Investigation of the Photo-Assisted Adsorption of Gases on Irradiated Titanium Dioxide

Abstract

As reported in a recent study, NO can decompose on an irradiated surface of TiO2 as the catalyst in the presence of oxygen. It was observed, however, that the reaction system did not reach a steady state, which was interpreted as a deactivation of the photocatalyst caused by the strongly adsorbed O and N atoms formed during the NO decomposition. The catalyst quickly deactivated in the absence of oxygen. TPD‐measurements with deactivated material led to the assumption that NO itself is chemisorbed very strongly on the irradiated semiconductor surface.

Light intensity dependence of the kinetics of the photocatalytic oxidation of nitrogen(ii) oxide at the surface of TiO2

“…This value is in a good agreement with the value of 2.7 Â 10 À6 mol m À2 calculated from the data published 4. by Hesse and Bredemeyer for the anatase TiO 2 Sachtleben Hombifine N. 71,72 To obtain information concerning the participation of molecular oxygen in the photocatalytic reaction of NO at the TiO 2 surface, experiments have been performed varying the O 2 concentration in the feed gas by mixing the NO-N 2 test gas with oxygen-free molecular nitrogen, pure molecular oxygen, and air resulting in an NO inlet concentration of 1 ppm. The average reaction rates obtained in this set of experimental runs are plotted versus the O 2 inlet concentration in Fig.…”

“…Oxidation products, i.e., HNO 2 / NO 2 À , NO 2 , and HNO 3 /NO 3 À , are formed and accumulated on the surface. The possibility of a photoadsorption process of NO [71][72][73] during this early stage of the photocatalytic reaction cannot be excluded. After a multiple of the residence time the gradient of the NO concentration in the direction of the gas flow is fully established resulting in a high photocatalytic reaction rate at the entrance region of the photocatalytically active area, where the NO concentration is high, and a lower reaction rate at the outlet, where the NO concentration is decreased.…”

Kinetics of the photocatalytic total oxidation of different alkanes and alkenes on TiO2 powder

“…In writing down Equation (5), it i s tacitly assumed that the surface reaction does not influence the photo-assisted adsorption process. Since we can suppose (see Hesse, 1999, andLopp, 1997) the thermal desorption process to occurs with a much lower rate than the photodesorption process, i.e.…”

“…The development of kinetic expressions to describe reaction rate as a function of the influencing parameters are not so numerous (e.g. Peral et al, 1997;Childs and Ollis, 1981;Blake and Griffin, 1988;Cunningham and Hodnett, 1981;Bredemeyer and Hesse, 1999;Lopp, 1997 andBredemeyer et al, 2000). In addition, the proposed kinetics make use of the classical concepts: the Langmuir-Hinshelwood or the Eley-Rideal mechanisms.…”