Promoted catalysts for hydrogenation of bicyclic aromatic hydrocarbons obtained in situ from molybdenum and tungsten carbonyls

Promoted Мo and W catalysts have been prepared in situ via thermal decomposition of precursors, oil-soluble salts Mo(CO)₆, W(CO)₆, С°C₁₆H₃₀O₄, and NiC₁₆H₃₀O₄. TiO₂, Al₂O₃, and ZrO(NO₃)₂ · 6H₂O have been used as the acidic additives. Also, Mo and W unsupported sulfide catalysts have been prepared in the presence of elemental sulfur as the sulfiding agent. The catalysts have been characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The activity of the catalysts prepared in situ has been evaluated in the hydrogenation reaction of bicyclic aromatic hydrocarbons by the example of model mixtures of 10% solutions of naphthalenes (unsubstituted naphthalene, 1- and 2-methylnaphthalenes, and 1,5- and 2,3-dimethylnaphthalenes) in n-hexadecane. The effect of the precursor/acidic oxide ratio on the activity of the formed catalyst has been found. Hydrogenation of bicyclic aromatic hydrocarbons has been conducted at a hydrogen pressure of 2 and 5 MPa and a temperature of 380 and 400°C for 2 h. Hydrogenation of the unsubstituted aromatic ring has been preferable due to the absence of steric hindrances. The degree of conversion of n-hexadecane under the reaction conditions has been 1.5–7.5% depending on the reaction temperature. It has been found that the activity of the sulfided catalyst in the conversion of 1- and 2-methylnaphthalenes is inferior to the activity of the unsulfided analogue, while partial replacement of TiO₂ by Al₂O₃ results in a decrease in the conversion of the substrates as opposed to the unsulfided catalysts, in which the use of nanocrystalline Al₂O₃ promotes an increase in the conversion.     

Quantum-chemical study of interaction between hydrogen sulfide and sulfides of iron,titanium, and tungsten

A quantum-chemical study of the interaction between hydrogen sulfide and the simplest MeS and MeS₂ (Fe, Ti, W) sulfides was carried out. The correlations of catalytic activity in photodecomposition of hydrogen sulfide on Me/Al₂O₃ catalysts with the heat of formation of complexes MeS₂ with hydrogen sulfide and changes in charge values of active metal upon complexation were found.     

Influence of Pt nanoparticles modified by La and Ce oxides on catalytic dehydrocyclization of n-alkanes

Catalytic reforming accounts for a large share of the world’s gasoline production, it is the most important source of aromatics for the petrochemical industry. In addition, reforming of hydrocarbon on the dual-function catalysts has been found to form fundamentally different products in hydrogen diluents. Typical catalysts employed for this reforming process are Pt/Al₂O₃ and Pt-M/Al₂O₃, M being the promoter. These solids are characterized by both acid and metal functions which catalyze dehydrocyclization, dehydrogenation, isomerization and cracking processes. In this regard, information about cerium and lanthanum, as promoters, is hardly revealed. The present work aims to study the performance of Pt/Al₂O₃ catalysts modified by lanthanum or cerium during the conversion of cyclohexane, n-hexane and n-heptane. Catalytic activities of the prepared catalysts were tested using a micro catalytic pulse technique. Physicochemical characterization of the solid catalysts such as, surface area (S_BET), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hydrogen-temperature programed reduction (H₂-TPR), hydrogen-temperature-programed desorption (H₂-TPD), CO₂-TPD, NH₃-TPD, high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were depicted. Results indicated clearly that Pt/Al₂O₃ catalyst is selective toward dehydrogenation to benzene which could be explained as due to the decrease in the active acid sites and the comparative segregation of the alumina support especially at 3% load of CeO. The presence of La₂O₃ in the Pt/Al₂O₃ catalyst promotes aromatization of n-hexane and n-heptane, also the dehydrocyclization of n-hexane is more difficult than that of n-heptane. Thus, modification of the Pt/Al₂O₃ catalyst by La, resulted in a more active and selective reforming catalyst.     

