Plasma assisted oxidative coupling of methane (OCM) over Ag/SiO2 and subsequent regeneration at low temperature

Abstract

In this study, oxidative coupling of methane (OCM) was carried out to produce C-2 and C-3 hydrocarbons directly from methane in a plasma-catalyst hybrid system. Since catalyst only reaction requires high temperature above 700 degrees C, dielectric barrier discharge (DBD) plasma was applied as plasma source to lower the reaction temperature. Among various supports, only SiO2 showed the higher yield than plasma only reaction when combined with DBD plasma, which led us to focus on the SiO2-based catalyst. It was found that Ag/SiO2 demonstrated the highest C2+ hydrocarbon yield of about 9.7% at 385 degrees C. In this process, oxygen was proved to play an essential role in the coupling of methane to C2+ hydrocarbons over Ag/SiO2 catalyst. However, Ag/SiO2 catalyst under plasma condition became deactivated with time-on-stream because of coking. It was demonstrated that plasma regeneration at 378 degrees C gave rise to the full recovery of activity while thermal regeneration did not due to the partial removal of coke and the sintering of Ag.