Photocatalytic Reaction NO + CO + <i>h</i>ν → CO₂ + 1/2N₂ Activated on ZnO_1–<i>x</i> in the UV–Vis Region

It is shown for the first time that the photocatalytic reaction of NO reduction by CO into N₂ can occur on self-sensitized ZnO_1–<i>x</i> catalysts upon visible light irradiation (λ > 400 nm) at room temperature with the selectivity reaching 95%. The reaction proceeds in two stages through the intermediate product N₂O. The formed CO₂ remains on the surface and can be completely desorbed after completion of the photoreaction by heating ZnO_1–<i>x</i> up to 820 K. The spectral dependencies of the first and of the second stages repeat the optical absorption spectra of the ZnO_1–<i>x</i> intrinsic color centers: the oxygen vacancies having captured one or two electrons (F⁺ and F centers), the Zn⁺ ions, and the Zn vacancies having trapped the hole (V^– centers). High values of quantum yields in the vis region are caused by large (up to 10³ s) lifetimes of photoexcited centers.The reaction mechanism is proposed; it includes the following stages: (a) the NO photoadsorption (PA) on the F-type and on V-type centers producing the adsorbed NO^– and NO₂^– species, respectively; (b) the reduction of NO^– and NO₂^– into N₂O and further into N₂ by CO which regenerates the donor centers