Platinum-rhodium catalysts

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. 

Commercially, nitric acid is made by a three-step process developed by the German physical chemist Wilhelm Ostwald (1853-1932). The starting material is ammonia, which is burned in an excess of air at 900°C, using a platinum-rhodium catalyst ... 

The oxidation is carried out over layers of platinum-rhodium catalyst and the reaction conditions are selected to favour reaction 1. Yields for the oxidation step are reported to... 

Approximately 80% of all hydrogen cyanide is manufactured by the reaction of air, ammonia, and natural gas over a platinum or platinum-rhodium catalyst at elevated temperature. The reaction is referred to as the Andrussow process. Hydrogen cyanide is also available as a by-product from aciylonitrile manufacture by ammoxidation (20%). 

However, reaction at 750°C to 900°C in presence of platinum or platinum-rhodium catalyst produces nitric oxide and water ... 

It is worth looking for a catalyst because the negative value of AG° indicates that the reaction is spontaneous under standard-state conditions. (This reaction is the first step in the Ostwald process for production of nitric acid. In industry, the reaction is carried out using a platinum-rhodium catalyst.)... 

Nitric acid is produced industrially by the multistep Ostwald process, which involves (1) air oxidation of ammonia to nitric oxide at about 850°C over a platinum-rhodium catalyst, (2) rapid oxidation of the nitric oxide to nitrogen dioxide, and (3) disproportionation of N02 in water ... 

The major process units include an air compressor to provide feed air to the process, and an ammonia vaporizer and superheater for pretreatment of the feed ammonia. A reactor vessel with a fixed platinum/rhodium catalyst bed quickly oxidizes the ammonia at reaction temperatures approaching 950°C. The reaction yield is 95%. A heat exchanger train immediately following the reactor is used to recover reaction heat. Reaction heat is recovered for both gas expansion (to provide shaft power for the air compressors) and for production of medium-pressure steam (at 380°C and 4000 kPa). The high-level energy available in the process is shared approximately equally between gas expansion and steam production. About 40% of all steam production is delegated to in- house process requirements, leaving about 3200 kg/hour available for export. 

The first reaction is run over platinum-rhodium catalysts at around 900°C (1,652°F). In the second and third stages, a mixture of nitric oxide and air circulates through condensers, where it is partially oxidized. The nitrogen dioxide is absorbed in a tower, and nitric acid sinks to the bottom. Nitric acid is mainly used to make ammonium nitrate, most of it for fertilizer although it also goes into the production of explosives. Nitration is used to manufacture explosives such as nitroglycerine and trinitrotoluene (TNT) as well as many important chemical intermediates used in the pharmaceutical and dyestuff industries. 

The Andrussow process was patented by Dr. L. Andrussow of I.G. Farben AG in Germany in 1933 (U.S. Patent 1,934,838). Its main advantages are low converter investment, low maintenance costs and high natural gas yields when the waste gas is used as a boiler fuel. The Andrussow process produces HCN by the reaction of ammonia, air and natural gas at 1,000°C to 1,200°C in the presence of a platinum/rhodium catalyst. The reaction is ... 

For propane oxidation, sulfation with SO2 induces an inhibiting effect on monometallic pfatinum catalysts which increases with the amount of sulfur accumulated on the catalyst (Fig 3b). On the other hand, sulfur storage enhances the activity of coimpregnated platinum-rhodium catalysts oxidized before hydrocarbon oxidation. However, it seems that an optimum sulfur storage exists since catalyst activity decreases as the amount of sulfur stored on the sample increases (Fig 3b). We examined also the effect of sulfation on catalyst activity for... 

Andrussov A process for making hydrogen cyanide by reacting ammonia, methane, and air at approximately 1,000°C over a platinum-rhodium catalyst ... 

Benzene undergoes an addition reaction with hydrogen with a platinum/rhodium catalyst at 2-3 atm pressure and at 30°C. 

Gavril, D. Katsanos, N.A. Karaiskakis, G. Gas chromatographic kinetic study of carbon monoxide oxidation over platinum-rhodium catalysts. J. Chromatogr., A 1999, 852, 507-523. 

Nitrogen(II) oxide in 80 to 90% yield is produced by the catalytic combustion of ammonia in oxygen in the presence of water vapor on a platinum-rhodium catalyst ... 

Platinum/Rhodium catalysts were first used on European cars to reduce NOx emissions for the US 1975 emissions regulations, using open loop three way catalysis. 

The reaction takes place over a platinum or platinum-rhodium catalyst at temperatures of 1000—1500°C and atmospheric pressure [2,4—6]. 

Nitric acid is one of the most important inorganic acids. It is used in the production of fertilizers, dyes, drugs, and explosives. The major industrial method of producing nitric acid is the Ostwald process. The starting materials, ammonia and molecular oxygen, are heated in the presence of a platinum-rhodium catalyst (Figure 13.22) to about 800°C ... 

FIGURE 13.22 Platinum-rhodium catalyst used in the Ostwald process. 

B. J. Cooper, B. Harrison, E. Shutt and I. Lichtenstein, The Role of Rhodium in Platinum/Rhodium Catalysts for Carbon Monoxide/Hydrocarbon/Nitrogen Oxides (NOx) and Sulphate Emission Control - The Influence of Oxygen on Catalyst Performance, SAE 770367. 

In this paper we investigated the properties of three-way automotive Pt-Rh / Al203-Ce02 catalysts prepared either by simultaneous impregnation of the two noble metals (coimpregnation = Cl) or by the technique of successive impregnations (S.I.). Their catalytic performances were measured after reduction or calcination at 500°C, for the oxidation of a propane-propene mixture under lean conditions and for the reduction of NO by CO under stoichiometric mixtine. Monometallic platinum catalysts and an alumina supported bimetallic platinum-rhodium catalyst were also prepared for a comparative study. ... 

On thermally aged catalysts, the pretreatment (calcination or reduction at 500°C) does not affect catalyst activity for propene oxidation (Fig 2a). On the other hand, the results reported in Fig 2b show that coimpregnated bimetallic platinum-rhodium catalysts endure an increase in their hght-off temperature with respect to propane oxidation after an oxidizing treatment at 500°(j. The same effect is observed when prereduced samples are submitted to a second oxidation cycle after a first cycle up to 850°C under lean conditions (Fig 3). As for the... 

The most deactivating conditions for a Platinum/Rhodium catalyst are high temperature lean ... 

Rayong, Thailand, 127, 128 Rotterdam, 122 Ruhr Valley, Germany, 122 Piperdine, 200 Pivaloyl chloride, 263 Plasticizer, 160, 259-264 Plasticizer alcohols, 225, 259, 260, 264 Plate-fin exchanger, 8, 9, 17, 18, 29-31 Platinum-rhodium catalyst, 192 Poly (alfa) olefins, 200 Polyvinylchloride (PVC), 160, 168, 170 Polyamide, 190, 202, 243 Polybutene-1, 200 Polybutylene teraphthalate, 148... 

The ammonia and air are passed over a platinum/rhodium catalyst at 900 C ... 

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