Knowledge Bank

A myriad of metal oxide catalysts have been explored for upgrading methane into higher hydrocarbons in a process called oxidative coupling of methane (OCM). Because of the ramifications of utilizing methane as a chemical feedstock, efforts to optimize the reactor design and catalyst for OCM process have been ongoing since 1980. Catalytic oxygen carriers (COCs) used for cycling oxygen to the reactant gas in OCM reaction processes have shown distinct advantages over cofeeding reaction schemes. Manganese based COCs have exhibited multiple oxidation states that function in the cyclic reduction oxidation reactions of OCM. This study aims to elucidate the different forms of oxygen delivery strategies that can be leveraged from a deeper understanding of how these COC oxidation states effect product distributions. The COC particles used to facilitate this oxygen transfer in this study were Mg6MnO8 and Li0.2Mg5.8MnO8. Thermogravimetric analysis and fixed bed experiments were performed to characterize the effects of the Mn4+ and Mn3+ oxidation states on methane conversion and C2+ selectivity. The Mn4+ oxidation state was shown to experience higher reduction rates, higher conversion, and lower selectivity than the Mn3+ oxidation state. Li doping of the manganese oxide was shown to reduce reduction rates, lowering conversion and raising selectivity. This study showed that reduction rate and ultimately product distribution can be tuned by adjusting the oxidation state of manganese based COCs.