We have examined the interaction of NO2 and CH3CHO with Na-Y zeolite under conditions relevant to low-temperature plasma-activated reduction of NOx. Acetaldehyde interacts weakly with the surface primarily via electrostatic and ion-dipole interactions and is not present at appreciable levels in the molecular adsorbed state at temperatures exceeding 350 K. The interaction of NO2 with Na-Y zeolite produces various forms of adsorbed nitrogen oxide species that are primarily present in the form of nitrites and nitrates. The nitrites can be present in the nitrito, (-O-N-O-) and nitro (-NO2-) configurations and nitrates in the (-NO3-) and nitrato (-O-NO2-) configurations. Reactions of NO2 with a Na-Y zeolite surface containing pre-adsorbed acetaldehyde at room temperature are primarily limited to oxidation of the organic fragments and reduction of the surface nitrates to surface nitrites. Reactions of NO2 on Na-Y zeolite surfaces containing a low coverage of acetaldehyde at temperatures >350 K produces a dehydrogenated surface adsorbed species that likely contains C, N and O. This deposit or adsorbate is also produced when the surface is directly dosed with nitromethane and isopropyl nitrate. The surface reactions seem to involve the Al and associated acid sites. (C) 2003 Elsevier B.V. All rights reserved.