Zeolite Structure Determination Research Articles

NMR crystallography strategies for structure determination of zeolites and layered silicates

NMR crystallography strategies for structure determination of zeolites and layered silicates

Using a novel parallel genetic hybrid algorithm to generate and determine new zeolite frameworks

Abstract Zeolite structure determination and zeolite framework generation are not new problems but due to the increasing computer power, these problems came back and they are still a challenge despite the recent progress in terms of structural resolution from X-rays and electron diffraction. The infinite number of potential solutions and the computational cost of this problem make the use of metaheuristics significant for this problem. In this paper, we propose a new approach based on parallel genetic hybrid algorithm for zeolites using a modified modelization of the objective function to find hypothetical zeolite structures, close to the thermodynamic feasibility criterion. A population made of random atoms is initialized. At each generation, a crossover operator and a mutation heuristic are applied. Each individual of the population generates a potential zeolitic structure by applying the symmetry operators of a given crystallographic space group. This structure is evaluated with our objective function. From the unit cell parameters and the number of T atoms in the asymmetric unit, 6 possible zeolitic interesting structures have been found.

Synthesis and Structure determination of a new interrupted zeolite PKU-14

Zeolites have been extensively studied over many years due to their widely applications in catalysis, ion exchange, adsorption, and separation.[1] Knowing the structure of zeolite is important for understanding their properties and predicting possible applications of such materials. Structure determination of zeolites has remains challenging, as submicro- and nano-sized crystals are often obtained. Here, we elucidate a novel germanate-based zeolite PKU-14 with a 3D 12*12*12-ring channel system. The structure was solved by combing high-resolution PXRD, rotation electron diffraction method, NMR and IR spectroscopy. Ordered Ge4O4 vacancies inside the [46612] cages has been found in PKU-14, where a unique water dimer was located at the vacancies and played a structure-directing role.

Structural Determination of Ordered Porous Solids by Electron Crystallography

Knowing the structure of porous materials is essential for understanding their properties and exploiting them for applications. Electron crystallography has two main advantages compared to X‐ray diffraction for structure determination. Crystals too small or too complicated to be studied by X‐ray diffraction can be studied by electron crystallography. The crystallographic structure factor phase information, which is lost in X‐ray diffraction, can be obtained from high‐resolution transmission electron microscopy (HRTEM) images. Here, different electron microscopic techniques and their applications for structure determination of porous materials are reviewed. The recently developed automated diffraction tomography (ADT), the rotation electron diffraction (RED), and the through‐focus structure projection reconstruction (QFcous) methods make the structure determination by electron crystallography more feasible for non‐TEM experts and as efficient as that by X‐ray diffraction. How the various electron crystallographic methods are chosen are demonstrated and these methods used for solving different structural problems in porous materials. The benefits of combining electron crystallography and X‐ray diffraction for studying complex zeolite structures are also shown. A large number of examples are given to demonstrate the use of various electron crystallographic techniques for structure determination of zeolites, metal‐organic frameworks and ordered mesoporous materials. These electron crystallographic methods are general and can also be used for structural studies of other functional materials.

Structure determination of zeolites and ordered mesoporous materials by electron crystallography

Structure determination of porous materials is important for understanding the materials properties and exploiting their applications. Compared to X-ray diffraction, electron crystallography has two unique advantages. Crystals that are too small to be studied by X-ray diffraction can be studied by electron crystallography. The structure factor phase information, which is lost in diffraction, can be obtained from high resolution transmission electron microscopy (HRTEM) images. Here we will present different techniques and applications of electron crystallography for structure determination of zeolites and ordered mesoporous materials, based on electron diffraction data and/or HRTEM images. Electron crystallography and X-ray diffraction are complementary in many aspects. Their combinations show great potentials for structure determination of complex porous materials.

