Conversion of dimethyl disulfide in the presence of zeolites

Dimethyl disulfide conversion in the presence of zeolites was studied at atmospheric pressure and T = 190–350°C. For all catalysts, the products of the reaction at T = 190°C—methanethiol, dimethyl sulfide, and hydrogen sulfide—result directly from dimethyl disulfide. The relative reaction rate and the dimethyl sulfide selectivity decreases in the order HZSM-5 ≥ CoHZSM-5 > HNaY > NaX, NaY. The methanethiol formation selectivity changes in the reverse order. The highest methanethiol selectivity at T = 190°C is shown by the sodium zeolites; the highest dimethyl sulfide selectivity, by the high-silicz zeolite HZSM-5. Raising the reaction temperature increases the reaction rate and changes the process route: at high temperatures, dimethyl disulfide decomposes to methanethiol, which then condenses to yield dimethyl sulfide and hydrogen sulfide. The observed regularities are explained in terms of the different acidic properties of the zeolite surfaces.     

Nonoxidative conversion of methane and <Emphasis Type="Italic">n</Emphasis>-pentane over a platinum/alumina catalyst

Methane adsorption on the Pt–H/Al₂O₃ and Pt/Al₂O₃ catalysts begins at Т = 475°C and is accompanied by the appearance of hydrogen in the reaction medium. At a higher temperature is raised to 550°C, the amount of adsorbed hydrogen increases to 1.1 and 0.8 mol/(mol Pt), respectively. According to the calculated degree of methane dehydrogenation on platinum sites at Т = 550°C, the Н/C ratio is 1.3 (at/at) for the Pt–H/Al₂O₃ catalyst and 1.5 (at/at) for the Pt/Al₂O₃ catalyst. The introduction of n-pentane into the reaction medium increases the yield of aromatic hydrocarbons (benzene and toluene) by a factor of 8.8 over the arene yield observed in individual n-pentane conversion. A mass spectrometric analysis of the arenes obtained with the Pt/Al₂O₃ catalyst has demonstrated that 37.5% of the adsorbed methane is involved in the methane–n-pentane coaromatization yielding benzene and toluene.     

Influence of chelate ring size on the properties of phosphine-sulfonate palladium catalysts

Phosphine-sulfonate based palladium is one of the most extensively studied catalyst systems in olefin polymerization.This type of catalyst features six-membered chelate ring size,and can enable the copolymerizations of ethylene with a wide variety of polar monomers.In this contribution,we decide to investigate the influence of chelate ring size on the properties of phosphinesulfonate palladium catalysts.As such,a series of phosphine-sulfonate ligands and the corresponding seven-membered ring Pd(II)complexes[κ~2-(P,O)-2-(CH_2-PR_1R_2)-4-methylphenyl-sulfonato]Pd(Me)(DMSO)(Pd1,R_1=R_2=Cy,Pd2,R_1=R_2=o-Me O-C_6H_4;Pd3,R_1=Ph,R_2=2-[2,6-(Me O)_2C_6H_3]C_6H_4;DMSO=dimethyl sulfoxide)were designed,prepared and characterized.These palladium complexes are moderately active when they were applied in ethylene polymerization and copolymerizations with methyl acrylate and butyl vinyl ether.However,their properties are greatly reduced from those of the classic six-membered ring phosphine-sulfonate palladium complex Pd2′.The experimental results indicate that the bigger chelate ring size can increase the ligand flexibility and damage the catalytic properties for the phosphine-sulfonate type palladium catalysts.     

