Hydrogenation of carbon monoxide on platinum metals

Together with methane, methanol is the main product of the hydrogenation of CO in the presence of platinum, palladium, and iridium, applied to Y-Al₂O₃, at atmospheric pressure and temperatures of 473–573 K. Dimethyl ether is also formed on platinum and palladium, while small amounts of ethanol and acetaldehyde are formed on iridium. The hydrogenation of CO in the presence of Rh and Ru leads to the formation of normal C₁-C₅ alcohols and C₂-C₅ aldehydes. Reduction of the energy of the metal-carbon bond in the platinum metals (Pd, Ir, Pt, Rh, Ru) increases their specific catalytic activity with respect to the formation of methane and oxygenated organic compounds, and increases the selectivity for higher alcohols and aldehydes.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 75–81, January–February, 1988.     

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH₄–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH₄ and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C₃–C₅ hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H₂ reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H₂ reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.     

Synthesis and study of 4-aminopyrazolones (5)

Some 4-N-thioureido- and -ureido derivatives are synthesized by reacting 1-phenyl-3-methyl-4-aminopyrazolone(5) hydrochloride at 40–50°, in alcohol solution, with potassium thiocyanate in the presence of sodium acetate plus carbon disulfide, phenylisothiocyanate, and hexamethylenediisocyanate. Acetylation of 1-phenyl-3-methyl-4-aminopyrazolone(5) with C₁–C₈ aliphatic carboxylic acids takes place under more drastic conditions at 100–150°, to give the corresponding 1-phenyl-3-methyl-4-acylaminopyrazolones(5), isolated in 40–60% yield. The UV spectra of the compounds studied are investigated.For Part I, see [1].     

High-Temperature Oxidation of Methane by Supported Lead Oxide

The kinetics of the reduction of PbO supported on Al₂O₃by methane is studied in the temperature range 760–927°C. The reaction order with respect to methane is equal to unity and the apparent activation energy is 40 kcal/mol. When the extent of PbO reduction is 0.5–0.6, the selectivity of methane conversion changes drastically: only CO₂is formed at lower extents of reduction, whereas CO is the main product at higher extents.     

Reduction of nitrobenzene to aniline with carbon monoxide and water

Modified catalyst systems composed of palladium or its chloride and co-catalysts such as FeCl₃, Fe₂O₃, metallic Fe-powder, metallic Fe-wire net, iodine, pyridine or aniline, applied in the reduction of nitrobenzene to aniline in the presence of carbon monoxide and water are described. The reaction proceeds at 150–180 °C and 2.5–7 MPa gauge pressure. After 1–7 h the reaction was complete, reaching nitrobenzene conversions of 98–100%. Selectivity of the reaction with respect to aniline was also 100%.     

Solubility of methane in aqueous solutions of triethylenediamine

The solubilities of methane were measured in water and aqueous solutions of triethylenediamine (TED), triethylenediamine hydrochloride (TED·HCl), and HCl at several concentrations up to 1M at 5° intervals from 5 to 25°C. Methane solubilities in solutions of TED·HCl and HCl are lower than those in water and decrease with increasing cosolute concentration. In contrast, the solubilities in TED solutions are greater than those in water and increase with increasing TED concentration. The order of methane solubilities at 25°C in water and in 0.5M aqueous solutions is TED>H₂O>HCl>TED·HCl with Ostwald coefficients of 3.57×10^–2, 3.44×10^–2, 3.26×10^–2, and 3.19×10^–2, respectively, and with an experimental precision of about ±0.2×10^–3. Thermodynamic functions for the transfer of methane from water to 0.25, 0.50, and 0.75M aqueous solutions have been calculated on the molar concentration scale. The free energies of transfer are compared with previous results for methane in aqueous solutions of tetraalkylammonium halides.     

Methane conversion by an air microwave plasma

Activation of methane is carried out by means of an air microwave plasma (2.45 GHz). The experiments cover the absorbed microwave power range 350–650 W (20–50 W cm³ with 17–62%, of methane in the gas mixture, with pressures of 10–66 mbar and flow rates of 140700 ml min¹. Methane, dioxygen, and dinitrogen consumptions as well as C₂ hydrocarbons, carbon monoxide, and dihydrogen yields are analyzed hr gas chromatography. The distance of methane addition from the end of the discharge plays an important role in the composition and the concentration of the products obtained. This distance mainly determines the energy concentrated in the active species of the plasma when they react with methane. A kinetic mechanism jar the activation and decay of inethane and for the formation of C₂ hydrocarbons and carbon monoxide is discussed based on the experimental results and kinetic data in the literature.     

High-Sensitivity Determination of Hydrocarbon Impurities in Arsine by Reaction Gas Chromatography

It is shown that the results of determining methane in high-purity arsine by reaction gas chromatography can be overestimated by more than two orders of magnitude. This overestimation is caused by the formation of methane as a side product of the reaction. Cryogenic preconcentration at the injection stage is proposed to improve the accuracy of determination of methane, and the cryofocusing of impurity hydrocarbons is proposed to improve separation. Detection limits of (3–10) × 10^–6 vol % are achieved for C₁–C₅ hydrocarbons.     

