Recently plasma catalysis with pellets made from industrial waste is gaining significance in enhancing the removal efficiency of oxides of nitrogen (NOX) in diesel exhaust. In this paper, an attempt has been made to understand the role played by the size of the pellets when they are packed in a finite volume of plasma reactor. The parametric study was carried out on the exhaust of a 10 hp diesel engine by exposing the gaseous pollutants to pulsed discharge plasma in the presence of lignite ash pellets. Different sizes of the pellets were tested for NOX removal efficiency and a pellet size of about 5 mm diameter appeared to be critical. The next phase of the experiments was carried out with this critical diameter of pellets but made from another major industrial waste, broken ceramic tiles. About 89% decrease in NOX (DeNOX) efficiency was achieved with these broken tiles in plasma catalysis mode. A comparative study was also made at a larger diameter of tiles-based pellets which exhibited lesser DeNOX efficiency, thus emphasizing the need for identifying suitable size of the pellets in plasma catalysis. Further, a study was carried out to ascertain the fact that catalytic reaction dominates in plasma catalysis rather than the adsorption.