Nitrous oxide formation in low temperature selective catalytic reduction of nitrogen oxides with V2O5/TiO2 catalysts

Nitric oxide and nitric dioxide compounds (NOx) present in stack gases from nitric acid plants are usually eliminated by selective catalytic reduction (SCR) with ammonia. In this process, small quantities of nitrous oxide (N2O) are produced. This undesirable molecule has a high greenhouse gas potential and a long lifetime in the atmosphere, where it can contribute to stratospheric ozone depletion. The influence of catalyst composition and some operating variables were evaluated in terms of N2O formation, using V2O5/TiO2 catalysts. High vanadia catalyst loading, nitric oxide inlet concentration and reaction temperature increase the generation of this undesirable compound. The results suggest that adsorbed ammonia not only reacts with NO via SCR, but also with small quantities of oxygen activated by the presence of NO. The mechanism proposed for N2O generation at low temperature is based on the formation of surface V-ON species which may be produced by the partial oxidation of dissociatively adsorbed ammonia species with NO + O-2 (eventually NO2). When these active sites are in close proximity they can interact to form an N2O molecule. This mechanism seems to be affected by changes in the active site density produced by increasing the catalyst vanadia loading. (c) 2006 Elsevier B.V. All rights reserved.