Effect of structural,redox and acid characteristics of M<Subscript>x</Subscript>O<Subscript>y</Subscript>/ZrO<Subscript>2</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) (M-Mn,Co, Cr) oxide nanocomposites on their catalytic properties in the deep oxidation of methane

Alumina-and zirconia-manganese catalysts for the deep oxidation of methane were studied by X-ray phase analysis, temperature-programmed hydrogen reduction, and IR spectroscopy. The most active catalyst has the optimal combination of dimensional, redox, and acid characteristics. The zirconia-manganese catalysts formed on the surface of a kaolin-aerosil honeycomb matrix provides for 80–100% conversion of methane to CO₂ at 690–750 °C. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 367–372, November–December, 2007.     

Mesophilic Digestion Kinetics of Manure Slurry

Anaerobic digestion kinetics study of cow manure was performed at 35°C in bench-scale gas-lift digesters (3.78 l working volume) at eight different volatile solids (VS) loading rates in the range of 1.11–5.87 g l⁻¹ day⁻¹. The digesters produced methane at the rates of 0.44–1.18 l l⁻¹ day⁻¹, and the methane content of the biogas was found to increase with longer hydraulic retention time (HRT). Based on the experimental observations, the ultimate methane yield and the specific methane productivity were estimated to be 0.42 l CH₄ (g VS loaded)^–1 and 0.45 l CH₄ (g VS consumed)^–1, respectively. Total and dissolved chemical oxygen demand (COD) consumptions were calculated to be 59–17% and 78–43% at 24.4–4.6 days HRTs, respectively. Maximum concentration of volatile fatty acids in the effluent was observed as 0.7 g l^–1 at 4.6 days HRT, while it was below detection limit at HRTs longer than 11 days. The observed methane production rate did not compare well with the predictions of Chen and Hashimoto’s [1] and Hill’s [2] models using their recommended kinetic parameters. However, under the studied experimental conditions, the predictions of Chen and Hashimoto’s [1] model compared better to the observed data than that of Hill’s [2] model. The nonlinear regression analysis of the experimental data was performed using a derived methane production rate model, for a completely mixed anaerobic digester, involving Contois kinetics [3] with endogenous decay. The best fit values for the maximum specific growth rate (μ _m) and dimensionless kinetic parameter (K) were estimated as 0.43 day^–1 and 0.89, respectively. The experimental data were found to be within 95% confidence interval of the prediction of the derived methane production rate model with the sum of residual squared error as 0.02.     

Kinetics of nonstationary condensation of methane on a perovskite catalyst

The interaction of methane with the oxidized surface of the KNaSrCoO_3−x is first order in methane with respect to formation of higher hydrocarbons and zero order with respect to formation of CO₂. At the initial stage the rate of formation of the reaction products is independent of the amount of oxygen from the catalyst consumed (up to 5–7 monolayers of oxygen), after which the rate of the reaction falls linearly. The overall amount of oxygen consumed in the reaction reaches 30 monolayers. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 182–187, May–June, 2000.     

Conversion of natural gas to C2 hydrocarbons through dielectric-barrier discharge plasma catalysis

The experiments are carried out in the system of continuous flow reactors with dielectric-barrier discharge (DBD) for studies on the conversion of natural gas to C₂ hydrocarbons through plasma catalysis under the atmosphere pressure and room temperature. The influence of discharge frequency, structure of electrode, discharge voltage, number of electrode, ratio of H₂/CH₄, flow rate and catalyst on conversion of methane and selectivity of C₂ hydrocarbons are investigated. At the same time, the reaction process is investigated. Higher conversion of methane and selectivity of C₂ hydrocarbons are achieved and deposited carbons are eliminated by proper choice of parameters. The appropriate operation parameters in dielectric-barrier discharge plasma field are that the supply voltage is 20–40 kV (8.4–40 W), the frequency of power supply is 20 kHz, the structure of (b) electrode is suitable, and the flow of methane is 20–60 mL · min⁻¹. The conversion of methane can reach 45%, the selectivity of C₂ hydrocarbons is 76%, and the total selectivity of C₂ hydrocarbons and C₃ hydrocarbons is nearly 100%. The conversion of methane increases with the increase of voltage and decreases with the flow of methane increase; the selectivity of C₂ hydrocarbons decreases with the increase of voltage and increases with the flow of methane increase. The selectivity of C₂ hydrocarbons is improved with catalyst for conversion of natural gas to C₂ hydrocarbons in plasma field. Methane molecule collision with radicals is mainly responsible for product formation.     

