Plasma-driven non-oxidative coupling of methane to ethylene and hydrogen at mild temperature over CuxO/CeO2 catalyst

Abstract

We report one-step non-oxidative coupling of methane (CH₄) to ethylene (C₂H₄) at atmospheric pressure and mild temperature (ca. 180–190 °C), by a combination of non-thermal plasma and a CuO_x/CeO₂ catalyst. The C₂H₄ selectivity gradually increases during an induction period. The corresponding spent catalysts at different stages were systematically characterized to disclose the evolution of the CuO_x/CeO₂ catalyst. During the induction period, the CuO/CeO₂ catalyst was partially reduced to generate Cu⁺, Ce³⁺ and O_v species, which accompany the formation of Cu⁺-O_v-Ce³⁺ sites, as proven by XRD, HRTEM, XPS, Raman, EPR and H₂-TPR. In addition, the C₂H₄ selectivity is proportional to the fraction of Cu⁺, Ce³⁺, O_v and Cu-O-Ce species, which indicates that Cu⁺-O_v-Ce³⁺ is the active site for non-oxidative coupling of CH₄ to C₂H₄. Furthermore, in-situ FTIR results indicate that the Cu⁺-O_v-Ce³⁺ interface sites can promote dehydrogenation of CH₃* (from CH₄ plasma) to produce CH₂* on the catalyst surface, which is the basic reason why CuO_x/CeO₂ acts as a catalyst in speeding up the non-oxidative coupling of CH₄ for C₂H₄ production.