Structural and morphological features of the formation of polyfunctional nanocatalysts in a reverse microemulsion medium

The formation of ultrafine and nanosized particles of multicomponent catalysts of the Me _x O _y /Al₂O₃ and Me_2x S _y /Al₂O₃ types (Me = Mo, Ni, Co, Fe) has been studied. Their samples have been synthesized by the thermal decomposition at T ～ 240°C and P = P _atm of reverse microemulsions (MEs) with precursors in the aqueous phase. The ME dispersion medium has been hydrocarbons containing synthetic (AOT, Span 80) or native (resins, asphaltenes, polycyclic aromatics) stabilizers. It has been shown that the mean diameter, structure, and morphology of the two- and three-component ultrafine and nanosized particles synthesized depend on the precursor introduction mode, ME composition, and microemulsion treatment conditions. It has been found that for the synthesis of spherical binary nanoparticles with the core-shell structure, the sequential introduction of precursors is preferable when the particle core phase (Al₂O₃) is synthesized in the first step and then a component that inevitably becomes the shell (Me _x O _y , Me _x S _y ) is generated.     

Activity of Co(Ni)MoS/Al2O3 catalysts, derived from cobalt(nickel) salts of H6[Co2Mo10O38H4], in hydrogenolysis of thiophene and hydrogen treatment of diesel fraction

Co(Ni)MoS/Al₂O₃ catalysts have been prepared from ammonium 10-dodecamolybdodicobaltate (NH₄)₆[Co₂Mo₁₀O₃₈H₄] (further, Co₂Mo₁₀HPC) and cobalt(nickel) salts of 10-dodecamolybdodicobaltic acid H₆[Co₂Mo₁₀O₃₈H₄] (hereinafter, Co₂Mo₁₀HPA). It has been found that a high activity of the Co(Ni)₃-Co₂Mo₁₀HPA/Al₂O₃ catalysts in the hydrodesulfurization and hydrogenation reactions is due to the formation of a nanostructured type II CoMoS phase via the contact of the metals (Mo and Co(Ni)) at the molecular level. The use of Ni as a copromoter in the Ni₃-Co₂Mo₁₀HPA/Al₂O₃ catalyst leads to a simultaneous increase, compared with Co₃-Co₂Mo₁₀HPA/Al₂O₃, in the linear size of nanoparticles and the number of MoS₂ layers in the packing of active phase. The nature of the promoter X has a substantial effect on the properties of X₃Co₂Mo₁₀HPC/Al₂O₃ catalysts. It has been found that the catalysts with X = Co exhibit the highest activity in the hydrodesulfurization reactions and those with X = Ni, in hydrogenation reactions.     

The role of sulfur in modification of active sites of reforming catalysts

The features of the interaction of hydrogen sulfide with the surface of supports (alumina and silica) and catalysts (Pt/SiO₂, Pt/Al₂O₃, Re/Al₂O₃, and Pt–Re/Al₂O₃) have been studied. It has been found that the adsorption of sulfur on the supports is completely reversible. The amount of irreversibly adsorbed sulfur (S_irrev) and S_irrev/metal ratios in the catalysts after treatment in a hydrogen atmosphere at 500°C have been determined. Sulfurization reduces the dispersion of platinum to 5% and increases the amount of ionic platinum on the catalyst surface. Regarding the dehydrocyclization reaction of n-heptane, the optimal amount of sulfur required for sulfurization of the catalyst with the composition 0.25% Pt 0.3% Re/γ-Al₂O₃ (0.3% Zr) is 0.072 wt %.     

