Spark Discharge and Dielectric Barrier Discharge Plasma Catalysis for the Nonoxidative Coupling of Methane to Ethylene with Pd Atomically Dispersed Pd-Cu/γ-Al2O3-R Catalyst

Methane valorization is important for climate change mitigation and sustainable carbon utilization, but conventional nonoxidative coupling of methane (NOCM) suffers from the high activation barrier of CH4, limited product selectivity, and rapid coking-induced deactivation. Herein, we develop a spark discharge−dielectric barrier discharge (DBD) coupled plasma-catalytic system for the selective conversion of high-concentration methane to ethylene. Spark discharge first activates CH4 and preferentially converts it to C2H2, while a downstream catalyst bed, maintained at 100−130 °C by residual discharge heat, enables acetylene semihydrogenation to C2H4. A coupled DBD unit is further introduced for in situ carbon removal and catalyst regeneration. Among the tested catalysts, impregnation−reduction-derived 0.1Pd-5Cu/γ-Al2O3-R with atomically dispersed Pd exhibited the best performance, achieving 72.38% CH4 conversion, 72.19% C2H4 selectivity, 92.48% acetylene-based C2H4 selectivity, and a C2H4 space-time yield of 69.97 mmol·g·−1·h−1 at 36.2 kJ·L−1. With DBD-assisted regeneration, efficient NOCM operation was maintained for 630 min. Mechanistic analyses associate the enhanced ethylene selectivity with highly dispersed Pd sites and their electronic modulation by predominantly low-valent Cu species, which suppress overhydrogenation and facilitate ethylene desorption.