Surface groups thermal decomposition

The chemisorption and thermal decomposition of ethylene over platinum (111) surfaces have been extensively studied by several groups using a range of modern surface science techniques (1-3 ). Chemisorption at low temperatures is molecular, with the... 

During the past decade a very considerable literature has developed concerning the generation and reactivity of alkyl and alkylidene groups adsorbed on metal single-crystal surfaces produced via the photochemical or thermal decomposition of adsorbed alkyl halides or nitrogen-substituted alkanes. In this review, we concentrate on publications which exhibit VEEL or RAIR spectra of the hydrocarbon groupings that can be used as reference spectra for the identification of such species in spectra of species derived from hydrocarbon chemisorption. Reviews of such work cover the kinetic as well as spectroscopic aspects of this area of research (142-144). 

Grassian and Pimentel (210) prepared such surface groups by thermal decomposition of cis- and frans -dichloroethenes at temperatures >200 K or by their photolysis at 110 K on Pt(lll). An ethyne type B spectrum was obtained, as had also been obtained from the direct low-temperature adsorption of ethyne on this surface (Section II.B.l). 

VEEL spectra of surface phenyl groups have been obtained by ultraviolet photolysis of phenyl chloride on Ag(lll) at 300 K (211) and by thermal decomposition of phenyl iodide on Cu(lll) (212). The spectra are similar, and the strengths of the absorptions from the out-of-plane yCH modes, at 740 and 725 cm-1 respectively, show that the phenyl group is also more near to parallel than to perpendicular to the metal surfaces, again probably because of a combination of cr- and 77-bonding. 

The use of the molecules of other (ethyl and heavier) alcohols with this object allows the replacement of the surface hydroxyl groups by the alcohol groups, although the pyrolysis of the latter does not remove oxygen atom. For the groups with a more complicated structure, new transformation channels arise with a higher transformation rate. For example, the thermal decomposition of the surface ethoxy groups follows the scheme... 

The 1273 K treated sample (figure 14.9a) shows 2 bands, at 3740 and 2290 cm 1. These may be assigned to surface hydroxyls and silane groups, respectively. Upon thermal decomposition of the alkyl chain, hydrogen gas is formed. The evolved gas may react with the silica surface siloxanes, according to reaction (E). 

Among monomeric metal carbonyls, Mo(CO)6, Cr(CO)6, Fe(CO)5, and Ni(CO)4 have been most studied. Their stepwise decomposition on the support may lead to the formation of grafted species. For example, Mo(CO)6 is first physically adsorbed onto hydroxylated alumina at room temperature [2, 62, 63, 68]. Thermal decomposition leads to the formation of adsorbed subcarbonyl species such as Mo(CO)s and then Mo(CO)3 at 373 K. Complete dccarbonylation at 573 K is observed upon oxidative addition of the metal on surface hydroxy groups ... 

Ash fouling appears to be initiated by the formation of a layer of sodium sulfate on the boiler tube. It is thought that thermal decomposition of sodium salts of carboxylic functional groups in the coal is the start of a sequence of reactions leading ultimately to the formation of sodium sulfate in the flame or flue gas. The convective mass transfer diffusion of the sodium-containing species through a boundary layer around the tube results in deposition of sodium sulfate on the tube surface. 

In the case of MgO, various types of OH groups can form, depending on the sites involved in the chemisorption process. In a periodic ab initio molecular dynamics study [113], it has been shown that the faces which are energetically unfavorable in the clean MgO surface may become favored in the presence of water. The calculations indicated that there is a net stabilization upon going from the MgO(lOO) surface covered with molecularly adsorbed water to the MgO(lll) surface covered with dissociated water. This is not too surprising if we consider that brucite, Mg(OH)2, is a mineral with hexagonal structure which exhibits the (0001) face as the most stable one and that MgO is often produced by thermal decomposition of brucite. 

In G, the methyl disproportionation reaction observed in thermal decomposition of tetramethylammonium cations, the hydride receiver may be a surface methoxyl group, v hile the hydrogen-deficient ( oxidized ) moiety is a formaldehyde-like species, and ultimately, C=0 and H2. Ethane was detected (H) as a minor product during the alkylation of isobutane with ethylene over REHX catalyst assuming a classical... 

The deposition of platinum, rhodium and ruthenium acetylacetonates on titania takes place by reaction with the surface hydroxy groups to give a supported complex. Thermal decomposition of these supported complexes in vacuum gave highly dispersed titania supported metal catalysts having metal particles about 2 nm in diameter. ... 

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