Nitrogen monoxide rhodium

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. 

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. 

Figure 6. One electron oxidation of [M (R)(CO)(PP1i3)3] or release of nitrogen monoxide ftom [Ir (Cl)(NO )(CO)(PPh3)]" yields paramagnetic rhodium or iridium complexes of the type [M (R)(CO)(PPh3)3]+.

For several couples of sensitive electrodes to oxygen action, it seemed interesting to test them in the presence of other gases like carbon monoxide or nitrogen oxides. Rhodium is indeed considered a good catalyst for the reduction of nitrogen oxides. Thus, we wanted to compare the observed sensitivities in order to determine selectivity criteria, and subsequently to be able to detect these different gases. 

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 ... 

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%. 

In addition to these homometallic (rhodium) clusters, several hetero-metallic clusters of the type [M M CO o]2, where M and M1 are each different metals selected from the Co, Rh, Ir triad (jc = 1-11), have been described and claimed to be useful catalysts in the reaction between carbon monoxide and hydrogen to produce oxygenated products (68, 69). These complexes can be prepared from the heterometallic dodecacar-bonyl complexes, [MuM (CO)12] (M, M1 = Co, Rh, or Ir y = 1-3), by simply mixing the appropriate dodecacarbonyl species in THF under nitrogen and then adding water (70). They can be isolated by adding a suitable cation e.g., Al3+, Mg2+, Ca2+, etc. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

When the oxidation of 24 is carried out under nitrogen instead of carbon monoxide, two larger rhodium clusters are produced. Rhl2C2(CO)25, 32 (74), forms slowly from solutions of the other product, [Rhl5C2(CO)2g], 33 (60, 75), which is unstable in solution. 

The trans- [Rh(PR3)2Cl(CO)] complexes were prepared by treating [RhCl(CO)2]2 under nitrogen in chloroform solution with 2 equiv of tertiary phosphine per rhodium atom. The only side product was carbon monoxide so that purification by recrystallization from ethanol or ethanol-chloroform was relatively simple. The lower-molecular-weight trialkylphosphine and higher-molecular-weight triarylphos-phine complexes were orange, viscous oils the others were cream-colored, low-melting crystalline solids. 

Unlike cobalt and rhodium, the chemistry of polynuclear iridium carbonyl derivatives has not been studied in detail (15a). Reduction of Ir4(CO)i2 under carbon monoxide with K2C03 in methanol gives the yellow tetranuclear hydride derivative [Ir4(CO)nH], whereas under nitrogen the brown dianion [Ir8(CO)2o]2- has been isolated as a tetraalkylam-monium salt (97). It has been suggested that the structure of the dianion could result from the linking of two iridium tetrahedra, although its formulation so far is based only on elemental analyses. Clearly such an interesting compound deserves further chemical and structural characterization. 

Automotive emission control is a major catalyst market segment. These catalysts perform three functions (1) oxidize carbon monoxide to carbon dioxide (2) oxidize hydrocarbons to carbon dioxide and water and (3) reduce nitrogen oxides to nitrogen. The oxidation reactions use platinum and palladium as the active metal. Rhodium is the metal of choice for the reduction reaction. These three-way catalysts meet the current standards of 0.41 g hydrocarbon per mile, 3.4 g carbon monoxide per mile, and 0.4 g nitrogen oxides per mile. 

The catalyst system for the modem methyl acetate carbonylation process involves rhodium chloride trihydrate [13569-65-8]y methyl iodide [74-88-4], chromium metal powder, and an alumina support or a nickel carbonyl complex with triphenylphosphine, methyl iodide, and chromium hexacarbonyl (34). The use of nitrogen-heterocyclic complexes and rhodium chloride is disclosed in one European patent (35). In another, the alumina catalyst support is treated with an organosilicon compound having either a terminal organophosphine or similar ligands and rhodium or a similar noble metal (36). Such a catalyst enabled methyl acetate carbonylation at 200°C under about 20 MPa (2900 psi) carbon monoxide, with a space-time yield of 140 g anhydride per g rhodium per hour. Conversion was 42.8% with 97.5% selectivity. A homogeneous catalyst system for methyl acetate carbonylation has also been disclosed (37). A description of another synthesis is given where anhydride conversion is about 30%, with 95% selectivity. The reaction occurs at 445 K under 11 MPa partial pressure of carbon monoxide (37). A process based on a montmorillonite support with nickel chloride coordinated with imidazole has been developed (38). Other related processes for carbonylation to yield anhydride are also available (39,40). 

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. 

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