Abstract
The NOx storage mechanism on BaTi0.8Cu0.2O3 catalyst were studied using different techniques. The results obtained by XRD, ATR, TGA and XPS under NOx storage–regeneration conditions revealed that BaO generated on the catalyst by decomposition of Ba2TiO4 plays a key role in the NOx storage process. In situ DRIFTS experiments under NO/O2 and NO/N2 show that nitrites and nitrates are formed on the perovskite during the NOx storage process. Thus, it seems that, as for model NSR catalysts, the NOx storage on BaTi0.8Cu0.2O3 catalyst takes place by both “nitrite” and “nitrate” routes, with the main pathway being highly dependent on the temperature and the time on stream: (i) at T < 350 °C, NO adsorption leads to nitrites formation on the catalyst and (ii) at T > 350 °C, the catalyst activity for NO oxidation promotes NO2 generation and the nitrate formation.
Highlights
NOx Storage and Reduction (NSR) is one of the proposed technologies for the effective abatement of NOx from exhaust gas emitted by lean burn engines
The present paper aims to elucidate a mechanism for NOx storage on this free-noble-metal catalyst (BaTi0.8 Cu0.2 O3 )
BaTi0.8 Cu0.2 O3 catalyst synthetized by sol–gel method is a mixed oxide with perovskite structure (XRD) and negligible porosity
Summary
NOx Storage and Reduction (NSR) is one of the proposed technologies for the effective abatement of NOx from exhaust gas emitted by lean burn engines. Based on the high chemisorption capacity of the alkaline/alkaline earth oxide, the NSR catalyst is able to store a high amount of NOx during the short time of the lean conditions step (oxygen rich atmosphere). The NSR process involves several steps: (i) during the lean cycle, NO (main nitrogen oxide compound in gas exhaust conditions) to NO2 oxidation followed by its storage in the form of nitrites/nitrates on the surface of the basic oxide component of the catalyst, while afterwards, (ii) during the rich cycle, reductant feed or generation causes NOx release from the catalyst and their subsequent reduction to N2 [4]. According to the NOx storage mechanism proposed by Fridell and co-workers [5], NO2 , coming from the oxidation of NO onto Pt active sites, is mainly adsorbed on BaO forming surface nitrates by a disproportionation reaction that involves the release of one molecule of NO for every three molecules of NO2 adsorbed (1)
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