Zeolite chemistry metal species

Arrangements of atoms which are unfamiliar to chemistry (because they are unstable) may be found in intrazeolitic space (because they are stable within the zeolite). The cationic clusters of the alkali metals (Section 6.2.1.2.) are an example of this. Within the zeolite, such new species may be studied and put to use. Allotropes of elements and compounds (continua), some charged, will continue to be found within zeolites substances must adopt new structures if they choose to conform to the geometrical requirements of intrazeolitic space, with different structures for different zeolites. In all cases, the properties of these allotropes must be different from those of the native substances in their original crystal structures. 

In fact, the reaction also occurs by heating the mixture in a vacuum (autoreductive SSIE)." " The In species are readily oxidised to InO species upon exposure to air, as demonstrated by infrared spectroscopy using pyridine as a molecular probe of the metal species present. Similar chemistry is observed upon heating Ga203/H-zeolite mixtures. 

As in zeolite chemistry, the most important species determining the properties of geopolymeric systems are metal cations that compensate for the negative charge of the aluminosilicate frameworks. Because the cationic species bind to AIO4 tetrahedra, the position and structural properties of aluminum sites can provide a clue to the physicochemical behavior of the prepared... 

The first two examples both involved the creation of cationic species on an acidic zeolite. In both cases we did not need to model the interaction of the cation with the zeolite framework good agreement was obtained with just calculation of the isolated cation. Apparently, the cation is not strongly perturbed by the presence of the zeolite. Such fortunate circumstances are rare. Here we show an example of how theoretical NMR calculations can help elucidate chemistry on a basic metal oxide surface, in particular, the adsorption of acetylene on MgO (26). For this study we needed to model the active sites of the catalyst, for which there are many possibilities. It is assumed the reactive sites are those in which Mg and O are substantially less coordinated than in the bulk. Comer sites are those in which Mg or O are three-coordinate, whereas Edge sites have four-fold coordination. These sites are where the strongest binding of the adsorbates are obtained. 

The work has largely focused on the coordination chemistry of transition metal ions (i.e., on the description of the nature and symmetry of their environments) (Section 2.1), in line with other spectroscopies, mainly optical (UV-vis), magnetic (EPR and NMR), which take advantage of partly filled d orbitals, and structural (EXAFS) (Sojka and Che, 2009). It has even become possible with PL via well-resolved fine structures to determine the extent of distortion of the environment of tetrahedral species (e.g., vanadium species in zeolites (Section 2.1.2)). It is likely that such information combined with that derived from other spectroscopies, vibrational on one hand, such as IR and Raman, and electronic on the other hand, such as EPR, will be applied by theoreticians to further improve the existing models and our understanding of the nature and role of surface species involved in catalytic processes. 

Interpolation or intercalation (see Intercalation Chemistry) is said to occur when additional species are placed into a host stmcture to change either composition or properties. At one extreme, intercalation can refer to the insertion of gnest molecnles into cage stmctures such as that of the zeolites (see Zeolites), or between the layers of laminated compounds snch as the clays (see Silicon Inorganic Chemistry). At the other extreme, the insertion of small atoms snch as C or N into metal phases to form interstitial alloys (see Alloys Carbides Transition Metal Solid-state Chemistry Nitrides Transition Metal Solid-state Chemistry), is inclnded in the category. A large variety of stmctures can be found in snch materials, and... 

In this chapter we describe some applications of inelastic neutron scattering in surface chemistry, more particularly in studies of catalysts and adsorbed species [1]. Our emphasis will be on the spectroscopy. The subject matter is arranged broadly according to the type of catalyst metals ( 7.3), oxides ( 7.4), zeolites and microporous materials ( 7.5) and sulfides ( 7.6) and, within each group, according to the reactant molecules. We start ( 7.1) with a general discussion of surface vibrations. 

Metal clusters in zeolites an intriguing class of catalysts Zeolite-supported transition metal catalysts Stoichiometric and catalytic reactivity of organometallic fragments supported on inorganic oxides Silver clusters and chemistry in zeolites Structure and reactivity of surface species obtained by interaction of organometallic compounds with oxidic surfaces infra-red studies... 

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