Catalysis Today, Vol.45, No.1-4, 109-115, 1998
Reversible sorption-desorption of NOx by mixed oxides under various atmospheres
Characteristics of MnOy-ZrO2 and Pt-ZrO2-Al2O3 as reversible sorbents of NOx were investigated under dynamic changes in atmosphere. These sorbents can be used reversibly with a change of C3H8 concentration in the reaction gases. Catalytic reduction of NO occurred in the presence of propane, which was more pronounced on Pt-ZrO2-Al2O3 than on MnOy-ZrO2 due to high activity of Pt surface for this reaction on MnOy in MnOy-ZrO2. The sorption was observed as soon as the atmosphere changed from a reducing to an oxidizing one. This implies that a high equilibrium partial pressure of O-2 is necessary for NO uptake since the sorbed NO3- species becomes stable. The beginning of NOx desorption atmospheres was somewhat dependent on the amount of stored NOx. The presence of propane in the gas phase strongly affected the characteristic sorption and desorption properties of MnOy-ZrO2 and Pt-ZrO2-Al2O3. The sorption and desorption properties are different for MnOy-ZrO2 and Pt-ZrO2-Al2O3, since the noble metal or metal oxide possesses unique activity for the NO reaction with C3H8 and the amount of oxygen available for oxidative sorption of NO.