INVESTIGATION OF THE REACTION PATHWAYS IN SELECTIVE CATALYTIC REDUCTION OF NO WITH NH3 OVER V2O5 CATALYSTS - ISOTOPIC LABELING STUDIES USING O-18(2), (NH3)-N-15, (NO)-N-15, AND (NO1)-N-15-O-18

Isotopic tracer studies were performed to investigate the reaction net work of selective catalytic reduction of nitric oxide over vanadia cat alysts having preferential exposure of different crystal planes. The c atalysts were characterized using BET surface area analysis, X-ray dif fraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, 3-D imaging, and thermal analysis techni ques. The product analysis was carried out by a combination of chemilu minescence NOx analysis, gas chromatography-mass spectrometry, and che mical titration methods. The isotopic labeling experiments were perfor med under steady-state reaction conditions by using NH3 + NO + O-16(2) --> NH3 + NO + O-18(2), (NH3)-N-14 + NO + O-2 --> (NH3)-N-15 + NO + O -2, NH3 + (NO)-N-14 + O-2 --> NH3 + (NO)-N-15 + O-2, and NH3 + (NO)-N- 14-O-16 + O-16(2) --> NH3 + (NO)-N-15-O-18 + O-18(2) switches. Interac tion of NO with the vanadia surface was also studied using a (NO)-N-14 -O-16 --> (NO)-N-15-O-18 switch. The results obtained in these experim ents were combined with the tracer studies performed in ammonia oxidat ion reactions over the same catalysts to elucidate the reaction pathwa ys involved in SCR reactions, to compare the surface residence times o f nitrogen containing species, as well as to quantify the role of ammo nia oxidation in SCR reactions. (C) 1994 Academic Press, Inc.