Absorption/desorption of NOx process on perovskites: performances to remove NOx from a lean exhaust gas

NOx adsorption/desorption capacities of perovskites (ABO3) were measured under representative exhaust gas mixture conditions at temperatures below 550°C, with A=Ca, Sr, Ba and B=Sn, Zr, Ti. The solids exhibited good NO2 sorption capacities with a reversible adsorption to desorption process according to the sequence Ba>Sr>Ca for A, while for element B the sequence Sn>Zr>Ti is observed. In the case of alkaline earth metals, the absorption behaviour proved to be directly related to their electropositivity (Ba>Sr>Ca). The key factors which control the absorption of NO2 are the bonding energy between the element B and the oxygen atom on one hand and the electropositivity of the element A on the other. The best result was obtained with the perovskite BaSnO3. The absorption of NO2 is favoured at low temperature and in the presence of water. The addition of platinum has no significant influence upon any NO2 absorption.