Hydrogenolysis of dimethyl disulfide in the presence of bimetallic sulfide catalysts

The hydrogenolysis of dimethyl disulfide in the presence of Ni,Mo and Co,Mo bimetallic sulfide catalysts was studied at atmospheric pressure and T = 160–400°C. At T ≤ 200°C, dimethyl disulfide undergoes hydrogenolysis at the S-S bond, yielding methanethiol in 95–100% yield. The selectivity of the reaction decreases with increasing residence time and temperature due to methanethiol undergoing condensation to dimethyl disulfide and hydrogenolysis at the C-S bond to yield methane and hydrogen sulfide. The specific activity of the Co,Mo/Al₂O₃ catalyst in hydrogenolysis at the S-S and C-S bonds is equal to or lower than the total activity of the monometallic catalysts. The Ni,Mo/Al₂O₃ catalyst is twice as active as the Ni/Al₂O₃ + Mo/Al₂O₃ or the cobalt-molybdenum bimetallic catalyst.     

Effect of catalyst structure on the reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane

Reaction of α-methylstyrene with 1,1,3,3-tetramethyldisiloxane in the presence of the complexes of platinum(II), palladium(II) and rhodium(I) is explored. It is established that in the presence of platinum catalyst predominantly occurs hydrosilylation of α-methylstyrene leading to formation of β-adduct, on palladium catalysts proceeds reduction of α-methylstyrene, on rhodium catalysts both the processes take place. In the reaction mixture proceeds disproportion and dehydrocondensation of 1,1,3,3-tetramethyldisiloxane that leads to formation of long chain linear and cyclic siloxanes of general formula HMe₂Si(OSiMe₂) _n H and (-OSiMe₂-)m (n = 2–6, m = 3–7), respectively. Platinum catalysts promotes formation of linear siloxanes, while both rhodium and palladium catalysts afford linear and cyclic siloxanes as well. Structure of intermediate metallocomplexes is studied.     

Physicochemical and catalytic characteristics of La-H-ZSM-5 zeolite in converting dimethyl ether to the mixtures of gasoline hydrocarbons: Effect of ion exchange conditions

The effect of the manner and conditions of introducing lanthanum cations into NH₄-ZSM-5 zeolite on the properties of catalysts for the conversion of dimethyl ether into the mixtures of gasoline hydrocarbons is studied. The physicochemical properties of synthesized catalysts are studied by means of temperature-programmed ammonia desorption, the adsorption of benzene, atomic absorption spectroscopy, differential scanning calorimetry, and thermogravimetry. It is shown that the degree to which lanthanum cations are replaced by ammonium cations both depends on the conditions of ion exchange in the zeolite and affects its acidity spectrum and the selectivity of the formation of paraffin hydrocarbons with isostructure. It is concluded that an increase in the amount of introduced lanthanum leads to an increase in the content of iso-paraffins from 69 to 76 wt % and a decrease in the content of aromatic hydrocarbons from 10.5 to 5.5 wt % and that of durene from 1.5 to 0.2 wt % in the products.     

Co oxidation with oxygen in the presence of hydrogen on CoO/CeO<Subscript>2</Subscript> and CuO/CoO/CeO<Subscript>2</Subscript> catalysts

The catalytic activity of the CoO/CeO₂ and CuO/CoO/CeO₂ systems in selective CO oxidation in the presence of hydrogen at 20–450°C ([CuO] = 1.0–2.5%, [CoO] = 1.0–7.0%) is reported. The maximum CO conversion (X) decreases in the following order: CuO/CoO/CeO₂ (X = 98–99%, T = 140–170°C) > CoO/CeO₂ (X = 67–84%, T = 230–240°C) > CeO₂ (X = 34%, T = 350°C). TPD, TPR, and EPR experiments have demonstrated that the high activity of CuO/CoO/CeO₂ is due to the strong interaction of the supported copper and cobalt oxides with cerium dioxide, which yields Cu-Co-Ce-O clusters on the surface. The carbonyl group in the complexes Co^δ+-CO and Cu⁺-CO is oxidized by oxygen of the Cu-Co-Ce-O clusters at 140–160°C and by oxygen of the Co-Ce-O clusters at 240°C. The decrease in the activity of the catalysts at high temperatures is due to the fact that hydrogen reduces the clusters on which CO oxidation takes place, yielding Co⁰ and Cu⁰ particles, which are inactive in CO oxidation. The hydrogenation of CO into methane at high temperatures is due to the appearance of Co⁰ particles in the catalysts.     

