A study on active sites of A2BO4 catalysts with perovskite-like structures in oxidative coupling of methane

Abstract

• Active sites of catalysts of oxidative coupling of methane (OCM) were investigated. • Adsorbed oxygen species play the role of converting methane into methyl radicals. • The methyl radicals are consecutively converted into ethane in the atmosphere. • The ethane molecules are additionally converted depending on lattice oxygen species. • Particularly, electrophilic lattice oxygen species convert ethane into ethylene. We attempted to thoroughly investigate active sites of catalysts for oxidative coupling of methane (OCM) using SrLaXO 4 (X = Al, Fe, or Co) catalysts with not only clear structures but also considerable catalytic activities. In this regard, various characterization tools at high-temperature conditions and at room temperature were employed. The results of characterizations clearly confirmed that oxygen properties of catalysts for OCM are considerably related to their catalytic activities in OCM. Concretely, adsorbed oxygen species (O ads ) on the catalysts play the role of converting methane into methyl radicals. Herein, the methyl radicals are consecutively converted into ethane in the atmosphere, and the generated ethane molecules are additionally converted depending on lattice oxygen species of applied catalysts, which can be divided into nucleophilic lattice oxygen species (O lat(n) ) and electrophilic lattice oxygen species (O lat(e) ). O lat(n) is a favorable oxygen species for producing carbon monoxide and carbon dioxide from ethane, whereas O lat(e) functions as an oxygen species in the conversion ethane into ethylene. Consequently, we concluded that preparation of catalysts with abundant amounts of O ads and O lat(e) is a key strategy for achieving high performances in OCM.