Hydrotreating of vacuum gas oil on modified Ni–Mo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The effect of the introduction of P₂O₅ into Ni–Mo/Al₂O₃ catalysts on their activity in the hydrotreating of vacuum gas oil has been studied. As the support, γ-Al₂O₃ prepared from aluminum hydroxide AlOOH powder of the TH-100 brand (Sasol) has been used. The catalytic properties of the catalysts obtained have been examined in the hydrotreating of vacuum gas oil in a continuous-flow unit under hydrogen pressure. The amounts of sulfur and polycyclic aromatic hydrocarbons, the hydrocarbon group composition, and the carbon residue of the feedstock and the hydrotreating product have been determined. The catalysts after testing have been studied using differential thermal analysis in combination with thermogravimetry (DTA–TGA); the influence of the amount of the modifier on the catalytic activity and coking of the catalysts has been shown.     

邻甲酚加氢脱氧还原型催化剂的实验研究

以邻甲酚为生物质热解油模型化合物,研究了几种还原型加氢催化剂的催化脱氧性能的差异。采用孔饱和浸渍法制备了Mo/Al₂O₃、CoMo/Al₂O₃和CoMoEDTA/Al₂O₃加氢脱氧催化剂,采用H₂ -TPR、XRD对它们进行了表征;在H2气氛下对催化剂进行了还原,并在连续流动固定床加氢微反装置中,考察了邻甲酚在不同还原态催化剂催化下加氢脱氧反应的转化率和产物的选择性。结果表明,在相同的加氢反应条件下,CoMoEDTA/Al₂O₃的催化活性和稳定性均比Mo/Al₂O₃和CoMo/Al₂O₃催化剂高;在反应过程中,Mo/Al₂O₃催化剂表现出较高的直接脱氧选择性,而CoMo/Al₂O₃和CoMoEDTA/Al2O3催化剂表现出较高的加氢脱氧选择性。     

Influence of Anderson and Keggin heteropoly compounds as precursors of oxide phases in hydrotreating catalysts on their performance

Unpromoted and nickel-promoted catalysts were synthesized on the basis of the Anderson heteropoly compounds (NH₄)_{6 ? x} [X ^x (OH)₆Mo₆O₁₈] · nH₂O, where heteroatom X is Cr(III), Mn(II), Fe(II), Ni(II), Co(II), Cu(II), Zn(II), or Ga(III), and their activity in the thiophene hydrogenolysis reaction and hydrofining of diesel fraction was examined. It was shown that the most active hydrotreating catalysts under the test conditions in a flow unit were the samples with X = Ni, Mn, or Zn. The catalysts synthesized from the Keggin heteropoly compounds H₄[SiMo₁₂O₄₀] · 17H₂O, H₃[PMo₁₂O₄₀] · 19H₂O, H₃[PVMo₁₁O₄₀] · nH₂O, and (NH₄) _x [V(MoO₃)₁₂] · nH₂O were tested in the hydrofining of light coker gas oil. The maximum activity was displayed by the catalysts prepared on the basis of the vanadium-containing heteropoly compounds H₃[PVMo₁₁O₄₀] · nH₂O and (NH₄) _x [V(MoO₃)₁₂] · nH₂O.     

Effect of Vanadium Introduction on the Activity of NiMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts in the Hydrotreating of Diesel Fractions

The influence of the introduction of V₂O₅ into NiMo/Al₂O₃ catalysts on their activity in hydrodesulfurization (HDS) and hydrogenation reactions of the components of petroleum fractions has been studied. The activity of the synthesized catalysts has been determined in the straight-run diesel and light coker gas oil hydrotreating processes in a flow-through unit under hydrogen pressure. The most active catalyst for HDS and hydrogenation of polycyclic aromatic hydrocarbons has been synthesized using VMo₁₂ heteropoly compounds: the activity increases by 6–10 and 11–13 wt % in HDS and PAH hydrogenation, respectively, at different temperatures. It has been shown that the activity of the regenerated catalyst further impregnated with the vanadium compound in HDS and PAH hydrogenation increases by 2–5 rel. %, as compared to the regenerated catalyst.     

