NOx Removal by Oxidation on Alumina Supported Metal Oxide Catalysts Followed by Alkaline Absorption

NO oxidation is the key reaction for the oxidative NOx removal process. In this work, the catalytic NO oxidation performance of the Al2O3 supported metal oxide catalysts (M-Al2O3, M = V, Mn, Fe, Co, Ni and Ce) is evaluated. The oxidation product is absorbed by the alkaline solution for NOx removal. The NO oxidation activity increases in the following order: V << Ce < Ni < Fe < Co < Mn. As the NO oxidation involves the O uptake into the metal oxide lattice and oxidation of the adsorbed NO by the lattice O, the highest activity of Mn is attributed to the appropriate redox potential of Mn, which favors both the O uptake and the NO oxidation steps. For all the M-Al2O3 catalysts, there is an intermediate temperature to achieve maximum NO conversion, which is lower for more efficient M-Al2O3 catalyst. The temperature dependence suggests that the NO oxidation at low temperature is kinetically controlled while it is thermodynamically limited at higher temperature. The NOx removal ratio by the alkaline solution absorption increases with the NO2/NO ratio, with a maximum removal ratio of 80% when the NO2/NO ratio is higher than 3, indicating that a very high NO conversion is unnecessary.