Photocatalytic oxidation of nitrogen oxide over titania–zeolite composite catalyst to remove nitrogen oxides in the atmosphere

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_x 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 larger than that in the bare 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.