Co-hydrotreating of straight-run diesel fraction and vegetable oil on Co(Ni)-PMo/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The process of co-hydrotreatment of straight-run diesel fraction (DF) and vegetable oil (VO) on Co(Ni)-PMo/Al₂O₃ catalysts prepared from H₃PMo₁₂O₄₀ and cobalt (nickel) citrate has been studied. It has been shown that under conditions close to those in the industry, the complete conversion of fatty acid triglycerides (FATG) is achieved on the catalysts of both types to give an ultraclean hydrotreating product in a 97% yield and a cetane number of 5 points above that of the hydrotreating product of the DF alone. The degree of hydrodesulfurization (HDS) is reduced more significantly on the Co-PMo/Al₂O₃ catalyst than in the case of Ni-PMo/Al₂O₃. The catalysts are more susceptible to deactivation in the hydrotreating of the blended feedstock containing VO. The Co-PMo/Al₂O₃ sample is less stable than Ni-PMo/Al₂O₃. Examination of the spent catalysts by transmission electron microscopy has shown that the average particle length of the active phase of Co-PMo/Al₂O₃ increases, whereas this increment for Ni-PMo/Al₂O₃ is insignificant, indicating higher stability of particles of the NiMoS phase. Thus, the co-hydrotreating of petroleum fractions and vegetable oil is more reasonable to carry out on NiMo/Al₂O₃ catalysts.     

An in situ study of dimethyl ether conversion over HZSM-5/Al2O3 zeolite catalysts by high-temperature diffuse reflectance infrared fourier transform spectroscopy

Isolated and associated OH groups have been in situ identified by high-temperature diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy of the surface of zeolites calcined until complete removal of water. It has been shown that the Brønsted acid sites (BASs) involved in dimethyl ether (DME) conversion on the zeolite surface exhibit two characteristic bands in the DRIFT spectra. It has been found that the composition of DME conversion products on HZSM-5 zeolite catalysts modified with Mg or Rh is temperature-dependent. Ethanol and a small amount of methanol were detected on an Rh-HZSM-5/Al₂O₃ zeolite catalyst at T = 270°C and were not observed on Mg-HZSM-5/Al₂O₃ under the same conditions. Spectral features of ketene were detected in the DRIFT spectra of the surface of Mg-HZSM-5/Al₂O₃ in a stream of DME. The spectrum of Rh-HZSM-5/Al₂O₃ calcined at 200°C exhibited spectral features of ethyl alcohol and bands characterizing a strong Lewis acid site (LAS) capable of hydrogenating ketene to ethyl alcohol. The spectra of the surface of all the zeolite catalysts tested in a DME stream at 320°C contain bands characterizing olefins and alkanes and do not exhibit the spectral features of alcohols and ketene.     

Catalytic transformations of mixtures of ethers with aliphatic and aromatic nitriles on solid acids under supercritical conditions

The catalytic conversion of mixtures of ethers with aliphatic and aromatic nitriles in supercritical conditions on zeolites (HY, HCaREEY), individual oxides (Al₂O₃, SiO₂, MoO₃, WO₃, TiO₂), and oxide systems (Al₂O₃-SiO₂, H₈[Si(Mo₂O₇)₅], Al₂(WO₄)₃) has been studied. It has been found that acid catalysts, such as zeolites, mixed oxides, and TiO₂ (anatase), are active at 350°C in the direct synthesis of N-acylpyrrolidines from tetrahydrofuran and nitriles (CH₃CN, n-C₄H₉CN, C₆H₅CN): the product yield reaches 40% and the selectivity is 65–94%. The activity and selectivity of TiO₂ samples increase with an increase in the specific surface area (from 37 to 139 m²/g) or with a decrease in the particle size of anatase (from 43 to 13 nm according to XRD data). The character of interaction of the components of the reaction mixture with the TiO₂ surface has been studied by the TG-DTA technique. After oxidative regeneration, TiO₂ exhibits the initial catalytic properties, suggesting the possibility of its repeated use in the direct synthesis of acylpyrrolidines. Replacing THF by other compounds (diethyl ether, 1,4-dioxane, tetrahydropyran) drastically reduces the yield of respective alkylamides.     

