Competitive Adsorption of NOx and Ozone on the Catalyst Surface of Ozone Converters

Abstract

Four catalysts—1%Pd-2%Mn/γ-Al2O3, 1%Pd/γ-Al2O3, 2%Mn/γ-Al2O3 and γ-Al2O3—were synthesized via a sol–gel method and characterized using various techniques to evaluate their physicochemical, textural, surface and acidic properties. They were used in the catalytic transformation of ozone and nitrogen oxides using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis. Different consecutive gas sequences were followed to unravel the poisoning role of nitrogen oxides and the possible reactivation by ozone. It has been proven that on palladium and manganese-based catalysts, the inhibition effect of nitrogen oxides was due to the formation of monodentate nitrites, monodentate, bidentate and bridged nitrates, which are difficult to desorb and decompose into gaseous NOx, either by oxidation or by thermal treatment. Interestingly, monodentate nitrites could be eliminated if the catalyst went through a co-adsorption of NOx and ozone prior to exposure in clean ozone flow. This transformation could be the reason why the catalytic conversion of ozone could return to its original value before the poison effect of nitrogen oxides.