Oxygen States in Oxides with a Perovskite Structure and Their Catalytic Activity in Complete Oxidation Reactions: System La1 – x Ca x FeO3 – y (x = 0–1)

Oxygen states in the La_{1 – x} Ca _x FeO_{3 – y} perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH₄ oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La_{1 – x} Ca _x FeO_{3 – y} series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La_{1 – x} Ca _x FeO_{3 – y} samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.     

Peroxide compounds of niobium

Summary 1. A study of the reaction of sodium and potassium metaniobates with hydrogen peroxide at 0° showed that for low H₂O₂ concentrations (3–6%) peroxide compounds of niobium are formed Na(K)NbO₄· nH₂O (n=1.5–3.5). With high H₂O₂ concentrations (10–54%) the compounds formed are not those described in the literature but more soluble peroxide compounds of the perhydrate type Na(K)NbO₄-nH₂O₂· mH₂O (n=1.3–1.5; m =1.5-3), rather unstable at 0°.At –10° the perhydrates of permetaniobates form in a more stable form and with a higher content of active oxygen (11–12.3%); they were separated and studied in the solid state.     

Influence of added water on pathways and efficiency of photocatalytic reactions in ethanol solutions of titanium tetrachloride

Electronic spectroscopy, ESR, and gas-liquid chromatography have been used in studying the action of light with =254 nm on ethanol-water solutions of titanium tetrachloride. It has been established that, in the course of irradiation, a photocatalytic process develops with the participation of coordination compounds of titanium(IV) and (III), resulting in oxidation and breakdown of the ethanol to form acetaldehyde, methane, ethane, ethyl chloride, and molecular hydrogen. In the presence of small amounts of added water (up to 0.5 M), the efficiency of CH₄ and C₂H₇ formation is much lower but the yield of H₂ is higher, in comparison with the yields of these products in absolute ethanol. With further increases in the water concentration, the rates of formation of methane, ethane, and acetaldehyde increase. The maximum quantum yields () are as follows: (CH₄)=1.8 · 10^–4 and (C₂H₆)=1 · 10^–3 in absolute ethanol; (CH₃CHO)= 1.6·10^–2 in ethanol with the addition of 6.0 M H₂O; (H₂)=6.7·10^–3 in solutions containing 0.5 M H₂O. The observed differences in the product yields are explained by a change in the composition and structure of the titanium compounds that act as the photocatalyst, a change that takes place when the water concentration is varied. A mechanism is proposed for these reactions.Translated from Teoreticheskaya i Éksperimentai'naya Khimiya, Vol. 22, No. 1, pp. 51–58, January–February, 1986.     

Retention of 1,ω-bis-(dialkylamino)-polysulphides and related compounds in reversed-phase HPLC

Summary The reaction of secondary amines R₂NH with disulfur dichloride S₂Cl₂ in dichloro methane yields mixtures of bis-dialkylamino polysulphides R₂N–S_n–NR₂ with sulphur chain lengths varying from n_s=2 to 14. The S chains are believed to be non-branched. The compounds form homologous series in each of which sulphur atoms give a constant contribution to retention. The sulphur retention index depends slightly on the carbon number in the terminal alkyl groups R. The presence of nitrogen lowers retention. The index increment of N is ca. –160 units, which is distinctly less negative than values found in alkylamines.     

Reasons for increased selectivity of catalysts for partial oxidation of methane using N2O as oxidizing agent

It was found that the increase in the selectivity of catalysts of the partial oxidation of methane by nitrous oxide (compared with the oxidation by molecular oxygen) is due to the participation in the reaction of adsorbed oxygen anion radicals O^·–, with which the differences in the reactivity of methane and its mild oxidation products are leveled out. With O₂, the reactivity of methane is much lower than that of formaldehyde and methanol and, as a result, the selectivity is low, and a postoxidation of the partial oxidation products rapidly takes place. The formation of O^·– is promoted by low concentrations of metal ions in the catalyst. The influence of the geometrical factor is thus also manifested: at low concentrations of the metal ions (M), the surface postoxidation of the adsorbed formaldehyde (the nonlinear stage) is hindered, which favors increase in the selectivity with respect to HCHO.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 727–729, November–December, 1988.     

Partial oxidation and oxidative condensation of methane with the participation of N2O on a V2O5/SiO2 catalyst

The catalytic reaction of CH₄, with N₂O at 773–823 K on a V₂O₅/SiO₂ catalyst affords products of the partial oxidation (HCHO and CH₃OH), exhaustive oxidation (CO), and oxidative condensation (C₂H₅OH and CH₃CHO) of methane. A mechanism is proposed for the complex reaction, including the intermediate compounds V⁵⁺O and V⁴⁺CH₃OH as common intermediates for all the routes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 5, pp. 641–646, September–October, 1987.     