Transformations of tetradecane on La/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> + ZSM catalysts

The behavior of La/Al₂O₃ + ZSM catalysts has been studied in the process of the hydrogen-free conversion of tetradecane. The structure and state of active centers of catalysts have been investigated using a combination of physicochemical and instrumental methods (TPD of ammonia, IR spectroscopy, electron microscopy). It was found that the catalysts are characterized by the presence of acid (Brönsted and Lewis) sites and M⁰ and Mⁿ⁺ metal centers. Lanthanum in different oxidation states can be included in the acid sites. The degree of tetradecane conversion and the product composition are determined by the SiO₂/Al₂O₃ ratio of the zeolite and the conditions of the process. The mechanism of the cracking and transformations of tetradecane on La/Al₂O₃ + ZSM catalysts is discussed.     

Fischer-Tropsch synthesis in a slurry reactor in the presence of nanosized cobalt catalysts synthesized in situ in a hydrocarbon medium

Fischer-Tropsch synthesis in a slurry reactor at a pressure of 20 atm and a temperature of 220–300°C in the presence of 100Co : 2Pd : (5–50)Al₂O₃ and 100Co : 2Pd : (20–50)ZrO₂ (parts by weight) catalysts in situ synthesized in a hydrocarbon medium has been studied. The catalysts were prepared by the decomposition of cobalt salts and promoters in melted petroleum paraffin P-2 at 300°C and in situ reduced with hydrogen. It has been found that the nanocatalyst containing 20 parts by weight of ZrO₂ exhibits the highest activity in the Fischer-Tropsch synthesis and provides the yield of liquid products of 70 g/m³ at a CO conversion of 80%.     

Conversions of mixtures of propane and benzene on Pt,Re/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> + H-zeolite systems

The conversion of C₆H₆: C₃H₈C mixtures on mixed catalysts composed of the metal catalysts Pt,ReOx/Al₂O₃ and zeolites Y, M, and ZSM-5 in the H form was studied. The products of benzene dehydroalkylation by propane and propane dehydrogenation products are formed at 180–350°C. It has been shown that propane is activated on the metal catalysts and C₆H₆ interacts with the zeolites yielding the C₆H₇ ⁺ intermediate, which acts as an agent of proton transfer from a zeolite to a metal catalyst, and another intermediate C₉H₁₃⁺ (I). Cumene, alkylbenzenes, and propene are formed as a result of the conversion of I. A comparison of the results of the conversion of these mixtures on the composite catalysts with different zeolites shows that the formation of cumene and propene is thermally controlled and the formation of the other products is kinetically controlled. It has been concluded that the coupling of the redox properties of the metal catalysts with the acid-base properties of the zeolite catalysts facilitates the low-temperature transformations of the mixtures.     

Steam reforming of gaseous by-products from bitumen oil using various supported Ni-based catalysts

The steam reforming process is an efficient route for producing hydrogen gas which, along with lower costs compared to other methods, has an acceptable efficiency rate. In this study, by using an experimental setup we tried to investigate the effect of various catalysts on the amount of tar and produced hydrogen from steam reforming of gas by products from bitumen oil and to introduce effective parameters in the process of hydrogen production. As temperature increased, the amount of tar conversion to gas increases and the amount of hydrogen surged accordingly. With increase in temperatures from 400 to 900°C, tar elimination also improved from 39% to 99% for Ni/Al₂O₃, from 30.5 to 93.1 for Ni/olivine and from 25.7 to 83.6 for Ni/Fe₂O₃. As a result, it was concluded that the Ni/Al₂O₃ catalyst has been more successful in eliminating the tar, although there is not much difference between the activities of the three catalysts.     

