Influence of the washcoat characteristics on NH3-SCR behavior of Cu-zeolite monoliths

摘要

The preparation procedure of a structured SCR catalyst is investigated by optimizing preparation method, varying active phase's incorporation order: on one hand, cordierite substrates were washcoated with bare zeolite and afterwards Cu ion exchange was carried out over the previously zeolite washcoated monoliths and, on the other hand, Cu ions were first exchanged over powder zeolite and then the Cu-zeolite was deposited on the cordierite monolith. BETA and ZSM-5 zeolites have been used. The copper content was also varied in prepared catalysts, i.e., 3% and 5%. A monolith of zeolite was also extruded and directly exchanged on the monolith with 2% of copper. Monoliths prepared by first exchanging the powder zeolite and using it for washcoating the monolith (IE-W) achieved better SCR behavior with respect to catalysts prepared in the opposite order (W-IE), for a feedstream with 750 ppm NO, 750 ppm NH3 and 7.5% O2 in Ar, and a space velocity of 30,000 h~(-1), due to higher efficiency of the ion-exchange and to the better Cu distribution in the washcoat, as revealed from the XPS results. Besides, the extruded BETA catalyst achieved better SCR conversion than Beta zeolite washcoated monoliths.