Oxidation products surface catalysis

A novel chemical functionalization method for MWCNTs through an oxidation and silylation process was reported in 2002. Purified and oxidatively functionalized MWCNTs were reacted with 3-mercaptopropyltrimethoxysilane, the CNT surface being joined to the organosilane moieties through OH groups [143], Similarly, MWCNTs were functionalized by KMn04 oxidation under PTC catalysis and subsequent reaction with the hydrolysis product of 3-methacryloxypropyltri-methoxysilane (3-MPTS) (Scheme 1.13). The O-silyl-functionalized MWCNTs were characterized by FT-IR spectroscopy and energy-dispersive spectroscopy... 

This equation explains the observed rate dependency in Eq. (9.41), where the rate constant in the observed reaction, k, is equal to the product, kK, K 2- The surface catalysis of manganese oxidation is veiy effective in natural waters. The strength of the catalysis as indicated by the catal5Tic turnover number (CTN) in Table 9.7 is less than some of the other catalysts listed, but particle surfaces are ubiquitous. 

TNT that resides in aerobic environments at the surface of the soil is often degraded by photocatalyzed oxidation of the methyl carbon. This oxidation is probably a multistep process by which the methyl group is initially oxidized to an alcohol, then to an aldehyde, and finally to a carboxylic acid. Decarboxylation of the resultant product yields trinitrobenzene. Evidence for this pathway was supplied by Spanggord et al. [29], who reported formation of trinitrobenzaldehyde and trinitrobenzoic acid during the degradation of TNT to trinitrobenzene. It has been reported that oxidation of the methyl group of TNT is mediated by surface catalysis on soil minerals [30], by ozonation [31], and by the action of sunlight [29], At sites where the TNT contamination is localized to the soil surface, the concentration of trinitrobenzene may often exceed that of TNT [32],... 

Comparing the results of EC-NMR and IR investigations, we find that the potential dependence of C NMR shift and the vibrational frequency of adsorbed CO are primarily electronic in nature, and originate from changes in the f-LDOS. C NMR results show that CO adsorbed on Pt, either directly from CO gas or from methanol oxidation, have the same electronic properties. That is, the chemisorbed product (surface CO) from CO solutions and from methanol decomposition is the same. The electrode potential dependence of the C NMR spectra of CO adsorbed on Pt and Pd nanoparticles provide direct evidence for electric field induced alterations in the E/ -LDOS. In relation to fuel cell catalysis, EC-NMR investigations of Pt nanoparticles decorated with Ru show that there exist two different kinds of CO populations having markedly different electronic properties. COs... 

Surface catalysis routes using alkaline earth oxides have yielded mixtures of various (CO) n = 2-6 ) species from CO [91]. These routes are of mechanistic interest, but are of no synthetic value as only trace amounts of product are detected. Recent work has been reported that shows the formation of the rhodizonate mono-anion from the reaction of CO with molybdenum suboxide cluster anions Mo Oy" (y < 3x), which are generated using pulsed laser ablation/molecular beam methods [92]. The results suggest that a series of reactions occur involving the oxidation of CO until the oxygen content of the clusters is depleted, followed by metal carbonyl formation and, ultimately, free C Oe" formation. 

The rate of this and many other such phase boundary reactions depends upon the instantaneous state of the surface. For tarnishing processes, this generally means that the rate depends upon the instantaneous activities of the components at the phase boundary as well as upon the temperature. As long as diffusional equilibrium is maintained, and the outer phase boundary reaction alone is rate-controlling, the activity of the metal at the phase boundary between oxidation product and gas is constant and equal to one. There are indications [50] that the electronic defects can particularly influence the rate of dissociation of the gases at the phase boundary between oxidation product and gas. Use is made of this property of solid surfaces in the field of heterogeneous catalysis [4]. Since the defect concentration is determined by the activities of the components in the reaction product, it is understandable that the rate of the phase boundary reaction should, in general, depend upon the component activities in the reaction product at the phase boundary. 

In addition to the wide range of metal oxide catalysts that can cany out oxidation via redox catalysis, there are a host of other materials that can carry out oxidation over non-reducible metal oxides. The oxidation mechanisms over non-reducible metal oxides are quite different and typically involve the production of free radical intermediates. The mechanisms tend to contain both heterogeneous and homogeneous activation and functionality. The oxide is used to activate a free radical process that can then proceed in the gas phase or at the surface. Li-substituted MgO and the rare earth metal oxides are two classes of materials that are considered non-reducible oxidation catalysts. Here we wiU specifically focus on the activation of alkanes over non-reducible metal oxides. 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

Apart from the application of XPS in catalysis, the study of corrosion mechanisms and corrosion products is a major area of application. Special attention must be devoted to artifacts arising from X-ray irradiation. For example, reduction of metal oxides (e. g. CuO -> CU2O) can occur, loosely bound water or hydrates can be desorbed in the spectrometer vacuum, and hydroxides can decompose. Thorough investigations are supported by other surface-analytical and/or microscopic techniques, e.g. AFM, which is becoming increasingly important. 

The decarbonylation of oxide-supported metal carbonyls yields gaseous products including not just CO, but also CO2, H2, and hydrocarbons [20]. The chemistry evidently involves the support surface and breaking of C - O bonds and has been thought to possibly leave C on the clusters [21]. The chemistry has been compared with that occurring in Fischer-Tropsch catalysis on metal surfaces [20] support hydroxyl groups are probably involved in the chemistry. 

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