Post-Plasma Catalytic Partial Oxidation of Methane to Light Oxygenates Over Cu- and Ag-Modified CHA Zeolites

Abstract

Selective oxidation of methane to light oxygenates under mild conditions remains challenging because thermal activation commonly leads to deep oxidation and carbon deposition. Here, a post-plasma catalysis (PPC) system integrating dielectric barrier discharge (DBD) plasma with Cu- and Ag-exchanged CHA-type zeolites, SAPO-34 and SSZ-13, enabled room-temperature conversion of methane to methanol and other oxygenates. Structural characterization confirmed that the CHA framework was largely preserved after metal exchange, with Cu species finely dispersed within the zeolite matrix, whereas Ag species were located mainly on the external surface. Under mild plasma conditions, CHA-based supports outperformed MFI- and BEA-type zeolites, giving higher selectivity toward oxygenates, including methanol and formaldehyde, together with lower coke formation, underscoring the role of zeolite confinement. Among the catalysts examined, Cu/SAPO-34 and Cu/SSZ-13 showed the best balance of methane conversion and oxygenate selectivity, and maintained performance over five consecutive short-term cycles. The introduction of Ag further shifted the product distribution from methanol toward formaldehyde. These findings identify Cu- and Ag-supported CHA zeolites as promising catalysts for energy-efficient plasma-assisted methane upgrading and highlight the combined importance of zeolite confinement and metal identity in governing oxygenate distribution.