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Zeolite Framework (zeolite + framework)
Selected AbstractsUnambiguous Observation of Electron Transfer from a Zeolite Framework to Organic Molecules,ANGEWANDTE CHEMIE, Issue 36 2009Lu Li Wer bekommt das Elektron? Sauerstoffatome, die zwei Siliciumatome in einem protonierten Zeolithen verbrücken, können durch Reaktion mit einem Alkylbromid oxidiert werden, wodurch ein Zeolithgerüst mit paramagnetischen Zentren entsteht (siehe Strukturen und EPR-Spektrum; rot O, blau Si, violett Al, grün C, gelb Br, weiß H). Ein solcher Elektronentransfer vom Zeolithgerüst kann die Produktbildung in säurekatalysierten Reaktionen mit Zeolithkatalysatoren erklären. [source] Adsorption of water in mordenite,An ab initio studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2001Th. Demuth Abstract The adsorption of water in mordenite has been investigated using density functional theory using gradient corrections to the exchange,correlation functional. In the neutral complex water is strongly physisorbed through two different hydrogen bonds, the stronger between the acid site and the water oxygen atom, the weaker between a hydrogen atom of the adsorbed molecule and a framework oxygen atom. Strong polarizations and structural distortions of both the acid site and the molecule have been observed. To elucidate the question if a chemisorbed complex (creation of a hydroxonium ion) is possible, ab initio molecular dynamics have been performed, indicating that a protonation of water occurs even for the low coverage of one water molecule per unit cell. However, this ionic configuration cannot be stabilized by the electrostatic field of the zeolite framework and is therefore not a minimum of the potential energy surface. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 110,116, 2001 [source] Application of QM simulations and multivariate analysis in the study of alkene reactivity in the zeolite H-ZSM5JOURNAL OF CHEMOMETRICS, Issue 6 2008Duangkamol Gleeson Abstract Reported herein are the results of an investigation into the effect of the extended framework of the zeolite ZSM-5 on the reaction energetics and structures of (a) the physisorbed complex formed between the zeolite and six alkenes, (b) the corresponding chemisorbed alkoxide intermediate and (c) the transition states (TS) connecting the two. For this, quantum mechanical (QM) simulations of ZSM-5 in the presence and absence of the zeolite framework have been employed. A 46T density functional theory (DFT) cluster model and a 3T:46T DFT:UFF ONIOM model are used to represent the former scenario and a simple 3T DFT cluster model for the latter. The structural implications of neglecting the zeolite framework have been rigorously compared using the multivariate statistical method principal components analysis (PCA). This method allows one to assess the correlated nature of the changes in structure along the reaction coordinate, for multiple different alkenes, in a facile, reliable way. Copyright © 2008 John Wiley & Sons, Ltd. [source] Electronic and Vibrational Properties of Fluorenone in the Channels of Zeolite LCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2004André Devaux Dr. Abstract Fluorenone (C13H8O) was inserted into the channels of zeolite L by using gas-phase adsorption. The size, structure, and stability of fluorenone are well suited for studying host,guest interactions. The Fourier transform IR, Raman, luminescence, and excitation spectra, in addition to thermal analysis data, of fluorenone in solution and fluorenone/zeolite L are reported. Normal coordinate analysis of fluorenone was performed, based on which IR and Raman bands were assigned, and an experimental force field was determined. The vibrational spectra can be used for nondestructive quantitative analysis by comparing a characteristic dye band with a zeolite band that has been chosen as the internal standard. Molecular orbital calculations were performed to gain a better understanding of the electronic structure of the system and to support the interpretation of the electronic absorption and luminescence spectra. Fluorenone shows unusual luminescence behavior in that it emits from two states. The relative intensity of these two bands depends strongly on the environment and changes unexpectedly in response to temperature. In fluorenone/zeolite L, the intensity of the 300 nm band (lifetime 9 ,s) increases with decreasing temperature, while the opposite is true for the 400 nm band (lifetime 115 ,s). A model of the host,guest interaction is derived from the experimental results and calculations: the dye molecule sits close to the channel walls with the carbonyl group pointing to an Al3+ site of the zeolite framework. A secondary interaction was observed between the fluorenone's aromatic ring and the zeolite's charge-compensating cations. [source] Preparation and Charactrization of Fibrous Crystals of Boron-containing MTW-type ZeoliteCHINESE JOURNAL OF CHEMISTRY, Issue 2 2004Mao-Ying Song Abstract Fibrous crystals of boron-containing MTW-type zeolite have been hydrothermally synthesized in B2O3 -SiO2 -HF-H2O gel system at 170 °C in 20 to 28 d by using 1, 4-diazabicyclo[2.2, 2]octane (DABCO) and methylamine as the co-template, and characterized with XRD, SEM, TEM, HRTEM and SAED. The results of characterizations show that B atoms are incorporated into the zeolite framework as tetrahedron of B(OSi)4. The fibrous single crystals of 5,50 ,m in length and 100,500 nm in width inter-grow along the c -axis of the zeolite, and the one dimension 12 oxygen ring channels are perpendicular to the fibber axis. [source] | ||||||||||