Platinum stepped

Climent V, Attard GA, Feliu JM. 2002a. Potential of zero charge of platinum stepped surfaces a combined approach of CO charge displacement and N2O reduction. J Electroanal Chem 532 67-74. 

Climent V, Coles BA, Compton RG, Feliu JM. 2004. Coulostatic potential transients induced by laser heating of platinum stepped electrodes Influence of steps on the entropy of double layer formation. J Electroanal Chem 561 157-165. 

Macia MD, Campina JM, Herrero E, Feliu JM. 2004. On the kinetics of oxygen reduction on platinum stepped surfaces in acidic media. J Electroanal Chem 564 141 -150. 

The reactions of C labeled hydrocarbons on platinum catalysts under hydrogen atmosphere are structure-sensitive (14) and isomerization reactions are very sensitive to the crystallographic planes as observed on the platinum stepped surfaces where the bond shift mechanism is favored compared with the cyclic mechanism (15). 

D.R. Kahn, E.E. Petersen, and G.A. Somoijai. The Hydrogenolysis of Cyclopropane on a Platinum Stepped Single Crystal at Atmospheric Pressure. J. Catal. 34 294... 

Because oxidation of ammonia on a nonplatinum catalyst differs substantially from the process on a platinum catalyst, the use of nonplatinum catalysts is restricted. In the republics of the QS two-step catalysts are widely used. One or several platinum gauzes are used as the first step, and a bed of nonplatinum oxide catalyst is used as the second step. The platinum step offsets the drawbacks of the nonplatinum step. A significant share of the ammonia burners in the CIS operate with the two-step catalysts. Reportedly, this allows the platinum input to be reduced by 40%-50% and platinum losses to be reduced by 15%-30% under equal conditions. The ammonia conversion efficiency is considered to be approximately the same as with conventional catalysts [8,9]. 

Abd-El-Latif AA, Mostafa E, Huxter S, Attard G, Baltruschat H (2010) Electrooxidation of ethanol at polycrystalline and platinum stepped single crystals a study by differential electrochemical mass spectrometry. Electrochim Acta 55(27) 7951-7960... 

Clavilier J, Armand D, Sun SG, Petit M. Electrochemical adsorption behaviour of platinum stepped surfaces in sulphuric acid solutions. J Electroanal Chem 1986 205 267-77. 

Methyl tert-Butylluther Methyl /-butyl ether (MTBE) is an increasingly important fuel additive. Platinum—tin and other PGM catalysts are used for the dehydrogenation of isobutane to isobutene, an intermediate step in MTBE manufacture. 

A major step in the production of nitric acid [7697-37-2] (qv) is the catalytic oxidation of ammonia to nitric acid and water. Very short contact times on a platinum—rhodium catalyst at temperatures above 650°C are required. 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

The catalysts with the simplest compositions are pure metals, and the metals that have the simplest and most uniform surface stmctures are single crystals. Researchers have done many experiments with metal single crystals in ultrahigh vacuum chambers so that unimpeded beams of particles and radiation can be used to probe them. These surface science experiments have led to fundamental understanding of the stmctures of simple adsorbed species, such as CO, H, and small hydrocarbons, and the mechanisms of their reactions (42) they indicate that catalytic activity is often sensitive to small changes in surface stmcture. For example, paraffin hydrogenolysis reactions take place rapidly on steps and kinks of platinum surfaces but only very slowly on flat planes however, hydrogenation of olefins takes place at approximately the same rate on each kind of surface site. 

The next step of the UOP method of CCR regeneration is oxidation and chlorination. In this step, the catalyst is oxidized in air at about 510°C. A sufficient amount of chloride is usually added as an organic chloride, such as trichloroethane, to restore the chloride content and acid function of the catalyst to that of the fresh catalyst. If the platinum crystaUites ate smaller than about 10 nm, sufficient chlorine is present in the gas to completely tedispetse agglomerated platinum on the catalyst, as a result of the Deacon equUibtium ... 

