Molybdenum-containing Catalysts Research Articles

Molybdenum-Containing Catalysts Based on Porous Aromatic Frameworks as Catalysts of Oxidation of Sulfur-Containing Compounds

Molybdenum-Containing Catalysts Based on Porous Aromatic Frameworks as Catalysts of Oxidation of Sulfur-Containing Compounds

Molybdenum-Containing Catalysts Based on Porous Aromatic Frameworks as Catalysts of Oxidation of Sulfur-Containing Compounds

New molybdenum-containing catalysts based on PAF-30 mesoporous carbon material for oxidation of sulfur-containing compounds (SCs) in a model fuel were synthesized. The PAF-30 support was modified with functional groups containing a positively charged nitrogen atom with various substituents. The modified supports were studied by the methods of low-temperature nitrogen adsorption/desorption, IR spectroscopy, and elemental analysis. The major factors affecting the oxidation were considered: reaction temperature and time, oxidant amount, catalyst dosage, and kind of sulfur-containing substrate. For the Мо/PAF-30-NEt3 catalyst, optimum conditions were found for oxidation of various classes of SCs in model mixtures: H2O2 : S molar ratio 6 : 1, 60°С, 60 min. The Мо/PAF-30-NEt3 catalyst operates in dibenzothiophene (DBT) oxidation during five cycles without appreciable activity loss.

New Mesoporous Molybdenum-Containing Catalysts for Fast Oxidation of Sulfur-Containing Substrates

New Mesoporous Molybdenum-Containing Catalysts for Fast Oxidation of Sulfur-Containing Substrates

New Molybdenum-Containing Mesoporous Catalysts for Fast Oxidation of Sulfur-Containing Substrates

The possibility of using molybdenum-containing catalysts based on SBA-15 synthesized in one stage by the co-condensation method were used in the process of oxidation of various organosulfur compounds for the first time. The composition and structure of the obtained materials are reliably confirmed by a set of modern physicochemical methods: low-temperature nitrogen adsorption/desorption, XRD, TEM, IR spectroscopy. The effect of the amount of the active phase and influence of the conditions of the process on the oxidation of a model mixture of dibenzothiophene was investigated. It was shown that obtained catalyst continues to retain its activity at least during 4 cycles without significant loss of activity. The synthesized catalyst containing 5 wt % of molybdenum makes it possible to achieve 100% conversion of dibenzothiophene in 5 minutes under the following conditions: 0.5 wt % 5%Mo-SBA-15, H2O2 : S = 6 : 1 (mol.), T = 80°C.

Review of modern scientific developments in the field of molybdenum recovery from spent catalysts

The widespread use of rare metals in industry requires an increase in the amount of their production and expansion of methods for obtaining them. In this regard, the use of secondary raw materials in modern production is growing rapidly and steadily. Molybdenum is a refractory metal, which is used as an alloying element in various steels, heating elements of electric furnaces, special purpose alloys, electrovacuum equipment and other fields. Data on the volume of consumption of catalysts in the oil refining and petrochemical industries, as well as on the import of molybdenum-containing catalysts are given. The technologies for processing spent hydro-treating catalysts with production of molybdenum oxide are considered, including oxidative roasting of the feedstock, as well as such operations as: leaching by sulfuric, hydrochloric, and nitric acids, sodium carbonate [7]. Hydrometallurgical methods of decomposition of raw materials are usually combined with the subsequent extraction of molybdenum by extraction with citric acid [16], MTAA carbonate [15], or ion-exchange sorption. High purity molybdenum is characterized by a number of unique properties that are important for its use in modern technology. Most of the hard-to-remove impurities get into molybdenum oxide from the feedstock, so one of the important tasks is to optimize the leaching process at the stage of uncovering of technogenic raw materials. Recently, more and more attention has been paid to obtaining high-purity molybdenum oxide, as well as to the separation of molybdenum and tungsten. One of the promising processes seems to be ion exchange, which makes it possible to purify solutions from metal impurities from solutions and pulps formed during the decomposition of molybdenite concentrates or during leaching of raw materials. The review was carried out under the agreement between the National University of Science and Technology “MISiS” and JSC “Company Wolfram” (Moscow region, Russia) No. 0422-341 dated April 22, 2021, implemented with the financial support of the Ministry of Science and Higher Education of the Russian Federation by order of the Government of the Russian Federation No. 218 of 04/09/2010.

Model Fuel Oxidation in the Presence of Molybdenum-Containing Catalysts Based on SBA-15 with Hydrophobic Properties.

