In this investigation samples of exhaustively Ba-exchanged zeolites Ba-A, Ba X, and Ba-LSX were subjected to thermal treatments in the temperature range 200-1550 degreesC for times up to 40 h. Their thermal transformations were comparatively studied by room temperature X-ray diffraction. Upon heating, the three zeolites undergo the following sequence of transformations: zeolite-->amorphous phase-->hexacelsian-->monoclinic celsian in strongly different ways. In particular it was found that: (1) The crystallisation of nuclei of monoclinic celsian dispersed in the amorphous phase arising from the thermal collapse of the structure of zeolite Ba-A, recorded above 500 degreesC in a previous work, did not occur for zeolites Ba-X and Ba-LSX. (2) Zeolite Ba-A exhibited a far greater reactivity than zeolites Ba-X and Ba-LSX; actually, the conversion of hexacelsian into monoclinic celsian attained completion at 1300 degreesC, starting from zeolite Ba-A, whereas did not attain completion in the most severe experimental conditions experienced (1550 degreesC, 24 h), starting from zeolites Ba X and Ba-LSX. Such different thermal behaviours could be reasonably ascribed to the different middle-range order occurring in the amorphous phases arising from the thermal collapse of the microporous structures of zeolites Ba-A, Ba-X, and Ba-LSX.
A comparative study of the thermal transformations of Ba-exchanged zeolites A, X and LSX
FERONE, Claudio;
2004-01-01
Abstract
In this investigation samples of exhaustively Ba-exchanged zeolites Ba-A, Ba X, and Ba-LSX were subjected to thermal treatments in the temperature range 200-1550 degreesC for times up to 40 h. Their thermal transformations were comparatively studied by room temperature X-ray diffraction. Upon heating, the three zeolites undergo the following sequence of transformations: zeolite-->amorphous phase-->hexacelsian-->monoclinic celsian in strongly different ways. In particular it was found that: (1) The crystallisation of nuclei of monoclinic celsian dispersed in the amorphous phase arising from the thermal collapse of the structure of zeolite Ba-A, recorded above 500 degreesC in a previous work, did not occur for zeolites Ba-X and Ba-LSX. (2) Zeolite Ba-A exhibited a far greater reactivity than zeolites Ba-X and Ba-LSX; actually, the conversion of hexacelsian into monoclinic celsian attained completion at 1300 degreesC, starting from zeolite Ba-A, whereas did not attain completion in the most severe experimental conditions experienced (1550 degreesC, 24 h), starting from zeolites Ba X and Ba-LSX. Such different thermal behaviours could be reasonably ascribed to the different middle-range order occurring in the amorphous phases arising from the thermal collapse of the microporous structures of zeolites Ba-A, Ba-X, and Ba-LSX.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
