Selektive katalytische Reduktion von NO durch NH3 an vanadyl-ausgetauschten ZSM-5-Zeolithen

Vanadium-containing ZSM-5 zeolites were prepared by exchanging Na-ZSM-5 with vanadyl sulphate solution at different pH. The samples were investigated by spectroscopic techniques (UV-VIS, ESR), and their activity in the selective catalytic reduction (SCR) of NO by NH 3 was studied in a wide temperature range (450-870 K). At pH≥3, the exchange of vanadyl cations is accompanied by the deposition of small intra-zeolite vanadium oxide clusters, which can be avoided at pH≤2.8. At elevated temperature (673 K), part of the vanadyl cations aggregates to V(V) clusters. Under more severe calcination conditions (823 K, air), these clusters can be disaggregated. Vanadyl-exchanged ZSM-5 catalysts are highly active in the SCR of NO by NH 3 competing with V 2 O 5 /TiO 2 catalysts. By comparing the catalytic behaviour of (VO)-ZSM-5 samples after specific pretreatments, isolated vanadyl cations could be identified as the active sites.