THE POSSIBLE ROLE OF NITROMETHANE IN THE SCR OF NOX WITH CH4 OVER M-ZSM5 (M = CO, H, FE, CU)

The reactions of nitromethane with NO2 or NO in the presence of excess O-2 have been studied and the results compared over four catalysts: C o-, H-, Fe-, and CuZSM-5. Data were collected at a series of temperatu res for the selective catalytic reduction of NO with CH4 (SCR) for the former two catalysts for comparison. Product composition data were ob tained both chromatographically and by IR analysis of the exit gases, The data showed hat, whereas the light-off temperatures were lower whe n CH3NO2 was substituted far CH4, they passed through peak conversion to N-2 at the same temperature and then fell off rapidly at higher tem peratures in the way typical for SCR reactions. The reaction of CH3NO2 with O-2 alone produced results similar to those for the SCR reaction , but with roughly 50% of the peak conversion to N-2. The activity of CuZSM-5 in these reactions was much greater than for tie other three c atalysts. The IR data showed the presence of HCN, NH3, and HNCO in var ious low concentrations below 400 degrees C. N-2 and N2O were obtained by GC, these data differed over the four catalysts, All of these comp ounds have been suggested in the literature as possible intermediates in thr formation of N-2 and their behavior in these experiments was no t inconsistent with these ideas. These results suggested, however, tha t one single pathway to N-2 formation does not exist; several optional mechanisms may function as suggested by the earlier literature, When (NO)-N-15-O-18 + O-2 Was substituted for the unlabeled molecule, the p redominant N-2 product was (NN)-N-15-N-14, suggesting that one N-atom is supplied by each of the two reacting molecules, CH3NO2 and NO2, (C) 1998 Academic Press.