Decomposition of carbon monoxide

Radushkevich LV, Lukyanovich VM (1952) About structure of carbon created at thermal decomposition of carbon monoxide on iron contact. J Phys Chem 26 88-95... 

Most gases do not affect refractory bricks. Under high pressure hydrogen gas can reduce silicon dioxide. At appr. 400-800 °C, carbon monoxide is converted into carbon and carbon dioxide. The carbon is deposited on the brick and this may lead to brick s compression. However, a solution has been found. The decomposition of carbon monoxide appeared to be stimulated by certain iron compounds. By firing the bricks at a sufficiently high temperature, you can convert these iron compounds into iron silicates which do not act as catalysts. 

A study of the velocity of reduction of carbon dioxide by carbon at 850° C. shows that the reaction is monomoleeular, and the same is true for the reverse reaction, namely the decomposition of carbon monoxide, which, however, proceeds 166 times more slowly. Undoubtedly, therefore, the reactions arc essentially surface phenomena, the rates varying directly with the partial pressure of the gas in either case. Since the decomposition of carbon monoxide is accompanied by a reduction m volume, increase of pressure should facilitate the reaction at constant temperature, and shift the equilibrium... 

Decomposition of carbon monoxide takes place when it is exposed to radiation of wavelength 1,295 A, but not when exposed to 1,470 A -0. Herzberg2i5 has concluded from this that Z)(CO)<9-57 eV, but Gaydont< 6 has pointed out that when vibrational and rotational energy are taken into account the upper limit may be as high as 10 1 eV, and further that it is not established that photodissociation is the primary act in the reaction. 

The mechanism of the reaction which takes place in the presence of nickel as well as certain other of the metal catalysts, has been explained by assuming that metallic carbonyls are formed by the action of carbon monoxide on the metal and that these compounds represent intermediate products in the catalyses. Evidence in support of this theory has been brought forward by Mond, Langer and Quinke,0- who studied the decomposition of carbon monoxide in contact with nickel at temperatures between 350° and 450° C. In examining the carbonized nickel catalyst at the end of the experiment these investigators discovered that when heated, it gave off a volatile inflammable nickel compound which could be condensed to a liquid and which was later identified as nickel carbonyl. Metals, such as nickel, cobalt, and iron, which form distinct metallic carbonyls are particularly active catalysts for the decomposition, a fact which adds weight to this theory. 

At 250° C. this reaction occurs with the liberation of almost 20,000 calories of energy per mol. In the presence of active catalysts especially, this decomposition of carbon monoxide to form carbon dioxide and a highly reactive carbon, complicates any attempt to use it as an oxygenating agent in vapor phase reactions. Consequently, very little experimentation has been done with the direct object of reacting hydrocarbons with carbon monoxide to form oxygen containing compounds. 

The feasibility of continuous operation counts among the major advantages of the HiPCo-process over most alternative methods. The catalytic decomposition of carbon monoxide can thus be considered as a potential way of scaling up SWNT-production from a few grams to kilograms or even tons. 

The decomposition of carbon monoxide is a good example of a complex dissociation process for a diatomic molecule. The reaction has been studied over the temperature range 6000—15,000°K using pure CO [124] and dilute mixtures in argon [125—127] by the techniques of infrared emission [124—128] from CO, visible and ultraviolet emission [126] from C2 and C respectively, and vacuum-ultraviolet absorption [128] by CO. 

The decomposition of ethylene on spherical nickel crystals at higher temperature was also studied, but the results cannot be correlated with hydrogenation rates. The relative reactivities of the face are also different from those found in the decomposition of carbon monoxide on nickel. The possible catalytic importance of dislocations, as indicated by the decomposition experiments, is also discussed. 

As already stated, the gaseous product consists of carbon dioxide in addition to unreacted carbon monoxide. With a view to suggest the probable course of the reaction, the decompositions of carbon monoxide, formaldehyde, and glycolic acid were separately studied using 38.9 % nickel... 

This equilibrium has been studied. Using a catalyst consisting of 73 per cent charcoal and 27 per cent nickel, which resulted from carbonizing a mixture of sugar and nickel acetate, the decomposition of carbon monoxide into carbon and carbon dioxide was entirely suppressed and the catalyst maintained its activity for months in producing methane. Ferric oxide, vanadium pentoxide, and cerium oxide are promoters for the nickel-charcoal catalyst. Studies have also been made of the various reactions involved in the reduction of carbon monoxide and dioxide. ... 

Figure 8-56. TEM of a single iron nanocigar in a graphitic cell synthesized in the RF-CCP discharge at pressure 110 Pa (iron carbonyl Fe(CO)5 is a precursor of ferromagnetic iron core decomposition of carbon monoxide leads to individual encapsulation of the ferromagnetic iron core in a carbon/graphite matrix).

Below cs 300 °C the equilibrium is far on the right-hand-side but the decomposition of carbon monoxide with formation of CO2 and deposition of solid carbon proceeds only at an extremely slow rate because of the high dissociation energy of CO A weak discharge operating at a current density of a few mA/cm efficiently enhances the reaction rate the probable reaction mechanism being the dissociative attachment on CO followed by associative detachment of 0 and CO... 

Figure 2. The selective deposition of carbon on the (111) faces of a nickel single crystal during the catalytic decomposition of carbon monoxide at 550 C. (Reproduced from Ref.11. Copyright 1948, American Chemical Society.)...

Figure 5.9 Decomposition of carbon monoxide. Equilibrium constant for Ni/MgO catalyst [378]. Reproduced with the permission of Elsevier.

The exothermic reactions for decomposition of carbon monoxide, (Reactions R7 and R8 in Table 5.2) means that for a given gas composition and pressure, there is a temperature below which there is a thermodynamic potential for carbon formation. Likewise for the endothermic decomposition of methane, (Reaction R6 in Table 5.2), there is a temperature above which there is a thermodynamic potential for carbon formation. These carbon limits assume that there is no reaction during cooling or heating the gas. This is the situation when no catalyst is present such as in heat exchangers, boilers and convective reformers. Carbon formation may lead to fouling of the equipment or to metal dusting corrosion [211],... 

The decomposition of carbon monoxide (Reactions R7 and R8, Table 5.2) may take place without catalyst on the surfaces of the equipment (e.g. heat exchangers). This may also lead to metal dusting corrosion [121] [211] [535]. Reaction R7 in Table 5.2 appears to be involved [211] [293]. It means that for a given gas composition (and pressure) there will be potential for metal dusting below the carbon limit temperature (see Example 5.1). At very low temperature, the rate will be too small. 

Methane reforming Eq. (2.36) is the simplest example of steam reforming (SR). This reaction is endothermic at MCFC temperatures and over an active solid catalyst the product of the reaction in a conventional reforming reactor is dictated by the equilibrium of Eq. (2.36) and the water-gas shift (WGS) reaction Eq. (2.37). This means that the product gas from a reformer depends only by the inlet steam/ methane ratio (or more generally steam/carbon ratio) and the reaction temperature and pressure. Similar reaction can be written for other hydrocarbons such as natural gas, naphtha, purified gasoline, and diesel. In the case of reforming oxygenates such as ethanol [125, 126], the situation is in some way more complex, as other side reactions can occur. With simple hydrocarbons, like as methane, the formation of carbon by pyrolysis of the hydrocarbon or decomposition of carbon monoxide via the Boudouard reaction Eq. (2.38) is the only unwanted product. 

---