We have studied for the first time the role of hydrophobicity of the mesoporous silicate SBA-15 on the activity and the service life of a catalyst in the peroxide oxidation of sulfur-containing compounds. Immobilization of the molybdate anion on the SBA-15 support via ionic bonding with triethylammonium groups allows us not only to decrease the reaction temperature to a relatively low value of 60 °C without a drop in the dibenzothiophene conversion degree but also to increase the service life of the catalyst to many times that of the known analogs. The support and catalyst structures were investigated by low-temperature nitrogen adsorption/desorption, Fourier-transform infrared spectroscopy, X-ray fluorescence analysis, and transmission electron microscopy. Immobilization of the molybdate anion on the SBA-15 support, modified with ammonium species, prevents the leaching of active sites. However, only alkyl-substituted ammonium species minimize DBT sulfone adsorption, which significantly increases the catalyst’s service life. The synthesized catalyst Mo/Et3N-SBA-15 with hydrophobic properties is not sensitive to the initial sulfur content and hydrogen peroxide amount and retains its activity for at least six cycles of oxidation without regeneration. These catalysts can be efficiently used for clean fuel production.

Nickel- and Molybdenum-Containing Catalysts for Direct Synthesis of Propylene from Ethylene: Effect of the Support

Nickel- and Molybdenum-Containing Catalysts for Direct Synthesis of Propylene from Ethylene: Effect of the Support

ОКИСНЮВАЛЬНА ДЕСУЛЬФУРИЗАЦІЯ НАФТОПРОДУКТІВ

The modern world market makes stringent requirements for the quality of motor fuels, in particular for sulfur content in them. The main classes of sulfur-containing compounds in petroleum fractions are thiols, dialkyl and cycloalkyl sulfides, alkylaryl sulfides, as well as heteroaromatic compounds – benzothiophene, dibenzothiophene and their alkyl derivatives. They have a negative impact on the quality of petroleum products. Growing demands on the quality of oil and petroleum products have led to the search for ways to reduce the sulfur content in oils and which would not lead to deterioration of physicochemical parameters of oil, such as viscosity, density, acidity, elemental and fractional composition, etc. Among the existing methods of desulfurization of oils and their fractions, special attention is drawn to oxidation methods that allow organic sulfur compounds to be converted into sulfoxides and sulfones which are easily removed by conventional separation methods, in particular by extraction or adsorption. The prospects of the oxidation method are due to the possibility of practical use of sulfoxides and sulfones in various sectors of the economy. The most common oxidants in the processes of oxidative desulfurization of petroleum fractions are hydrogen peroxide and alkylhydroperoxides in combination with catalysts that provide high selectivity and speed of the process. Transition metal compounds (Mo, V, W,) are most often used as catalysts because they are able to form peroxocomplexes in the presence of peroxides. Heterogeneous catalytic systems consisting of various solid carriers (salts, oxides, activated carbon, zeolites) and peroxide oxidants (hydrogen peroxide or alkyl hydroperoxides) are actively developing. Molybdenum-containing catalysts are one of the most efficient heterogeneous systems for oxidative desulfurization of diesel fuel. There is proved the effectiveness of oxidative desulfurization, which is a combination of catalytic oxidation of sulfur-containing compounds in the presence of a heterogeneous catalyst and adsorption on activated carbon. Methods of oxidative desulfurization with their advantages and disadvantages can be logical addition to large-tonnage hydrotreating processes, and also potentially can be used as an independent method of deep purification of oil and petroleum products from sulfur-containing compounds.

Oxidative Dehydrogenation of Ethane on Oxide Materials in a Pulsed Microcatalytic and a Membrane Reactor

This paper presents a study of oxidative dehydrogenation of ethane (ODHE) on nanostructured single-component and multicomponent catalysts based on V5+, Mo5+, and Nb5+ oxides and produced on alumina by molecular layering. It has been shown that the molybdenum-containing catalysts exhibit higher activity for ODHE in both single-component and binary samples and ensure higher ethylene selectivity. We have demonstrated advantages of ODHE on membrane–catalyst systems in the form of asymmetric ceramic tubes, with catalysts placed inside of them. The membrane–catalyst systems produced by molecular layering offer considerably higher activity and selectivity in ODHE.

Recirculation and Regeneration of Molybdenum-Containing Ultradispersed Catalysts in the Hydroconversion Processes of Carbon-Containing Raw Materials: A Review

It was shown that hydroconversion processes with the use of ultradispersed molybdenum-containing catalysts are promising lines in the production of motor fuels from different forms of organic raw materials. Molybdenum disulfide is the catalytically active form regardless of the method of introduction and the composition of precursors used. This fact makes it possible to develop the general principles of the extraction of molybdenum compounds from the residues of the hydroconversion of organic raw materials. The known data on methods used for the extraction and regeneration of Mo-containing compounds in the hydrotreating of heavy charges and from molybdenite-containing minerals were generalized.

