Nitrogen monoxide platinum

Another example is the use of catalytic metals (platinum and rhodium) in the catalytic converter of a motor car. These solid metals catalyse the reaction between the pollutant gases carbon monoxide and nitrogen monoxide. 

Tanaka, T Okuhara, T Misono, M. Intermediacy of organic nitro and nitrite surface species in selective reduction of nitrogen monoxide by propene in the presence of excess oxygen over silica-supported platinum. Appl. Catal, B Environmental, 1994, Volume 4, Issue 1, L1-L9. 

The feed mixture oxidises over the platinum catalyst, thus converting the ammonia into nitrogen monoxide (NO) with a yield of 95%. The remaining 5% forms nitrogen gas and thus remains essentially inert to the reaction in all subsequent process units. 

How a catalytic converter works A typical catalytic converter consists of particles of platinum and rhodium deposited on a ceramic structure that is like a honeycomb. The platimun and rhodium catalyze reactions that remove pollutants such as nitrogen monoxide (NO), carhon monoxide (CO), and unhurned hydrocarbons. When nitrogen monoxide binds to the rhodimn surface, it breaks down to oxygen and nitrogen. The bound oxygen reacts with carbon monoxide, which has also become bound to the rhodimn surface. The reaction produces carbon dioxide. The oxidation of unburned hydrocarbons produces carbon dioxide and water. 

Some results in the literature show that nitrogen monoxide (NO) is bound N-down and is normal to the platinum surface at hollow sites with an increase in the N-O bond length by 0.046 A over the gas phase. The GGA-calculated adsorption energies in [54] at the 1/16 and 1/4 monolayer are 2.00 and 1.93 eV, respectively. Previously reported values at the 1/4 monolayer are from 1.75 to 2.10 eV [64,67]. These differences arise from the difference in the number of atoms simulating the cluster surface that affect the absolute value of adsorption energies. The adsorption of NO causes the platinum atoms local to the adsorbate to relax laterally or parallel to the surface and away from the adsorbate, as well as vertically, or normal to, and upward from the surface. These relaxations can result in substantial changes in the platinum-platinum separations near the adsorbates. In the case of... 

Bolten, H., Hahn, Th., LeRoux, J., Lintz, H.-G., 1985. Bistability of the reaction rate in the oxidation of carbon monoxide by nitrogen monoxide on polycrystalline platinum. Surf. Sci. 160, L529-L532. 

Ostwald process The manufacture of nitric acid by the catalytic oxidation of ammonia. In the first step of the process, compressed air and ammonia react (at 1,472°F [800 C] in the presence of a platinum gauze catalyst) to give nitrogen monoxide and water. 

A.P. (1994) Mechanism of the selective reduction of nitrogen monoxide on platinum-based catalysts in the presence of excess oxygen. AppL Catal. B Environ., 4, 65-94. 

In the case of the catalytic destraction of ozone, the catalyst speeds up a reaction that we do not want to happen. Most of the time, however, catalysts are used to speed up reactions that we do want to happen. For example, your car most likely has a catalytic converter in its exhaust system. The catalytic converter contains solid catalysts, such as platinum, rhodium, or palladium, dispersed on an underlying high-surface-area ceramic structure. These catalysts convert exhaust pollutants such as nitrogen monoxide and carbon monoxide into less harmful substances ... 

PRACTICE EXAMPLE A The first step in making nitric acid is to convert ammonia to nitrogen monoxide. This is done under conditions of high temperature and in the presence of a platinum catalyst. What volume of 02(g) is consumed per liter of NO(g) formed ... 

PGM catalyst technology can also be appHed to the control of emissions from stationary internal combustion engines and gas turbines. Catalysts have been designed to treat carbon monoxide, unbumed hydrocarbons, and nitrogen oxides in the exhaust, which arise as a result of incomplete combustion. To reduce or prevent the formation of NO in the first place, catalytic combustion technology based on platinum or palladium has been developed, which is particularly suitable for appHcation in gas turbines. Environmental legislation enacted in many parts of the world has promoted, and is expected to continue to promote, the use of PGMs in these appHcations. 

In one patent (31), a filtered, heated mixture of air, methane, and ammonia ia a volume ratio of 5 1 1 was passed over a 90% platinum—10% rhodium gauze catalyst at 200 kPa (2 atm). The unreacted ammonia was absorbed from the off-gas ia a phosphate solution that was subsequently stripped and refined to 90% ammonia—10% water and recycled to the converter. The yield of hydrogen cyanide from ammonia was about 80%. On the basis of these data, the converter off-gas mol % composition can be estimated nitrogen, 49.9% water, 21.7% hydrogen, 13.5% hydrogen cyanide, 8.1% carbon monoxide, 3.7% carbon dioxide, 0.2% methane, 0.6% and ammonia, 2.3%. 

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

Whereas determination of chemisorption isotherms, e.g., of hydrogen on metals, is a means for calculating the size of the metallic surface area, our results clearly demonstrate that IR studies on the adsorption of nitrogen and carbon monoxide can give valuable information about the structure of the metal surface. The adsorption of nitrogen enables us to determine the number of B5 sites per unit of metal surface area, not only on nickel, but also on palladium, platinum, and iridium. Once the number of B5 sites is known, it is possible to look for other phenomena that require the presence of these sites. One has already been found, viz, the dissociative chemisorption of carbon dioxide on nickel. 

Sconox A catalytic process for oxidizing oxides of nitrogen and carbon monoxide. The catalyst is in the form of a ceramic honeycomb coated with platinum and containing potassium carbonate. The platinum oxidizes the carbon monoxide to carbon dioxide, and the potassium carbonate absorbs the NO,. Developed in 1995 by Sunlaw Energy Corporation, CA, and Advanced Catalytic Systems, TN. 

It will be noted that on Langmuir s hypothesis the surface becomes saturated when it is covered with a unimolecular thickness of adsorbed gas. By measuring the adsorption of gases on the surface of mica and of platinum Langmuir showed that with the exception of carbon monoxide, gases such as oxygen, nitrogen and methane apparently when adsorbed to a saturation value covered the surface with a unimolecular thickness of gas. 

Houdry s solution to the problem was the first catalytic converter ever designed for an automotive vehicle. The catalytic converters found on almost all cars and trucks in use today are still strikingly similar to his invention. Exhaust gases passed into the converter and over a bed of platinum catalyst, then exited with a greatly reduced concentration of carbon monoxide, nitrogen oxides, and unburned hydrocarbons. Houdry obtained a patent for his device in 1956 and founded a company, Oxy-Catalyst, to manufacture and sell the new product. 

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