Catalytic promoters

Wimmer E, Fu C L and Freeman A J 1985 Catalytic promotion and poisoning all-electron local-density-functional theory of CO on Ni(001) surfaces coadsorbed with K or S Phys. Rev. Lett. 55 2618-21... 

Powerforming is basically a conversion process in which catalytically promoted chemical reactions convert low octane feed components into high octane products. The key to a good reforming process is a highly selective dual-function catalyst. The dual nature of this catalyst relates to the two separate catalyst functions atomically dispersed platinum to provide... 

This process is used to treat gas streams containing high concentrations of H2S. The chemistry of the units involves partial oxidation of hydrogen sulfide to sulfur dioxide and the catalytically promoted reaction of hh.S and SO2 to produce elemental sulfur. The reactions are staged and arc. is lollows ... 

He became intimately familiar with a wide range of catalytic materials—including aluminum oxide, silica, and clay, as well as nickel, platinum, zinc, and copper—and their role individually and as mixtures 111 effecting chemical transformation. One of Ipatieffs most important lines of research was his breakthrough work on the nature and mechanisms of catalytic promoters on organic reactions. 

At UOP, Ipatieff had the opportunity to apply his former research in catalytic promoters and high-pressure technique to develop important catalytic petroleum processing technologies. In contrast to the way he conducted science, Ipatieff s technical efforts were conducted in teams comprised of a wide assortment of specialists. 

The stability of tin over the middle pH range (approximately 3-5-9), its solubility in acids or alkalis (modified by the high hydrogen overpotential), and the formation of complex ions are the basis of its general corrosion behaviour. Other properties which have influenced the selection of tin for particular purposes are the non-toxicity of tin salts and the absence of catalytic promotion of oxidation processes that may cause changes in oils or other neutral media affecting their quality or producing corrosive acids. 

A more robust way to write a rate law for a catalytically promoted reaction is to include the concentrations of one or more surface complexes, in place of the surface area As. In this case, the simulation can account not only for the catalyzing surface area, since the mass of a surface complex varies with the area of the sorbing surface, but the effects of pH, competing ions, and so on. 

Catalytic promotion of carbon deposition from carbon-containing fuels. Carbon deposited in the anode will generally cause irreversible damage (disintegration) of the anode structure. 

The combined use of the modem tools of surface science should allow one to understand many fundamental questions in catalysis, at least for metals. These tools afford the experimentalist with an abundance of information on surface structure, surface composition, surface electronic structure, reaction mechanism, and reaction rate parameters for elementary steps. In combination they yield direct information on the effects of surface structure and composition on heterogeneous reactivity or, more accurately, surface reactivity. Consequently, the origin of well-known effects in catalysis such as structure sensitivity, selective poisoning, ligand and ensemble effects in alloy catalysis, catalytic promotion, chemical specificity, volcano effects, to name just a few, should be subject to study via surface science. In addition, mechanistic and kinetic studies can yield information helpful in unraveling results obtained in flow reactors under greatly different operating conditions. 

In the chemical industry, iodine and/or iodine compounds are often used as catalysts and/or catalytic promoters for the production of value-added organic chemicals. As with other catalytic reactions, the catalyst or promoter must be removed from the products after completing the reaction. However, removing trace amounts of organic iodide contaminates from the product by conventional distillation techniques is difficult primarily due to the fact that iodine compounds are unstable and split off into various boiling ranges. 

A number of simple and inexpensive materials catalytically promote the cobalt-carbonylation (Reaction 2) in aqueous solution. These include ion-exchange resins, zeolites, or special types of activated carbon. Formation of the active catalyst in a separate reactor is thus economically feasible. The mechanism of this catalysis has not yet been elucidated and seems to differ for each promoter mentioned. After an induction period during which the cobalt fed to the reactor is partially retained by the promoter, fully active materials have absorbed cobalt carbonyl anion Co(CO)4 (ion exchange resins), Co2+ cation (zeolites), or a mixture of Co2+, cobalt carbonyl hydride, and cluster-type cobalt carbonyls (activated carbon). This can be shown by analytical studies (extraction, titration, and IR studies) of active material withdrawn from the reactor. 

The reaction of enyne with either an Au(I) or Au(III) catalytic promoter gave a 6-oxabicyclo[3.2.1]octane (Scheme 98).141 The use of Au(PPh3)Cl in combination with AgC104 is equally effective. The possible involvement of the conjugate Brpnsted acid in the alkyne activation of the alcohol was excluded since treatment with HC1 in the absence of AuC13 gave exclusively tetrahydrofuran. 

The formation of some organic hydroperoxides by oxidation with molecular oxygen is catalytically promoted by metals like silver or copper 171). A dissociative chemisorption of oxygen cannot be active in these processes they probably proceed via the chemisorption of O7 ions (or O2 molecules forming a covalent bond resonating with an ionic bond). 

