A non-thermal plasma reactor and method for preparing same for conversion of exhaust gas constituents is prepared from an extruded monolith comprising a plurality of conductive and exhaust channels separated by substantially planar dielectric barriers. Conductive material printed onto selected monolith channels form the conductive channels, which are connected along bus paths to form an alternating sequence of polarity, separated by exhaust channels. Conductive channels and channels not selected for exhaust flow are plugged to exclude exhaust gases and to prevent electrical leakage. During operation, exhaust gas flows through exhaust channels and is treated by the high voltage alternating current flowing through the conductive channels. The substantially planar dielectric barriers provide a uniform electrical response throughout the exhaust channels. In a preferred embodiment, the monolith comprises a perimeter boundary wall of increased wall thickness to provide electrical insulation between the conductive channels and the housing and to further provide robust crush resistance when inserting the element into a reactor housing. The one-piece monolith is specifically designed for fabrication via extrusion. A minimal number of in-line structural ligaments are preferably extruded as part of the monolith for providing optimal structural support while minimizing backpressure losses.