Activity of catalysts in the synthesis of dimethyl sulfide from dimethyl disulfide

Dimethyl disulfide conversion at T = 190–350°C over catalysts containing acid and basic sites is reported. The products of this reaction are dimethyl sulfide, methanethiol, hydrogen sulfide, carbon disulfide, methane, and ethylene. At 190°C, these products form via parallel reactions. At higher temperature of up to 350°C, dimethyl sulfide can form by the condensation of the resulting methanethiol. The strong basic sites of the catalysts are uninvolved in dimethyl sulfide formation. Over catalysts whose surface has only strong protonic or strong Lewis acid sites, dimethyl sulfide formation does take place, but slowly and nonselectively. The highest dimethyl sulfide formation activity and selectivity are shown by catalysts having medium-strength basic sites along with strong protonic and strong Lewis acid sites.     

One-Pot Synthesis of Secondary Amines from Nitroarenes and Aldehydes on Supported Copper Catalysts in a Flow Reactor: The Effect of the Support

The effect of the support on the properties of copper catalysts supported on γ-Al₂O₃, SiO₂, and TiO₂–SiO₂ with a ~5 wt % Cu content was studied in the one-pot synthesis of N-heptyl-p-toluidine from p-nitrotoluene and n-heptanal. The catalysts were characterized by elemental analysis, X-ray diffraction analysis, transmission electron microscopy, temperature-programmed reduction, and low-temperature nitrogen adsorption. The reaction was carried out in a flow reactor with the use of molecular hydrogen as a reducing agent. It was established that the nature of the support exerts a profound effect on the yield of the target secondary amine; in this case, 5%Cu/Al₂O₃ was found the most active catalyst. A combination of high catalyst activity in the hydrogenation of a nitro group to an amino group with the presence of acid sites, which facilitate imine formation as a result of the interaction of n-heptanal with p-toluidine, on the catalyst surface is necessary for reaching the greatest yield of N-heptyl-p-toluidine. The study of reaction mechanism on the 5%Cu/Al₂O₃ catalyst showed that p-nitrotoluene inhibits the hydrogenation of n-heptanal, and aldehyde hydrogenation into alcohol begins only after the conversion of the major portion of p-nitrotoluene as a result of the selective adsorption of the nitroarene under the conditions of the simultaneous presence of p-nitrotoluene and n-heptanal in the reaction mixture.     

State of palladium in palladium-aluminosilicate catalysts as studied by XPS and the catalytic activity of the catalysts in the deep oxidation of methane

Palladium catalysts based on Siralox and AS aluminosilicate supports for the deep oxidation of methane were studied. With the use of XRD analysis, it was found that they were heterophase systems consisting of an amorphous aluminosilicate and γ-Al₂O₃ stabilized against agglomeration. It was found that the catalytic activity of palladium-aluminosilicate catalysts in the deep oxidation of methane at 500°C depended on the support precalcination temperature. X-ray photoelectron spectroscopy (XPS) was used to study the states of the AS-30 aluminosilicate support calcined at 600, 800, or 1000°C and palladium supported on it. It was found that the action of an acid impregnation solution of palladium nitrate on the aluminosilicate calcined at 800°C resulted in a structural rearrangement of the aluminosilicate surface. This rearrangement resulted in the stabilization of both palladium oxide and palladium metal particles at surface defects and the incorporation of these particles into the aluminosilicate after catalyst calcination. As a result, an anomalous decrease in catalytic activity was observed in aluminosilicate samples calcined at 800°C. According to XPS data, palladium in the catalyst was stabilized in the following three phases: metal (E _b(Pd 3d _5/2) = 334.8 eV), oxide (E _b(Pd 3d _5/2) = 336.8 eV), and “interaction” (E _b(Pd 3d _5/2) = 335.8 eV) phases. The ratio between these phases depended on support and catalyst calcination temperatures. The interaction phase, which consisted of PdO_x clusters stabilized in the aluminosilicate structure, was responsible for the retention of activity after calcination at high temperatures (800°C). Based on an analysis of XPS data, it was hypothesized that palladium in the interaction phase occurred in a charged state with the formal charge on the Pd atom close to 1 + (δ+ phase).     