Selective conversion of methane to aromatic hydrocarbons on large crystallite zeolite catalysts with mesoporous structure

Large crystallite mesoporous MFI (ZSM-5) zeolite was synthesized by using carbon nano-powder as a secondary template. The surface properties, morphological and phase composition of the synthesized material and of the commercial ZSM-5 (Zeolyst) zeolite were studied by nitrogen porosimetry, XRD and scanning electron microscopy. The results showed that the volume of mesopores volume increases with development of a secondary mesoporosity in the structure of zeolite. The obtained zeolite supports were used to prepare molybdenum-containing catalysts for the methane aromatization by solid phase preparation technique. Based on the XPS data, molybdenum particles in these catalysts are characterized by more uniform size distribution. The formation of a secondary pore structure restrains the carbon deposit formation as well as increases the methane conversion and the yield of the aromatic compounds.

Sol-gel (template) synthesis of macroporous Mo-based catalysts for hydrothermal oxidation of radionuclide-organic complexes

Molybdenum compounds are industrially demanding as heterogeneous catalysts for oxidation of various organic substances. Highly porous structure of molybdenum-containing catalysts avoids surface's colmatation and prevents blocking catalytic sites that makes these materials play a key role in processes of hydrothermal oxidation of radionuclide organic complexes. The study presents an original way of sol-gel synthesis of new macroporous molybdenum compounds using “core-shell” colloid template (polymer latex) as poreforming agent. We have described three individual routs of template removal via thermal decomposition to obtain porous materials based on molybdenum compounds. Thermal treatment conditions (temperature, gaseous atmosphere) have been studied with respect to their influence on composition, structure and catalytic properties of synthesized molybdenum systems. The optimal way to synthesis of crystal molybdenum (VI) oxide with ordered porous structure (mean pore size 100–160 nm) has been suggested. Catalytic properties of macroporous molybdenum materials have been investigated in the process of liquid phase and hydrothermal oxidation of such organic substances thiazine and stable Co-EDTA complex. It was shown that macroporous molybdenum oxides could be applied as prospective catalysts for hydrothermal oxidation of organic radionuclide complexes during the processing of radioactive waste.

Introduction to Catalysis and Industrial Catalytic Processes

Molybdenum compounds are industrially demanding as heterogeneous catalysts for oxidation of various organic substances. Highly porous structure of molybdenum-containing catalysts avoids surface's colmatation and prevents blocking catalytic sites that makes these materials play a key role in processes of hydrothermal oxidation of radionuclide organic complexes. The study presents an original way of sol-gel synthesis of new macroporous molybdenum compounds using “core-shell” colloid template (polymer latex) as poreforming agent. We have described three individual routs of template removal via thermal decomposition to obtain porous materials based on molybdenum compounds. Thermal treatment conditions (temperature, gaseous atmosphere) have been studied with respect to their influence on composition, structure and catalytic properties of synthesized molybdenum systems. The optimal way to synthesis of crystal molybdenum (VI) oxide with ordered porous structure (mean pore size 100–160 nm) has been suggested. Catalytic properties of macroporous molybdenum materials have been investigated in the process of liquid phase and hydrothermal oxidation of such organic substances thiazine and stable Co-EDTA complex. It was shown that macroporous molybdenum oxides could be applied as prospective catalysts for hydrothermal oxidation of organic radionuclide complexes during the processing of radioactive waste.

New approach to active sites analysis of molybdenum-containing catalysts for hydrodesulfurization and hydrodenitrogenation based on inverse problem, fractal and site-type analyses

A new approach to the active sites of Mo-containing catalysts for hydrodesulfurization and hydrodenitrogenation was studied by three methods, i.e., the inverse problem, fractal and site-type analyses. The distribution of the active sites of the sulfided and nitrided Mo/Al2O3 catalysts was studied based on the inverse problem using the Fredholm integral equation. The two active sites of the nitrided Mo/Al2O3 catalyst have a distribution involving the reaction rate and population; one site for a fast rate and large population and the other site for a slow rate and small population. The fractal analysis was applied to the morphology of the Mo nitride and the reactivity for the carbazole hydrodenitrogenation and related to the Mo0 or Moδ+ species. The fractal dimension of the Mo nitride surfaces was calculated to be from 2.02 to 2.60 and estimated the two active sites for the hydrogenation and denitrogenation. These sites were related to the Mo3+of γ-Mo2N from the XPS analysis. The active sites for the hydrodesulfurization of 4,6-dimethyldibenzothiophene on a sulfided NiMo/Al2O3 catalyst were discussed based on the site-type analysis. A third active site of the sulfided NiMo/Al2O3 catalyst was proposed for the simultaneous desulfurization and hydrogenation from 4,6-dimethyldibenzothiophene to 3,3-dimethylbicyclohexyl as well as the two active sites for the hydrogenation to 3-methylcyclohexyltoluene and the desulfurization to 3,3-dimethylbiphenyl.

