02488nas a2200265   4500008004100000022001400041245020700055210006900262260007300331300001200404490000800416520142000424653002101844653003601865653002101901653001701922653002401939653002601963653002901989653001402018653001202032100002702044700001902071856013202090       2009                        eng d  a1387-181100aDependence of Si-29 NMR chemical shielding properties of precursor silicate species, Q(0) on its local structure at the pre-nucleation stages of zeolite synthesis - a DFT based computational correlation0 aDependence of Si29 NMR chemical shielding properties of precurso  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcJUN  a105-1130 v1223 a<p>The exploration for new zeolite structures with tailored framework architectures for enhanced catalytic applications requires the knowledge about their nucleation and crystallization at molecular level. Nuclear magnetic resonance (NMR) is one of the most widely tried techniques to understand this. However, by NMR, it is difficult to accurately assign the molecular level precursor silicate structures at the pre-nucleation stages of zeolite synthesis. Hence, understanding the chemical shielding of such precursor molecules using quantum mechanical (QM) computations is extremely useful. Alkali is a fundamental component in the alkali based hydrothermal zeolite synthesis and its nature plays a major role. In the present report, we attempt to understand the differences in the local structure of the primary building block such as Si(OH)(4) (Q(0) silicate species) due to the associated alkali and their influence on NMR chemical shielding properties. Present work reports the calculation of Si-29 NMIR isotropic chemical shifts of T species with different cations such as Na, K and Ca using density functional theory (DFT). Results of natural bonding orbital (NBO) analysis, Perturbation theory energy analysis and electron density iso-surfaces were employed to obtain a deeper insight about their influence on the chemical shielding and on zeolite synthesis. (C) 2009 Elsevier Inc. All rights reserved.</p>10aAb initio method10aDensity Functional Theory (DFT)10aElectron density10aNBO analysis10aPerturbation theory10aQ(0) silicate species10aSi-29 NMR chemical shift10asynthesis10azeolite1 aSelvaraj, Kaliaperumal1 aKurian, Reshmi  uhttps://library.ncl.res.in/content/dependence-si-29-nmr-chemical-shielding-properties-precursor-silicate-species-q0-its-local-001985nas a2200205   4500008004100000022001400041245015400055210006900209260007300278300001000351490000800361520116700369653001701536653002001553653002501573653001501598653001201613100002701625856012701652       2010                        eng d  a1387-181100aTransformation of chemically fine tuned zeolite A precursor into dense lithium aluminosilicates - a comprehensive phase evolution and sintering study0 aTransformation of chemically fine tuned zeolite A precursor into  aPO BOX 211, 1000 AE AMSTERDAM, NETHERLANDSbELSEVIER SCIENCE BVcNOV  a82-890 v1353 a<p>Beyond their conventional revelation as catalysts, zeolites are being perceived as more challenging materials for modern applications. Thermal recrystallization of zeolite precursors is an efficient method for the preparation of dense aluminosilicate ceramics. However, factors viz., nature of the precursor and the way of firing it etc., influence the product quality. The present report is a systematic and detailed account of a phase transformation of Li modified zeolite A precursor using powder X-ray diffraction (PXRD), thermogravimetry (TG), differential thermal analysis (DTA), scanning electron micrographs (SEM), atomic absorption spectroscopy (MS), energy dispersive X-ray (EDX) and density measurement techniques. It involves an amorphisation followed by a recrystallization into lithium aluminosilicate (LAS). A comprehensive correlation of PXRD, TG/DTA, SEM, EDX and density data explains the complexity of high temperature phase transition (25-1200 degrees C). A qualitative phase analysis revealed the mediation of formation of LAS ceramic, beta-spodumene by few satellite transitions of SiO(2). (C) 2010 Elsevier Inc. All rights reserved.</p>10aLAS silicate10aPhase evolution10aPhase transformation10aPowder XRD10azeolite1 aSelvaraj, Kaliaperumal  uhttps://library.ncl.res.in/content/transformation-chemically-fine-tuned-zeolite-precursor-dense-lithium-aluminosilicates-0