AgY zeolite as catalyst for the selective catalytic oxidation of NH3

Abstract

Ag-exchanged Y zeolites (Si/Al = 2.5; Ag/Al = 0.30–0.95) have been tested in the NH 3 –SCO reaction, the most promising method for the elimination of ammonia emissions, and deeply characterized before and after reaction by using a variety of techniques (XRD, TEM, UV–Vis, 109 Ag NMR, XAS spectroscopies). The most active centres for the NH 3 –SCO reaction are Ag 0 nanoparticles (NPs) formed under reduction conditions and both activity and selectivity to N 2 increase with the silver loading. The Ag 0 NPs are dramatically modified under reaction conditions, being most of them dispersed resulting in small clusters and even atomically Ag + cations, the latter accounting for around half silver atoms. The presence of water into the reaction feed promotes the dispersion and oxidation of silver nanoparticles, but the catalyst performance is only slightly affected. The results are fully consistent with the previously proposed i-SCR mechanism for NH 3 –SCO reaction on silver catalysts. • Silver nanoparticles formed in AgNaY zeolites under hydrogen reduction are the active sites for NH 3 –SCO reaction. • The NH 3 conversion and N 2 selectivity on AgNaY increases with the silver loading. • Silver species change during the course of the NH 3 –SCO reaction. • Silver clusters and atomically dispersed Ag + are identified after the NH 3 –SCO reaction.