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

Abstract

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 (RBragg = 12.6%) was obtained with PDF analysis (Rw = 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.