Modified framework structures

Other related zeolites may also exist as families of framework structures. Models of modified framework structures of some of the other members of the mordenite family—i.e., ferrierite, dachiardite, and epistil-bite—have been constructed. Such structures have unit cell dimensions essentially equal to the reported structures, but of course they exhibit different symmetries. 

The isomorphous replacement of aluminum by gallium in the framework structure of zeolites (beta, MFI, offretite, faujasite) offers new opportunities for modified acidity and subsequently modified catalytic activity such as enhanced selectivity toward aromatic hydrocarbons [249,250]. The Ga + ions in zeolites can occupy tetrahedral framework sites (T) and nonframework cationic positions. 

The nucleation-condensation mechanism can be accommodated in modified framework and hydrophobic-collapse models the framework model must be modified so that formation of secondary structure is linked to the formation of tertiary interactions and the hydrophobic collapse model must have the formation of tertiary interactions linked to the formation of secondary structure. Another variation of concerted structure formation is the hydrophobic zipper. 68 Whatever the distinctions of names, stable tertiary and secondary structural interactions must form concurrently. 

The NMR and X-ray diffraction data are only consistent with substitution of boron into the framework structure of the mordenite. Although we prepared boron substituted mordenite directly from modified gels, direct synthesis has severe limitations. The solution chemistry of the substituting element can interfere with zeolite nucleation and crystallization, as... 

Ramamurthy and coworkers have utilized zeolites modified with chiral organic compounds [17,18]. Zeolites are crystalline aluminosilicates with open framework structures. In this approach, the zeolite is first loaded with a chiral inductor and the compound to be photolyzed is then added in a second, separate adsorption step. Asymmetric induction ensues as a result of the close proximity enforced between reactant and chiral inductor in the confined space of the zeolite supercage. The zeolite method has the disadvantage that the size of the substrate is limited by the pore size of the zeolite being used. Most of the work using the chirally modified zeolite approach was compared with the ionic chiral auxiliary method by Scheffer and coworkers. The enantiodifferentiations by the zeolites are usually low to moderate. 

Jackson, M. D., and G. V. Gibbs (1988). A modeling of the coesite and feldspar framework structure types of silica as a function of pressure using modified electron gas methods. J. Phys. Chem. 92, 540-45. 

Under the above mentioned assumptions, the global mass conservation equation does not modify its structure in the regime of turbulent flows. However the chemical species conservation equations and the energy equations, in the framework of k-e models, make use of the "turbulent" Schmidt and Prandtl numbers. 

Supported iridium clusters on oxides were intensively investigated [267] because they form rather stable metal frames such as Ir4. Despite the substantial work on such samples, questions remained due to limitations of EXAFS spectroscopy widely used for the characterization and the lack of other experimental techniques suitable for investigating metal species dispersed in porous solids. To clarify how the interaction with a zeolite framework can modify the structural and electronic properties of small supported metal particles, we carried out a scalar relativistic DKH DF study of the interaction between fr4 clusters and a zeolite fragment, using a cluster model of a faujasite six-ring [268]. 

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