EMM-17, a New Three-Dimensional Zeolite with Unique 11-Ring Channels and Superior Catalytic Isomerization Performance.

A new catalytically active zeolite, designated EMM-17 (ExxonMobil Material-17), with a three-dimensional (3D) 11 × 10 × 10-ring topology has been discovered from high throughput experiments while evaluating a family of new organic structure directing agents (OSDAs), 1-alkyl-4-(pyrrolidin-1-yl)pyridin-1-ium hydroxide. The framework structure was determined by model building techniques and confirmed by diffraction calculations. The EMM-17 structure is a random intergrowth of two polymorphs which have a 3D arrangement of intersecting 11 × 10 × 10-ring pores.

Rectangular chain packing of methyl-branched paraffins: persistence of an interchain interaction and forms of disorder.

The rectangular crystal packing of methyl-branched paraffins in their orthorhombic forms is studied systematically by electron diffraction to show that, irrespective of branch position on the chain, a close interaction of chain double rows occurs, placing the branch in the space between two chain ends. If the chain branches occur near the ends, the structure can slowly rearrange into a true bilayer. If the branch occurs near the center, then there are a large number of intermediate "nematocrystalline" disordered forms that are possible before the final ordered layered packing.

Solving the crystal structures of zeolites using electron diffraction data. II. Density-building functions.

A density-building function is used to solve the crystal structures of zeolites from electron diffraction data using both two- and three-dimensional data sets. The observed data are normalized to give unitary structure factors |U(h)|(obs). An origin is defined using one to three reflections and a corresponding maximum-entropy map, q(ME)(x), is calculated in which the constraints are the amplitudes and phases of the origin-defining reflections.

Solving the crystal structures of zeolites using electron diffraction data. I. The use of potential-density histograms.

The maximum-entropy and likelihood method for solving zeolite crystal structures from electron diffraction data is modified to use potential-map-density histograms as an additional figure of merit. The experimental histogram is compared to an idealized one (based on known zeolite structures) using Pearson and Spearman correlation coefficients. These supplement the use of log-likelihood estimates as figures of merit to select the optimal solution from a collection of phase sets.

Electron crystallography of organic materials.

The application of electron crystallography to the study of organic materials is reviewed, mainly in context of the author's own experience. Direct methods for crystallographic phase determination have been shown to be very effective for ab initio structure analyses with electron diffraction intensities, permitting the elucidation of previously uncharacterized crystal structures. Fruitful applications areas have included chain-folded linear polymers, pigments, polydisperse linear chain arrays and, surprisingly, the subgroup assembly of certain proteins.

Direct electron crystallographic determination of zeolite zonal structures.

The prospect for improving the success of ab initio zeolite structure investigations with electron diffraction data is evaluated. First of all, the quality of intensities obtained by precession electron diffraction at small hollow cone illumination angles is evaluated for seven representative materials: ITQ-1, ITQ-7, ITQ-29, ZSM-5, ZSM-10, mordenite, and MCM-68. It is clear that, for most examples, an appreciable fraction of a secondary scattering perturbation is removed by precession at small angles.

Structure of an aluminophosphate EMM-8: a multi-technique approach.

The crystal structure of an aluminophosphate, EMM-8 (ExxonMobil Material #8), was determined in its calcined, anhydrous form from synchrotron powder diffraction data using the computer program FOCUS. A linkage of double four-ring (D4R) building units forms a two-dimensional framework with 12-MR and 8-MR channels, and differs from a similar SAPO-40 (AFR) framework only by the relationship between paired D4R units. Rietveld refinement reveals a fit of the model to the observed synchrotron data by Rwp=0.

Crystal structure of MCM-70: A microporous material with high framework density.

The crystal structure of the borosilicate MCM-70 (siliceous framework formula Si12O24) was determined from synchrotron powder diffraction data with the program FOCUS. The framework crystallizes in space group Pmn2(1), where a = 13.663, b = 4.

P-derived organic cations as structure-directing agents: synthesis of a high-silica zeolite (ITQ-27) with a two-dimensional 12-ring channel system.

Recently, efforts have been made to synthesize large-pore, multidimensional zeolite frameworks as a basis for new catalysts to improve various hydrocarbon conversions. A new aluminosilicate zeolite, ITQ-27, has been prepared using the phosphorus-containing structure-directing agent, dimethyldiphenylphosphonium. Its crystal structure was determined in its calcined form by direct methods (FOCUS) on synchrotron powder diffraction data (lambda = 0.

Crystal structure of zeolite MCM-68: a new three-dimensional framework with large pores.

The crystal structure of the aluminosilicate MCM-68 was solved from synchrotron powder diffraction data by the program FOCUS. The unit cell framework contains Si100.6Al11.

Electron crystallography of zeolites--the MWW family as a test of direct 3D structure determination.

The efficacy of direct methods for solving the crystal structures of zeolites from electron diffraction data is evaluated for a series of related materials, i.e. MCM-22, MCM-49 and ITQ-1.