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.     

Evolution of active ingredients and catalytic properties of Pt-Sn/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts in the selective deoxygenation reaction of vegetable oils

The evolution of the structure of Pt–Sn/Al₂O₃ catalysts and their catalytic properties in the reaction of the reductive deoxygenation of rapeseed oil fatty acid triglycerides (FATGs) have been studied. The catalysts were prepared by deposition from an organic solution of a mixture of platinum and tin compounds, as well as a heterometallic (PPh₄)₃[Pt(SnCl₃)₅] complex, in which platinum and tin atoms are linked by a metal–metal bond. It has been shown that the use of the heterometallic complex as a precursor with a tin to platinum molar ratio of 5 results in the formation of clusters of nanosized tin (2+; 4+) oxides and particles of a metastable PtSn_{3 ± δ} alloy on the surface of the catalyst after reductive activation. In the presence of this catalyst, the exhaustive conversion of the feed FATGs and the selectivity for hydrocarbons above 98% have been achieved. The gaseous products CO, CO₂, and CH₄ are formed in trace quantities. The results show that the deoxygenation occurs not via the known decarboxylation and decarbonylation route, but also through the step of the selective reduction of oxygen and almost complete suppression of cracking of the organic moieties of FATGs.     

Mono- and Bimetallic Mo(W)S<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Mo(W)S<Subscript>2</Subscript>/SBA-15 Hydrotreating Catalysts Based on SiMo<Subscript>12</Subscript> and SiW<Subscript>12</Subscript> Heteropoly Acids

Mono- and bimetallic Mo(W)S₂ catalysts supported on γ-Al₂O₃ and SBA-15 have been prepared using the Keggin heteropoly acids (HPAs) H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀. The catalyst samples have been analyzed by temperature-programmed reduction with hydrogen, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic properties have been examined in the joint hydrotreating of dibenzothiophene and naphthalene on a flow-through unit. It has been shown that the use of mesoporous silica SBA-15 as a support can reduce the average length of Mo(W)S₂ particles from 4.9 to 3.7 nm and increase the average number of layers and the particle size of the active phase, changes that lead to an increase in catalytic activity by a factor of ~3 relative to the alumina-supported counterparts. The use of a mixture of SiMo₁₂HPA and SiW₁₂HPA for preparing MoW catalysts leads to a significant enhancement of catalytic activity, which is apparently due to the formation of mixed active sites.     

Efficacy ofapplication of zinc oxide on the surface of the NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalytic system

The surface and catalytic properties of the NiO/Al₂O₃ system after deposition of 3 to 7% zinc oxide on its surface and heat treatment at 400, 600, and 800°C were investigated by X-ray diffraction analysis, nitrogen adsorption at −196°C, and catalytic oxidation of carbon monoxide by oxygen at 150-250°C. It was shown that calcination of the catalyst at 400°C decreases the specific surface area, while it increases it at 600 and 800°C. The decrease in the specific surface area is accompanied by an increase in the size of the NiO/Al₂O₃ crystallites. The activity of the catalysts calcined at 400°C in oxidation of carbon monoxide by oxygen, manifested by a constant reaction rate, increases with an increase in the zinc oxide content on the surface. After deposition of the zinc oxide, the mechanism of the oxidation reaction remains as before, but the concentration of active centers in the catalyst changes.     

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.     

Conversion of dimethyl ether into lower olefins on a La-Zr-HZSM-5/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> zeolite catalyst

The catalytic properties of La-Zr-HZSM-5/Al₂O₃ in the synthesis of olefins from dimethyl ether (DME) were studied. It was shown by the method of temperature-programmed ammonia desorption that acid sites of medium strength are responsible for the high catalyst selectivity for lower olefins. It was found that the preliminary high-temperature treatment of zeolite or the replacement of nitrogen with steam increased not only the selectivity of the catalyst for lower olefins, but also its activity and stability. The effect of the operating parameters of the DME conversion into the lower olefins and the dependence of the catalyst activity on the number of regenerations were studied.     

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.     

