Enhanced Chemical looping oxidative coupling of methane by Na-doped LaMnO3 redox catalysts

Chemical looping oxidative coupling of methane (CLOCM) describes an energy-saving and redox approach to convert methane into C-2 products, which utilizes lattice oxygen in redox catalysts in place of molecular oxygen, to facilitate the oxidative coupling of methane reaction. This study synthesized a series of alkali Na-doping LaMnO3 as the redox catalysts for chemical looping oxidative coupling of methane. Incorporation of Na into LaMnO3 lattice induced the higher molar ratio of Mn4+/Mn3+ and more oxygen vacancies, which would be correlated to defects inside the material lattice and consequently promote the redox performance of Mn-based oxygen carriers. Characterizations and consecutive pulse tests showed that the surface oxygen species would be the active center for the methane activation, while a kind of un-fully reduced lattice oxygen (O alpha-, 0 < alpha < 2) caused by the doping of Na benefits the methane oxidative coupling reaction to form C-2 hydrocarbons. Among all the samples, 018Na-doped redox catalysts exhibited the highest C-2 product yield and 7.44 times increase in C-2 yield can be obtained compared to the un-doped LaMnO3. Good regenerability of 018Na-LaMnO3 was demonstrated through 20 consecutive cyclic redox tests, exhibiting above 30% methane conversion, similar to 55% C-2 product selectivity and 20% of C-2 hydrocarbon yield, which will substantially provide a screening strategy for oxygen carrier with good recyclability.

Automated summary

This study successfully utilized Na-doped LaMnO3 as redox catalysts to convert methane into C-2 products, achieving higher performance in oxidative coupling reaction. The incorporation of Na enhanced the redox properties of the catalyst, promoting the formation of C-2 hydrocarbons, with 019Na-LaMnO3 demonstrating the best results among all samples.