Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO₂ catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO₂. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO₂ catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO₂ was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO₂, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO₂ reforming of ethane and the ODHE with CO₂. As a consequence, the synthesis gas produced from CO₂ reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO₂, thus increasing the selectivity of ethylene.     

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.     

Aromatization of Heptene-2 on Pt/Al2O3 Catalysts

Heptene-2 aromatization on Pt/Al₂O₃ in a pulse microcatalytic reactor has been studied under H₂ and N₂ atmosphere at temperatures between 330 to 500°C and at a total pressure of 4.0 kg/cm². Results showed that the production of only cracked products (mainly methane) from deep fragmentation of heptene-2 in H₂ sharply contrasts with the reaction in N₂ in which the catalyst showed aromatic selectivity with the production of methane, benzene and toluene. In H₂-N₂ mixtures, 75% H₂ was required to reduce the aromatization activity of the catalyst to zero. A test of the kinetic data using Sica's method [15] of pulse kinetic analysis suggests a first order in heptene-2 with an activation energy of 102.61 kJ/mol in N₂ and 124.71 kJ/mol in H₂. The difference in activation energies has been attributed to a difference in reaction mechanisms in both gases.     

Effect of synthesis solution pH of Co/γ-Al_2O_3 catalyst on its catalytic properties for methane conversion to syngas

The cobalt nanoparticles over γ-Al_2O_3 support were prepared via chemical reduction of CoCl_2·6H_2O using NaBH_4 with various values of pH in the range of 11. 92-13. 80. Synthesized catalysts were studied through X-ray diffraction( XRD),N_2 adsorption/desorption( BET),H_2-temperature programmed reduction( H_2-TPR),H_2-chemisorption,O_2 pulse titration and temperature programmed oxidation( TPO) methods. Obtained results exhibited the synthesis solution pH showed a significant influence on the activity and selectivity in partial oxidation of methane reaction. The methane conversion,CO selectivity and H_2 yield were enhanced by increasing of the synthesis solution pH. Compared to other catalysts,the catalyst that synthesized at pH of 13.80,showed a superior ability in syngas production with a H_2/CO ratio of near 2 and also a proper stability against deactivation during the partial oxidation of methane.     

Methanol Decomposition on Fe2O3 /MCM-48 Silica Catalyst

Fe₂O₃/MCM-48 silica samples are characterized by high catalytic activity and methane selectivity in methanol decomposition. The catalytically active phase is substantially changed by the reaction medium and/or hydrogen pretreatment.     

The influence of La2O3 and TiO2 on NiO/MgO/α-Al2O3

Summary The effect of La₂O₃ and TiO₂ on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al₂O₃ catalyst were studied in a simultaneous steam and CO₂ reforming of methane to syngas. La₂O₃ and TiO₂ were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively.     

Regioselective alkane oxygenation with H2O2 catalyzed by titanosilicalite TS-1

Titanosilicalite TS-1 catalyses oxidation of light (methane, ethane, propane and n-butane) and normal higher (hexane, heptane, octane and nonane) alkanes to give the corresponding isomeric alcohols and ketones. The oxidation of higher alkanes proceeds in many cases with a unique regioselectivity. Thus, in the reaction with n-heptane the CH₂ groups in position 3 exhibited a reactivity 2.5 times higher than those of the other methylene groups. This selectivity can be enhanced if hexan-3-ol is added to the reaction mixture, the 3-CH₂/2-CH₂ ratio becoming 10. It is assumed that the unusual selectivity in the oxidation of n-heptane (and other higher alkanes) is due to steric hindrance in the catalyst cavity. As a result, the catalytically active species situated on the catalyst walls can only easily react with certain methylenes of the alkane, which is adsorbed in the cavity taking U-shape (hairpin) conformations.     

Effect of CO2/CO Addition in Dehydroaromatization of Methane on Zeolite-Supported Mo and Re Catalysts Towards Hydrogen, Benzene and Naphthalene

High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO₂ or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO₂. The route from methane to aromatics and the formation process of active phase of catalyst were discussed.     

