The effect of temperature on NOx reduction by H2 in the presence of excess oxygen on a Pt/Al2O3 monolithic catalyst

This study examined the reduction of NOx by H2 over a Pt/Al2O3 catalyst coated onto a monolith as a function of temperature. The formation of N2O began at a low temperature due to the chemisorption of NO on Pt metal and its resulting oxidation at the Pt active sites. The formation of N2 was possible at higher temperatures because at the high temperatures, the reaction rate for N2 formation was higher than the reaction rate for N2O formation. The formation of NO2 was predominant above 150 °C due to the excessive oxidation activity of the catalyst. The formation of N2O at low temperatures and that of N2 at high temperatures were found to be strongly related to the Pt loading and the temperature range in which the reductive activity was obtained, respectively. Therefore, both reductive conditions and an adequate reaction temperature are important factors for the selective formation of N2 from the reduction of NO on a Pt catalyst. The temperature-dependent change in the oxidation state of Pt during the reduction of NO was also examined to determine the mechanism for the reduction of NOx by H2. In addition, the reaction conditions for the selective reduction of NOx to N2 were determined.