Conversion of methanol into formaldehyde on supported molybdenum-containing catalysts

Molybdenum-containing catalysts supported by aluminum and silicon oxides were studied in conversion of methanol.

Parametric study of dealkylation–transalkylation reactions over mordenite-based bi-functional catalysts

Transalkylation of heavy reformate (96% A 9 and 4% A 10) without addition of toluene was conducted over four bifunctional mordenite-based catalysts at various process conditions using a flow reactor. The effects of (i) molybdenum content (3 vs. 1 wt.%); mordenite content (80 vs. 67 wt.%); and (iii) metal type (Re vs. Mo) were assessed. The composition of products and their trends was scrutinized to determine the influence of the aforesaid parameters on dealkylation–transalkylation reactions. Higher molybdenum content enhanced the methylethylbenzene (MEB) dealkylation as well as trimethylbenzene (TMB) transalkylation, resulting in increased toluene and xylene formation. Higher mordenite content had little effect on either MEB or TMB conversion. Compared to molybdenum-containing catalysts, rhenium-containing catalyst not only exhibited higher MEB dealkylation and TMB transalkylation, but also resulted in higher hydrogen consumption and methane formation. A reaction scheme for the transalkylation of heavy reformate without the addition of toluene is proposed. Among several reactions that occur during this type of a process, de-ethylation of MEBs is kinetically controlled and probable rate-determining step in the overall reaction scheme. A linear correlation between MEB conversion and xylene yield was observed, which also supports the above rationale.

Thermodynamic and quantum chemical study of the transformations and operation mechanism of molybdenum catalysts under hydrogenation conditions

Structural transformations and the mechanism of the operation of molybdenum-containing catalysts under hydrogenation conditions have been studied by chemical thermodynamics and quantum chemistry methods, as well as the role of sulfur compounds in this process. It has been shown that molybdenum disulfide, an effective hydrogenation catalyst, is produced via the reaction of molybdenum oxide with hydrogen sulfide, not elemental sulfur. It has been concluded that the introduction of elemental sulfur (which is subsequently converted into hydrogen sulfide) or an organic sulfur compound into the reaction system, on one hand, facilitates the transformation of molybdenum oxides into MoS2 and, on the other hand, yields the effective reagent H2S, which takes part in the disproportionation reactions involving hydrogen transfer.

Mechanochemical preparation of vanadium- and molybdenum-containing catalysts II: The effect of mechanochemical activation of vanadium pentoxide + ammonium dimolybdate compositions on chemical and phase transformations

We studied the effect of mechanochemical treatment (MCT) of V2O5 + (NH4)2Mo2O7 compositions (V: Mo = 0.7: 0.3) in ethanol, water, and air on the physicochemical properties of the compositions. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy showed that mechanochemical treatment in water or ethanol does not change the phase state of vanadium pentoxide. (NH4)2Mo2O7 partially decomposes during MCT to yield nonstoichiometric molybdenum oxides. MCT in water leads to the complete decomposition of (NH4)2Mo2O7, and the nonstoichiometric molybdenum oxides that have been formed in 60–120 min are segregated into a molybdenum phase during further treatment for 240–360 min. During such a treatment, V2O5 first forms V2O5 · nH2O intercalation compounds, which then react with ammonia during long-term treatment to form ammonium hexavanadate (AHV).

Synthesis and examination of antimicrobial properties of aminomethylated derivatives C6–C7 of alicyclic diols

Synthesis of C6–C7 alicyclic diols was studied by a catalytic oxidation of cyclohexene, norbornene and their methyl derivatives in the presence of heterogenized molybdenum-containing catalysts. By a triple condensation of the diols with formaldehyde and secondary amines a synthesis of their aminomethylated derivatives with various substituents at nitrogen atom was examined. Antimicrobial properties of the synthesized amino alcohols in M-10 oil as additives with fungicidal and bactericidal activities were studied.

Mechanochemical preparation of vanadium- and molybdenum-containing catalysts: I. Mechanochemical activation of vanadium oxide and ammonium dimolybdate

V2O5 and ammonium dimolybdate (ADM) were mechanochemically activated in various media. Physicochemical transformations were studied using X-ray powder diffraction, differential thermal analysis, and IR spectroscopy. During mechanochemical treatment in water, water molecules are intercalated into the interlayer spaces of V2O5 and hydrate ADM to yield ammonium paramolybdate (APM) tetrahydrate.