The structural response of the synthetic zeolite AlPO4-5 [AFI framework type (1), s.g. P6cc, a = 13.7188(1), b = 8.4103(1) Å] to the high-temperature (HT) induced dehydration was investigated by in situ synchrotron X-ray powder diffraction (XRPD). AlPO4-5 is an aluminophosphate (Al12P12O48) characterized by the presence of 12-ring, 6-ring and 4-ring channels parallel to the crystallographic c axis [001]. The 12-rings (free diameter 7.3 Å) are connected by oxygen bridge into sheets perpendicular to the c axis (2). The tetrahedra are alternatively centered by Al3+ and P5+. While previous studies investigated the water adsorption process in AlPO4-5 from 280 to 300 K (3), here we report the results of a HT XRPD dehydration experiment performed from 25 to 850 °C (ID22 beamline, ESRF, Grenoble). From the rT refinement, performed by Rietveld method, about 14 water molecules per unit cell are localized, distributed over five extraframework sites. All water molecules are completely released under 100° C, in agreement with the thermal gravimetric analysis. No phase transitions are observed in the investigated T-range. The unit cell volume increases of 1.3% up to 150°C (Fig. 1), as the result of the increase of both a and c cell parameters. After the complete dehydration, an inversion of the cell parameters behavior is observed, with a the final cell volume only 0.8% larger than the initial one at 850° C. Upon heating, some framework rearrangements occur. Namely, an overall increase of the T-O-T angles is observed during the first 100° C of the heating ramp, accompanied by an increase of the 12-ring channel diameters, becoming almost equivalent at 150 °C. As a consequence, the12-ring channel temporarily becomes almost circular at this temperature. We suggest that these deformations favor the total water release from the zeolite channels.(1) Baerlocher, Ch.; McCusker, L. B.; Olson D.H. Elsevier. 2007. (2) Klap, G. J.; van Koningsveld, H.; Graafsma, H.; Schreurs, A.M.M. Microporous Mesoporous Mater. 2000, 38, 403. (3) Floquet, N.; Coulomb, J.P.; Dufau, N.; Andre, G. J. Phys. Chem. 2004, 108, 13107.

THERMAL BEHAVIOR OF AlPO4-5 ZEOLITE: AN IN SITU SYNCHROTRON X-RAY POWDER DIFFRACTION STUDY

S. Quartieri;
2017-01-01

Abstract

The structural response of the synthetic zeolite AlPO4-5 [AFI framework type (1), s.g. P6cc, a = 13.7188(1), b = 8.4103(1) Å] to the high-temperature (HT) induced dehydration was investigated by in situ synchrotron X-ray powder diffraction (XRPD). AlPO4-5 is an aluminophosphate (Al12P12O48) characterized by the presence of 12-ring, 6-ring and 4-ring channels parallel to the crystallographic c axis [001]. The 12-rings (free diameter 7.3 Å) are connected by oxygen bridge into sheets perpendicular to the c axis (2). The tetrahedra are alternatively centered by Al3+ and P5+. While previous studies investigated the water adsorption process in AlPO4-5 from 280 to 300 K (3), here we report the results of a HT XRPD dehydration experiment performed from 25 to 850 °C (ID22 beamline, ESRF, Grenoble). From the rT refinement, performed by Rietveld method, about 14 water molecules per unit cell are localized, distributed over five extraframework sites. All water molecules are completely released under 100° C, in agreement with the thermal gravimetric analysis. No phase transitions are observed in the investigated T-range. The unit cell volume increases of 1.3% up to 150°C (Fig. 1), as the result of the increase of both a and c cell parameters. After the complete dehydration, an inversion of the cell parameters behavior is observed, with a the final cell volume only 0.8% larger than the initial one at 850° C. Upon heating, some framework rearrangements occur. Namely, an overall increase of the T-O-T angles is observed during the first 100° C of the heating ramp, accompanied by an increase of the 12-ring channel diameters, becoming almost equivalent at 150 °C. As a consequence, the12-ring channel temporarily becomes almost circular at this temperature. We suggest that these deformations favor the total water release from the zeolite channels.(1) Baerlocher, Ch.; McCusker, L. B.; Olson D.H. Elsevier. 2007. (2) Klap, G. J.; van Koningsveld, H.; Graafsma, H.; Schreurs, A.M.M. Microporous Mesoporous Mater. 2000, 38, 403. (3) Floquet, N.; Coulomb, J.P.; Dufau, N.; Andre, G. J. Phys. Chem. 2004, 108, 13107.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/3119703
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