In this study, the selective catalytic reduction (SCR) of NO2 to N-2 and O-2 with ammonia at 298 K on nanocrystalline NaY, Aldrich NaY and nanocrystalline CuY was investigated using in situ Fourier transform infrared (FTIR) spectroscopy. It was determined that the kinetics of SCR were 30% faster on nanocrystalline NaY compared to Aldrich NaY. The superior performance of the nanocrystalline zeolite was attributed to an increase in external surface reactivity. External surface sites, which include silanol groups and extra framework alumina (EFAL), gave rise to differences in the adsorption of NO2 and NH3 on nanocrystalline NaY compared to commercial NaY Copper cation-exchanged nanocrystalline Y resulted in an additional increase in the rate of SCR as well as distinct NO2 and NH3 adsorption sites associated with the copper cation. This is the first study of a transition metal cation-exchanged nanocrystalfine zeolite and its potential use as a catalyst in the SCR of nitrogen oxides. (c) 2008 Elsevier B.V. All rights reserved.