When first reported in 1905, the Reissert reaction demonstrated the addition of KCN to quinoline in the presence of benzoyl chloride, but many new modifications since then have employed other nucleophiles and catalytic promotion by a Lewis acid. Shibasaki reported in 2001 the first catalytic enantioselective Reissert-type reaction. Optimized reaction conditions involving an electron-rich aromatic acid chloride in a low-polarity solvent, and use of catalyst 14, were found to suppress the racemic pathway and resulted in good enantioselectivity (Scheme 2) <2001JA6801>. 

Indium trichloride catalytically promotes the alkynylation of aldehydes in which InCl3 plays two roles transme-tallation with tin compounds and activation of aldehydes as a Lewis acid (Equation (65)).219... 

Ferric Oxide as a Catalyst—Ferric oxide possesses the power of catalytically promoting the combination of sulphur dioxide and oxygen at red heat. The action is perceptible at temperatures just above 400° C., attaining a maximum at 625° C. when 70 per cent, of the sulphur dioxide is converted into trioxide.3 The origin of the ferric oxide is of considerable importance, that prepared from the hydroxide being particularly active. Admixture of copper oxide increases the efficiency, as does also the presence of arsenic at temperatures above 700° C.4... 

For a number of the most important groups of catalytically promoted reactive processes in the chemical industries—e.g., etherifications and esterifications—conversion is equilib-... 

The catalytically promoted liquid-phase etherification of isobutene with an excess of methanol to produce MTBE has been carried out on a commercial scale in conventional fixed-bed reactors since the 1970s isobutene conversion is on the order of 90-97%. MTBE can be subsequently separated from the inerts and excess methanol by distillation— although this is complicated by the presence of minimum boiling azeotropes between MTBE and methanol and between isobutene and methanol. Unreacted isobutene is, however, difficult to separate from n-butanes and n-butenes because of their low relative... 

A membrane reactor is a particular type of multifunctional reactor where one or more chemical reactions, generally catalytically promoted, are carried out in the presence of a membrane this last, thanks to its permselectivity, affects the course of the reactions, allowing improvements of either the achievable conversion (e.g., equilibrium reactions) or the selectivity toward intermediate products (e.g., consecutive reaction schemes). 

Besides other synthetic purposes, it finds use in the removal of sulphur, nitrogen and oxygen from petroleum feed stocks by catalytically promoted reactions ... 

Correlation between selected values of E, for decompositions of oxalates and mellitates with the enthalpies of oxide formation [108] (some mean values of E, are included). The magnitudes of E, thus appear to be controlled by the strengths of the M-0 bonds. Two trends may be discerned. Reactions where breakdown of the oxalate anion are believed to be catalytically promoted by the metal product, have slightly lower E, values ( ), compared to reactions in which the residual product does not promote decomposition, including the mellitates where carbon deposition inhibits catalysis (+). 

The initial or rate limiting step for anion breakdown in metal oxalate decompositions has been identified as either the rupture of the C - C bond [4], or electron transfer at a M - O bond [5], This may be an oversimplification, because different controls may operate for different constituent cations. The decomposition of nickel oxalate is probably promoted by the metallic product [68] (the activity of which may be decreased by deposited carbon, compare with nickel malonate mentioned above [65]). No catalytically-active metal product is formed on breakdown of oxalates of the more electropositive elements. Instead, they yield oxide or carbonate and reactions may include secondary processes [27]. There is, however, evidence that the decompositions of transition metal oxalates may be accompanied by electron transfers. The decomposition of copper(II) oxalate [69] (Cu - Cu - Cu°) was not catalytically promoted by the metal and the acceleratory behaviour was ascribed to progressive melting. Similarly, iron(III) oxalate decomposition [61,70] was accompanied by cation reduction (Fe " - Fe ). In contrast, evidence was obtained that the reaction of MnC204 was accompanied by the intervention of Mn believed to be active in anion breakdown [71]. These observations confirm the participation of electron transfer steps in breakdown of the oxalate ion, but other controls influence the overall behaviour. Dollimore has discussed [72] the literature concerned with oxalate pyrolyses, including possible bond rupture steps involved in the decomposition mechanisms... 

S. Valerio, A. Pastore, M. Adinolfi, and A. Iadonisi, Sequential one-pot glycosidations catalytically promoted Unprecedented strategy in oligosaccharide synthesis for the straightforward assemblage of the antitumor PI-88 pentasaccharide, J. Org. Chem., 73 (2008) 4496 1503. 

The cycloaddition of free carbenes to alkenes to give cyclopropanes is well known (see equation 10.2). Transition metal-carbene complexes, acting either stoichiometrically or catalytically, promote cyclopropanation, sometimes in a synthetically-useful manner. Several mechanistic pathways have been observed, some of which involve mid-transition metal alkylidenes. Two of the most common of these are outlined in Scheme 10.6.67... 

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