Chemical exchange between hydrogen and steam (catalyzed by nickel—chromia, platinum, or supported nickel catalysts) has served as a pre-enrichment step in an electrolytic separation plant (10,70). If the exchange could be operated as a dual-temperature process, it very likely... 

The PT-Al eoating is a preeious metal applied by uniformly eleetroplating a thin layer (0.00025 ineh) of platinum onto the bueket at the airfoil surfaee, followed by paek-diffusion steps to deposit a layer of aluminum and ehro-mium. The resulting eoating has an outer skin of an extremely eorrosion resistant, platinum-aluminum intermetallie eomposition. As seen in Figure 11-8... 

Hydrofining is applied to virgin naphthas mainly in the form of a pretreatment step for the feed to catalytic reformers (Powerforming). Sulfur levels of 5 parts per million (ppm) or less are required to avoid deactivation of the platinum reforming catalyst. 

This reaetion is very rapid and has been diffieult to study meehan-istieally. The direet oxidation of ammonia, NH3, to nitrie oxide, NO, over platinum eatalyst is one of the major steps in the manufaeture of nitrie aeid, HNO3. 

The reaction product (1-carbethoxymethyM-carbomethoxy-pyridinium bromide) was obtained in crystalline form. (It formed prisms melting at 166°-169°C after recrystallization from a mixture of isopropanol and acetone.) It was not necessary to isolate it. For the following reduction step, the reaction mixture was brought into solution by the addition of about 1 liter of warm ethyl alcohol. It was then hydrogenated at about 30 atm pressure in the presence of 2 g of platinum oxide. The temperature rose during this reaction to about 40°C. 

The product (12.1 mg) obtained in the above step was dissoived in 0.3 mi of water, to which was then added a catalytic quantity (about 5 mg) of platinum oxide. Hydrogenation was made with hydrogen gas at a pressure of 35 kg/cm for 1.5 hours. The reaction solution was filtered to remove the catalyst, and the filtrate was concentrated to dryness, giving the desired product 3, 4 -dideoxykanamycin B in the form of its monocarbonate. The yield was 11.5 mg (95%). -f 110° (c 1, water). The overall yield of 3, 4 -dideoxykanamycin B... 

The next step was then to simulate, a four layer CuaPt overlayer on the (100) surface of the platinum substrate. The first layer w as taken to he pure copper, as was found in the experiment, while the second was a mixed copper-platinum, the third a copper and the fourth again a mixed layer. The fifth and all other layers were pure platinum. For the alloy overlayer the same potentials as for the CuaPt single crystal w ere used, and the potential of pure platinum for the substrate. 

The second aromatization reaction is the dehydrocyclization of paraffins to aromatics. For example, if n-hexane represents this reaction, the first step would be to dehydrogenate the hexane molecule over the platinum surface, giving 1-hexene (2- or 3-hexenes are also possible isomers, but cyclization to a cyclohexane ring may occur through a different mechanism). Cyclohexane then dehydrogenates to benzene. 

More often than what has been mentioned above regarding the cyclization of paraffins over the platinum catalyst, the formed olefin species reacts with the acid catalyst forming a carbocation. Carbocation formation may occur by abstraction of a hydride ion from any position along the hydrocarbon chain. However, if the carbocation intermediate has the right configuration, cyclization occurs. For example, cyclization of 1-heptene over the alumina catalyst can occur by the following successive steps ... 

The formed methylcyclohexane carbocation eliminates a proton, yielding 3-methylcyclohexene. 3-Methylcyclohexene can either dehydrogenate over the platinum surface or form a new carbocation by losing H over the acid catalyst surface. This step is fast, because an allylic car-bonium ion is formed. Losing a proton on a Lewis base site produces methyl cyclohexadiene. This sequence of carbocation formation, followed by loss of a proton, continues till the final formation of toluene. 

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