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Summary: Biogas, which contains methane (CH4), carbon dioxide (CO2), hydrogen sulfide (H2S), and other minor compounds, is a promising energy source and chemical feedstock (not least because it is generated from waste); however, its application as fuel is limited because of its low calorific value, which can be mitigated by upgrading biogas to high‐quality fuels via the oxidative coupling of methane (OCM), a catalytic process that increases its higher heating value from 39.9 (CH4, Wobbe index = 53.5 MJ/Nm3) to 41.7 MJ/Nm3 (OCM product mixture, Wobbe index = 54.4 MJ/Nm3), thus achieving compliance with the fuel standards in many countries (Wobbe index = 45.5‐55.0 MJ/Nm3). Among the compounds produced during OCM, H2S is formed in minor amounts but strongly suppresses biogas valorization, mainly because of potential catalyst poisoning. To understand the effects of sulfur compounds on OCM catalysts, three such catalysts, namely perovskites (SrTiO3 and LaAlO3) and Na2WO4/Mn/SiO2 (NWM), were used to convert biogas into olefins and paraffins. The oxidation of H2S in biogas produced sulfur dioxide, which did not strongly affect NWM but was strongly adsorbed by perovskites and, in turn, significantly reduced their OCM activity. Furthermore, long‐term (100 hours) stability testing demonstrated that the OCM activity of NWM was stable in the presence of H2S. Consequently, the influence of sulfur compounds on the catalysts during the OCM process was elucidated, including catalyst poisoning via sulfur species adsorption. The strategy to suppress the detrimental effects of sulfur poisoning was suggested, which can contribute to the development of feasible process for valorizing biogas to high quality fuels and chemicals. [ABSTRACT FROM AUTHOR]

• Perovskite-supported alkaline-earth metal oxide catalysts were prepared. • These catalysts were applied in the oxidative coupling of methane. • The selective production of C 2+ compounds was observed below 700 °C. • Low temperature reaction was achieved with the described oxide/support combination. • Barium oxide exhibited the highest C 2+ yield at the desired temperature. Perovskite-supported alkaline-earth metal oxide catalysts were prepared for application in the oxidative coupling of methane (OCM). The selective production of C 2+ compounds, including ethane, ethylene, acetylene, propane, and propylene, was observed at reaction temperatures < 700 °C. This lower reaction temperature was not achieved with pure perovskites but only with the combination of alkaline-earth metal oxides and perovskite supports. The formation of complex mixed oxides, such as Ba-Ca-Ti-O x , Ba-Sr-Ti-O x , and Ba 2 TiO 4 , was also observed for these catalysts. This contributed to the improved C 2+ yield at the lower reaction temperature. The strong basicity, which contributes to the improved OCM activity, was also observed for these catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Na-W-Mn-Ba-Ti composite catalyst exhibited 26.0 % C 2+ yield at 700 °C. • Optimum temperature, 700 °C, is 100 °C lower than that of conventional Mn-Na 2 WO 4. • Nanostructures of catalyst adjusted the redox of Mn and W. • H 2 -TPR, TEM, XRD, Raman, and others elucidated the catalytic activity. The oxidative coupling of methane (OCM) using hybrid catalysts containing BaTiO 3 perovskite and Mn-Na 2 WO 4 exhibited high activity and high selectivity at low temperature: 66.3 % C 2+ (olefins and paraffins) selectivity and 25.9 % C 2+ yield at 700 °C which is 100 °C lower than that used for Mn-Na 2 WO 4 catalysts (800 °C). Upon the preparation of complex catalysts, the insertion of Mn into BaTiO 3 (BaTi(Mn)O 3) and the formation of Na x Mn(Ti)O 2 improved the oxygen-supplying ability of the catalysts. Additionally, strong interactions between the WO 4 2− anions and BaTi(Mn)O 3 or Na x Mn(Ti)O 2 stabilized the WO 4 2− anions on the surface and improved the methane activation ability of the catalysts for the favorable production of hydrocarbons. The nanoscopic modification of catalysts was confirmed using H 2 –temperature-programmed reduction, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy results. [ABSTRACT FROM AUTHOR]

A study of methane conversion from CO2 reforming of methane using dielectric barrier discharge over Ni/γ-Al2O3 catalyst was performed. The main products of reactions were CO, H2, C2H6, C3H8, and C4H10. The effects of input power, total flow rate, and CH4/CO2 ratio on conversion and product selectivity were investigated. Carbon dioxide and methane conversions were enhanced with increasing the input power and decreasing the total flow rate. Ni/γ-Al2O3 catalyst had a great effect on the CO selectivity and CO2 conversion. When Ni/γ-Al2O3 catalyst was applied to DBD, the CO selectivity increased from 49.17 to 60.9% and CO2 conversion increased by about 3%. Even though Ni/γ-Al2O3 catalyst was helpful to improve the CO2 conversion and CO selectivity, the fundamental mechanism of reaction and characterization of catalysts are still unknown and, therefore, further investigations are necessary. [Copyright &y& Elsevier]

