REVERSIBLE AND IRREVERSIBLE ADSORPTION OF NITROGEN MONOXIDE ON COBALT ION-EXCHANGED ZSM-5 AND MORDENITE ZEOLITES AT 273-523-K

The adsorbability of nitrogen monoxide (NO) on cobalt ion-exchanged zeolites has been studied by pressure swing adsorption (PSA), temperature-programmed desorption (TPD) and IR techniques on the following zeolite samples; ZSM-5, mordenite, ferrierite, offretite/erionite, L-, Y- and X-type. The amounts of NO reversibly (q(rev)*) and irreversibly (q(irr)*) adsorbed at 273 K per cobalt ion exchanged, increased with decreasing aluminium content of the parent zeolite. On Go-ZSM-5 zeolite, both q(rev)* and q(irr)* were constant, independent of the ion exchange level. Over the range 273-523 K the maximum amount of reversible adsorption on Go-ZSM-5 or Co-mordenite has been observed at around 323-473 K, while the amount of irreversible adsorption decreased monotonically with increasing adsorption temperature. It has been confirmed on Go-ZSM-5 that most of the reversible adsorbates at 298 K are NO2+. The irreversibly adsorbed NO species on Co-ZSM-5 have been attributed to two kinds of dinitrosyl adsorbates. One has an ON-Co-NO bond angle of 99 degrees and desorbs around 390 K, while the bond angle of the other is 123 degrees and the desorption temperature is ca. 510 K. On mordenite and Y-type zeolites only the latter species was observed.