Saleh Elomari

Studies of Aluminum Reinsertion into Borosilicate Zeolites with Intersecting Channels of 10- and 12-Ring Channel Systems

The work here describes the kinetic analyses of aluminum replacement for boron in a suite of borosilicate molecular sieves. While the method has been described before as a means of converting synthesized borosilicates (with weak inherent acidity) to aluminosilicates (with much stronger acid strength) when there are large pores in the structure, here we carry out the transformation under less than optimal replacement concentrations, in order to better follow the kinetics. We examined several zeolite structures with boundary conditions of boron MEL where there are only 10-ring (or intermediate) pore structures and no Al is taken up, to multidimensional large pore zeolites, like boron beta, where Al substitution can occur everywhere. We also studied materials with both intermediate and large pores, SSZ-56, 57, 70, and 82. In the case of 57 up to 90% of the structure is made up of boron MEL. We observe that the pH drop is proportional to the Al reinsertion and is the same for all zeolites we studied. In one case, we compared a zeolite (SSZ-24) with boron and then no boron sites and found that Al does not go into defect sites. It was again confirmed (shown in earlier work) that Al will go into nest sites created by boron hydrolysis out of the substrate before Al treatment. Along those lines we also made two new observations: (1) the profile for Al uptake, as followed by pH drop, is the same kinetically, whether the boron is there or not; and (2) NMR showed that the boron is leaving the structure faster than Al can go back in (SSZ-33 study), even when we treat a material with boron in the lattice.

Locating Organic Guests in Inorganic Host Materials from X-ray Powder Diffraction Data

Can the location of the organic structure-directing agent (SDA) inside the channel system of a zeolite be determined experimentally in a systematic manner? In an attempt to answer this question, we investigated six borosilicate zeolites of known framework structure (SSZ-53, SSZ-55, SSZ-56, SSZ-58, SSZ-59, and SSZ-60), where the location of the SDA had only been simulated using molecular modeling techniques in previous studies. From synchrotron powder diffraction data, we were able to retrieve reliable experimental positions for the SDA by using a combination of simulated annealing (global optimization) and Rietveld refinement. In this way, problems arising from data quality and only partially compatible framework and SDA symmetries, which can lead to indecipherable electron density maps, can be overcome. Rietveld refinement using geometric restraints were then performed to optimize the positions and conformations of the SDAs. With these improved models, it was possible to go on to determine the location of the B atoms in the framework structure. That is, two pieces of information that are key to the understanding of zeolite synthesis-the location of the organic SDA in the channel system and of the positions adopted by heteroatoms in the silicate framework-can be extracted from experimental data using a systematic strategy. In most cases, the locations of the SDAs determined experimentally compare well with those simulated with molecular modeling, but there are also some clear differences, and the reason for these differences can be understood. The approach is generally applicable, and has also been used to locate organic guests, linkers, and ligands in metal-organic compounds.

A comparative study of three closely related unsolved zeolite structures

Abstract In this report we discuss the synthesis and physicochemical characterizations of three zeolites with unsolved crystal structures: SSZ-57, SSZ-74, and IM-5. The diffraction data of SSZ-57 are similar to, but distinct from, the data for ZSM-5, ZSM-11, or ZSM-5/11 intergrowths. The powder diffraction data of SSZ-74 can be indexed in a unit cell with dimensions similar to those found in ZSM-5 and ZSM-11. The organic structure directing agents (SDA) used to prepare SSZ-74 and IM-5 are similar to SDA molecules that often yield multidimensional 10-ring zeolites. The micropore volumes, adsorption uptake rates of 2,2-dimethylbutane, and the constraint index tests of these three unknown materials are also consistent with those expected for multidimensional 10-ring zeolites.

SSZ-53 and SSZ-59: Two novel extra-large pore zeolites

The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures.

A polymorphic polycycle—evidence for a sickle-shaped dodecenyl oxyallylic cation

A polycycle containing a cyclodecanone ring gives two polymorphs on crystallization from hexanes. Form 1 is space group P21/n with a = 17.145(2), b = 6.8979(9), c = 13.721(2) Å, and = 99.689(5)°. Form 2 is space group P21/c, with a = 19.046(2), b = 6.8211(4), c = 12.890(1), and = 105.302(4)°.