Reduction of NO with NH3 over carbon catalysts - the influence of carbon surface structures and the global kinetics

The reduction of NO by NH3 over carbon catalysts was studied at temperature s in the range 140-320 degrees C, and at NO and NH3 concentrations varying within 290-1160 ppm. The carbon catalysts of different surface areas were p repared by gasifying bituminous and sub-bituminous coal chars in CO2 to dif ferent extents of burn-off. The NO reduction rate was found to increase wit h the carbon surface area, which is an increasing function of the burn-off level. However, the activity per unit surface area of the carbons decreases with the extent of burn-off. By adding oxygen in the reacting system, the NO conversion can be significantly enhanced. The apparent activation energy was found to be around 20 kJ/mol for the reactions with or without oxygen addition. The apparent reaction orders with respect to NO and NH3 are funct ions of the reaction temperature and are affected by the presence of oxygen . It has been suggested on the basis of the kinetic study that the catalyti c reduction of NO might be governed by two consecutive steps: the adsorptio n of NH3 on active sites, followed by the addition of NO or NO2 in the neig hborhood of the C(NH3) complexes. (C) 1999 Elsevier Science B.V. All rights reserved.