SPECTROSCOPIC STUDIES OF THE STABILITY OF ZEOLITIC DENO(X) CATALYSTS

Cu-ZSM-5 is considered for selective catalytic reduction (SCR) of NOx in streams with ca. 10% H2O which causes dealumination and activity lo ss. Multivalent Co2+, Ni2+, Pd2+, Cu2+, Ga3+, Al3+, Fe3+, La3+ and Ce3 + ions were tried as stabilizers. MAS-NMR of tetrahedral Al was the de alumination yardstick. Information was also obtained from NMR of H-1, Na-23 and Si-29. Some ions, La3+ and Ce3+, suppress the dealumination but samples containing the active Cu2+ and the La3+ are not as stable as singly modified materials and not more active in SCR than non-modif ied Cu-ZSM-5. The Cu2+ was monitored in-situ by ESR under flow-through conditions. Steaming at 650 degrees C or calcination at 850 degrees C irreversibly changes the co-ordination of all square-planar Cu2+. By incorporating ca. 5 wt% of La or Ce, apart of the copper (20-30%) pres erves the active square-planar Cu2+ co-ordination even after 0.5 h at 850 degrees C. This is reflected in a higher ethane oxidation activity .