ISOTOPIC EVIDENCE FOR DIRECT CONVERSION OF NO TO NH-3 IN THE ABSENCE OF O-2 OVER V2O5/TIO2 AND ALPHA-CR2O3 SELECTIVE CATALYTIC REDUCTION CATALYSTS

The products of the reaction between (NO)-N-15 and (NH3)-N-14 over V2O5/TiO2 and alpha-Cr2O3 catalysts in the absence of oxygen have been determined by mass spectrometry and Fourier transform infrared spectroscopy. With both catalysts (NN)-N-14-N-15 comprises approximately two-thirds of the nitrogen-containing products. Very surprisingly, (NH3)-N-15 makes up about one-half the remainder. This has significant implications for the likely mechanism of the SCR reaction in the absence of oxygen. Formation of (NH3)-N-15 by direct exchange of both hydrogen and oxygen between (NH3)-N-14 and (NO)-N-15 molecules can be ruled out since no (NO)-N-14 is produced. It seems that (NO)-N-15 is broken down to separate N-15 and oxygen species on reduced sites and that (NH3)-N-15 can then be made by reaction of the N-15 species with water. It is possible that the nitrogen-containing species is an NH group. With V2O5/TiO2 the only remaining product is (NNO)-N-14-N-15. However, this is largely replaced by doubly labeled products, N-14(2), N-15(2), and (N2O)-N-15, when using alpha-Cr2O3.