Carbon monoxide at high temperatures

Reduction with carbon monoxide at high temperatures can form either carbonyl sulfide or sulfur depending on the catalyst used. With cobalt molybdate, COS is the primary product. On the other hand, lanthanum titanate catalyzes the reaction to form sulfur. 

Figure 21.5 indicates that carbon reacts with carbon dioxide to form carbon monoxide at high temperatures ... 

The catalyst was deactivated by reaction with hydrogen chloride and hydrogen fluoride, but some of the activity could be recovered by exposing the deactivated catalyst to carbon monoxide at high temperatures. 

Dichlorotetracarbonyldirhodium has been obtained by the action of carbon monoxide at high temperature and pressure on a mixture of anhydrous rhodium(III) chloride and finely divided copper powder and by reaction of rhodium(III) chloride 3-hydrate with carbon monoxide saturated with methanol at moderate temperatures and atmospheric pressure. The preparation described here is a modification of the latter method, without use of methanol. This procedure is considerably simpler than the recently described preparation which involves adsorption of rhodium chloride on silica gel, chlorination, and subsequent carbonylation. ... 

Thermodynamic data have also been calculated for carbon—oxygen reactions in fused salts [7, 8], The oxidation of solid carbon principally yields carbon dioxide at low temperature and carbon monoxide at high temperature. In this case, at constant temperature, the CO/CO2 concentration ratio at solid carbon depends on pressure. The carbon—oxygen electrode is used as reference to investigate cryolite—alumina melts at c. 1000°C [9] and molten slags at higher temperatures. 

In strongly carbon-reducing atmospheres (e.g., carbon monoxide) at high temperatures, carburization of stainless steel takes place. In oxidizing atmospheres, such as steam or carbon dioxide, carbon may be selectively removed (decarburization). Usually, complex gas mixtures are involved and the net result of the H2/H2O and CO/CO2 is critical. Under some conditions of environment and temperature, a pitting-t) e phenomenon called "metal dusting" occurs. 

By contrast, formaldehyde is unstable in SCW, with its decomposition rate being strongly temperature-dependent. At temperatures above the critical, formaldehyde completely decomposes to methanol, formic acid, carbon oxide, and carbon dioxide. The main decomposition product at low temperatures is methanol, which gives way to carbon monoxide at high temperatures. At 300 atm, 300—500 °C, and a residence time of 2 min, formaldehyde decomposes almost completely. The rapid decomposition of formaldehyde seems to be the main reason for its absence in the reaction products in a number of works. The Cannizzaro reaction, leading to the formation of methanol and CO, makes it possible to purify dilute formaldehyde wastewater to form easily separable methanol [233]. 

The conditions utilized to generate the isotherms were chosen to induce minimal change to the surface and to somewhat enhance chemisorption relative to physisorption. Degas conditions utilized were similar to what would be used for samples prior to BET surface area analysis. It should be noted that chemisorption in the present context is used to denote irreversible adsorption under the conditions of the experimental protocol. It s not meant to imply chemical bond formation as one might determine for example on a metal catalyst with carbon monoxide at high temperature. 

Methanol, CHgOH, also known as wood spirit , was produced by destructive distillation of wood. Today, most of the methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of ZnO - CraOg catalyst. 

The early preparations gave poor yields but highly efficient methods have been developed recently. Optimum yields are obtained by the method of Pino and his coworkers9 in which tris(2,4-pentanedionato)ruthenium(III) is treated with equimolar mixtures of hydrogen and carbon monoxide at moderate temperatures and pressures (140-160°, 200-300 atmospheres). However, this method is limited by the availability of the tris-(2,4-pentanedionato)ruthenium(III) which is obtained in only low yields from the readily available ruthenium trichloride hydrate. The method given here is a modification on the Pino method. 

Reaction with CO2 gives hydrazinocarboxyclic acid (carbazidic acid) H2NNCO2H and ammonia. The reaction of hydrazine with carbon monoxide at high pressure and temperature in the presence of iron pentacarbonyl leads... 

A priori, one can imagine that the reverse of Eqs. (12) and (13), oxidative desorption, would lead to desorption of hydrogen and carbon monoxide. Alternatively, desorption of water or carbon dioxide as shown at the right of Eqs. (12) and (13) would lead to permanent reduction and to the formation of Cr2+ of low coordination number. It is quite possible that such reductive adsorption followed by loss of water or carbon dioxide at high temperatures accounts for the reduction of chromia which was mentioned in Section IV. Adsorption of water followed by oxidative desorption may account for the liberation of hydrogen observed when chromia reduced at 500° is treated with water (39). 

Finally, in this temperature range (30-250°), oxygen is adsorbed as O" ions. However, the heat of adsorption of a fraction of the oxygen species adsorbed at 250° is very high and consequently their reduced reactivity toward carbon monoxide at room temperature is not very different from the reactivity of lattice anions. 

Y. Nigara and B. Cales, Production of carbon monoxide by direct themal splitting of carbon dioxide at high temperature. Bull. Chem. Soc. ]pn., 59 (1986) 1997-2002. 

Most of the carbonyls can be prepared by the direct combination of the metal with carbon monoxide. It is necessary that the metal be in a very active state as when freshly reduced from the oxide or a salt of the metal. While finely divided, freshly reduced nickel combines readily with carbon monoxide at room temperature and atmospheric pressure (synthesis 75) other metals require more elevated temperatures (up to 400 ) and very high pressures (up to 700 atm.). Cobalt nitrosyl tricarbonyl is produced when specially prepared cobalt is treated with a mixture of carbon monoxide and nitric oxide. 

Reactions that involve adjacent monomer units have been proposed to account for the appearance of methane, carbon monoxide, methanol and carbon dioxide at high temperatures in the pyrolysis of PMMA polymers.(24,25). Our results suggest a more likely source is mechanochemical degradation products. 

There is a strong tendency for unsaturated alkylcobalt and acylcobalt tetra-carbonyls to form ir-allyl complexes. 3-Butenoylcobalt tetracarbonyl rapidly loses 2 moles of carbon monoxide at room temperature, forming w-allyl-cobalt tricarbonyl in high yield (6). 

The operation means catalyst sintering at high temperatures and exposure to high partial pressures of carbon monoxides at low temperatures. It is evident that the catalyst must maintain activity at low temperature after having been exposed to high temperatures. 

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