Catalyst-carbon interaction

Note how the key interaction boosting the catalytic effect is the protonation of the carbonyl group on the TG. Such catalyst-substrate interaction increases the electrophilicity of the adjacent carbonyl carbon atom, making it more susceptible to nucleophilic attack. Compare this to the base-catalyzed mechanism where the base catalyst takes on a more direct route to activate the reaction, creating first an alkoxide ion that directly acts as a strong nucleophile (Figure 4). Ultimately, it is this crucial difference, i.e., the formation of a more electrophilic species (acid catalysis) v.s. that of a stronger nucleophile (base catalysis), that is responsible for the differences in catalytic activity. 

Catalysts for coal liquefaction require specific properties. Catalysts of higher hydrogenation activity, supported on nonpolar supports, such as tita-nia, carbon, and Ca-modified alumina, are reasonable for the second stage of upgrading, because crude coal liquids contain heavy polar and/or basic polyaromatics, which tend to adsorb strongly on the catalyst surface, leading to coke formation and catalyst deactivation. High dispersion of the catalytic species on the support is very essential in this instance. The catalyst/support interactions need to be better understood. It has been reported that such interactions lead to chemical activation of the substrate 127). This is discussed in more detail in Section XIII. 

Aluminum-carbon bonds, CO and allene insertion, 3, 267 Aluminum(0)-carbon interactions, characteristics, 9, 250 Aluminum(I)-carbon interactions, characteristics, 9, 250 Aluminum(III)-carbon interactions, characteristics and studies, 9, 247 Aluminum catalyst system... 

Figure 14 shows the structures of the most stable transition states leading to the R products, for propene, 1-hexene and 1-decene. The authors claim that one can see how the elongation of the olefin chain from propene to 1-hexene increases the interactions between the olefin and the three most important parts of the catalysts, Quinoline A, PYDZ and Quinuclidine B. Moving from propene to 1-hexene, the carbon atoms added to the aliphatic chain are still close to these three parts of the catalyst, and can have strong interactions. In contrast, once the aliphatic n-alkene has six carbon atoms, all of the carbon atoms subsequently added to the chain are too far from the catalyst to interact strongly with it. These interactions between the aliphatic... 

One of the most controversial issues in AFCs is the formation of carbonates. It is generally accepted that the C02, both originally in the air and formed by corrosion reaction of the carbon catalyst support, interacts with the electrolyte according to the following equation ... 

M. Sheintuch, J. Schmidt, Y. Lecthman, and G. Yahav, Modelling catalyst-support interactions in carbon monoxide oxidation catalysed by Pd/Sn02, Appl. Catal. 49, 55-65 (1989). 

The surface properties of carbon play an important role in the dis persion and the sintering behavior of supported catalyst. The study of iron-phthalocyanine is of particularly interest for the investigation of catalyst-carbon support interactions. The coalescence of PcFe particles on graphitized carbon is considerably lowered by the... 

As IR-spectroscopic probes for basic centers in various catalysts, carbon dioxide, pyrrole, or chloroform were used [7-9]. Howerer, in most cases, these molecules strongly interacted with the surface and formed strong complexes that could be destroged only at elevated temperatures, which sometimes causes irreversible changes at the surface. 

This mechanism implies catalyst-oxygen interaction and excludes interaction between carbon and catalyst. It was used to explain successfully the observed features of the carbon dioxide gasification, including the deactivation (by oxidation) of the catalyst. Experimental evidence was presented to support the view that the metal acts as a dissociation centre, producing active species that diffuse across the metal to react at the graphite-metal interface. 

The rates of production of heat during interactions (Ic) and (5a) are similar and larger than the rate of production of heat for interaction (7a) [conversion of C03-(ads) into gaseous carbon dioxide by carbon monoxide] (83). Both interactions (Ic) and (5a) may therefore participate in the formation of C03"(ads) ions during the catalytic reaction on NiO(10 Li)(250°). Kinetic measurements of adsorption of reagents (74) and calorimetric determinations of the rate of production of heat have shown, moreover, that the conversion of C03"(ads) ions by carbon monoxide is a slower process than the adsorption of either reagent. It is concluded therefore that the rate-determining step of the reaction mechanism on the lithiated catalyst is interaction... 

O Grady and Koningsberger have studied metal-carbon interactions in carbon-supported platinum catalysts in fuel cells and concluded that there are two types of Pt-C interactions. 

Although the reaction requires no external catalyst, carbon dioxide is activated by the interaction of its electrophilic carbon atom and the negatively polarized carbon in the ortho (or para) position of the phenolate ring. This mechanism is supported by the fact that even under high CO2 pressure no salicylic acid is formed from phenol. The product is stabilized via an a > y proton migration. The free acid is obtained from the sodium salt in reaction with an external proton (usually from sulfuric acid). Formally, this reaction can be regarded as the insertion of CO2 into an aromatic C-H bond however, the above mechanism disproves this idea. 

The formation of carbon deposits is an undesirable feature of a number of industrial processes, for example on the fuel pins in nuclear reactors, on the catalysts and structural materials of reactors in petrochemical plant, and on furnace wall linings. A greater understanding of the mechanism of deposition is required in order to develop improved methods of control. Metal-carbon interactions are also important in the catalysis of carbon gasification for the manufacture of synthetic fuels. 

Augustine et al. working at atmospheric pressure observed that presulfiding has a profound effect on both the quantity and the quality of the carbonaceous overlayer formed during n-hexane conversion reactions, and the effects are greater for bimetallic samples than for Pt monometallic catalysts. Carbon is decreased in the presence of sulfur. The carbonaceous layer is more rich in hydrogen over the sulfided catalysts. They assumed that sulfur can interact with Lewis acid sites and thus deactivate sites for coking. 

Bayer BC, Hofmann S, Castellarin-Cudia C, Blmne R, Baehtz C, Esconjauregui S, et al. Support-catalyst-gas interactions during carbon nanotube growth on metallic Ta films. J Phys Chem C 2011 115 4359-69. 

Mattevi C, Wirth CT, Hofmann S, Blume R, Cantoro M, Ducati C, et al. In-situ X-ray photoelectron spectroscopy study of catalyst—support interactions and growth of carbon nanotube forests. J Phys Chem C 2008 112 12207-13. 

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