NO decomposition in non-reducing atmospheres. Technical progress report, March--May 1996

The studies with Co(II) ion exchanged erionite zeolites, with Si/Al molar ratio of 3.6, have been continued. It was found that the paramagnetic moment of Co(II) in erionite (8 wt% Co(II)) dehydrated at 525 C was higher than that obtained after dehydration to only 350 C. This indicated that dehydration temperatures higher than 350 C are needed for the Co(II) erionite to achieve complete dehydration and uniform dispersion of the Co(II) cations into trigonal coordination sites in the zeolite. In contrast, it appears that the Co(II) cations in A zeolite achieve the uniformly dispersed trigonal symmetry state at the dehydration temperature of 350 C. Diffuse reflectance spectroscopy was utilized to monitor the spectral changes that occurred upon adsorption of CO and ethylene on the low Co(II)-containing erionite samples after dehydration at 350 C. This demonstrated that the Co(II) cations were accessible to these ligands and that Co-Co(II) and ethylene-Co(II) complexes were formed in the zeolites. The siting and accessibility of the Co(II) cations is expected to influence the activity of zeolite catalysts for the selective catalytic reduction of NO by different reductants