Zeolites metal-exchanged solids

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

The most widely used conventional chemical methods are pyrolysis [21-25] and catalytic cracking [13, 26-30], The latter yields products with a smaller range of carbon numbers and of a higher quality than products generated by the former method. Several types of solid acid catalysts, which are known to be effective for catalytic cracking (e.g. HZSM-5, HY and rare earth metal-exchanged Y-type (REY) zeolite and silica-alumina (SA)) were evaluated by catalyst screening tests and are listed in Table 6.1. The acidic... 

Catalysts in which the active component is a metal, and solid-acid catalysts, are much used in the fine-chemical industry. Metal catalysts are generally used to perform hydrogenations and oxidations. Solid-acid catalysts can replace conventional liquid-acid catalysts, which avoids the production of waste acid. Solid-acid catalysts are usually ion-exchangers, though clay minerals and, especially, zeolites are also employed. With zeolites the shape selectivity can have additional advantages. 

The following approaches will be addressed (1) H202-assisted decomplexation of metallo-organic salts for ion-exchange, (2) om-pot synthesis of metal-exchanged-zeolites, and finally (3) room-temperature detemplation of parous solids (zeolites and mesoporous materials). The Fe-catalysts are comptued on the basis of their NaO-decomposition performance, both in pure N20/He and under simulated industrial conditions for nitric acid plants containing O2, NO and H2O. 

Photoemission techniques offer a variety of tools for the discrimination between extra- and intra-crystalline location of components introduced (e.g. metal ions, MI ). Nevertheless, due to the specific limitations of these tools, detailed studies, preferably combining several of them, are often required to derive sound conclusions, in particular if both extra- and intra-zeolite species are present. Apart from quality assessment after ion-exchange steps, photoemission has been increasingly applied to describe mobility phenomena, e.g., the preparation of zeolite catalysts by solid-state reactions (soHd-state ion exchange [86-89],reductive dispersion (Ga203 into H-ZSM-5 [90-93]),chemical transport [94-97]), the penetration of metal poisons (Ni,V) into FCC catalysts [98-101] and the redistribution of active catalytic components in zeoHte crystals under reaction conditions [102-105]. Much of the earlier work in this field has been reviewed by Shpiro et al. [33,35]. 

Although the main applications of zeohtic sohds in catalysis will continue to be as solid acids in the synthesis and transformations of petrochemicals and commodity chemicals they continue to be considered as catalysts and catalyst supports for a range of reactions of synthetic and industrial relevance. The most important of these are of titanium- and tin-containing solids in selective oxidations. Other well-studied reactions over zeohtes include light hydrocar-bons-to-aromatics (Ga-zeolites) selective catalytic reduction of NO (transition metal exchanged zeolites) C C bond formation (Pd zeohtes) selective alkane oxyfunctionalisation with air (MAPOs, M Mn, Fe, Co) and chiral catalysis over encapsulated chiral complexes. 

A series of cation exchanged Y-zeolites were prepared by exchanging cations with various alkali (M, M = Li, Na, K, Cs) metals. The structural and catalytic properties of the alkali metal exchanged Y-zeolites have been investigated by a number of analytical techniques. The framework and non-framework A1 coordination and the Si/Al ratios of the Y-zeolites were investigated by Al and Si MAS solid-state NMR spectroscopy. ... 

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