Transition metals atomic carbon adsorption

The Adsorption Energies (eV) of Atomic Carbon Adsorption (a) on Different Transition Metals and Their Alloys and (b) on Different Adsorption Sites of the Ni Surfaces... 

Fig. 20 The binding energy of different transition metal atoms on the outer surface of a carbon nanotube. The different labels T, H, Bl, and B2 mark different adsorption sites. Reproduced with permission of American Chemical Society from ref 64. 

The conclusions on the mechanism of the double bond hydrogenation on metallic catalysts can be summarized as follows (1) with respect to structure effects on rate, all transition metals behave similarly (2) the reactivity of the unsaturated compounds is governed mostly by the number and size of the substituents on the carbon atoms of the double bond through their influence on adsorptivity (3) the electronic nature of the substituents plays a minor if any role. 

Isolation and identification of surface-bonded acetone enolate on Ni(l 11) surfaces show that metal enolate complexes are key intermediates in carbon-carbon bond-forming reactions in both organometaUic chemistry and heterogeneous catalysis. Based on studies on powdered samples of defined surface structure and composition, most of the results were reported for acetone condensation over transition-metal oxide catalysts, as surface intermediate in industrially important processes. With the exception of a preoxidized silver surface, all other metal single-crystal surfaces have suggested that the main adsorption occurs via oxygen lone-pair electrons or di-a bonding of both the carbonyl C and O atoms. 

A high degree of hydrophobic character is an almost unique characteristic of silicon-rich or pure-silica-type microporous crystals. In contrast to the surface of crystalline or amorphous oxides decorated with coordinatively unsaturated atoms (in activated form), the silicon-rich zeolites offer a well-defined, coordinatively saturated sur ce. Such surfrces, based on the strong covalent character of the silicon-oxygen bond and the absence of hydrophilic centers, display a strong hydrophobic character unmatched by the coordinativeiy unsaturated, imperfect surfaces. Also, hydrophobic zeolite crystals have been reported to suppress the water affinity of transition metal cations contained in the zeolite pores. This property permits the adsorption of reactants such as carbon monoxide or hydrocarbons in the presence of water. 

Hypothesis for the atomic structure of the a and P states are obviously closely related to the suggested mechanism for the formation of these two phases. There appears, however, to be general acceptance of a description of the a phase in terms of a single-site adsorption complex bound to the surface via the carbon atom with a similar mechanism to that used to describe M—C O bonding in the binary carbonyls. Recently, good correlation between the shift in the infrared absorption bands measured by Blyholder and Allen 206) on the first-row transition metals from vanadium to copper has been found by them using a... 

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