Effect of platinum,palladium and rhodium on the activity and sulfur resistance of catalysts based on ZrO<Subscript>2</Subscript> in the oxidative conversion of methane

A study was carried out on the effect of noble metals (Pd, Pt, and Rh) on the activity and sulfur resistance of a Cu-Ni-Ce oxide composite on yttrium-stabilized zirconium in the oxidation of methane by oxygen. The enhancement in activity in the deep oxidation of methane, which is greatest for the pallaldium sample, is related to the oxidation-reduction properties of the composites. The platinum catalyst displayed greatest sulfur resistance, which may be attributed to the mechanism for the oxidation of SO₂ on platinum-group metals. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 170–174, May–June, 2008.     

Activities of δ-Al2O3-supported bimetallic Pt?NiO and Co?NiO catalysts for methane autoreforming: Oxidation studies

The methane oxidation activities of Pt−NiO and Co−NiO bimetallic catalysts have been investigated as part of a larger research program on the autothermal reforming of methane (combined methane oxidation and steam reforming) in a fluidized bed reactor. Experiments at atmospheric pressure and 783–1023 K for both catalysts showed that the reaction was more selective towards H₂ production at CH₄∶O₂ ratios greater than unity. Light-off temperature increased with decreasing CH₄∶O₂ ratios, but increase in gas velocity (beyond minimum fluidization) increased the light-off temperature. Co−NiO was as promising as the more expensive Pt−NiO catalyst for the oxidation.     

Influence of the composition of composites based on Y-and Sc-stabilized zirconium dioxide on catalytic properties in the oxidative conversion of methane

The effect of the composition of composites based on Y-and Sc-stabilized zirconium dioxide doped with CeO₂ and transition metal (Cu, Co, Ni) oxides on catalytic properties in the oxidative conversion of methane was studied. The activity of the composites correlated with the quantity and mobility of oxygen in them. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 184–188, May–June, 2006.     

Role of rare-earth element oxides in catalysts for the oxidative conversion of methane based on Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

It has been established that oxides of the rare-earth elements with moderate redox potentials (La₂O₃, CeO₂) increased the activity and working stability of Ni-Al₂O₃/cordierite catalysts in the reactions of deep and partial oxidation of methane. In the presence of the (NiO + La₂O₃ + Al₂O₃)/cordierite catalyst the process of carbon dioxide conversion of methane can be intensified by introduction of oxygen into the reaction gas mixture which decreases the temperature to achieve high conversion to 75–100 °C and has practically no effect on selectivity with respect to H₂. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 44, No. 6, pp. 359–364, November–December, 2008.     

Chain termination mechanism in the Fischer-Tropsch synthesis on a Co/SiO<Subscript>2</Subscript>Zr(IV) catalyst at elevated pressure

The mechanism for the formation of C₂₊ paraffins differs from the mechanism for the formation of methane. While methane is obtained due to hydrogenation of methyl groups, C₂₊ hydrocarbons are formed as the result of the conversion of alkyl intermediates into hydroalkene intermediates, which can decompose to give olefins or undergo hydrogenation to give saturated hydrocarbons. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 175–179, May–June, 2008.     

