The photooxidation of NO with oxygen over Hycom TiO2 and zeolite (A and Y form zeolite: TiO2-AZ and TiO2-YZ) composite catalysts was studied to remove NO, in the atmosphere. The photocatalytic oxidation activity of the titania in the composite catalyst in a proportion of AZ:TiO2 = 3:7 is about three times lager than that in the ban titania. The adsorption behaviors of NO and NO2 for the bare titania sample obey Langmuir adsorption equations of NO and NO2, respectively. In the titania-zeolite composite catalysts, the adsorption data indicate the increase in the amount of NO adsorption on the TiO2 phase and the decrease in the amount of NO2 adsorption, compared with the bare titania. The acceleration of NO photooxidation rate, resulting from the increase in the amount of NO adsorbed and the decrease in the amount of NO2 adsorbed, thus occurs on the TiO2 phase. IR spectra, when irradiating the catalysts with UV, showed the immediate formation of nitrate and NO2 species on the catalyst. The results lead to the conclusion that the zeolites promote the photocatalytic oxidation of NO over the titania. (C) 2001 Elsevier Science B.V. All rights reserved.