Photocatalytic Reaction NO + CO + hν → CO₂ + 1/2N₂ Activated on ZnO1–x in the UV–Vis Region

It is shown for the first time that the photocatalytic reaction of NO reduction by CO into N 2 can occur on self-sensitized ZnO 1– x 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 N 2 O. The formed CO 2 remains on the surface and can be completely desorbed after completion of the photoreaction by heating ZnO 1– x up to 820 K. The spectral dependencies of the first and of the second stages repeat the optical absorption spectra of the ZnO 1– x 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 10 3 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 NO 2 – species, respectively; (b) the reduction of NO – and NO 2 – into N 2 O and further into N 2 by CO which regenerates the donor centers.