Hydrogen activation hydride oxidation

Heterolytic cleavage. This leads to formation of a metal hydride with release of a proton (equation 1). The formal oxidation state of the metal does not change. This mode of hydrogen activation is common in hydrogenation by complexes of ruthenium(II). 

Catalysts are prepared by one of two methods. The support material is impregnated with the metal ion, then heated in air at a high temperature to form the metal oxide. Alternatively, when the support material is an oxide such as alumina, the two oxides are coprecipitated and dried in air. In such case the catalyst is activated by treatment with a reducing agent such as hydrogen, metal hydride, or carbon monoxide. The function of the support appears to be more than simply providing a large surface area. Some type of interaction must occur between the metal oxide and support because the oxide alone behaves differently. 

Apart from these specific hydrogen absorption and desorption properties, it is clear that the intermetallic compounds are more often used as precursors of new and more active catalysts. The decomposition of intermetallic compounds into transition-metal particles and rare-earth hydride, oxide or hydroxide in the course of the catalytic reaction was evidenced in a large number of catalytic reactions, especially those involving CO dissociation, which produces oxidizing species. The rise of catalytic activity was... 

Binuclear oxidative addition can occur in suitahle cases, the hrst example being Iguchi s Co(CN)5 system [103]. Two Co(II) precursors cooperate to homolyze H2 to give two moles of the Co(III) hydrides, [HCo(CN)5] . This allows the system to hydrogenate activated olehns, such as acrylic acid. 

High catalytic activity is exhibited when one unit cell of NHCO is occupied by one (Pt)2 or (Pt)3 cluster. Hydrogen activation is caused by decomposition of H2 molecules to the atomic state with subsequent formation of the hydride complex. Oxidation-reduction titration as well as electron-microscopy measurements show the incorporation of Pd crystallites inside nylon grains [114]. Most have a mean diameter of about 30 A. However, under the assumption that all the metal is located on the polymeric support surface, the calculated accessible metal surface amounts to several hundred Angstroms. Therefore, during preparation of the Pd-nylon catalyst, part of the metal penetrates into the organic matrix. 

The course of reaction on a semiconductor oxide may also depend on the sites to which the starting materials are boimd and the manner in which they are boimd. Consider the adsorption of hydrogen. It has been shown that hydrogen is heterol5d i-cally cleaved on a ZnO surface, so that simultaneous formation of a donor and an acceptor takes place. Active hydrides are boimd to the ZnO surface ... 

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