Zeolites matrix

Centi, G. Perathoner, S. Vazzana, F., Catalysis using guest single and mixed oxides in host zeolite matrices, in Catalysis by Unique Metal Ion Structures in Solid Matrices, Centi, G. Bell, A.T. Wichterlova, B. (eds.), Springer-Verlag. Dordrecht (The Netherlands), 2001,165-186. 

Cu isotopes both with nuclear spin I-3/2. The nucle r g-factors of these two isotopes are sufficiently close that no resolution of the two isotopes is typically seen in zeolite matrices. No Jahn-Teller effects have been observed for Cu2+ in zeolites. The spin-lattice relaxation time of cupric ion is sufficiently long that it can be easily observed by GSR at room temperature and below. Thus cupric ion exchanged zeolites have been extensively studied (5,17-26) by ESR, but ESR alone has not typically given unambiguous information about the water coordination of cupric ion or the specific location of cupric ion in the zeolite lattice. This situation can be substantially improved by using electron spin echo modulation spectrometry. The modulation analysis is carried out as described in the previous sections. The number of coordinated deuterated water molecules is determined from deuterium modulation in three pulse electron spin echo spectra. The location in the zeolite lattice is determined partly from aluminum modulation and more quantitatively from cesium modulation. The symmetry of the various copper species is determined from the water coordination number and the characteristics of the ESR spectra. 

It has been shown that the Cu luminescence and IR spectra of Cu -NO complexes are suitable tools for semiquantitative evaluation of the individual Cu sitings-coordinations in the zeolite matrices in a wide range of Cu concentrations. 

Thermal dealumination also tends to decrease the effective pore diameter either by shrinkage of the unit cell and/or by generating amorphous materials in the zeolite channels. This results in an increase of the resistance to diffusivity and an increased shape selectivity. This has opened several new potential applications for zeolite matrices with controlled selectivity. 

Zeolite matrices have appeared recently to be of fascinating interest both for industrial and universitary purposes. For the industry many applications, particularly for acidic zeolites, have been found saving billions of dollars each year. For university or basic research the well defined structure of the zeolite materials constitutes a relatively simple model. The main properties of the zeolites in catalysis arise from (70)... 

Forster H and Schuldt M (1977), IR active fundamentals of deuterium, nitrogen, and oxygen in zeolitic matrices , J Chem Phys, 66, 5237. 

The aim of this work is testing of SERS-activity of metal-containing microporous alumosilicates or zeolites. Porous structure of zeolite skeletons caused by coupling of tetrahedral [Si04] and [AIO4] building units is a unique basis for stabilization of a super-lattice of mono-dispersed metal clusters. Zeolite matrices combine the factors of nanoporosity and nanometer-scale chemical reactivity with respect to incorporated foreign ions, clusters, and nanoparticles [1]. 

In the present work, we consider the two approaches for synthesis of nanoparticles designed for metal particles and being in the progress for ultraflne semiconductors. They allow to fabricate nanocomposites of the type nanoparticles-in-dielectrics with amorphous and crystalline matrices. The first one is based on the sol-gel technique producing dielectric silica films with nanoparticles incorporated within silica matrix [1]. Nanoparticles provide an optical response of the material due to the plasmon resonance [2] with variable spectral position and band shape. In the second approach nanoparticles are produced within the crystalline zeolite matrices which stabilize both the few-atomic clusters (e.g., Agg) and metal particles in the size range of 1-20 nm [3], Chemical routes of their synthesis admit easy control of size and optical properties. The metal nanoparticles in zeolites can be transformed into semiconductors without destroy of the zeolite matrix and with incorporation of zeolite microcrystals into transparent silica films. This construction... 

Nitrogen dioxide. NO2 isolated in noble gas or zeolite matrices gives rise to an ESR spectrum, with S = Y2 due to the unpaired electron of this odd-electron molecule. The spectrum in Fig. 3.18 shows features of both g-anisotropy and an anisotropic hyperfine coupling due to with / = 1. A visual analysis of the spectrum could proceed as follows ... 

The major difficulty in assessing the catalytic activity of oxides is in discriminating their action from that of the isolated cation and particularly fi om that of cations pairs known to form in zeolite matrices (67). This difficulty mainly arises from the poor means to characterize small oxide particles in zeolites or over other supports in contrast to metal particles. 

Dipole-dipole interactions occurring during collisions provide a relaxation mechanism for atoms in the gas phase. Xenon-129 atoms in the gas phase have spin-lattice relaxation times on the order of minutes which are dependent on gas density, temperature and the amount of other gases in the sample. For xenon-129 adsorbed in cavities inside zeolite matrices relaxation occurs via dipole-dipole interactions with hydrogen atoms that are bound to the sides of the cavities. 

The catalyst is certainly an outstanding tool to help fulfill all these requirements. The FCC catalyst is a multicomponent product, comprising a zeolite, matrices, a binder, and functional ingredients. The zeolite is, undoubtedly, tbe most important component and tbe modifications thereof will fine-tune the products slate of the FCC process. Controlled steam calcination, rational use of REs, increase in the Si/Al ratio, and increased accessibility are some of the factors that will have to be carefully examined to improve the catalyst performance. 

Finally, the importance of SSIE with respect to an interaction of zeolite matrices and clays used as binders in catalyst formulations has been stressed several times. Thus, Canizares et al. [72] showed that SSIE between Na-mont-morillonite (binder material) and H-ZSM-5 or H-mordenite is the reason for decreased Bronsted acidity in the zeolite matrices as compared to the unbound zeolite. 

From the TPR experiments it was concluded that the upper Hmit of In incorporation was determined by the proton content. The ratio nin ncorp/iiH was always found to be close to 1 despite the fact that various zeolite matrices and Iri203 loadings were used. This ratio was never close to 0.33, which is the value that would be expected if three protons were replaced by one In as suggested by Zatorski for SSIE in a non-reductive atmosphere [270]. 

In view of the above redox cycles. In-containing zeoUte catalysts prepared by RSSIE are obviously promising candidates for redox reactions, because of their fully reversible changes in the oxidation state of the indium species incorporated and stabiUzed in the zeolite matrices. 

As a further illustration of the intracrystalline transformations which such compounds may undergo is provided by recent and exhaustive (infrared and NMR) investigations of the chemistry of Rh(I) carbonyl species in various zeolite matrices [22]. Dimerization of Rh (C0)2 in... 

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