and noncontact heating properties of the microwave system, higher conversion values could be achieved at relatively lower reaction temperatures, which is important for on-site COx-free hydrogen production. Multiwall carbon nanotube-supported molybdenum catalysts were prepared following the impregnation procedure with different metal loading (3.5%–12.5% wt%), and inductively coupled plasma, nitrogen physisorption, X-ray diffraction, and transmission electron microscopic techniques were employed to characterize the fresh and used samples. Reaction experiments were performed under the flow of pure ammonia with a gas hourly space velocity of 36,000 mL/gcat.h for both the microwave and conventionally heated reaction systems. It was found that ammonia conversion was obtained even at 400 °C, reaching 40%, and total conversion was observed even at 450 °C, while the activities of these catalysts were negligible at a reaction temperature lower than 550 °C, in the conventional heated system, which included an electrically heated furnace. Crystals of α-Mo2C as well as MoO2 were observed in the structures of the synthesized catalysts and the formation of nitride species was more easily observable under microwave heating, possibly due to the nitridation of molybdenum carbide species during the reaction.

Cover Picture: Recent Advances in Facile Liquid Phase Epoxidation of Light Olefins over Heterogeneous Molybdenum Catalysts (Chem. Rec. 03/2020

Cover Picture: Recent Advances in Facile Liquid Phase Epoxidation of Light Olefins over Heterogeneous Molybdenum Catalysts (Chem. Rec. 03/2020

Upgrading of cyclohexanone to hydrocarbons by hydrodeoxygenation over nickel–molybdenum catalysts

Cyclohexanone is largely generated in the direct or indirect conversion of lignin-derived bio-oils. Hence, the upgrading of cyclohexanone, i.e. deoxygenation in the presence of hydrogen is of great interest. In this regard, two nickel-molybdenum catalysts on alumina support were investigated in the temperatures up to 400 °C and pressures up to 15 bar. High activity, selectivity, and yield were achieved by utilizing these catalysts at the studied condition. The main products of the upgrading of cyclohexanone were C6, C7, and C12 cyclic, aromatic, and bicyclic including cyclohexane, cyclohexene, benzene, and cyclohexylbenzene. The results of the present study imply that these catalysts are beneficial in producing hydrocarbon-rich products from cyclohexanone and lignin-derived bio-oils. Based on the achievements of the present study, the nickel-molybdenum catalyst composed of 1.14 wt% nickel and 14.27 wt% molybdenum showed about 87%, 100%, and 116% conversion of cyclohexanone, total hydrocarbon selectivity, and total hydrocarbon yield, respectively. The optimum condition for obtaining such results was at 400 °C and 8 bar.

Design Parameters for Diesel Hydro Desulfurization (DHDS)

Apart from all gaseous contaminants in air, sulfur dioxide is considered to be the principal pollutant. The emission of sulfur dioxide is generally caused by combustion of sulfur bearing fuels. This further gets converted into sulfuric acid in atmosphere as a result of its reaction with oxygen and moisture. This air borne acid is responsible to damage steel buildings, bridges and machinery. Hence there is a major need to decrease sulfur percentage in the environment in order to lead a better and healthy living. As we can see the world runs on energy, for which fossil fuels are the main constituents. As these all are the complex network of hydrocarbons, when they are combusted or utilized, the products or effluents are somewhat harmful to the atmosphere. Sulfur is one such effluent, which seriously harms the environmental conditions. So this has to be recovered up to appreciable levels. In India diesel is mostly utilized as fuel and it is up to 70%. So in order to reduce the sulfur content diesel is chosen as fuel oil. The reduction of sulfur is done by hydro desulfurization and the process is termed as diesel hydro desulfurization (DHDS). This is achieved by converting the mercaptane state sulfur to hydrogen sulfide (H2S) by reacting it with hydrogen alone on a cobalt molybdenum catalyst. By this the sulfur content is reduced from 1 wt% to 0.25 wt%. This is further reduced to 0.05 wt% using trickle bed reactors.

Recycling and processing of spent molybdenum catalysts

Recycling and processing of spent molybdenum catalysts