Mechanism and kinetics of the reduction of nitric oxide by granular activated carbon induced by PdO/Ai2O3 in the presence of O2

NOx and particulate matter are the main environmental hazards found in Diesel exhaust. In order to explore a novel method to remove NOx as well as particulate matter, we examined the catalytic reduction of NOx with solid carbonaceous materials as a surrogate for soot in the presence of oxygen. Pd loaded on Al2O3 has been found to be an active catalyst that resists S and H2O poisoning. A catalyst containing of 2.5% PdO on Al203 exhibits as high as 90% conversion of NO to N2 at space velocities of up to 50,000 hr and at 500°C. Most of the experiments were conducted with a feed gas containing 590 ppm NO, 10% oxygen and the balance He as a function of space velocity in the range of 12,000 to 90,000 hr-1 and temperature in the range of 350 to 550°C. The result shows that a stable intermediate, CO, is formed by the oxidation of granular activated carbon (GAC) with 02, and the rate controlling step of the proposed reaction mechanism for the NO reduction is the reaction of NO + CO. Kinetic experiments were carried out in a fixed bed reactor to determine the apparent reaction order and activation energy of the rate determining step. It was found that the activation energy for the rate determine step was 24.1 kcal/mol. The apparent activation energy for the pore diffusion controlled region was 8.97 kcal/mol. Having an apparent activation energy below 10 kcal/mol. indicate that pore diffusion is the likely mechanism in this region