Studies on hydrothermal treatment of A-zeolites by Moessbauer and ESR spectroscopy

The influence of hydrothermal treatment on the structure of primary pores of A-zeolites was systematically investigated by ESR and Moessbauer spectroscopy. The structure of primary pores of these zeolites was modified by Mg2+, Li+ and paramagnetic Fe3+ ions incorporated into the initial zeolite. Coordinations and positions of the iron ions inside of the large cavity were investigated by ESR; magnetically ordered and not magnetically ordered phases of iron on the surface of the zeolites were identified by Moessbauer spectroscopy. The hydrothermal stability of A-zeolites is essentially lowered by Mg2+ cations at high degrees of iron exchange. On the other hand the hydrothermal treatment only changes positions of the iron ions and the mass ratios and particle sizes of the iron phases on the surface of the crystallites. The hydrothermal stability of the structure of primary pores is not influenced thereby. (author)