Nickel-copper-chromium catalyst for selective methane oxidation to synthesis gas at short residence times

Data on the selective oxidation of methane to synthesis gas on a 9% NiCuCr/2% Ce/(ϑ + α)-Al₂O₃ catalyst in dilute mixtures with Ar at short residence times (2–3 ms) are presented. The composition, structure, morphology, and adsorption properties of the catalyst with respect to oxygen and hydrogen before and after reaction were studied using XRD, BET, electron microscopy with electron microdiffraction, TPR, TPO, and TPD of oxygen and hydrogen. The following optimum conditions for the preparation and pretreatment of the catalyst for selective methane reduction were found: the incipient wetness impregnation of a support with aqueous nitrate solutions; drying; and heating in air at 873 and then at 1173 K (for 1 h at either temperature) followed by reduction with an H₂-Ar mixture at 1173 K for 1 h. At a residence time of 2–3 ms (space velocity to 1.5 × 10⁶ h⁻¹) and 1073–1173 K, the resulting catalyst afforded an 80–100% CH₄ conversion in mixtures with O₂ (CH₄/O₂ = 2: 1) diluted with argon (97.2–98.0%) to synthesis gas with H₂/CO = 2: 1. The selectivity of CO and H₂ formation was 99.6–100 and 99–100%, respectively; CO₂ was almost absent from the reaction products. The catalyst activity did not decrease for 56 h; carbon deposition was not observed. A possible mechanism of the direct oxidation of CH₄ to synthesis gas is considered.     

Influence of the composition of carriers based on ZrO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of cobalt-containing catalysts on the selective reduction of NO with methane

A series of cobalt-containing granulated and structured catalysts based on zirconium and aluminum oxides has been studied. The optimum composition of binary oxide samples (80% ZrO₂ − 20% Al₂O₃) for the selective reduction of nitrogen monoxide with methane (84% conversion of NO achieved at 320 °C) has been determined. The activity of the structured catalysts depends on both the composition of the secondary carrier (ZrO₂, Al₂O₃, and their mixture) and on the nature of the skeleton of the cellular structure (cordierite, kaolin-aerosil). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 237–241, July–August, 2007.     

Evaluation of La0.5Sr0.5FeO3 − δ membrane reactors for partial oxidation of methane

Dense planar and tubular oxygen separation membranes of La_0.5Sr_0.5FeO_{3 −  δ} were studied in the partial oxidation of methane to syngas process. The oxygen permeation properties were obtained from the analysis of the outlet gas and compared with the data calculated from conductivity measurements. For the planar reactor, the selectivity achieved 95% and the CH₄ conversion was 95–99% at 900 °C with pure methane. For the tubular reactor, the CO selectivity and CH₄ conversion were 90% and 100%, respectively, under the same conditions. In both cases, the H₂/CO ratio was 1.6–1.9. No degradation of membranes was observed after 250 h of operation.     

A method for increasing the surface area of perovskite-type oxides

A method based on hydrothermal treatments is described for increasing the surface area of sintered ABO₃-type perovskite oxides. Influence of hydrothermal treatments, such as water treatment at 125–300°C under autogeneous pressure and steam treatment at 350–800°C, to low surface area (or sintered) LaCoO₃ and LaMnO₃ perovskite oxides on their surface properties (viz. surface area, crystal size and morphology and surface La/(Co or Mn) ratio) and also catalytic activity in complete combustion of methane at different temperatures (450–600°C) has been thoroughly investigated. The hydrothermal treatments result in the activation of the perovskite oxides by increasing their surface area very markedly.     

On the Preparation of Ni–La Supported on Silica by Sol-gel Process via Propionates

Ni–La/SiO₂ catalysts were prepared by using a new metal organic precursor M(OC₃H₇)_n, dissolved in organic solvent, hydrolysed and finally condensed to form inorganic polymers containing M–O–M or M–(μOH)–M linkages. An optimal distribution of both the active phase ‘Ni’ and the promoter ‘La₂O₃’ was ensured by addition of their corresponding salts, previously dissolved in propionic acid, to a silica solution prior to gelation. After drying under vacuum the precursor was submitted to thermal treatment in air at 600°C with a heating rate of 1°C min^–1. The precursors and the corresponding catalysts were characterised by various techniques (TG-DTA, XRD, FTIR, TEM, BET and porosimetry) and tested for methane dry reforming. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene and methane on hydrides of intermetallic compounds of lanthanum with nickel