The oxidative coupling of methane using silica-supported Na 2 WO 4 (Na 2 WO 4 /SiO 2 ) catalysts is observed by adjusting additives in order to understand the roles of additives and to design more efficient catalysts. By observing the effects of additives on the catalytic OCM activity of Na 2 WO 4 /SiO 2 catalysts, the reducibility of metal additives, quantified by the standard reduction potentials, is observed to improve the methane conversion and olefin selectivity, indicating that the active sites of activating methane and dehydrogenating paraffin are identical. The supply of oxygen atoms from more easily reducible additives to tungsten oxide manipulate the OCM activity as described by the standard reduction potentials of the additives. The crystal and electronic structures of the catalysts depend on the additives, which can also be used to adjust the catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: The oxidative coupling of methane (OCM) to produce ethane and ethylene, valuable hydrocarbons, was scaled-up using differential, mid-scale, and bench-scale reactors with 0.030, 2.73, and 40g of packed catalysts, respectively. Organic and inorganic binders, such as methylcellulose, Al2O3, MgO, and TiO2, were mixed with Na2WO4/Mn/SiO2 catalyst powder to produce catalyst pellets, and TiO2-mixed catalyst pellets exhibited the highest C2 hydrocarbon yield despite the lowest active catalyst content. The formation of hot spots, which suppressed the selective conversion to C2 hydrocarbons by further oxidation to CO and CO2, was observed in the mid- and bench-scale reactors because of poor heat transfer. Inert-gas-diluted reactants and lower O2 flow may inhibit the formation of hot spots and allow the development of industry-feasible OCM processes. [Copyright &y& Elsevier]

Abstract: Methane conversion by plasma offers a promising route to produce higher value-added products. As plasma reaction is a relatively complex process, kinetic modeling is necessary to obtain a general pattern of the complex interaction on the basis of chemical reaction and products. In this paper, we present a method to obtain the kinetic rate coefficient (k) from the experimental data. Although plasma reaction was classified as chemically complex interaction, the reactions showed a certain pattern of the mechanism. In pure methane injection, the decomposition of methane by plasma could initiate coupling reactions and produce C2H6, C3H8, and C4H10. Dehydrogenation of C2H6 into C2H4 and then to C2H2 could be clearly seen by the higher value of the reaction rate constant of C2H n +2 to C2H n −2. Using the rate constant values (k) obtained by this method, the pathways of the methane conversion by a dielectric barrier discharge can be drawn. [Copyright &y& Elsevier]

Abstract: Plasma catalytic reactions were applied to the conversion of methane to C2, C3 or higher hydrocarbons in a dielectric-barrier discharge (DBD) reactor at atmospheric pressure. Methane conversion was increased with the increase of Pt loading on γ-Al2O3. The highest C2H6 selectivity was 50.3% when 3wt% Pt/γ-Al2O3 catalyst was calcined at 573K. Methane conversion was increased with the increase of the catalyst weight in DBD reactor. The major products were C2H6 and C3H8, which were independent of catalyst weight in the presence of catalyst. [Copyright &y& Elsevier]

Abstract: The catalytic oxidative coupling of methane (OCM) on transition metal-doped TiO2 nanowire catalysts was performed and the effects of metal dopants were studied. With transition metal doping, the electric and optical properties of nanowires were adjusted, which seemed to improve the catalytic activity and selectivity of the OCM reaction. A Mn-doped TiO2 nanowire catalyst exhibited the highest C2 yield with the highest (ethylene)/(ethane) ratio because of its moderate oxidation activity, while a highly active Rh-doped TiO2 nanowire catalyst converted methane into fully oxidized CO and CO2. The electric conductivity assessed by UV–vis absorption represented the oxidation activity of the nanowire catalysts. [Copyright &y& Elsevier]

Highlights: [•] Oxidative coupling of methane (OCM) on the Mg–Ti mixed oxide-supported catalysts. [•] High catalytic activity at the lower reaction temperature for the development of energy-saving processes. [•] Improved catalytic activity by the active surface lattice oxygen atoms. [Copyright &y& Elsevier]

Abstract: A kinetic model of the oxidative coupling of methane was developed by considering ethane, ethylene, carbon monoxide, and carbon dioxide production in such a way that the reactor was designed for the reactions to take place in the catalyst-loading region as much as possible. The effectiveness of the reactor specification was validated by low conversion of methane in the blank test. A mechanism for catalytic reactions on the surface of Na2WO4/Mn/SiO2 gel and gas-phase radical reactions was suggested based on a literature survey. Reaction rates were developed by applying rapid equilibrium for adsorption and the quasi steady state approximation to the intermediate on the catalytic surface. Kinetic parameters were estimated by fitting experimental data with temperature, space velocity, and CH4/O2 ratio varied in full factorial manner. The validity of the model was corroborated by comparing its simulated results with experimental data. The effectiveness of the estimated parameters was discussed with respect to reported values. The effects of operating conditions were assessed using the developed model. [Copyright &y& Elsevier]

Abstract: A series of methanol synthesis catalyst containing Cu–Zn–Al (CZA) were prepared by co-precipitation method and applied for partial oxidation of methane into methanol using dielectric barrier discharge (DBD). The methanol synthesis process was occurred at ambient temperature and atmospheric pressure. In our experiment, CZA showed a high catalytic activity to increase the production of methanol. The methanol selectivity of CZA-assisted plasma process was twice higher than that of non-catalytic plasma process. The addition of other metals on CZA catalyst also produced a significant effect on the methanol production and it was found that yttrium could the best addition metal compared to Pt, Fe, and Ni. Instead of methanol, the reaction products of plasma reactions were dominated by H2, CO, CO2, C2 and water. The optimum methanol selectivity reached 27% when 3% yttrium metal was doped over CZA. [Copyright &y& Elsevier]