The Possible Role of Nitromethane in the SCR of NOxwith CH4over M-ZSM5 (M=Co, H, Fe, Cu)

Abstract

The reactions of nitromethane with NO2or NO in the presence of excess O2have been studied and the results compared over four catalysts: Co-, H-, Fe-, and CuZSM-5. Data were collected at a series of temperatures for the selective catalytic reduction of NO with CH4(SCR) for the former two catalysts for comparison. Product composition data were obtained both chromatographically and by IR analysis of the exit gases. The data showed that, whereas the light-off temperatures were lower when CH3NO2was substituted for CH4, they passed through peak conversion to N2at the same temperature and then fell off rapidly at higher temperatures in the way typical for SCR reactions. The reaction of CH3NO2with O2alone produced results similar to those for the SCR reaction, but with roughly 50% of the peak conversion to N2. The activity of CuZSM-5 in these reactions was much greater than for the other three catalysts. The IR data showed the presence of HCN, NH3, and HNCO in various low concentrations below 400°C. N2and N2O were obtained by GC. These data differed over the four catalysts. All of these compounds have been suggested in the literature as possible intermediates in the formation of N2and their behavior in these experiments was not inconsistent with these ideas. These results suggested, however, that one single pathway to N2formation does not exist; several optional mechanisms may function as suggested by the earlier literature. When15N18O+O2was substituted for the unlabeled molecule, the predominant N2product was15N14N, suggesting that one N-atom is supplied by each of the two reacting molecules, CH3NO2and NO2.