The thermal behaviour of microporous materials is of essential importance both for their characterization and for their industrial applications and varies significantly from one material to another. The isomorphous substitution of Al and/or Si by other tri- and tetravalent metal ions is considered a tool for tailoring the catalytic properties of zeolites. In recent years, much attention has been given to boron substituted zeolites (borosilicates) because their weaker acidity is suitable for certain catalytic reactions that require mild solid acids as catalysts. (e.g. toluene alkylation with ethanol) [1]). The thermal dehydration and template burning process of a boron substituted levyne (B-LEV), synthesized in the presence of quinuclidine (Q) ([Na3, H2)[B5Si49O108]∙ 6Q ∙ n H2O) [2], were studied in situ by synchrotron powder diffraction up to 900°C. Time-resolved diffraction data were collected at the GILDA beamline at ESRF (Grenoble). TG and DTG analyses carried out from 25 to 900°C indicated that the overall weight loss is about 27%. The evolution of the structural features monitored by full profile Rietveld refinements reveals that the decomposition and expulsion of organic molecules (at ~ 600°C) causes a dramatic change in the unit-cell parameters. At the same time, a sudden change in the slope of the TG analyses is reported. At room temperature quinuclidine assumes two different orientations within the cage which are differently occupied. A sharp thermal expansion characterizes B-LEV when one of two possible orientations of the Q molecules is lost, whereas negative thermal expansion accompanies the expulsion of the second one. XRD diffraction patterns indicated that B-LEV maintains its crystallinity up to 800°C. At higher temperature it undergoes a partial structural collapse. References. [1] Chen, L.Z. & Feng, Y.Q. (1992): Zeolites, 12, 347-350; [2] Millini, R., Carati , A., Bellussi, G. (1992): Zeolites, 12, 265-268.
DEHYDRATION DYNAMICS OF B-LEVYNE BY IN SITU TIME RESOLVED SYNCHROTRON POWDER DIFFRACTION
LEARDINI, Lara;MARTUCCI, Annalisa;ALBERTI, Alberto;CRUCIANI, Giuseppe
2010
Abstract
The thermal behaviour of microporous materials is of essential importance both for their characterization and for their industrial applications and varies significantly from one material to another. The isomorphous substitution of Al and/or Si by other tri- and tetravalent metal ions is considered a tool for tailoring the catalytic properties of zeolites. In recent years, much attention has been given to boron substituted zeolites (borosilicates) because their weaker acidity is suitable for certain catalytic reactions that require mild solid acids as catalysts. (e.g. toluene alkylation with ethanol) [1]). The thermal dehydration and template burning process of a boron substituted levyne (B-LEV), synthesized in the presence of quinuclidine (Q) ([Na3, H2)[B5Si49O108]∙ 6Q ∙ n H2O) [2], were studied in situ by synchrotron powder diffraction up to 900°C. Time-resolved diffraction data were collected at the GILDA beamline at ESRF (Grenoble). TG and DTG analyses carried out from 25 to 900°C indicated that the overall weight loss is about 27%. The evolution of the structural features monitored by full profile Rietveld refinements reveals that the decomposition and expulsion of organic molecules (at ~ 600°C) causes a dramatic change in the unit-cell parameters. At the same time, a sudden change in the slope of the TG analyses is reported. At room temperature quinuclidine assumes two different orientations within the cage which are differently occupied. A sharp thermal expansion characterizes B-LEV when one of two possible orientations of the Q molecules is lost, whereas negative thermal expansion accompanies the expulsion of the second one. XRD diffraction patterns indicated that B-LEV maintains its crystallinity up to 800°C. At higher temperature it undergoes a partial structural collapse. References. [1] Chen, L.Z. & Feng, Y.Q. (1992): Zeolites, 12, 347-350; [2] Millini, R., Carati , A., Bellussi, G. (1992): Zeolites, 12, 265-268.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
