The step by step thermal dehydration process of the zeolites mordenite from Pashan (Poona, India) (Na3.51K0.14Ca1.89Mg0.09Sr0.01)[Fe0.033+Al7.40Si40.53O96].27.26H(2)O, has been studied in situ by synchrotron powder diffraction. The time-resolved experiment was performed using a translating imaging plate system. The structure refinements by full profile Rietveld analysis were performed in the Cmcm space group in the temperature range from 25 to 830degreesC. The results of structure refinements indicate that the slight cell-volume contraction (similar to1.9%) is related to the release of water molecules from the channels: above 375degreesC, the water loss lead to an enlargement of the 8-membered ring parallel to [010], which occurred by a flattening of T3-O9-T3 and T4-O4-T3 bridges. The dehydration process is reflected not only in the content of water molecules in the zeolite channel, but also in the temperature behaviour of the unit cell parameters. The cell parameters b and c decreased regularly as the temperature rose, whereas a decreased up to 400degreesC then increased up to 630degreesC, and finally decreased until the end of experiment. The removal of water molecules was accompanied by a spreading of the initial Ca sites into many positions bonded to the framework oxygens. The increased interaction with the framework oxygens of Ca sites was intimately related to the distortion of the 12-ring which is in turn related to the lengthening of the a cell parameter.
In situ time resolved synchrotron powder diffraction study of mordenite
MARTUCCI, Annalisa;CRUCIANI, Giuseppe;
2003
Abstract
The step by step thermal dehydration process of the zeolites mordenite from Pashan (Poona, India) (Na3.51K0.14Ca1.89Mg0.09Sr0.01)[Fe0.033+Al7.40Si40.53O96].27.26H(2)O, has been studied in situ by synchrotron powder diffraction. The time-resolved experiment was performed using a translating imaging plate system. The structure refinements by full profile Rietveld analysis were performed in the Cmcm space group in the temperature range from 25 to 830degreesC. The results of structure refinements indicate that the slight cell-volume contraction (similar to1.9%) is related to the release of water molecules from the channels: above 375degreesC, the water loss lead to an enlargement of the 8-membered ring parallel to [010], which occurred by a flattening of T3-O9-T3 and T4-O4-T3 bridges. The dehydration process is reflected not only in the content of water molecules in the zeolite channel, but also in the temperature behaviour of the unit cell parameters. The cell parameters b and c decreased regularly as the temperature rose, whereas a decreased up to 400degreesC then increased up to 630degreesC, and finally decreased until the end of experiment. The removal of water molecules was accompanied by a spreading of the initial Ca sites into many positions bonded to the framework oxygens. The increased interaction with the framework oxygens of Ca sites was intimately related to the distortion of the 12-ring which is in turn related to the lengthening of the a cell parameter.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