Effect of CO<Subscript>2</Subscript> on the oxidation of cyclohexene by H<Subscript>2</Subscript>O<Subscript>2</Subscript> using Co<Subscript>1.5</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst

Oxidation of cyclohexene by cheap and environmentally friendly oxidants, namely H₂O₂ and CO₂ has been catalyzed by Co_1.5PW₁₂O₄₀. It has been found that the main products of the oxidation are 2-cyclohexen-l-one (enone), 2-cyclohexen-l-ol (enol) and 1, 2-cyclohexanediol (diol) with the enone as the major product. Oxidation by CO₂ along with H₂O₂ remarkably increased the conversion compared to that by CO₂ and H₂O₂ separately. This might be due to the fact that CO₂ increases the percarbonate species (HCO₄ ^?) responsible of the oxidation by oxygen transfer, which indicated that the CO₂/H₂O₂ mixture is a useful reagent system. The decrease of both the selectivity of the enone and epoxide in favor of that of diol at higher conversions indicated that the diol was formed from the epoxide by consecutive reaction and/or directly from cyclohexene.     

Quantum-chemical and thermodynamic analysis of energy characteristics of main reactions and the initiator hydrogen peroxide in ethanol to divinyl conversion on a ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

The energy characteristics of the dehydration and dehydrogenation of ethanol have been evaluated by quantum-chemical analysis. It has been found that the dehydration of ethanol is an energetically favorable reaction. By analysis of the multiroute decomposition of hydrogen peroxide, the energy characteristics of individual reactions of the formation of hydroxyl and peroxide radicals and hydrogen and oxygen atoms have been determined. The transition state energies of the reactions of H₂O₂ degradation into various compounds have been estimated, allowing prediction of the behavior of radical sorption structures on the surface of the ZnO/γ-Al₂O₃ catalyst, in which ZnO is largely responsible for the dehydrogenation of ethanol to divinyl.     

Catalytic Cracking of <Emphasis Type="Italic">n</Emphasis>-Hexane and <Emphasis Type="Italic">n</Emphasis>-Heptane over ZSM-5 Zeolite: Influence of SiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Ratio

The performance of two types of ZSM-5 zeolite catalysts (MFI-type zeolite, SiO₂/Al₂O₃ = 50 and 300) was studied in the catalytic cracking of n-hexane and n-heptane as a model compound of light naphtha for production of light olefins at 500, 550, and 600°C. The physicochemical properties of ZSM-5 catalysts were characterized by means of XRD, BET, SEM and NH₃-TPD. The influence of SiO₂/Al₂O₃ molar ratio was investigated on conversion and product selectivity. ZSM-5 zeolite yielded higher conversion in the cracking of n-hexane compared to n-heptane and maximum conversion was achieved over ZSM-5(50) at 600°C. ZSM-5(50) showed higher alkane selectivity rather than olefins. It was found that ZSM-5(300) was more desirable in terms of having significant selectivity to light olefins as well as producing high propylene to ethylene ratio. The maximum propylene to ethylene ratio of 2.7 and 2.48 was observed over ZSM-5(300) at 500°C for n-hexane and n-heptane cracking, respectively.     

Ethylene oligomerization in the presence of ZrO(OCOR)<Subscript>2</Subscript>-Al(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>Cl-Modifier catalytic system

The kinetics of ethylene oligomerization and molecular-mass distribution of resulted oligomers on ZrO(OCOR)₂-Al(C₂H₅)₂Cl and ZrO(OCOR)₂-Al(C₂H₅)₂Cl-modifier catalyst systems, where the modifier was CCl₄, vinyl acetate, or zinc stearate, were studied depending on the modifier: ZrO(OCOR)₂ and Al(C₂H₅)₂Cl: ZrO(OCOR)₂ molar ratios, ethylene pressure, temperature, and modifier nature.     

Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr<Subscript>3</Subscript>)<Subscript>2</Subscript>]BF<Subscript>4</Subscript>/BF<Subscript>3</Subscript>OEt<Subscript>2</Subscript> catalytic systems

Selective dimerization of styrene to 1,3-diphenylbutene-1 in the presence of [(acac)Pd(PAr₃)₂]BF₄ + BF₃OEt₂ catalytic systems, where R = C₆H₅, o-CH₃C₆H₄, p-CH₃C₆H₄, or o-CH₃OC₆H₄, has been studied. Under the optimal conditions (B/Pd = 8, T = 75°C, R = C₆H₅), the conversion of styrene to the products exceeds the conversion for the known analogs and reaches 1.5 tons of styrene/g-atom of palladium with amounts of dimers and trimers of 91 and 9%, respectively. The dimers consist of up to 100% 1,3-diphenylbutene-1 with a trans/cis isomer ratio of 95/5.     

Cycloaddition of cage and polycyclic diazo compounds to C<Subscript>60</Subscript> fullerene catalyzed by Pd(acac)<Subscript>2</Subscript>-2PPh<Subscript>3</Subscript>-4Et<Subscript>3</Subscript>Al

Spirohomofullerenes were synthesized by cycloaddition of cage and polycyclic diazoalkanes generated in situ by oxidation of hydrazones of camphor, 2-adamantanone, and cholestane-3-one to C₆₀ fullerene in the presence of the Pd(acac)₂-2PPh₃-4Et₃Al three-component catalyst. It was found that the spiro-homofullerenes obtained from hydrazones of 2-adamantanone and cholestane-3-one and C₆₀ fullerene do not undergo thermal isomerization to the corresponding spiro-methanofullerenes.     

Conversion of dimethyl ether into C<Subscript>2</Subscript>-C<Subscript>4</Subscript> olefins on zeolite catalysts

The effect of the nature of the metal introduced into HZSM-5 on the properties of the catalysts for the synthesis of olefins from dimethyl ether was studied. By means of the ammonia temperature-programmed desorption technique, it was shown that a decrease in the total amount of acid sites increases the selectivity for lower olefins. As the ratio of the medium to strong acid sites increases, the yield of olefins increases. The effect of the nature of gaseous additives in the feedstock on the selectivity for lower olefins was studied at T = 340°C, p = 0.1 MPa, and ν ₀ = 2000 h^?1.     

Isomerization of <Emphasis Type="Italic">n</Emphasis>-hexane over bifunctional Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript> catalysts

The catalytic properties of model Pt/SiO₂ and Pt/Al₂O₃ catalysts and their physical mixtures with SO₄/ZrO2 in the reaction of n-hexane isomerization have been studied. Significant effects of the influence of the platinum state on the characteristics of isomerization on the catalysts and their physical mixtures with SO₄/ZrO₂ have been revealed. The observed changes in catalytic performance of the mixed catalysts have been explained from the position of a bifunctional mechanism with the participation of ionic platinum promoting the formation of hydride ions, which play an important role in the activation of transformations of intermediates in isomerization reactions.     

Kinetic aspects of the effect of the palladium phosphine complex Pd(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript> and free triphenylphosphine on hydrocarbomethoxylation of cyclohexene

The influence of temperature on the dependence of the cyclohexene hydrocarbomethoxylation reaction catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid system upon the Pd(PPh₃)₂Cl₂ and PPh₃ concentrations has been studied. The data have been interpreted in terms of the mechanism that involves as intermediates ion pairs containing cationic hydride, alkyl, and acyl palladium complexes. Using the quasi-equilibrium concentration approximation, a rate equation has been derived to adequately describe the experimental data. The parameters of the rate equation were estimated by the least-square technique. The apparent activation energies of these parameters have been determined, and the ratio between the enthalpies of the formation of inactive [Pd(PPh₃)₄] and \(H\mathop {Sol}\limits^ \oplus [Pd(PPh_3 )_2 (Cl)(Sol)]^ - \) complexes from [Pd(PPh₃)₂(Sol)]₂ has been evaluated on their basis.     