Carbon nanofibers were synthesized by the pyrolysis of ethylene and methane on hydrides of intermetallides LaNi_nH_x (n = 2, 3, 5; x = 0.1–4). The influence of parameters of the synthesis (temperature and the ratio of gases in an Ar: H₂: C₂H₄ (CH₄) mixture) on the structure of nanofibers thus formed was studied. Hydrides of nickel intermetallides are more efficient catalytic systems than metallic nickel. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2210–2214, October, 2005.     

Influence of preparation method on the performance of Mn–Ce–O catalysts

Mn–Ce–O catalysts were prepared by the sol–gel method with different citric acid amounts in preparation. The catalysts were characterized by using BET, XRD, TPR, XPS and their catalytic activities in methane combustion were also investigated. Results showed that the surface area, Mn⁴⁺ and O_latt are responsible for the high catalytic activity of Mn–Ce–O catalysts.     

Direct Oxidation of Methane to Methanol Over Cu-Based Catalyst in an AC Dielectric Barrier Discharge

In this paper, the conversion of methane to methanol on CuO/Al₂O₃ and Mo–CuO/Al₂O₃ catalysts in a plasma reactor was tested. A comparison between catalytic and plasma-catalytic systems had been made in tested temperature range of 50–300°C. Experimental results showed that plasma-catalytic system demonstrated a much better methane conversion than catalytic system in tested temperature range and Mo–CuO/Al₂O₃ revealed a higher catalytic activity than CuO/Al₂O₃ for methanol synthesis. Furthermore, an Arrhenius plot was made in order to deduce the mechanism of plasma activation, which revealed that the presence of plasma decreased the activation energy for both catalysts. In the case of Mo-CuO/Al₂O₃ catalyst, the enhanced activity for methanol synthesis was assumed due to the oxygen vacancies on Mo–CuO/Al₂O₃ catalyst, which can utilize plasma-induced species to improve the catalytic efficiency.     

Dehydrocondensation of methane to higher hydrocarbons on bifunctional catalysts in the absence of oxidizing agents in the gas phase

A study was carried out on the effect of the chemical nature of M_xL_y on the activity and selectivity of bifunctional M_xL_y/zeolite catalysts, where M_xL_y are metal-like transition metal compounds, M is a metal atom (Co, Mo, or W), and L is a nonmetal atom (B or Si), in the dehydrocondensation of methane to give higher hydrocarbons in the absence of gas-phase oxidizing agents. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from éksperimental’naya i Teoreticheskaya Khimiya, Vol. 33, pp. 243–247, July–August, 1997.     

Carbon dioxide-methane mixture adsorption on activated carbon

In this work, we report new experimental data of pure and binary adsorption equilibria of carbon dioxide and methane on the activated carbon RB2 at 273 and 298 K. The pressure range studied were 0–3.5 MPa for pure gases and 0–0.1 MPa for mixtures. The combination of the generalized Dubinin model to describe the pure CO₂ and CH₄ isotherms with the IAST (Ideal Adsorbed Solution Theory) for the mixtures provide a method for the calculation of the binary adsorption equilibria. This formulation predicts with acceptable accuracy the binary adsorption data and can easily be integrated in general dynamic simulation of PSA (pressure swing adsorption process) adsorption columns. It involves only three parameters, independent of the temperature, and directly determined with only one adsorption isotherm of CO₂.     

Catalytic activity of nanosized Co-Cu oxide systems in the deep oxidation of methane

The effect of the composition of nanosized catalysts, produced by thermal decomposition of Co(II) and Cu(II) formates deposited on ZrO₂, SBA-15, and MCM-41, on their activity in the deep oxidation of methane was investigated. It was shown that the activity of the catalyst depends on the nature of the support and on the Co/Cu ratio. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 41, No. 6, pp. 331–335, November–December, 2005.