Particular characteristics of silver species on Ag-exchanged LTL zeolite in K and H form

Abstract

Ag-exchanged L zeolites with different contents of K+ and H+ as co-cations were prepared. The effect of K+ and H+ in the Ag species nature and distribution was evaluated by PXRD, TEM, H2-TPR, in situ DRS UV–vis and NO and NO+O2 TPD experiments. The effect of oxidizing or reducing treatments in the Ag species distributions was also assessed.Although all calcined samples possess Ag0 particles, as detected by TEM, they have different Ag+ distributions in the zeolite exchange-sites, depending on the K+ exchange level.The importance of sample pre-treatment in the case of Ag-exchanged zeolites was put into evidence by H2-TPR, which also ascertained the possible presence of highly dispersed Ag2O on Ag/KL and Ag/HL.In situ oxidation and reduction treatments during DRS UV–vis were performed. Under oxidative conditions, only Ag/KL zeolite shows the formation of Ag0 particles, while the other two zeolites (Ag/HKL and Ag/HL) spectra do not present this feature.NO and NO+O2 TPD experiments revealed that Ag/KL adsorbs more strongly NO than Ag/HL. O2 co-adsorption also changes the adsorbed NOx species, while increasing their amount on both Ag/KL and Ag/HL.Ag/KL and Ag/HL have a similar maximum NO conversion in NOx Selective Catalytic Reduction (SCR) with decane as reducer, but at different temperatures (350 vs. 500°C) and with different selectivity to N2 (40% vs. 85%).