Formation of Co

Formation of CO occurs usually through one of the following three processes  

Incomplete combustion of carbon or carbon-containing compounds. This occurs when available oxygen is less than the amount required for complete combustion in which carbon dioxide is the product, or when there is poor mixing of fuel and air  

Reactions between C02 and carbon-containing materials at high temperature. This occurs at elevated temperature, common in many industrial devices such as blast furnaces. 

The CO produced in this way is beneficial and necessary in certain applications, as in the blast furnace, where CO acts as a reducing agent in the production of iron from Fe203 ores as shown below. Some CO may escape into the atmosphere, however. 

Dissociation of C02 at high temperature. Carbon dioxide dissociates into CO and O at high temperature as follows  

---

A closer analysis of die equilibrium products of the 1 1 mixture of methane and steam shows the presence of hydrocarbons as minor constituents. Experimental results for die coupling reaction show that the yield of hydrocarbons is dependent on the redox properties of the oxide catalyst, and the oxygen potential of the gas phase, as well as die temperamre and total pressure. In any substantial oxygen mole fraction in the gas, the predominant reaction is the formation of CO and the coupling reaction is a minor one. 

The evolution of gases, such as in dre example given above of dre formation of CO(g) in dre U airsfer of sulphur between carbon-saturated iron and a silicate slag, requires dre nucleation of bubbles before dre gas can be eliminated from the melt. The possibility of homogeneous nucleation seems unlikely, and the more probable source of gas bubbles would either be at the container ceramic walls, or on detached solid particles of the containing material which are... 

Aldehydes undergo two primary reactions photolysis and reaction with OH radicals. These reactions lead to formation of CO, H, and R radicals. 

Dithiiranone 57 also accounted for the formation of CO in the reaction of the 0( P) atom with CS2 in the gas phase (76JCP2528).Tlie semiempir-ical CNDO/B calculation on the reaction was reported (82JCC23). 

The increase in volume as gaseous products are formed in a chemical reaction is even larger if several gas molecules are produced from each reactant molecule, such as the formation of CO and CO, from a solid fuel (Fig. 4.17). Lead azide, Pb(N3)2, which is used as a detonator for explosives, suddenly releases a large volume of nitrogen gas when it is struck ... 

A different order of ligands is found for reactions leading to the formation of Co(I). In the transfer reaction (see also Section C,2)... 

Whereas the original Moffat-Pfitzner oxidation employs dicyclohexylcarbodiimide to convert DMSO into the reactive intermediate DMSO species 1297, which oxidizes primary or secondary alcohols via 1298 and 1299 to the carbonyl compounds and dicyclohexylurea [78-80], subsequent versions of the Moffat-Pfitzner oxidation used other reagents such as S03/pyridine [80a, 83] or oxalyl chloride [81-83] to avoid the formation of dicyclohexylurea, which is often difficult to remove. The so-called Swern oxidation, a version of the Moffat-Pfitzner oxidation employing DMSO/oxalyl chloride at -60°C in CH2CI2 and generating Me2SCl2 1277 with formation of CO/CO2, has become a standard reaction in preparative organic chemistry (Scheme 8.31). 

Platinum is the only acceptable electrocatalyst for most of the primary intermediate steps in the electrooxidation of methanol. It allows the dissociation of the methanol molecule hy breaking the C-H bonds during the adsorption steps. However, as seen earlier, this dissociation leads spontaneously to the formation of CO, which is due to its strong adsorption on Pt this species is a catalyst poison for the subsequent steps in the overall reaction of electrooxidation of CHjOH. The adsorption properties of the platinum surface must be modified to improve the kinetics of the overall reaction and hence to remove the poisoning species. Two different consequences can be envisaged from this modification prevention of the formation of the strongly adsorbed species, or increasing the kinetics of its oxidation. Such a modification will have an effect on the kinetics of steps (23) and (24) instead of step (21) in the first case and of step (26) in the second case. 

Bowker, 1993]. This is supported by the TAP reactor experiments since the maximum of the CO response curve occurs between 5.5-6.0 seconds, while the CO2 evolution occurs earlier between 4.5-5.0 seconds. It is also seen that both KOAc and Au enhance the formation of CO. This agrees with the earlier observations with the CO response curves, and supports the hypothesis that the secondary COj peak occurs from the conversion of CO to CO. ... 

The catalytic tests show that, over the Pt(l 0 0)/Al2O3 catalyst, the formation of CO and NH3 is largely prevented, whereas the yield of N2O increases compared with the Pt(polycrystalline)/Al203 catalyst. These main differences observed should be ascribed to the morphological differences between two catalysts, i.e., the dominant orientation of the crystallographic facets and the average size... 

As already mentioned, the poison formation reaction is potential-dependent, and the poisoning rate for the basal planes is Pt(llO) > Pt(lOO) > Pt(lll) [Sun et al., 1994 Iwasita et al., 1996]. The case of Pt(lll) is special, since the poisoning has been associated with the presence of defects on the surface. Selective covering of the defects on the Pt(l 11) electrode by some adatoms prevents the formation of CO on the electrode surface [Macia et al., 1999, 2001 Smith et al., 2000]. 

The first IR studies detected the formation and adsorption of CO, and therefore CO was proposed as the poisoning intermediate [Beden et al., 1981 Nichols and Bewick, 1988 Corrigan and Weaver, 1988]. The formation of CO is stmcture-dependent and takes place at open circuit, and the maximum amount accumulated on the electrode... 

Another important difference in the poison formation reaction is observed when studying this reaction on Pt(lll) electrodes covered with different adatoms. On Pt(lll) electrodes covered with bismuth, the formation of CO ceased at relatively high coverages only when isolated Pt sites were found on the surface [Herrero et al., 1993]. For formic acid, the formation takes place only at defects thus, small bismuth coverages are able to stop poison formation [Herrero et al., 1993 Macia et al., 1999]. Thus, an ideal Pt(lll) electrode would form CO from methanol but not from formic acid. This important difference indicates that the mechanism proposed in (6.17) is not vahd. It should be noted that the most difhcult step in the oxidation mechanism of methanol is probably the addition of the oxygen atom required to yield CO2. In the case of formic acid, this step is not necessary, since the molecule has already two oxygen atoms. For that reason, the adatoms that enhance formic acid oxidation, such as bismuth or palladium, do not show any catalytic effect for methanol oxidation. 

Perez JM, Munoz E, Moralldn E, Cases F, Vazquez JL, Aldaz A. 1994. Formation of CO during adsorption on platinum electrodes of methanol, formaldehyde, ethanol and acetaldehyde in carbonate medium. J Electroanal Chem 368 285-291. 

Riedmiiller B, Papageorgopoulos DC, Berenbak B, van Santen RA, Kleyn AW. 2002. Magic island formation of CO coadsorbed with H on Ru(OOOl). Surf Sci 515 323. 

Together with the fast oxidation (at low temperatures) of NO to N02, the plasma causes the partial HC oxidation (using propylene, the formation of CO, C02, acetaldehyde and formaldehyde was observed). Both the effects cause a large promotion in activity of the downstream catalyst [86]. For example, a "/-alumina catalyst which is essentially inactive in the SCR of NO with propene at temperatures 200°C allows the conversion of NO of about 80% (in the presence of NTP). Formation of aldehydes follows the trend of NO concentration suggesting their role in the reaction mechanism. Metal oxides such as alumina, zirconia or metal-containing zeolites (Ba/Y, for example) have been used [84-87], but a systematic screening of the catalysts to be used together with NTP was not carried out. Therefore, considerable improvements may still be expected. 

---