Kinetics of cyclohexene hydrocarbalkoxylation with cyclohexanol catalyzed by the Pd(PPh<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>-PPh<Subscript>3</Subscript>-<Emphasis Type="Italic">p</Emphasis>-toluenesulfonic acid system

The reaction kinetics of cyclohexene hydrocarbalkoxylation with cyclohexanol catalyzed by the Pd(PPh₃)₂Cl₂-PPh₃-p-toluenesulfonic acid system was studied over the temperature range 363–393 K. The reaction rate was found to be a nonlinear function of the Pd(PPh₃)₂Cl₂ concentration or a nonmonotonic function of the PPh₃ and cyclohexanol concentrations or p _CO. The experimental data were interpreted in terms of a mechanism that involves ion pairs containing alkyl and acyl palladium complexes of the cationic type as intermediates. Based on the quasi-steady-state approximation, a rate equation was obtained to adequately describe the experimental data. The rate equation parameters were estimated using the least squares technique. The apparent activation energies of these parameters were determined. The heats of formation of Pd(PPh₃)₂(C₆H₁₁OH)₂, Pd(PPh₃)₂(CO)₂, and Pd(PPh₃)₄ complexes from Pd(PPh₃)₂(C₆H₅CH₃)₂ were estimated. A symbatic change in these values with the donor-acceptor properties of ligands was demonstrated.     

Conversion of lower alcohols into C<Subscript>2</Subscript>–C<Subscript>4</Subscript> olefins over acid-base catalysts

The conversion reactions of methanol, ethanol, and their ethers in the presence of acid-base catalysts based on mesoporous ZSM-5 and ZSM-11 zeolites, microporous SAPO zeolites, heteropoly acids, and perfluorinated sulfonated cation exchangers are discussed. The set of reactions reflects the formation of olefins beginning from ethylene to butenes. The heats of reaction were estimated from the calculated values of the equilibrium constants and enthalpies at 700 K. It was assumed that the available experimental data for all three types of catalysts should be described by a complex mechanism of transformations of alcohols and ethers. The reaction sequence includes fast dehydration of alcohols into ethers. It is likely that, at temperatures of 512–573 K, the initial reactions have a common initiation mechanism for all three types of catalysts, which involves the formation of the protonated forms of substrate molecules that trigger the olefin synthesis reactions. For thermally stable catalysts (zeolites), the mechanism with participation of free radicals and olefins generated from the alkoxylated hydroxyl groups of zeolites is possible above 573 K. As the degree of conversion of ethers increases, carbenium and arenonium ions begin to play a progressively increasing role as active intermediates instead of the alkoxy groups. This crossover may be responsible for changes in both the kinetic parameters of the substrate transformation and the direction of the reaction over zeolites at 573–623 K. The schemes proposed in some published works for the conversion of oxygen-containing organic compounds and olefins with participation of superacid centers of the catalysts in question should be considered speculations in light of the effect of water leveling the strength of Brönsted sites.     

Hydrodearomatization catalysts based on molybdenum hexacarbonyl Mo(CO)<Subscript>6</Subscript> supported on mesoporous aromatic frameworks

A method for synthesizing fine hydrodearomatization catalysts based on the immobilization of molybdenum carbonyl into the pores of mesoporous aromatic frameworks is proposed. It is shown that the amount of the deposited metal and the average size of the resulting particles depend on the support and the deposition method characteristics. The catalytic activity of the synthesized materials in the hydrogenation of bicyclic hydrocarbons at a hydrogen pressure of 5.0 MPa in a temperature range of 330–500°C is studied using the example of naphthalene, methylnaphthalenes, and biphenyl as model substrates.     

Dissociation behavior of （CH4 ＋ C2H4） hydrate in the presence of sodium dodecyl sulfate

Separation of a mixture of CH4+C2H4 gas by forming hydrate in ethylene production has become of interest,and the dissociation behavior of(CH4+C2H4) hydrate is of great importance for this process. The hydrate formation rate could be increased by adding a small amount of sodium dodecyl sulfate(SDS) into water. In this work,the kinetic data of CH4(18.5 mol%) +C2H4(81.5 mol%) hydrate decomposition in the presence of 1000 mg·L-1 SDS at different temperatures and pressures were measured with the depressurizing m...