Non-oxidative coupling of methane to C2 hydrocarbons: integration of dielectric barrier discharge plasma and catalyst packed bed

Direct conversion of methane has attracted increasing attention, considering its potential for large-scale production of chemicals and fuels via processes which are environmentally more favorable due to a lower emission of CO2, as well as are more economical owing to the integration of a multistep process to a single step process. However, the conversion of methane via non-oxidative route is still challenging considering the high thermodynamic barrier of C-H bond activation. Non-thermal plasma has the capability to activate C-H bond through collisions of high energy electrons with methane molecules, going beyond the thermodynamic limit of methane activation. Dielectric barrier discharge (DBD) is a type of non-thermal plasma (i.e., cold plasma), which can be used for dissociation of methane into CHx fragments, capable of being operated in atmospheric pressure and ambient temperature, where no external heat source is needed. However, the random interactions amongst plasma generated species can terminate to the generation of unwanted products (e.g., deposits in methane coupling). The presence of catalyst in a plasma-catalyst hybrid system can influence these interactions, aiming at increasing the selectivity of the desired products via the synergy of the plasma and the catalyst. DBD plasmas are suitable to be integrated with catalyst surfaces considering its versatility for applying different configurations of packed bed DBD plasma reactors (PBRs). In this dissertation, the synergistic effect of the plasma and the catalyst was investigated using post-plasma catalysis (i.e., catalyst packed downstream of the plasma discharges) as well as in-plasma catalysis (i.e., catalyst packed inside the plasma discharges) configurations. Several packing materials (catalyst support and metal-supported catalyst) were utilized in combination with the implemented DBD plasma reactor and evaluated in different process conditions including discharge power, residence time, etc. The underlying mechanism of the involved radical chemistry for coupling of methane to C2 hydrocarbons is furthermore discussed