Sb modified Fe–Mn/TiO<Subscript>2</Subscript> catalyst for the reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> with NH<Subscript>3</Subscript> at low temperatures

Manganese-based catalysts have attracted much attention due to their excellent performance for NO reduction with NH₃ (NH₃-SCR) at low temperatures. In the current study, the novel metal Sb was modified into Mn/TiO₂ and Fe–Mn/TiO₂, and the NO _x conversion was compared with those of Mn/TiO₂ and Fe–Mn/TiO₂ catalysts to investigate the effect of the Sb. The NO _x reduction activities of the catalysts were evaluated in the temperature range of 100–250 °C at a space velocity of 60,000 h^?1. The physicochemical properties of all the catalysts were characterized by Brunauer–Emmett–Teller surface area, temperature-programmed desorption of ammonia, temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Interestingly, the Sb-promoted Mn-based catalysts showed significantly higher NO _x conversion than the other catalysts with or without 6 vol% of H₂O. The high performance of the Sb-modified catalysts could be related to the increase of acid sites and redox properties.     

Catalytic activity of H-forms of zeolites in the isomerization of supercritical <Emphasis Type="Italic">n</Emphasis>-pentane and their physicochemical properties

The acidic properties of the H-forms of zeolites ZSM-5, Beta, Y, and mordenite are studied by diffuse reflectance IR spectroscopy using n-pentane as a probe molecule. The decreasing order of Brønsted acid site strengths is constructed. The isopentane selectivity in n-pentane isomerization under supercritical conditions (260°C, 130 atm) increases in the order H-ZSM-5 < H-Beta < H-mordenite(11) ≈ H-Y with decreasing strength of Brønsted sites. Catalytic data are analyzed jointly with the results of physicochemical studies of H-mordenite (temperature-programmed ammonia desorption, benzene adsorption, and IR spectroscopy). Under the supercritical conditions, the conversion of n-pentane on mordenite is determined by the total acidity of the zeolite and also by the accessibility of the acid sites inside the zeolite channels to the reactant.     

Mechanism of the decomposition of the surface oxide film on polycrystalline palladium

The decomposition of thin surface oxide films on polycrystalline palladium Pd(poly) at 500–1300 K was investigated by mathematical modeling. This process was analyzed in terms of a model including O₂ desorption from the chemisorbed oxygen layer (O_ads) and the passage of oxygen inserted under the surface layer of the metal (O_abs) and oxygen dissolved in metal subsurface layers (O_dis) to the surface. O₂ desorption was modeled on a surface with a square lattice of adsorption sites, with account taken of the energy of the lateral repulsive interactions between adjacent O_ads atoms (ε_aa). At ε_aa = 10 kJ/mol and when the activation energy of O₂ desorption for a chemisorbed-oxygen surface coverage of θ ≈ 0 is E_des⁰ = 230 kJ/mol, the calculated spectra are in agreement with the oxygen temperature-programmed desorption (TPD) spectra obtained for Pd(poly) at θ ≤ 0.5. The passage of O_abs and O_dis atoms to the surface was calculated using a first-order equation, with account taken of the activation energy for these atoms coming out to the surface (E₂ and E₃, respectively). As the oxide film is heated, O₂ desorption is accompanied by the passage of O_abs and then O_dis to the surface, which leads to an increase in the O_ads surface coverage and, accordingly, to a buildup of lateral surroundings in the adsorbed layer. Owing to this fact and to the repulsive interactions between O_ads atoms, the bonds between O_ads and the surface weaken and E_des decreases. As a consequence, the O₂ desorption rate increases and a low-temperature peak with T_max ≈ 710 K, which is due to the passage of O_abs atoms to the surface, and then a high-temperature peak with T_max ≈ 770 K, which is due to the passage of O_dis atoms to the surface, appear in the TPD spectrum. At ε_aa = 10 kJ/mol, E_des⁰ = 230 kJ/mol, E₂ = 145 kJ/mol, and E₃ = 160 kJ/mol and when the number of inserted oxygen monolayers is θ_abs ≤ 0.3 and the number of oxygen monolayers dissolved in subsurface layers is θ_dis ≤ 10, the TPD spectra calculated for the given model are in agreement with the O₂ TPD spectra that are observed for Pd(poly) and are due to the decomposition of surface oxide films.     

