4 research outputs found
Photocatalytic Reaction NO + CO + <i>h</i>ν → CO<sub>2</sub> + 1/2N<sub>2</sub> Activated on ZnO<sub>1–<i>x</i></sub> in the UV–Vis Region
It is shown for the
first time that the photocatalytic reaction
of NO reduction by CO into N<sub>2</sub> can occur on self-sensitized
ZnO<sub>1–<i>x</i></sub> 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<sub>2</sub>O. The formed CO<sub>2</sub> remains on the surface
and can be completely desorbed after completion of the photoreaction
by heating ZnO<sub>1–<i>x</i></sub> up to 820 K.
The spectral dependencies of the first and of the second stages repeat
the optical absorption spectra of the ZnO<sub>1–<i>x</i></sub> intrinsic color centers: the oxygen vacancies having captured
one or two electrons (F<sup>+</sup> and F centers), the Zn<sup>+</sup> ions, and the Zn vacancies having trapped the hole (V<sup>–</sup> centers). High values of quantum yields in the vis region are caused
by large (up to 10<sup>3</sup> 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<sup>–</sup> and NO<sub>2</sub><sup>–</sup> species, respectively; (b) the reduction of NO<sup>–</sup> and NO<sub>2</sub><sup>–</sup> into N<sub>2</sub>O and further into N<sub>2</sub> by CO which regenerates the donor
centers