The effect of the nature of a modifying additive (Pt,Zn, Ga) on the activity of oxide and zeolite catalysts in ethane dehydrogenation and aromatization

The catalytic properties of Pt, Zn, and Ga deposited on supports of various natures (Al₂O₃, SiO₂, NaZSM, and HZSM) in the dehydrogenation and aromatization of ethane were investigated. Pt-containing catalysts are the most active in the conversion of ethane: the selectivity with respect to ethylene is 25–87 % depending on the nature of the support. In the presence of Zn- and Ga-containing catalysts the yield of ethylene is 2–3 times lower than with Pt-catalysts. With HZSM modified by Pt, Zn, or Ga aromatic hydrocarbons (ArH) and methane are the main products of ethane transformation. Ga/HZSM is the most efficient catalyst of the aromatization of ethane under the conditions studied (550 °C, 120 h^–1).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 606–609, April, 1994.     

Formation of C1–C5 Hydrocarbons from CCl4 in the Presence of Carbon-Supported Palladium Catalysts

Along with hydrodechlorination, the formation of C₁ and higher hydrocarbons takes place in a flow system in the presence of catalysts containing 0.5–5.0% Pd supported on a Sibunit carbon carrier at 150–230°C. In the entire range of conditions examined, the reaction products are primarily methane, C₂–C₄ hydrocarbon fractions, and C₅ traces. The catalysts are stable in operation, and a high conversion of CCl₄ was retained for a long time interval. The nonselective formation of linear and branched hydrocarbons is indicative of a radical mechanism of the process.     

Cesium dimethyltetrachloroplatinate,a complex of dimethylplatinum(IV). Synthesis and some reductive elimination reactions involving the monomethylplatinum(II) complex as an intermediate

The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs₂PtMe₂Cl₄, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl^–, Br^–, I^–, and PtCl₄ ^2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and Pt^IIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na₂PtCl₆) it gives rise to the Pt^IVMe species. The kinetics of decomposition of Cs₂PtMe₂Cl₄ in aqueous HCl-KCl systems (2M or 3M in Cl^–; [Pt^IVMe₂][Cl^–]) were studied. The reaction takes place as anS _N 2 attack of X^– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe₂Cl₃(H₂O)]^– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993.     

(2-Chlorovinyl)chlorocarbenes: Generation and reactions with alkenes

The treatment of Z-1,1,3-trichloro-4,4-dimethyl-2-pentene (Ia) with t-C₄H₉OK in boiling hexane or benzene gave rise to (Z-2-chloro-3,3-dimethyl-1-butenyl)chlorocarbene (IVa), which reacted with alkenes to give the cyclopropane derivatives (V) in 44–57% yields. Dichloro-(2-chloro-1-alkenyl)methanes (Ib-d), which have a hydrogen atom at the C₃ position of the alkenyl substituent, were also used as carbene precursors under these conditions. These compounds gave rise to mixtures of the cyclopropanes (VI)–(VIII) (obtained in up to 57% yields) and the dienes (IX)–(XI) (yields up to 54%). The reaction of cis-2-butene with (2-chloro-1-cyclopentenyl)chlorocarbene (IVd) was found to be completely stereospecific, indicating that this carbene exists in a singlet ground state.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2552–2558, November, 1991.     

Thermogravimetric studies of the synthesis of cas from gypsum, CaSo4·2H2O and phosphogypsum

Using a heating rate of 2°C min^–1, CaS reacts with oxygen in air from 700°C to form CaSO₄, with a complete conversion at 1100°C. Synthesis of CaS from the reaction between CaSO₄ containing compounds and carbon compounds in air would not be possible, as the carbon reacts from 600°C with oxygen in the air to give CO₂. Heating stoichiometric amounts of carbon and pure CaSO₄, synthetic gypsum or phosphogypsum in a nitrogen atmosphere, results in the formation of CaS from 850°C. Using a heating rate of 10°C min^–1, the formation of CaS is completed at 1080°C. Addition of 5% Fe₂O₃ as a catalyst lowers the starting temperature of the reaction to 750°C. Activation energy values at different fraction reaction values () differ between 340 and 400 kJ mol^–1. The relationship between the activation energy values and conversion () indicates that the reaction proceeds via multiple steps.     

Conversion of methane/carbon dioxide mixtures on vermiculite

A study has been made of the conversion of methane/carbon dioxide mixtures on a vermiculite catalyst of composition 22MgO·22SiO₂·5Al₂O₃·Fe₂O₃·4OH₂O. It has been established that at 900–970°C with molar ratios of CO₂/CH₄ of 0.5–1.5 and contact times of 10.5–21 sec the conversion proceeds quantitatively but the main products, H₂ and CO, are formed in varying proportions. An explanation has been given for the effect of the process parameters on the conversion and selectivity.Chernogolovka Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1511–1515, July, 1992.