The role of electron diffraction in zeolite structure determination

Because electron diffraction can sample individual microcrystals, it is clear that this single crystal method can facilitate, in at least two ways, structure determination for inorganic materials, such as zeolites, that are preferentially microcrystalline. First, in a qualitative application, three-dimensional tilts of individual small crystals, to map the reciprocal lattice, greatly facilitates unit cell and space group determination when powder diffraction indexing programs fail. If incoherent multiple scattering leads to violation of systematic absences, these absences can be restored by collection of precession diffraction patterns based on the Vincent-Midgley method [1], as demonstrated recently [2]. The second, quantitative application, i. e. ab initio structure determination from electron diffraction intensity data, also seems to be feasible. In the auspicious case of thin layered zeolite crystals in the MWW framework, the three-dimensional structure was determined by direct methods based on maximum entropy and likelihood [3], the only difficulty arising from the ’missing cone’ of structural information imposed by the goniometric tilt limit. Possible methods for restoration of the missing information, although approximately provided by phase and amplitude prediction (Sayre equation), include alternate crystallization of the desired crystal projection by appropriate structure directing agents, or, simply, by sectioning the desired view of the structure in available samples. Multiple scattering perturbations include both n-beam dynamical and secondary scattering; collection of precession data greatly reduces the latter influence [2], facilitating ab initio analyses via direct methods (e. g. tests on LTA, ITQ-1, ITQ-7, ZSM-10, MOR, MCM-68), while systematic dynamical diffraction is still observed (even at 300 kV). Improved collection of intensity data via imaging plates, exploiting a much greater linear response to intensity, is also recommended. One other, largely unexplored, possibility is to collect zero loss electron diffraction intensities in electron microscopes with in-line ’omega’ energy filters. Generally, for unknown zeolite structures, electron diffraction analyses have been carried out in parallel with the usual powder determinations, not only to provide needed symmetry information but also to detect structural details of important zones, e. g. the location of porous channels to guide the powder determination; in some cases, the crystal structure would not have been solved without this electron crystallographic information. Whether or not true ab initio electron crystallography can ever exist as an independent structural tool for zeolites remains a question to be answered by ongoing research.

Structure determination of zeolites: making all the pieces fit

Structure determination of zeolites: making all the pieces fit

Structure solution of zeolites from powder diffraction data

AbstractThis article reviews methods in structure determination of zeolites from powder diffraction data. First, examples of different model building techniques are discussed. Then the applications and limitations of conventional direct methods in zeolite structure solution are examined. Methods for partitioning overlapping peak intensities are also discussed, and examples are given to illustrate improvements in structure elucidation when these techniques are applied.Ab initiostructure determination of zeolites from powder data has made great progress within the past 10 years. In particular, the developments of the ZEFSAII, FOCUS, and XLENS algorithms have allowed rapid structure solutions of zeolites, in some cases a few days after their initial discoveries.

Zeolite structure determination from powder diffraction data: applications of theFOCUSmethod

TheFOCUSapproach to zeolite structure determination from powder diffraction data has been applied to data from four different zeolitic materials. The solutions of the structures of two aluminophosphate molecular sieves, YUL-89 (AWO topology) and YUL-90 (ZON topology), are used to demonstrate routine applications of the procedure. The high-silica zeolite ZSM-5 (MFI topology), which has 12 Si atoms (38 framework atoms) in the asymmetric unit, and the gallophosphate cloverite (-CLO topology), the framework of which is not fully fourfold connected, provide examples of extreme cases, which challenge the limits of theFOCUSalgorithm. Taken together, the four examples give an overview of the practical aspects of theFOCUSmethod and illustrate its potential and its limitations.

Use of Electron Microscopy and Microdiffraction for Zeolite Framework Comparison

Recent successful zeolite structure determination based on electron diffraction and image analysis data shows interesting prospects to characterize zeolitic frameworks provided the crystals are thin enough to produce useful crystallographic phases from image analysis. Zeolite SSZ-25 and porosil ITQ-1 structures were compared to reveal if they are isomorphous to MCM-22 zeolite. By using electron microdiffraction intensity data in the [0001] axis and phases extracted from HREM images taken at different defocus conditions, the resulting projected [0001] potential maps are found to be very similar for both structures and close to that of the MCM-22 zeolite.

Zeolite structure determination from powder data: computer-based incorporation of chemical information

Zeolite structure determination from powder data: computer-based incorporation of chemical information

Zeolite structure determination by solid state MAS NMR and synchrotron powder diffraction

Zeolite structure determination by solid state MAS NMR and synchrotron powder diffraction

Quantitative analysis of low-dose high-resolution images and diffraction patterns from zeolites using a slow-scan CCD camera

Zeolites are an important class of low-density aluminosilicates framework structures with applications to the field of catalysis and molecular sieves. In order to understand die origin of die unique properties of these materials and hence optimize their performance, it is essential to have a detailed description of their structures. Zeolite structure is often described in terms of the secondary building unit (SBU) which is a specific configuration of the SiO4 tetrahedrons. Structure determination of zeolites is then reduced to determine the types of SB Us and their connectivities when forming the 3-D framework structure.It has been recognized that zeolites undergo rapid structural damage under electron beam irradiation. The use of a slow-scan CCD camera to record low-dose high resolution electron microscope (HREM) images from zeolites with the combination with real-space averaging techniques has been shown to be successful in obtaining the averaged unit cell with high signal-to-noise ratio (SNR).