The thermal behaviour of boron substituted ZSM-5 synthesized in the presence of ethylenediamine as an organic template was highlighted for the first time by in situ time-resolved synchrotron powder diffraction in the 25–900 °C temperature range. The evolution of the structural features was followed by full profile Rietveld refinements at up to 730 °C. Above this temperature, a structural breakdown occurs and B-ZSM-5 is converted into a β-cristobalite phase. A continuous increase in unit-cell parameters as a function of temperature is observed both during calcination (between 200 and 500 °C) and afterwards. This behaviour is completely unusual when compared to that assumed by other boron-free MFI-type materials both in their as-synthesized as well as calcined forms. On the basis of all these results, B-ZSM-5 represents the first example of positive thermal expansion in a material with an MFI type topology.
The unusual thermal behaviour of boron-ZSM-5 probed by “in situ” time-resolved synchrotron powder diffraction
LEARDINI, Lara;MARTUCCI, Annalisa;CRUCIANI, Giuseppe
2013
Abstract
The thermal behaviour of boron substituted ZSM-5 synthesized in the presence of ethylenediamine as an organic template was highlighted for the first time by in situ time-resolved synchrotron powder diffraction in the 25–900 °C temperature range. The evolution of the structural features was followed by full profile Rietveld refinements at up to 730 °C. Above this temperature, a structural breakdown occurs and B-ZSM-5 is converted into a β-cristobalite phase. A continuous increase in unit-cell parameters as a function of temperature is observed both during calcination (between 200 and 500 °C) and afterwards. This behaviour is completely unusual when compared to that assumed by other boron-free MFI-type materials both in their as-synthesized as well as calcined forms. On the basis of all these results, B-ZSM-5 represents the first example of positive thermal expansion in a material with an MFI type topology.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
