Rhodium platinum containing

Black nickel oxide is used as an oxygen donor in three-way catalysts containing rhodium, platinum, and palladium (143). Three-way catalysts, used in automobiles, oxidize hydrocarbons and CO, and reduce NO The donor quaUty, ie, the abiUty to provide oxygen for the oxidation, results from the capabihty of nickel oxide to chemisorb oxygen (see Exhaust control, automotive). 

Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium, platinum, palladium, or irridium. The oxidizing agent is nitrous oxide, which is unavoidable a byproduct from the oxidation of KA oil (see KA oil, this chapter) to adipic acid using nitric acid as the oxidant. 

Alloys with rhodium Rhodium alloys readily with platinum in all proportions, although the workability of the resulting alloy decreases rapidly with increasing rhodium content. Alloys containing up to about 40% rhodium, however, are workable and find numerous applications. The principal physical and mechanical properties of rhodium-platinum alloys are listed in Table 6.3. 

Alloys with iridium Iridium alloys with platinum in all proportions, and alloys containing up to about 40% iridium are workable, although considerably harder than pure platinum. The creep resistance of iridium-platinum alloys is better than that of rhodium-platinum alloys at temperatures below 500°C. Their stability at high temperatures, however, is substantially lower, owing to the higher rate of formation of a volatile iridium oxide. 

Rhodium-platinum alloys containing up to 40% Rh are used in the form of wire or ribbon in electrical resistance windings for furnaces to operate continuously at temperatures up to 1 750°C. Such windings are usually completely embedded in a layer of high-grade alumina cement or flame-sprayed alumina to prevent volatilisation losses from the metal due to the free circulation of air over its surface. Furnaces of this type are widely employed for steel analysis, ash fusions and other high-temperature analytical procedures. 

For the noble metals used in oxidation, the loading is about 0.1 oz per car, with calls for a million ounces per year. The current world production rates of platinum, palladium, and rhodium are 1.9, 1.6, and 0.076 million ounces respectively the current U,S. demand for platinum, palladium, rhodium, and ruthenium are 0.52, 0.72, 0.045, and 0.017 million ounces respectively (72, 73). The supply problem would double if NO reduction requires an equal amount of noble metal. Pollution conscious Japan has adopted a set of automobile emission rules that are the same as the U.S., and Western Europe may follow this creates a demand for new car catalysts approaching the U.S. total. The bulk of world production and potential new mines are in the Soviet Union and South Africa. The importation of these metals, assuming the current price of platinum at 155/oz and palladium at 78/oz, would pose a balance of payment problem. The recovery of platinum contained in spent catalysts delivered to the door of precious metal refiners should be above 95% the value of platinum in spent catalysts is greater than the value of lead in old batteries, and should provide a sufficient incentive for scavengers. 

Likewise, mononuclear complexes of rhodium and platinum containing only one meth-ylenecyclopropane ligand are prepared by ligand exchange reactions of the Feist s esters with (acac)Rh(CO)2 and trans-C 2(pyr)Pt(et hylene), giving complexes (acac)(CO)Rh(tF) and franj-Cl2(pyr)PtL (L = cF, tF), respectively (equation 311). 

On the whole, with each catalytic system, the same face of the substituted unsaturated carbon atoms is attacked for different substrates. There are 2 exceptions out of 32 cases for rhodium- and 2 exceptions out of 8 cases for platinum-containing catalytic systems. 

The amount of wash coat which was deposited in the testing reactors was in the same range, between 14 and 17 mg, for the rhodium, platinum and palladium samples tested. The platinum sample was calcined after impregnation at a lower temperature of 450 °C, all other samples at 800 °C. The reason for this will be explained below. The content of the active noble metal was around 5 wt.%. All noble metal-containing samples were laboratory-made catalysts. A commercial a-alumina-based catalyst containing 14 wt.% Ni was added for comparison, as nickel catalysts are applied in industrial steam reforming [52],... 