Atomically Dispersed Nickel Anchored on a Nitrogen-Doped Carbon/TiO2 Composite for Efficient and Selective Photocatalytic CH4 Oxidation to Oxygenates

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO₂ composite (Ni−NC/TiO₂) as a highly active and selective catalyst for photooxidation of CH₄ to C1 oxygenates with O₂ as the only oxidant. Ni−NC/TiO₂ exhibits a yield of C1 oxygenates of 198 μmol for 4 h with a selectivity of 93 %, exceeding that of most reported high-performance photocatalysts. Experimental and theoretical investigations suggest that the single-atom Ni−NC sites not only enhance the transfer of photogenerated electrons from TiO₂ to isolated Ni atoms but also dominantly facilitate the activation of O₂ to form the key intermediate ⋅OOH radicals, which synergistically lead to a substantial enhancement in both activity and selectivity.     

Effect of ceria loading on the carbon formation during low temperature methane steam reforming over a Ni/CeO2/ZrO2 catalyst

The characterization and catalytic activity of a Ni/CeO₂/ZrO₂ catalyst for methane steam reforming at 600°C were investigated. The addition of ceria increased the surface area and basicity of the catalysts. The redox reaction capability of the ceria increased the hydrogen yield and carbon monoxide selectivity, and inhibited carbon formation.     

Syngas production in a novel perovskite membrane reactor with co-feed of CO2

Partial oxidation of methane（POM） co-fed with CO₂ to syngas in a novel catalytic BaCo_0.6Fe_0.2Ta_0.2O_3-δ oxygen permeable membrane reactor was successfully reported.Adding CO₂ to the partial oxidation of methane reaction not only alters the ratio of CO/H₂,but also increases the oxygen permeation flux and CH₄ conversion.Around 96%CH₄ conversion with more than 93%CO₂ conversion and 100%CO selectivity is achieved,which shows an excellent reaction performance.A steady oxygen permeation flux of 15 mL/（cm² min） is obtained during the 100-h operation,which shows good stability as well.     

Effect of CO2/CO Addition in Dehydroaromatization of Methane on Zeolite-Supported Mo and Re Catalysts Towards Hydrogen, Benzene and Naphthalene

High activity and high formation selectivity for aromatics in the dehydrocondensation reaction of methane were realized only on selected catalysts. The requisites of a metal and a zeolite support as the selected catalyst were described. However, the catalytic activity steadily declined even on the selected catalysts with time on stream because of coke accumulation. A stable catalytic activity was obtained when CO₂ or CO was added into methane feed due to effective removal of coke from the catalyst surface by CO or CO₂. The route from methane to aromatics and the formation process of active phase of catalyst were discussed.     

Low-temperature utilization of CO2 and CH4 by combining partial oxidation with reforming of methane over Ru-based catalysts

Combination of partial oxidation of methane (POM) with carbon dioxide reforming of methane (CRM) has been studied over Ru-based catalysts at 550 ℃. POM, CRM and combined reaction were performed over 8wt%Ru/γ-Al2O3 and the results show that both POM and CRM contribute to the combined reaction, between which POM plays a more important role. Moreover, the addition of Ce to Ru-based catalyst results in an improvement in the activity and CO selectivity under the adopted reaction conditions. The Ce-doped catalyst was characterized by N2 adsorption-desorption, SEM, XRD, TPR, XPS and in situ DRIFTS. The mechanism has been studied by in situ DRIFTS together with the temperature distribution of catalyst bed. The mechanism of the combined reaction is more complicated and it is the combination of POM and CRM mechanisms in nature. The present paper provides a new catalytic system to activate CH4 and CO2 at a rather low temperature.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMST effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO-H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

Effect of decomposition of catalyst precursor on Ni/CeO2 activity for CO methanation

