Mae K. Rubin

MCM-22: A Molecular Sieve with Two Independent Multidimensional Channel Systems

The molecular sieve MCM-22 contains structural features previously unobserved in this class of materials. Its framework topology, derived from high-resolution electron micrographs and refined with synchrotron x-ray diffraction powder data, contains two independent pore systems, both of which are accessed through rings composed of ten tetrahedral (T) atoms (such as Si, Al, and B). One of these pore systems is defined by two-dimensional, sinusoidal channels. The other consists of large supercages whose inner free diameter, 7.1 angstroms, is defined by 12 T—O species (12-rings) and whose inner height is 18.2 angstroms. These coexisting pore systems may provide opportunities for a wide variety of catalytic applications in the petrochemical and refining industries. Another structural feature is an unusual -T-O-T- chain that passes through the center of a modified dodecasil-1H [435663] cage.

Twelve-ring pockets on the external surface of MCM-22 crystals

MCM-22 is a synthetic high-silica zeolite which crystallizes as very thin plates. Its internal structure contains two independent internal pore systems accessible through 10-ring apertures. A high concentration of external zeolitic pockets, with 12-ring openings and having an approximate depth of 7 A, covers the hexagonal faces of the thin crystals. Evidence for the presence of these pockets was established by high-resolution electron microscopy. Experimental evidence to support this was obtained from ion-exchange studies using tetramethylammonium and tetraethylammonium ions, and from dynamic sorption studies using n-heptane and 2,2,4-trimethylpentane. The results suggest that the surface pockets unique to the MCM-22 structure have zeolitic characteristics and may play a significant role in certain catalytic processes.

The framework topology of ZSM-23: A high silica zeolite

Abstract ZSM-23, a high-silica zeolite, is orthorhombic, space group, Pmmn, with lattice parameters of: a = 5.01 ± 0.02A, b = 21.52 ± 0.04A, and c = 11.13 ± 0.03A. The crystal structures of ZSM-22 and ZSM-23 are closely related in that both zeolites contain structurally identical subunits which generate noninterpenetrating, one-dimensional channels defined by 10-rings which are parallel to the short 5 A axis. The 10-ring channel dimensions in ZSM-22 and ZSM-23 are essentially the same, though subtle differences exist in the shapes of the openings.

Kinetics of dehydration of ter-Butyl alcohol catalyzed by ion exchange resins

Abstract The dehydration of tert-butanol catalyzed by 2% and 8% cross-linked Dowex 50 W is studied. Assuming the reactions to be heterogeneous, the data are found to agree with a simple Langmuir-Hinshelwood model in which the competitive chemisorption of alcohol and water is postulated. The most likely catalytic sites are the anhydrous, un-ionized sulfonic acid groups, or their monohydrates. Increased cross-linking affects the energetics of the sulfonic acid groups. This is reflected in changes in the chemisorption constants, increased rates of conversion, and perhaps an alteration of the activation energy of the reaction.

Synthesis and proposed framework topology of zeolite SUZ-4

Crystalline SUZ-4, with anhydrous composition K5Al5Si31O72, is hydrothermafly synthesized in a reaction mixture of SiO2, Al3, KOH, tetraethylammonium hydroxide and quinuclidine; its proposed framework topology is related to zeolites ferrierite and ZSM-57 and contains straight channels having apertures defined by rings of ten (Si,Al)–O species; a novel cage may as the site for non-exchangeable potassium ions.

Synthetic offretite: III. Physicochemical aspects of crystallization

Abstract The progress of crystallization of tetramethylammonium (TMA) offretite from an alumina-silica gel at 97 °C has been monitored by sorptive, thermochemical, spectroscopic, and other physicochemical probes. Initial ordering of gel particles into large agglomerates and onset of crystallization occurred within the first 20 hr. During the critical interval of 20–44 hr, the gel was transformed into a crystalline phase, with incorporation of aluminum and TMA cations into the aluminosilicate lattice, and after this period showed all characteristics of crystalline offretite, including maximum sorption capacity and typical crystal morphology.

Cracking process and ZSM-5 catalyst produced therefor

A process for converting feedstock hydrocarbon compounds to product hydrocarbon compounds having a lower molecular weight than the feedstock hydrocarbon compounds comprises contacting said feedstock at conversion conditions with a catalyst composition comprising a large-pore molecular sieve material and an additive catalyst composition comprising crystalline material having the structure of ZSM-5 and a silica/alumina mole ratio of less than 30, said crystalline material having, as-synthesized, the following formula on an anhydrous basis: (x)M2O: (0.2 to 1.4)R2O:Al2O3: (y)SiO2 wherein x is a number greater than 0.1, M is alkali or alkaline earth metal, R is n-propylamine, and y is a number less than 30, and said additive catalyst composition having an alpha value greater than 30.

The framework topology of zeolite MCM-22

Summary The framework topology of the molecular sieve MCM-22 has been determined from high resolution electron micrographs and refined with synchrotron X-ray diffraction powder data. MCM-22 crystallizes as very thin sheets. The borosilicate form of this material, having unit cell framework composition (Al 0.4 B 5.1 Si 66.5 )O 144 , may be indexed on a hexagonal lattice in space group P6/mmm (D 1 6h , No. 191). The refined unit cell parameters are a = 14.1145(8) and c = 24.8822(18) . The MCM-22 structure contains hexagonal sheets constructed by interconnecting modified DOH cages through shared 4-ring faces in a manner analogous to that found in DOH. This modified cage has a TO 3 cap on top (forming a small [4 3 ] unit) and a -T-O-T- chain passing through its center. The MCM-22 sheets bond together in two ways— one side involving an oxygen bridge between TO 3 caps and the other side through double 6- rings. The net effect is to produce two different, independent pore systems with 10-ring apertures. One of these pore systems is defined by two-dimensional, sinusoidal channels. The other consists of large supercages whose inner free diameter, 7.1 , is defined by 12- rings and whose inner height is 18.2