Study of the NO adsorption capacity on Co ion exchanged mordenite

L.B. GUTIERREZ; E.E. MIRÓ; A. FESER; M.A. ULLA

Rio de Janeiro (Brasil)

Congreso; ENPROMER 2005. 2nd Mercosur Congress on Chemical Engineering and 4th Mercosur Congress on Process Systems Engineering; 2005

In order to study the contribution of Co species to the activity of NO selective reduction with methane, a thorough characterization of Co,H-mordenites was carried out using NO–TPD, H2-TPR, RAMAN, DRX and FTIR with NO as probe molecule. Different cobalt-loading catalysts (8.85, 5.70, 2.91, 2.45 and 1.15 wt.%) were prepared by ion exchange over NH4-mordenite and they were treated with different procedures (heated on He, O2 and H2). The NO adsorption capacity not only depended on the Co/Al ratio and pretreatments but also on the presence of Co oxides. In fact, for similar Co/Al ratios, Co2.91H-MOR showed a lower NO/Co ratio than Co2.45H-MOR. The presence of high concentrations of Co3O4 negatively affected both the NO to N2 conversion and the NO adsorption capacity for all pretreatments. These species probably blocked the main mordenite channels and/or produced the formation of some Co island on the zeolite surface, lowering the amount of surface Co. The main NO surface species detected were dinitrosyl and mononitrosyl. Their stability and relative amount depended on the cobalt species and the pretreatments. Heating in He or H2 induced the stabilization of part of the exchanged Co in sites less accessible to gases, whereas the calcination with O2 involved the mobilization of Co to more external sites. However, those effects were less significant for samples containing Co oxides suggesting that the spinel hampers the Co migration.