CO methanation on Ni/CeO₂ has recently received increasing attention. However, the low-temperature activity and carbon resistance of Ni/CeO₂ still need to be improved. In this study, plasma decomposition of nickel nitrate was performed at ca. 150°C and atmospheric pressure. This was followed by hydrogen reduction at 500 °C in the absence of plasma, and a highly dispersed Ni/CeO₂ catalyst was obtained with improved CO adsorption and enhanced metal-support interaction. The plasma-decomposed catalyst showed significantly improved low-temperature activity with high methane selectivity (up to 100%) and enhanced carbon resistance for CO methanation. For example, at 250°C, the plasma-decomposed catalyst showed a CO conversion of 96.8% with high methane selectivity (almost 100%), whereas the CO conversion was only 14.7% for a thermally decomposed catalyst.     

Catalytic performance of Fe modified K/MO2C catalyst for CO hydrogenation

Fe modified and un-modified K/Mo2C were prepared and investigated as catalysts for CO hydrogenation reaction. Compared with K/Mo2C catalyst, the addition of Fe increased the production of alcohols, especially the C2+OH. Meanwhile, considerable amounts of C5+ hydrocar- bons and C2= -C4= were formed, whereas methane selectivity greatly decreased. Also, the activity and selectivity of the catalyst were readily affected by the reaction pressure and temperature employed. According to the XPS results, Mo4+ might be responsible for the production of alcohols, whereas the low valence state of Mo species such as Mo0 and/or Mo2+ might be account for the high activity and selectivity toward hydrocarbons.     

Methane Conversion to C2 Hydrocarbons Using Dielectric-barrier Discharge Reactor: Effects of System Variables

The partial oxidation of methane to C₂ hydrocarbons was investigated experimentally in a dielectric-barrier discharge (DBD) reactor. The effects of reactor wall temperature, input gas flow rate and volumetric ratio of methane to oxygen over methane conversion and C₂ production were investigated. The highest C₂ selectivity of about 50% was achieved at 1.8% methane conversion. Finally the model equations were used to correlate methane conversion and ethylene selectivity with the system variable within the studied range of them. The correlation equation shows the sole effects and interaction effects of system variables on methane conversion and ethylene selectivity.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMSI effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO?H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

CO2 在高分散 Ni/La2O3 催化剂上的甲烷化

 以 La2O3 为载体, 采用浸渍法制备了 10%Ni/La2O3 催化剂, 考察了该催化剂的 CO2 甲烷化反应性能. 结果表明, 在较低的温度 (350 oC) 和高空速 (约 30000 h–1) 下, 甲烷时空收率可大于 3000 g/(kg•h), 无论转化率高低, 甲烷选择性始终保持在 100%. X 射线衍射和 H2-程序升温还原等表征结果表明, CO2 在 Ni/La2O3 催化剂上的加氢机理可能与 Ni/γ-Al2O3 上不同, 并且 La2O2CO3 的形成有利于提高催化剂活性.     

The cooperative effect of Zn on Co/HZSM-5 catalyst for NO reduction with methane

The cooperation of Zn and Co in the Zn-Co/HZSM-5 catalyst was investigated. NO was selectively reduced by CH4 to N₂ in the presence of excess O₂, and the catalytic activity depended on both the activation of CH4 and the adsorption properties of NO_x. It was found that the addition of Zn could effectually heighten the selectivity of methane to NO_x. The results of H₂-TPR, NH₃-TPD and XPS proved that addition of Zn into Co/HZSM-5 could inhibit the formation of bulk Co₃O₄ on the outer surface of the catalyst. Reducing the bulk Co₃O₄ would restrain the combustion of methane and improve the selectivity of methane to NO_x, which was very consistent with the experimental results. MS-TPD results showed that Zn contributed the form of NO₂ and strengthened its adsorption on the Co/HZSM-5 catalyst. So the reaction mechanism is proposed to occur via two successive elementary steps. First NO is oxidized to NO₂ on the dispersed CoOx sites or Co²⁺ active sites; then NO₂ is adsorbed on Zn²⁺ sites, and further reacts with methane on proton acid sites. The key step is the adsorption of NO₂. Zn directly participates in the reaction by adsorption of NO₂.