Crystal Structure of MCM-22 (MWW) and Its Delaminated Zeolite ITQ-2 from High-Resolution Powder X-Ray Diffraction Data: An Analysis Using Rietveld Technique and Atomic Pair Distribution Function

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• 作者：Vaishali V. Narkhede ; Hermann Gies
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：September 22, 2009
• 年：2009
• 卷：21
• 期：18
• 页码：4339-4346
• 全文大小：881K
• 年卷期：v.21,no.18(September 22, 2009)
• ISSN：1520-5002

文摘

The three-dimensional structure of crystalline, calcined pure siliceous MCM-22 (which has a chemical formula of Si₇₂O₁₄₄) and its delaminated derivative, ITQ-2 (which has a chemical formula of Si₁₄₄O₂₈₈), also in its calcined form, have been studied using synchrotron radiation-based powder diffraction experiments employing full pattern Rietveld analysis for structure elucidation. Because of the limited structural coherence in ITQ-2, conventional analysis of the X-ray diffraction experiments using Bragg peaks only is not suitable. Instead, we applied the pair distribution function (PDF) technique to study the structure of ITQ-2, in particular, the termination of the layer slab. Despite of the structural complexity of the zeolite materials, excellent confirmation of the crystal structure based on Rietveld analysis (R_Bragg = 12.6%) was obtained with PDF analysis (R_w = 18.3%) for the calcined siliceous MCM-22. Based on results of the crystalline compound, we only succeeded to refine the diffraction data set of the delaminated material applying PDF analysis.