Metal Oxides as Catalysts and Adsorbents in Ozone Oxidation of NO_<i>x</i>

Abstract

NO _x represents an important group of pollutants that are formed in fuel combustion. As these pollutants cause significant environmental problems, removal of NO _x from exhaust gases is necessary. The present study investigated the influence of metal oxide powders on the removal of NO _x by oxidation with ozone. The aim of the study was to compare the catalytic effect of TiO₂, Al₂O₃, and Fe₂O₃ and to investigate the dependence of the effective rate constant on temperature. NO (400 ppm) and a variable concentration of ozone in a mixture of N₂ and O₂ was directed through the catalyst chamber and heated to 60-140 °C. The addition of metal oxides resulted in a significant increase in the efficiency of the oxidation of NO to N₂O₅. Fe₂O₃ had the largest effect with a maximum of an approximately 3-fold increase in the effective rate constant at 100 °C. At the same time Fe₂O₃ had the lowest NO _x adsorption capacity. In the case of all metal oxides, oxidation of NO to N₂O₅ caused an abrupt increase in adsorption of NO _x.