The similarities and differences in structural characteristics and physico-chemical properties of AgAlBEA and AgSiBEA zeolites
Résumé
AgAlBEA and AgSiBEA zeolites have been prepared by two preparation procedures. The conventional wet impregnation is used to obtain AgAlBEA with silver present mainly in extra-framework position. The two-step postsynthesis procedure which consists of first creating the vacant T-atom sites with associated silanol groups by treatment of TEABEA zeolite with nitric acid and then impregnating of resulting SiBEA zeolite with an aqueous solution of AgNO3 is used to obtain AgSiBEA zeolites with silver present mainly in framework position. The incorporation of Ag ions into the vacant T-atom sites of the framework of SiBEA zeolite as mononuclear Ag(I) has been evidenced by combined use of P-XRD, diffuse reflectance UV-vis, FTIR and XPS. The consumption of OH groups has been monitored by FTIR. The Brønsted and Lewis acidity of AlBEA, AgAlBEA, SiBEA and AgSiBEA has been identified by FTIR spectroscopy of adsorbed pyridine and CO as probe molecules. The catalytic activities of AgAlBEA and AgSiBEA in SCR of NO with ethanol have been investigated. These studies show that silver environment and acid-base properties play a significant role in catalytic activities of these Ag containing BEA zeolites.