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

Abstract

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.

Fabrication of Ln2Zr2O7 Fluorite and LnAlO3 Perovskite (Ln = La, Nd, Sm) Compounds to Catalyze the OCM Reaction: On the Temperature-Induced Phase Transformation and Oxygen Vacancy

“…Hence, it is very necessary to achieve catalysts with improved performance. 19,20 Besides the most widely studied OCM catalysts such as Li/MgO, 21−24 pure or doped rare earth oxides, 16,25−27 and Mn/Na 2 WO 4 /SiO 2 , 28−31 composite oxides such as ABO 3 perovskites 32−34 and A 2 B 2 O 7 pyrochlores 35,36 also exhibit promising OCM performance, but researchers are still short of a systematic understanding on their structure−reactivity relationship.…”

“…Since the early studies in the 1980s, numerous catalyst formulations have been investigated for OCM, but a catalyst that can meet the demands of industrialization has not yet been accomplished. Hence, it is very necessary to achieve catalysts with improved performance. , Besides the most widely studied OCM catalysts such as Li/MgO, − pure or doped rare earth oxides, ,− and Mn/Na 2 WO 4 /SiO 2 , − composite oxides such as ABO 3 perovskites − and A 2 B 2 O 7 pyrochlores , also exhibit promising OCM performance, but researchers are still short of a systematic understanding on their structure–reactivity relationship.…”

Catalytic Routes for Direct Methane Conversion to Hydrocarbons and Hydrogen: Current State and Opportunities

“…MnNaW/SiO 2 is one of the most studied and promising catalysts due to its high C2 yield and stability on stream. ,, Serres et al showed that increasing the quantity of active sites in the catalyst contributes to an increase of the catalytic activity up to 19.5% . However, by increasing the concentration of active sites up to 41%, a drop in activity is observed, and associated with a loss of surface area.…”

“…The oxidative coupling of methane has been vastly developed and described in the open literature since the work of Keller and Bhasin . Important review papers reveal the particularities of the OCM reaction in detail. ,− Specific attention to the OCM process engineering and the reaction mechanism has been paid and will be discussed in this review. More specifically the nature of the catalysts and supports with a significant impact on the reaction will be considered. ,− In addition, the impact of several parameters such as temperature, space velocity, dilution, and others will be addressed, and preferable conditions favoring the OCM reaction will be revealed.…”

Preparation of La2Zr2O7 composite oxides with fluorite/pyrochlore phases by excluding element influences for catalyzing oxidative coupling of methane

“…Ever since OCM was first reported in the early 1980s, more than 2000 catalyst formulations have been discovered for it. [1][2][3] Generally, a favorable catalyst for OCM exhibits good thermal resistance, appropriate surface basicity, 4,5 considerable oxygen ion conductivity, 6 and a substantial amount of oxygen vacancies for generating reactive oxygen anions. 7,8 To industrialize OCM, there is a need to develop catalysts having excellent efficiency, which is a great challenge that relies on achieving a breakthrough in catalyst design.…”