activate the C-H bond. This high reaction temperature establishes a secondary gas-phase reaction mechanism pathway, whereby the desired reaction of methyl radical coupling to products (leading to ethylene) strongly competes with COx side reactions. The high temperature also presents a challenge for the reaction engineering. Among the process engineering challenges are the requirements for expensive metallurgy, lack of industry experience with high temperature catalytic processes and the potential need for new reactor design to manage heat transfer efficiently. Labinger postulated an inherent limit to OCM selectivity, concluding that "expecting substantial improvements in the OCM performance might not be wise". Labinger's argument, later demonstrated experimentally by Mazanec et al., is based on the mechanism of methane activation, which is a radical mechanism, forming H and CH3 radicals by the homolytic cleavage of the C-H bond. Ethylene and ethane that are proposed products have C-H bonds of similar strength. Thus, any catalyst that can activate methane can also activate the products. The yield of ethylene (and/or ethane) is limited by the relative rates of the methane and ethylene reactions, and these rates are very similar. Reactions of the products lead to higher homologues, and eventually to aromatics and coke. The same limitation applies to direct pyrolysis of methane, which is also a radical process. Nevertheless, some recent work have shown that the mechanism of the OCM could be initiated by an heterolytic cleavage of the C-H bond on magnesium oxide in the presence of atmosphere. Eventually, the inability to discover a selective catalyst led to a gradual loss of interest in OCM. Beginning in the mid-1990s, research activity in this area began to decline significantly, as evidenced by the decreasing number of patents filed and peer-reviewed publications. The research company Siluria attempted to develop a commercially viable OCM process, but did not succeed. The company sold their OCM technology to McDermott in 2019. References Chemical reactions Methane