In this process (Fig. 1), the reactor contains a rhodium-platinum catalyst (2 to 10% rhodium) as wire gauzes in layers of 10 to 30 sheets at 750 to 920°C, 100 psi, and a contact time of 3 X 10"4 second. After cooling, the product gas enters the absorption tower with water and more air to oxidize the nitric oxide and hydrate it to nitric acid in water. Waste gases contain nitric oxide or nitrogen dioxide, and these are reduced with hydrogen or methane to ammonia or nitrogen gas. Traces of nitrogen oxides can be... 

For our system we chose the simplest approach — a fast sample conduit with quick quench into an evacuated sample container. For temperature measurements we used a similar probe outfitted with platinum/6% rhodium-platinum/30% rhodium thermocouple. For pressure measurements the same general type probe mentioned was employed but without extracting samples. This probe had one hole opening perpendicular to the longitudinal axis of the probe such that when inserted into the reactor it could be rotated 360°. In this manner the pressures were read from a precision pressure gauge with the opening facing 0°, 90°, 180°, and 270° relative to the direction of flow in the reactor. 

Occurrence and History.—Rhodium occurs as an alloy in platinum ore and osmiridium. An alloy with gold, known as rhodite or rhodium gold, contains from 30 to 43 per cent, of rhodium, and has a density of 15-5 to 16-8.1 The metal was discovered by Wollaston,2 and so named from the Greek p6Sov, a rose, in recognition of the colour of aqueous solutions of its salts. 

Rhodium readily alloys with platinum, stiffening it and yielding mixtures that are useful for a variety of laboratory purposes. Rhodium reduces the loss in weight of platinum by volatilisation at all temperatures above 900° C., and it has therefore been suggested that a useful alloy for best quality crucibles would be platinum containing 3 to 5 per cent, of rhodium, practically free from iron and iridium, and containing no other detectable impurities. 2... 

All sol-gel derived catalysts were stable under reaction conditions, except the rhodium and iridium catalysts, whose colour changed significantly during reaction. The catalysts could easily be separated from the reaction mixture by simple filtration. The filtrated liquid product, that flew out colourless, exhibited no further catalytic activity. GC analysis of the liquid phase indicated the production of dmf with 100% selectivity in all cases, except for the platinum containing catalyst (Table 1). 

This couple gives an e.m.f. of about - millivolt per 1° C. For high temperatures, above the melting point of constantan, Le Chatelier s pyrometer is used. It is a thermocouple consisting of pure platinum and an alloy of platinum containing 10 per cent, of rhodium. 

Proton magnetic resonance studies have also shown the presence of metal-hydrogen species in cyanide solutions of rhodium, platinum, and iridium (Table IX). In particular, the addition of CN- to a boiled aqueous solution of rhodium trichloride, followed by reduction with sodium boro-hydride, yields a solution that contains an Rh—H complex in moderately high concentrations and is stable in the absence of oxygen for several years (108). The observed coupling of the proton with the Rh10 nucleus (spin ) confirms the presence of an Rh—H bond (108). 

Cobalt-based low temperature Fischer—Tropsch catalysts, appHed at approximately 220 °C and 30 atm, are usually supported on high-surface-area Y-AI2O3 (150—200 m g ) and typically contain 15—30% weight of cobalt. To stabihze them and decrease selectivity to methane, these catalysts may contain small amounts of noble metal promoters (typically 0.05—0.1 wt% of ruthenium, rhodium, platinum, or palladium) or an oxide promoter (e.g., zir-conia, lanthana, cerium oxide, in concentrations of 1—10 wt%) (409). 

Various alloys and metalBc oxides have been tried as catalysts, but platinum containing between 2% and 10% rhodium is usuaQy preferred 161. Nitric oxide produced in the ammor converter must be oxidized furiher to nitrogen dioxide by the excess air present in the reaction mixture ... 

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