Study of the deactivation of Co- and Pt,Co-mordenite during the SCR of NO x with CH 4

Abstract

Co- and Pt,Co-mordenite catalysts were found to lose about 50% of their initial NO-reduction and CH 4-oxidation activity during a long catalytic NO x -SCR test. Adsorption capacities for N 2, X-ray diffraction and Raman spectroscopic results suggested that the activity loss cannot be explained by either mordenite dealumination or extensive Co 3O 4 formation. Infrared spectra of the adsorbed pyridine showed that fresh catalysts have strong Brönsted and Lewis acidity. The Brönsted acidity was attributed to bridging OH groups of mordenite, formed from H 2O by heterolytic dissociation in the electric field around the Co 2+ ions. During the catalytic reaction, a large fraction of both kinds of acid sites was lost. The drop of acidity and catalytic activity was explained by migration of the Co 2+ ions to lattice positions where the ion is not accessible by pyridine and is coordinated by framework oxygen atoms only. High-pressure DRIFTS spectra of adsorbed N 2 and H 2-TPR results provided additional evidence of the connection between the deactivation and cation migration processes.