Sorption of nitrogen oxides on MnOy-ZrO2 and Pt-ZrO2-Al2O3

Manganese zirconium oxide (MnOy-ZrO2) and platinum-zirconium oxide supported on Al2O3 (Pt-ZrO2-Al2O3) were investigated as effective and reversible sorbents for NOx. The sorption is initiated by oxidation of NO on a Mn or Pt surface. Then, the oxidized NOx species are stored as nitrate ions on ZrO2. These sorbents exhibited rapid and large sorption of NO in the presence of gaseous O-2 Coexisting CO2 in the atmosphere hardly affected the sorption and desorption properties. The sorbed NOx species desorbed on heating or on exposure to a reducing atmosphere. The evolved gas was quite dependent on the active catalytic component, such as Pt or Mn. Selective catalytic reduction of NOx or decomposition of NO easily proceeded on Pt during desorption in the reducing atmosphere. In this case, the desorption gas contained a large proportion of N-2 or N2O species for Pt-ZrO2-Al2O3. But the desorbed gas from MnOy-ZrO2 contained mainly NO and NO2, whereas the NO desorption was dominant in the reducing atmosphere. The difference in desorption species is suggested to result from the existence of the active lattice oxygen on Mn oxide. (C) 1998 Elsevier Science B.V.