Oxidative Coupling of Methane: Perspective for High-Value C2 Chemicals

The oxidative coupling of methane (OCM) to C2 hydrocarbons (C2H4 and C2H6) has aroused worldwide interest over the past decade due to the rise of vast new shale gas resources. However, obtaining higher C2 selectivity can be very challenging in a typical OCM process in the presence of easily oxidized products such as C2H4 and C2H6. Regarding this, different types of catalysts have been studied to achieve desirable C2 yields. In this review, we briefly presented three typical types of catalysts such as alkali/alkaline earth metal doped/supported on metal oxide catalysts (mainly for Li doped/supported catalysts), modified transition metal oxide catalysts, and pyrochlore catalysts for OCM and highlighted the features that play key roles in the OCM reactions such as active oxygen species, the mobility of the lattice oxygen and surface alkalinity of the catalysts. In particular, we focused on the pyrochlore (A2B2O7) materials because of their promising properties such as high melting points, thermal stability, surface alkalinity and tunable M-O bonding for OCM reaction.

OXIDATIVE DIMERIZATION OF METHANE TO C2 HYDROCARBONS

The world's oil reserves are decreasing every day due to the continuous production and processing of the most modern technologies. Scientists all over the world are looking for various raw materials and methods to use the vast resources of natural gas as a substitute for petrochemicals. In this regard, great attention is drawn to natural gas as an alternative source of raw materials for petrochemical industries. The purpose of this work is to study the reaction of methane dehydrogenation on new 20%La-10%Ce20%Mg-50% glycine catalysts prepared by the SHS method to identify the optimal conditions for their preparation, concentration and ratio of metals, the influence of contact time and process temperature on the direction and mechanism of the reaction. The results of the study of 20% La-10% Ce-20% Mg-50% glycine catalyst prepared by the SHS method in the process of oxidative dehydrogenation of methane into C2 hydrocarbons are presented. On the basis of experimental studies, it was found that the composition of the catalyst exhibits high activity in the above reaction under the found optimal conditions. Thus, the influence of reaction temperature on the developed composition of catalysts for oxidative conversion of methane has been determined that the optimum temperature for the selective formation of ethane and ethylene is T=700o С. It was found that for selective oxidation of a mixture of CH4: O2 : Ar in C2 hydrocarbons the optimal conditions are: T=700o С, CH4:O2=2,5:1, 5000 h-1.

Alkali-Added Catalysts Based on LaAlO3 Perovskite for the Oxidative Coupling of Methane

In this study, we aimed to enhance the catalytic activity of perovskite catalysts and elucidate their catalytic behavior in the oxidative coupling of methane (OCM), using alkali-added LaAlO3 perovskite catalysts. We prepared LaAlO3_XY (X = Li, Na, K, Y = mol %) catalysts and applied them to the OCM reaction. The results showed that the alkali-added catalysts’ activities were promoted compared to the LaAlO3 catalyst. In this reaction, ethane was first synthesized through the dimerization of methyl radicals, which were produced from the reaction of methane and oxygen vacancy in the perovskite catalysts. The high ethylene selectivity of the alkali-added catalysts originated from their abundance of electrophilic lattice oxygen species, facilitating the selective formation of C2 hydrocarbons from ethane. The high COx (carbon monoxide and carbon dioxide) selectivity of the LaAlO3 catalyst originated from its abundance of nucleophilic lattice oxygen species, favoring the selective production of COx from ethane. We concluded that electrophilic lattice oxygen species play a significant role in producing ethylene. We obtained that alkali-adding could be an effective method for improving the catalytic activity of perovskite catalysts in the OCM reaction.