Catalysis platinum oxide

IsoquinoUne was converted to 1,2,3,4-tetrahydroisoquinoline in 89% yield by reduction with sodium in liquid ammonia and ethanol [473], and to a mixture of 70-80% cis- and 10% trans-decahydroisoquinoline by catalytic hydrogenation over platinum oxide in acetic and sulfuric acid [474]. Without sulfuric acid the hydrogenation stopped at the tetrahydro stage. Catalytic hydrogenation of isoquinoline and its derivatives is the topic of a review in Advances in Catalysis [439]. 

Platinum oxide-Fe or Cu-containing catalysts allow hydrogenation of furfural to furfurylalcohol". Ruthenium catalysts (Ru—C, RuOj) are successful in this specific case they have an activity well preserved through reuses. Otherwise Ru exhibits little activity in the heterogeneous hydrogenation of aromatic aldehydes. Other heterogeneous catalysis include platinized (PtC ) Raney Ni and copper chromite. 

Figure 7.15. NOx to N2 activity with octane as a reducing agent over silver on alumina catalyst and a platinum oxidation catalyst depending on the distance between the catalysts (K. Eranen, L.-E.Lindfors, F. Klingstedt, D.Yu.Murzin, Continuous reduction of NOx with octane over a silver/alumina catalyst in oxygen-rich exhaust gases combined heterogeneous and surface mediated homogeneous reactions, Journal of Catalysis, 219 (2003) 25).

Hwang, C.-P. Yeh, C.-T. Platinum-oxide species formed by oxidation of platinum crystallites supported on alumina. Journal of Molecular Catalysis A Chemical 112, 295-302 (1996). 

Several inososes have already been mentioned. Historically, myo-inosose-2 (2-keto-m2/o-inositol, scyHo-inosose, scyUo-mesoAnososey bioinos-ose) (Fig. 1), the product from m /o-inositol (49, 89, 90), is best known. This same inosose is obtained when m /o-inositol is oxidized with oxygen in the presence of platinum oxide in weakly acid solution (91), The yield is about half that obtained in the bacterial oxidation (85%) (90), but it is striking that both chemical (platinum) and biochemical (enzymes of A, suboxydans) catalysis cause oxygen to attack the substrate in the same position. 

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

Oxidation catalysts are either metals that chemisorb oxygen readily, such as platinum or silver, or transition metal oxides that are able to give and take oxygen by reason of their having several possible oxidation states. Ethylene oxide is formed with silver, ammonia is oxidized with platinum, and silver or copper in the form of metal screens catalyze the oxidation of methanol to formaldehyde. Cobalt catalysis is used in the following oxidations butane to acetic acid and to butyl-hydroperoxide, cyclohexane to cyclohexylperoxide, acetaldehyde to acetic acid and toluene to benzoic acid. PdCh-CuCb is used for many liquid-phase oxidations and V9O5 combinations for many vapor-phase oxidations. 

Perhaps the most familiar example of heterogeneous catalysis is the series of reactions that occur in the catalytic converter of an automobile (Figure 11.12). Typically this device contains 1 to 3 g of platinum metal mixed with rhodium. The platinum catalyzes the oxidation of carbon monoxide and unburned hydrocarbons such as benzene, C6H6 ... 

By far the most important use of the platinum metals is for catalysis. The largest single use is in automobile catalytic converters. Platinum is the principal catalyst, but catalytic converters also contain rhodium and palladium. These elements also catalyze a wide variety of reactions in the chemical and petroleum industry. For example, platinum metal is the catalyst for ammonia oxidation in the production of nitric acid, as described in Pt gauze, 1200 K... 

CO oxidation, an important step in automotive exhaust catalysis, is relatively simple and has been the subject of numerous fundamental studies. The reaction is catalyzed by noble metals such as platinum, palladium, rhodium, iridium, and even by gold, provided the gold particles are very small. We will assume that the oxidation on such catalysts proceeds through a mechanism in which adsorbed CO, O and CO2 are equilibrated with the gas phase, i.e. that we can use the quasi-equilibrium approximation. 

Mossbauer spectroscopy is a specialist characterization tool in catalysis. Nevertheless, it has yielded essential information on a number of important catalysts, such as the iron catalyst for ammonia and Fischer-Tropsch synthesis, as well as the CoMoS hydrotreating catalyst. Mossbauer spectroscopy provides the oxidation state, the internal magnetic field, and the lattice symmetry of a limited number of elements such as iron, cobalt, tin, iridium, ruthenium, antimony, platinum and gold, and can be applied in situ. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

Watanabe M, Motoo S. 1975. Electro catalysis by ad-atoms. Part III. Enhancement of the oxidation of carbon monoxide on platinum by ruthenium adatoms. J Electroanal Chem 60 275. 

Important inherent characteristics of an enzyme that should be considered are the substrate affinity, characterized by the Michaelis constant the rate of turnover fecat> providing the catalytic efficiency fecat/ M. and the catalytic potential. Several attempts to compare enzyme catalysis with that of platinum have been published. Direct comparisons are difficult, because enzyme electrodes must be operated in aqueous electrolyte containing dissolved substrate, whereas precious metal electrodes aie often supplied with a humidified gaseous stream of fuel or oxidant, and produce water as steam. It is not straightforward to compare tme optimal turnover rates per active site, as it is often unclear how many active sites are being engaged in a film of enzyme on an electrode. 

Platinum(O) phosphine complexes undergo a variety of oxidative addition reactions with compounds containing Group 14 elements. These reactions are of widespread interest because similar processes are probably involved in the catalysis by platinum complexes of reactions such as the hydrosilation of alkenes and the disilylation of dienes and alkenes. 

Platinum is a true treasure in catalysis. Many reactions proceed faster and more effectively in the presence of platinum this is specially true for oxidations. 

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