02695nas a2200193   4500008004100000022001400041245013300055210006900188260010600257300001200363490000700375520187900382653002602261653002202287653002202309100002002331700002002351856013002371       2007                        eng d  a0025-540800aThermal stability of the Mobil Five type metallosilicate molecular sieves - an in situ high, temperature X-ray diffraction study0 aThermal stability of the Mobil Five type metallosilicate molecul  aTHE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLANDbPERGAMON-ELSEVIER SCIENCE LTDcMAY  a851-8600 v423 a<p>We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si4+ by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at similar to 960 cm(-1) by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K in S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along `a' axes is more than along `b' and V axes in S- 1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients (alpha(v)) in the temperature range 298-1023 K were -6.75 x 10(-6) K-1 for S-1, -12.91 x 10(-6) K-1 for FeS-1, -16.02 x 10(-6) K-1 for TS-1 and -17.92 x 10(-6) K-1 for ZrS-1. The highest lattice thermal expansion coefficients (alpha(v)) obtained were -11.53 x 10(-6) K-1 for FeS-1 in temperature range 298-1173 K, -20.86 x 10(-6) K-1 for TS-1 and -25.54 x 10(-6) K-1 for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si4+ in the lattice leads to a high thermal stability as compared to substitution by trivalent cations. (c) 2006 Elsevier Ltd. All rights reserved.</p>10amicroporous materials10aThermal expansion10aX-ray diffraction1 aBhange, Deu, S.1 aRamaswamy, Veda  uhttps://library.ncl.res.in/content/thermal-stability-mobil-five-type-metallosilicate-molecular-sieves-situ-high-temperature-x02412nas a2200217   4500008004100000022001400041245009800055210006900153260007300222300001200295490000800307520162800315653001801943653002201961653001401983653001201997653002202009100001802031700002002049856012502069       2008                        eng d  a1387-181100aThermal stability of mesoporous SBA-15 and Sn-SBA-15 molecular sieves: an in situ HTXRD study0 aThermal stability of mesoporous SBA15 and SnSBA15 molecular siev  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcSEP  a270-2800 v1143 a<p>Highly ordered SBA-15 and Sn-SBA-15 mesoporous molecular sieves with Si/Sn = 80, 60, 40 and 10 have been prepared through direct synthesis route under milder acidic conditions, which were used for the in situ high temperature X-ray diffraction (HTXRD) studies in the temperature range 298-1573 K for the first time in the literature. SBA-15 is found to be thermally stable up to 1473 K and appearance of alpha-cristobalite was observed at 1573 K also supported by the thermogravimetric (TG) data. A strong negative thermal expansion was observed on heating from 298 to 1573 K (alpha(a) = -4.3 x 10(-6) K-1). Sit containing samples (Si/Sn = 80 and 60) showed a positive thermal expansion (6.75 x 10(-6) K-1 and 9.04 x 10(-6) K-1, respectively). On the other hand, the samples with Si/Sn = 40 and 10 showed a strong negative thermal expansion (-4.12 x 10(-6) K-1 and -7.56 x 10(-6) K-1) similar to SBA-15. The linear thermal expansion coefficient varied in the order: Si/Sn = 60 &gt; 80 &gt; 40 &gt; 0 &gt; 10. Sn4+ ions exhibit both tetrahedral and octahedral coordination depending upon the location of these ions either on the walls of the silica (Si/Sn = 80 and 60) or in the corona region of the structure (Si/Sn = 40 and 10), respectively. The thermal decomposition of the samples (TG data) is correlated to the thermal expansion behavior (HTXRD data). The decomposition behavior of template ions located within the pores is strongly influenced by the presence of Sn in the framework and a `soft' interaction probably exists between the template ions and the Sn sites. (C) 2008 Elsevier Inc. All rights reserved.</p>10aHTXRD studies10aphase transitions10aSn-SBA-1510aTG data10aThermal expansion1 aShah, Pallavi1 aRamaswamy, Veda  uhttps://library.ncl.res.in/content/thermal-stability-mesoporous-sba-15-and-sn-sba-15-molecular-sieves-situ-htxrd-study-0