The Role of Nitrogen in Facilitating Methylcyclohexane Aromatization on Pt/Al2O3 and Pt-Re/Al2O3 Catalysts

Abstract

The kinetics of methylcyclohexane aromatization on commercial Pt/Al₂O₃ and Pt-Re/Al₂O₃ catalysts was investigated in a micro-reactor using N₂ and/or H₂ as carrier gases at temperatures ranging between 300–500°C, W/F values ranging between 0.83–3.75 mg min/mL and at a total pressure of 4.0 kg/cm². On both catalysts in N₂ atmosphere, aromatization accompanied by demethylation was observed with the formation of cracked products, benzene and toluene. However, in H₂ methane was the predominant product of methylcyclohexane reforming on PtA1₂O₃ and Pt-Re/Al₂O₃ at 500°C and 400–500°C respectively, whereas at 350°C, aromatization was predominant on Pt/Al₂O₃ but on Pt-Re/Al₂O₃, aromatization was accompanied by fragmentation to methane. In N₂–H₂ mixtures, demethylation activity was observed to decrease with H₂ content of the mixture on Pt-Re/Al₂O₃. A preliminary test of the kinetic data using Sica's method of pulse kinetic analysis suggests a first order rate in methylcyclohexane with activation energies of 3.21 kcal/gmol in N₂ and 19.70 kcal/gmol in H₂ for the Pt/Al₂O₃ catalyst and 16.66 kcal/gmol in N₂ and 34.94 kcal/gmol in H₂ for the Pt-Re/Al₂O₃ catalyst. However, a more comprehensive kinetic analysis suggested an aromatization mechanism for Pt-Re/Al₂O₃, where adsorbed H₂ was a participant. A different aromatization mechanism for the reaction in N₂ where hydrogen was not needed explained the data on Pt/Al₂O_3. In both cases, the desorption of toluene was determined as the rate determining step.     

Selective Hydrogenolysis of Glycerol to 1,2-Propylene Glycol on Ultrafine Copper Particles

Hydrogenolysis of glycerol to 1,2-propylene glycol at 200°C in the presence of Cu/Al₂O₃ catalysts prepared by coprecipitation from copper nitrate and aluminum nitrate using NaOH and NH₄OH has been studied. The kinetics of the reaction is described by the first-order rate law. It has been found that the selectivity for the target product for all catalyst samples is 98% and the activity of the catalysts depends on their synthesis conditions. By using X-ray diffraction analysis, transmission electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy, it has been revealed that the active phase of Cu/Al₂O₃ samples is made of particles with an average size of 20 to 140 nm, whose surface consisted of CuO and Cu₂O. The catalysts with different particle sizes the active phase but close chemical composition exhibits comparable activity (67.5 ± 5 h^–1mol^—1). This finding indicates that the hydrogenolysis reaction run in the presence of Cu/Al₂O₃ is not structure-responsive. A decrease in concentration of the Cu₂O phase of the catalyst leads to a decrease in the hydrogenolysis rate, thereby this indicating a higher activity of the Cu₂O phase in comparison with the CuO phase.     

The features of the catalytic synthesis of methanethiol from dimethyl sulfide

The characteristic features of methanethiol synthesis from dimethyl sulfide and H₂S in the presence of Al₂O₃ at atmospheric pressure and T = 320–500°C have been studied. It has been shown that the yield of methanethiol increases with an increase in the temperature, the H₂S-to-dimethyl sulfide ratio, and the contact time, attaining equilibrium values. The methanethiol formation rate is proportional to the dimethyl sulfide partial pressure raised to a power of 0.4 and the H₂S partial pressure raised to a power of 0.8. An increase in the specific surface area and the volume of transport pores and a decrease in the particle sizes of Al₂O₃ facilitate the augmentation of the catalyst activity in methanethiol formation. At T ～ 400°C, a low H₂S concentration, and a long contact time, the side reaction of dimethyl sulfide cracking occurs to result in the release of methane and the deposition of sulfur-containing and carbonaceous compounds on the surface, which lower the activity of alumina. The deactivated catalyst can be regenerated by oxidation.