Optimizing the Proportion of Framework Elements and the Distribution of Active Sites in Pd–SSZ-13 for Better Passive NOx Adsorber Performance

Abstract

This study focuses on exploring the effects of Si–Al ratio, Pd loading, and the presence of C3H6 on the performance of the Pd–SSZ-13 catalyst. When the Si–Al ratio is 15 and the Pd loading is 1%, the catalyst has the best adsorption performance. NO can be adsorbed in the form of NO+ with the cation exchange sites through two different paths. The catalyst with a Si–Al ratio of 15 has the highest Pd2+ content, so it can undergo oxidation–reduction reactions with NO to generate a large amount of NO+. A certain amount of Pd content can provide a large number of weak adsorption sites for NO and NO2, but when the Pd content increases, there will be too much palladium oxide material generated to cover the surface of the molecular sieve. C3H6 competes with NO and then blocks the pores of the molecular sieve, making the active sites difficult to use.