Clusters metal oxide

Cf produces two fission products that travel in opposite directions. If one projectile hits the sample, ions will be produced. These ions may then be focused and measured by TOF MS. The other projectile may be used to measure the start of the ionization process. This method has been used to study the ions produced from the ionization of metal complexes such as cadmium thiolates (33) and lanthanide phthalocyanine complexes (34). This method has also been used on metal oxides such as La203 to produce metal oxide cluster ions (35). 

Gas-phase metal oxide cluster cations have become increasingly interesting because of the possibility that a controlled reaction of size selected clusters might shed some light on condensed-phase catalysts. The possibility of producing small clusters in the condensed phase from deposition of gas-phase clusters has also been a driving force in the study of the reactivity of gas-phase ions. 

The reactions of MeOH with some transition metal oxide cluster anions [M O J, where M = Mn, Fe, Co, Ni, Cu n = 1,2 x = 2—4, have been studied (254). The [M03] anions were unreactive toward MeOH, unlike [Nb03]. The addition of the hydrogen molecule to the other cluster anions was the common reaction yielding the following transformations,... 

The addition of H2 to the metal oxide cluster anions appears to be a common reaction but the products could be either the dihydrogen adducts or more likely the dihydroxy adducts. The reactivity of the [M203] anions decreases in the series Mn > Fe > Co > Ni, which suggests increasing electron density in the cluster reduces the reactivity with the alcohols. 

Chaur MN, Melin F, Ortiz AL et al (2009) Chemical, electrochemical, and structural properties of endohedral metallofullerenes. Angew Chem Int Ed 48 7514-7538 Stevenson S, Mackey MA, Stuart MA et al (2008) A distorted tetrahedral metal oxide cluster inside an icosahedral carbon cage, synthesis, isolation, and structural characterization of Sc4(p3-O)2 lh-Cgo. J Am Chem Soc 130 11844-11845... 

The oxidation of CO to CO2 by metal-oxide clusters has received quite some attention, in part due to its relevance for the catalytic converters in automobiles, in part also because carbon monoxide is often used as a probe molecule in surface science and the reasonable simplicity of the system may still permit adequate theoretical treatments. In addition to the various systems involving PtmO cations as well as PtmO anions (see above), considerable efforts have been devoted to cluster anions of silver and gold, as reviewed recently [87]. A particular highlight is a conceptual catalytic cycle for the Au2 -mediated oxidation of CO with molecular oxygen, for which... 

The interest in the redox, catalytic, and electrocatalytic properties of unsubstituted and substituted polyoxometalates arouses much attention [2-15] because they are a versatile family of molecular metal-oxide clusters with applications in catalysis as well as in medicine and material science. Such versatility must be traced to at least two main characteristics. First, the size and mass of these unique molecular oxides place their solution chemistry in an intermediate position between small molecule solution chemistry and infinite lattice solid-state chemistry. Second, their redox behaviors may be very flexible and finely tuned on purpose, by changing smoothly their composition, with a... 

Side-Chain Alkylation. There is continued interest in the alkylation of toluene with methanol because of the potential of the process in practical application to produce styrene.430 Basic catalysts, specifically, alkali cation-exchanged zeolites, were tested in the transformation. The alkali cation acts as weak Lewis acid site, and the basic sites are the framework oxygen atoms. The base strength and catalytic activity of these materials can be significantly increased by incorporating alkali metal or alkali metal oxide clusters in the zeolite supercages. Results up to 1995 are summarized in a review.430... 

Alkenes may also be used as reagents in side-chain alkylation. Zeolites with occluded alkali metal and alkali metal oxide clusters were tested in alkylation of toluene with ethylene439 440 Alkali metal clusters created by decomposing Na or... 

Cs azide were active catalysts in the alkylation reaction, whereas alkali metal oxide clusters showed no activity at all. 

Okuhara, Mizuno, and Misono report the catalytic properties of heteropoly compounds as exemplified by H,PWl3O40 and the anion [PW,2O40p. Some of these compounds are strongly acidic, and some have redox properties the large-scale applications involve acid-catalyzed reactions. The heteropoly compounds are metal oxide clusters, used as both soluble and solid catalysts. Their molecular character provides excellent opportunities for incisive structural characterization and for tailoring of the catalytic properties. Physical properties also affect catalytic performance. Catalysis sometimes occurs on the surface of the solid material, and sometimes it occurs in the swellable bulk. 

A review of recent research, as well as new results, are presented on transition metal oxide clusters, surfaces, and crystals. Quantum-chemical calculations of clusters of first row transition metal oxides have been made to evaluate the accuracy of ab initio and density functional calculations. Adsorbates on metal oxide surfaces have been studied with both ab initio and semi-empirical methods, and results are presented for the bonding and electronic interactions of large organic adsorbates, e.g. aromatic molecules, on Ti02 and ZnO. Defects and intercalation, notably of H, Li, and Na in TiC>2 have been investigated theoretically. Comparisons with experiments are made throughout to validate the calculations. Finally, the role of quantum-chemical calculations in the study of metal oxide based photoelectrochemical devices, such as dye-sensitized solar cells and electrochromic displays, is discussed. 

For very small metal-oxide clusters, the band-gap increases. This becomes a concern for clusters which are just a few nanometer in diameter. This effect is most readily understood in the quantum chemical model of a cluster, where the bands develop due to interactions between more and more atoms. For clusters with, say, up to 1000 atoms, the addition of new atoms to the cluster broadens the bands, and thus narrows the band-gaps. For large clusters this effect levels off, and for clusters with a diameter of more than a few nanometers band-widths and band-gaps stabilize at their bulk values. 

Novel photocatalytic membranes have been prepared by the heterogenization in PVDF membrane ofthe decatungstate (W10O324 ), a polyanionic metal-oxide cluster used as photocatalysts for oxidation reactions. 

After these stages, the treated sample undergoes a meticulous thermal treatment. During this treatment, the dehydration and dehydroxylation of the exchanged material take place, the stable metal oxide clusters then develop, which carry out the layer separation, generating a two-dimensional interlayer space with an aperture, which, if the process is correctly performed, can be larger than 10 A [12,36] (see Figure 2.25). The obtained materials are stable up to 625-725 K [31]. 

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