Influence of CO₂ on storage and release of NO_x on barium‐containing catalyst

Abstract

A barium‐containing three‐way automotive emission catalyst was submitted to a NO_x storage step in flowing lean gas mixture containing 340 ppm NO and 8 vol% O₂ in helium. NO_x release was carried out in the 250–550°C temperature range, either in pure helium or in the presence of a 10 vol% CO₂ in helium mixture. It was shown that at 450–550°C all of the stored NO_x on the barium trap can be released fastly in the CO₂‐containing gas mixture or, after a longer time, in pure helium: these data show that NO_x release can occur in the absence of a reducing agent. The NO_x release was not complete at 350°C and did not occur at 250°C. The assisting effect of CO₂ as regards to NO_x release was interpreted in terms of the existence of the CO_2,gas + *NO_2,stored ⇌ *CO_2,stored + NO_2,gas equilibrium, suggesting the competitive storage of CO₂ and NO₂ for a unique type of barium storage sites (*).