Surface reaction with carbon monoxid

The adsorbed oxygen atom on the copper surface is removed by reaction with carbon monoxide and provides a pathway for the formation of the carbon dioxide needed in the main reaction. 

The chemisorption and reactivity of the oxides of nitrogen on metal surfaces are of great environmental interest because of their connection to the reaction with carbon monoxide, leading to innocuous products, e.g. 

Automobile exhaust catalysts typically contain noble metals such as Pt, Pd and Rh with a ceria promoter supported on alumina. Traditionally, the principal function of the Rh is to control emissions of nitrogen oxides (NO ) by reaction with carbon monoxide, although the increasing use of Pd has been proposed. For example, recent X-ray absorption spectroscopy studies of Holies and Davis show that the average oxidation state of Pd was affected by gaseous environment with an average oxidation slate between 0 and +2 for a stoichiometric mixture of NO and CO. Exposure of Pd particles to NO resulted in the formation of chemisorbed oxygen and/or a surface oxide layer. 

Tris(allyl)rhodium(in) was reported to react with the hydroxyl-terminated surfaces of silica, titania and alumina to form a surface bis(allyl)rhodium(III) fragment, which on reaction with carbon monoxide afforded hexa-1,5-diene in quantitative fashion by reductive coupling of two allyl ligands. 

V.V. Gorodetskii, W.M.H. Sachtler, G.K. Boreskov, B.E. Nieuwenhuys, Adsorption of oxygen and its reactions with carbon-monoxide and hydrogen on rhodium surfaces— comparison with platinum and iridium. Appl. Surf. Sci. 7(4), 355-371 (1981)... 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Adsorbed carbon monoxide on platinum formed at 455 mV in H2S04 presents a thermal desorption spectrum as shown in Fig. 2.4b. As in the case of CO adsorption from the gas phase, the desorption curve for m/e = 28 exhibits two peaks, one near 450 K for the weakly adsorbed CO and the other at 530 K for the strongly adsorbed CO species. The H2 signal remains at the ground level. A slight increase in C02 concentration compared to the blank is observed, which could be due to a surface reaction with ions of the electrolyte. Small amounts of S02 (m/e = 64) are also observed. 

Carbonaceous species on metal surfaces can be formed as a result of interaction of metals with carbon monoxide or hydrocarbons. In the FTS, where CO and H2 are converted to various hydrocarbons, it is generally accepted that an elementary step in the reaction is the dissociation of CO to form surface carbidic carbon and oxygen.1 The latter is removed from the surface through the formation of gaseous H20 and C02 (mostly in the case of Fe catalysts). The surface carbon, if it remains in its carbidic form, is an intermediate in the FTS and can be hydrogenated to form hydrocarbons. However, the surface carbidic carbon may also be converted to other less reactive forms of carbon, which may build up over time and influence the activity of the catalyst.15... 

Scheme 7.3 Reaction of surface Jt-allyl rhodium siloxide complex with carbon monoxide.

At first sight, scheme (371) does not agree with the results of our adsorption experiments these experiments showed that activated charcoal does not chemisorb CO at 100°C. It should, however, be taken into consideration that the surface of charcoal subjected to activation or even simply after storage in contact with air is covered with chemisorbed oxygen. The studies of the reactions of carbon with C02 and steam (see Section XX) have demonstrated that oxygen chemisorbed on carbon is indistinguishable from chemisorbed carbon monoxide. So it may be reckoned that activated charcoal is already covered with carbon monoxide before the contact with this gas. 

In certain catalytic reactions, such as the reaction of carbon monoxide on nickel and of ethylene on nickel, carbonaceous deposits built up on the surface, and the rate of formation of these deposits varied greatly with the face exposed. In some cases, even when the deposit was very thick on certain faces, no carbon could be detected on others. 

Now possibilities of the MC simulation allow to consider complex surface processes that include various stages with adsorption and desorption, surface reaction and diffusion, surface reconstruction, and new phase formation, etc. Such investigations become today as natural analysis of the experimental studying. The following papers [282-285] can be referred to as corresponding examples. Authors consider the application of the lattice models to the analysis of oscillatory and autowave processes in the reaction of carbon monoxide oxidation over platinum and palladium surfaces, the turbulent and stripes wave patterns caused by limited COads diffusion during CO oxidation over Pd(110) surface, catalytic processes over supported nanoparticles as well as crystallization during catalytic processes. 

The BET surface areas of both the amorphous and the crystalline Fe2oNi6oP2o catalysts were nearly the same and constant during the reaction, but the surface characters of the amorphous and the crystalline phases of FegoZrio alloy were quite different with each other. For the crystalline catalyst, the BET surface area was kept constant during the reaction at about 0.25 m2/g. On the other hand, the amorphous catalyst ribbons broke into fine chips of different sizes and the BET surface area after the reaction went up to 0.9 m2/g. Since the pretreatment with a stream of hydrogen did not produce any breakage of the alloy ribbon, and also because the catalytic acitvity had been kept constant shortly after the start of the reaction, the increase of the surface area of the amorphous catalyst is considered to take place at the initial period of the reaction by carbon monoxide and hydrogen. 

Table 1(b) on the formation or removal in vacua of carbon monoxide by reaction of surface oxides with carbon in the metal shows the results of these calculations. The reactions are feasible thermodynamically in vacua of the order of 10-10 atm. at temperatures of 600°C. or higher for the metals tungsten, chromium, and iron. Thus, carbon monoxide will be formed by the diffusion of carbon to the surface and subsequent reaction with the surface oxides. This reaction has been discussed for the case of steels by Holm (11). The effect of carbon content on the reaction is not shown in the table. However, the effect can be seen from the expression for the equilibrium constant K for the reaction of ferrous oxide with carbon in the iron ... 

Table 1(c) on the formation or removal in vacua of carbon dioxide by reaction of the surface oxides with carbon in the metal shows the results of these calculations. The reactions are feasible for tungsten and iron but not for zirconium and magnesium. Chromium presents an intermediate case with an equilibrium pressure of 10-12-46 at 800°C., 10-9,88 at 1000°C., and 10 768 at 1200°C. The reverse reaction is feasible for zirconium and magnesium and for chromium at low temperatures. From a kinetic viewpoint the probability that this reaction will occur is small compared to the reaction to form carbon monoxide gas. In this case zirconium will act as a getter for carbon dioxide, while tungsten, iron, and chromium will be relatively inert to carbon dioxide molecules. 

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

The reactivity of high-surface-area (typically 200-300 m g ) MgO is demonstrated by the large number of species that are formed upon interaction with carbon monoxide at 300 K these are formed in a complex sequence of surface reactions... 

The study of the various reactions of carbon monoxide, hydrogen, and oxygen at oxide surfaces holds a particularly important place in the development of research in heterogeneous catalysis. Not only are the well-established technical aspects of these reactions continuously monitored by those engaged in chemical industry, but the chemist interested in fundamental studies of the interaction of gases with oxides naturally turns to the behavior of these gases because of the combination of high reactivity and molecular simplicity which they afford. Finally, for the chemical physicist,... 

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