Reduction of NO with NH3 over carbon catalysts: The effects of treating carbon with H2SO4 and HNO3 Original Research Article

The influence of treating carbon with sulfuric and nitric acids on the activity of the carbon catalyst for NO reduction with NH3 was examined in a fixed bed reactor at temperatures in the range 110–200°C. The original carbon catalyst (AD) was prepared from a sub-bituminous coal. The transient behavior of NO reduction over the original and the treated carbons was found to vary with the surface characteristics of the carbons. This suggests that the number of oxygen-containing sites significantly affects the reaction pattern before steady state being reached. In oxygen-free systems the catalytic activity of the nitric-acid-treated carbon (ADN) was higher than AD, but it was lower for the sulfuric-acid-treated carbon (ADS). The activity of these carbons in the absence of oxygen was found to be an increasing function of the amount of CO2 evolved during temperature-programmed desorption. In the presence of oxygen the activity had an order of ADN>ADS>AD, which was found to be identical to that for the amount of CO evolved in the desorption process. It has been suggested on the basis of this study that the formation of CO−(NH4)+ and C(ONO) on surface oxides and further interactions of these complexes are important steps for NO reduction with NH3 over carbons.