Conversion of Dimethyl Ether to a Mixture of Liquid Hydrocarbons with Increased Triptane Content

The influence of the structural type and of the textural and acid properties of the zeolite on the catalyst selectivity in synthesis of a mixture of liquid hydrocarbons with increased content of isoalkanes from dimethyl ether was examined. The synthesis of liquid hydrocarbons enriched in triptane in the course of gasoline production from CO and H₂ via dimethyl ether in the presence of La-H-Y zeolite was performed for the first time. Excess hydrogen in the system and relatively short contact time of the catalyst with the feed favor an increase in the triptane yield. Additional modification with palladium leads to optimization of the acid properties of the La-H-Y zeolite and, as a consequence, to an increase in the triptane content of the gasoline from 2.0 to 9.4 wt %.

     

Synergetic effect in PdAu/CeO<Subscript>2</Subscript> catalysts for the low-temperature oxidation of CO

Gold-palladium catalysts supported on cerium oxide were synthesized with the double complex salts. X-ray photoelectron spectroscopy (XPS) and other physicochemical methods (TEM, TPR) were used to demonstrate that synthesis of highly active palladium catalysts requires the oxidative treatment stimulating the formation of a catalytically active surface solid solution Pd _x Ce_1?x O₂, which is responsible for the lowtemperature activity (LTA) in the reaction CO + O₂. In the case of gold catalysts, active sites for the lowtemperature oxidation of CO are represented by gold nanoparticles and its cationic interface species. Simultaneous deposition of two metals increases the catalyst LTA due to interaction of both gold and palladium with the support surface to form a Pd_1?x CexO₂ solid solution and cationic interface species of palladium and gold on the boundary of Pd-Au alloy particles anchored on the solid solution surface.     

Gas-phase carbonylation of dimethoxymethane to methyl methoxyacetate over the Cs<Subscript>2.5</Subscript>H<Subscript>0.5</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> catalyst

It has been shown that cesium hydrogen phosphotungstate Cs_2.5H_0.5PW₁₂O₄₀ is a promising catalyst of the gas-phase carbonylation of dimethoxymethane (DMM) to methyl methoxyacetate (MMA). This catalyst provided the MMA selectivity and yield of 54% and 40%, respectively, under mild experimental conditions: T = 110°C, P = 10 bar, and GHSV = 6000 h^–1 for DMM/CO/Ar = 4/76/20 mol/mol/mol. The carbonylation of DMM to MMA is accompanied by side reactions of DMM disproportionation into dimethyl ether (DME) and methyl formate (MF), as well as by secondary side reactions of MF decomposition into methanol and CO and methanol dehydration into DME.     

Influence of sulfation conditions on the acidic and catalytic properties of sulfated alumina in isobutane alkylation with butylenes and <Emphasis Type="Italic">n</Emphasis>-pentane isomerization

The influence of the sulfation parameters (the source and concentration of sulfate ions) and the calcination temperature on the acidic and catalytic properties of sulfated alumina in the alkylation of isobutane with butylenes and n-pentane isomerization was studied. IR spectroscopy of adsorbed probe molecules and temperature-programmed desorption of ammonia were used to characterize the acidic properties of the catalysts. An increase in the content of sulfate groups to the value corresponding to a formal value of the monolayer capacity increases the activity of alkylation and the concentration of strong Brönsted sites. The dependence of the stability of activity in alkylation on the sulfate group concentration is extreme with a maximum at the concentration close to the monolayer capacity. It was concluded from the IR spectroscopic data that the decrease in the stability of activity with the further increase in the content of sulfate groups is due to an increase in the concentration of strong Lewis sites and/or an increase in the surface density of strong Brönsted sites. The absence of the correlation between the catalytic behavior of sulfated alumina samples in n-pentane isomerization and acidity indicates that paraffin activation on these samples occurs via the non-acidic mechanism.     

