Enhanced C2+ selectivity in plasma-assisted chemical looping oxidative coupling of methane using (Na, Li, and K) doped LaMnO3

Abstract

Plasma-assisted chemical looping oxidative coupling of methane (CLOCM) is a process that holds promise for the direct conversion of methane to hydrocarbons at low temperatures. However, the tendency of the products to be prone to overoxidation, leading to the formation of CO₂ and CO, reduces the C₂₊ selectivity. In this study, a series of alkali metals (Na, Li, and K) were doped into LaMnO₃ to serve as the redox oxygen carrier in plasma-assisted CLOCM, with the aim of improving its performance. The results showed that K-doped LaMnO₃ exhibited the highest level of performance, with a single-pass CH₄ conversion of 9.85% and C₂₊ selectivity of 88.71%, which remained stable after 20 cycles. Mechanism studies showed the doping of K in LaMnO₃ inhibits the bulk diffusion of lattice oxygen and the subsequent surface evolution to highly active oxygen species, reducing the concentration of surface-active oxygen and the occurrence of overoxidized products.