Dependence of the properties of Ce-Zr-Y-La-M-O systems on synthetic conditions and on the nature of the transition metal M (Mn,Fe, Co)

The effects of synthetic conditions, component ratios, and the nature of the transition metal on the physicochemical and catalytic properties of Ce-Zr-Y-La-M-O (M = Mn, Fe, Co) systems are studied. The Ce-Zr-Y-La-M-O samples precipitated at ～23°C and calcined at 600°C are single-phase and are solid solutions with a fluorite structure, which persists upon calcination at 1150°C. The Ce-Zr-Y-La-Fe(Co)-O samples precipitated at 70°C and calcined at 1150°C consist of two solid solutions, one cubic, and the other tetragonal. The specific surface area (S _sp) of the samples precipitated at ～23°C and calcined at 600°C increases in the order Ce-Zr-Y-La-O < Ce-Zr-Y-La-Mn-O < Ce-Zr-Y-La-Co-O ≈ Ce-Zr-Y-La-Fe-O. The specific surface area of the samples precipitated at 70°C is independent of M and is ～110 m²/g. Calcination at 1150°C reduces S _sp approximately by two orders of magnitude. The TPR of the unpromoted systems in H₂ proceeds in two steps at 600–650 and 750–840°C. The introduction of M decreases the reduction temperatures and gives rise to a lower temperature peak between 150 and 300°C. The most effective promoter is cobalt. The fluorite-type catalysts containing no noble metal are active in NO reduction (X _NO ≈ 100%) at T _react = 400–450°C. The cobalt-containing catalysts are the most active in the oxidation of CO (X _max = 28%) and hydrocarbons (X _max = 4.3%).     

Monofluoro-substituted azomethine ylides in fluorocarbene reactions with imines. Synthesis and transformations of monofluoroaziridines

N-Arylmethylene and N-benzhydrylideneamines react with fluorocarbene yielding fluoro-substituted azomethine ylides that undergo 1,3-π-cyclization into aziridines. Generation of fluoroylides in the presence of dipolarophiles (dimethyl maleate or dimethyl acetylenedicarboxylate) led to the reaction of 1,3-dipolar cycloaddition resulting in substituted 2-pyrrolines or pyrroles. 2-Fluoroaziridines, products of N-alkyl-N-benzhydrylideneamines 1,3-π-cyclization, in the presence of acid catalysts suffer isomerization into α-fluoroimines and 1,3-disubstituted indoles.     

Hetero-diels–alder reaction of 5-ylidene-4-sulfanylidene-1,3-thiazolidin-2-ones with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-bis(methoxycarbonyl)-1,4-benzoquinone diimine

Hetero-Diels–Alder reaction of 5-(propan-2-ylidene)-4-sulfanylidene-1,3-thiazolidin-2-one with N,N′-bis(methoxycarbonyl)-1,4-benzoquinone diimine in boiling toluene afforded 87% of dimethyl 9,9-dimethyl-2-oxo-8a,9-dihydro-2H-thiochromeno[2,3-d][1,3]thiazole-5,8(3H,4aH)-diylidenedicarbamate. Analogous reactions of 5-benzylidene-, 5-{[4-(dimethylamino)phenyl]methylidene}-, and 5-[(2-hydroxyphenyl)-methylidene]-4-sulfanylidene-1,3-thiazolidin-2-ones led to the formation of the corresponding dimethyl 9-aryl-2-oxo-3,9-dihydro-2H-thiochromeno[2,3-d][1,3]thiazole-5,8-diyldicarbamates in 64–82% yield.