CO + H2 mixture

The solution is illustrated in Fig. 8.15, which shows the equilibrium concentration of methanol for different initial gas mixtures. Note that the maximum methanol concentration occurs for the pure CO + H2 mixture. Hence, in principle, a mixture of just CO and H2 could be used, with minor amounts of CO2, to produce the maximum amount of methanol. However, it is not only the equilibrium constant that matters but also the rate of methanol formation, and one must remember that methanol forms from CO2 not CO. Hence, the rate is proportional to the CO2 pressure and this is why the methanol synthesis is not performed with the simple stoichiometric 3 1 mixture of H2 and CO2 that Eq. (19) suggests. 

In this paper we attempt a preliminary investigation on the feasibility of catalytic combustion of CO/ H2 mixtures over mixed oxide catalysts and a comparison in this respect of perovskite and hexaaluminate type catalysts The catalysts have been characterized and tested in the combustion of CO, H2 and CH4 (as reference fuel). The catalytic tests have been carried out on powder materials and the results have been scaled up by means of a mathematical model of the catalyst section of the Hybrid Combustor. 

The first stage of the process is a hydroformylation (oxo) reaction from which the main product is n-butyraldehyde. The feeds to this reactor are synthesis gas (CO/H2 mixture) and propylene in the molar ratio 2 1, and the recycled products of isobutyraldehyde cracking. The reactor operates at 130°C and 350 bar, using cobalt carbonyl as catalyst in solution. The main reaction products are n- and isobutyraldehyde in the ratio of 4 1, the former being the required product for subsequent conversion to 2-ethylhexanol. In addition, 3 per cent of the propylene feed is converted to propane whilst some does not react. 

In view of the size of operation being contemplated, it is unlikely that homogeneous catalysts will play a primary role in the production of synthetic oil. However, from the standpoint of the chemical industry, the complex mixture of products obtained from the classical Fischer-Tropsch process is generally unattractive owing to the economic constraints imposed by costly separation/purification processes. What is needed is a catalyst system for the selective conversion of CO/H2 mixtures to added-... 

It is now superflous to point out the renewed interest for the Fischer-Tropsch (F-T) synthesis (j) i. . the conversion of CO+H2 mixtures into a broad range of products including alkanes, alkenes, alcohols. Recent reviews (292.9k ) emphasized the central problem in F-T synthesis1 selectivity or more precisely chain-length control. 

Figure 1.19 AES data from a Ru/Al203 catalyst aged in a reaction (CO+H2) mixture containing trace amounts of H2S [148], Spectra are shown for the sample before (a) and after (b) sputtering with an Ar+ beam for 2 min. The difference between the two spectra indicates the presence of S on the surface but not the subsurface of the poisoned catalyst. (Reproduced with permission from Elsevier.)...

An aqueous solution of the reactant was pumped into an autoclave charged with the Rh precursor complex, the fluorinated hgand, the CO/H2 mixture and CO2. During the reaction the catalyst/scC02 phase and the sub-strate/water phase were intimately contacted in an emulsion-hke mixture upon rapid stirring of the reactor contents. The substrate was converted completely to aldehydes 15a and 15b within 20 h, and depending on catalyst loadings the turnover numbers varied between 500 and 1720. The aqueous phase was isolated readily from the bottom of the reactor after phase separa-... 

It was discovered in the late nineteenth century that coal can be incompletely burned to yield a gas consisting primarily of CO and H2, and many people were undoubtedly asphyxiated and kUled by explosions before these processes were harnessed successfully. We wfil see later that the use of a CO + H2 mixture (now called synthesis gas) for the production of chemicals has had an important role in chemical synthesis (it was very important for explosives and synthetic fuels in both World Wars), and it is now one of the most promising routes to convert natural gas and coal into liquid diesel fuel and methanol. We will describe these processes in more detail in later chapters. 

We next return to another reaction of a CO + H2 mixture, which we called synthesis gas or syngas. It has this name because it is used to synthesize many chemicals such as methanol. Another synthesis reaction from CO and H2 is a polymerization process called the Fisher Tropsch synthesis of synthetic diesel fuel. 

Hydroformylation is clearly related to the Fischer-Tropsch reactions, in which CO/H2 mixtures (in effect, water-gas Section 9.3) react over heterogeneous catalysts to give organic compounds such as methanol. 

Some nickel(II) tetraaza macrocycles have been proved to act as efficient catalysts for the electrochemical reduction of C02 in H20/MeCN medium. This indirect electroreduction occurs at potentials in the range -1.3 to -1.6 V vs. SCE and mainly produces either CO or a CO/H2 mixture, depending upon the type of complex.2854 The five-coordinate complexes [NiL] (394) formed by some deprotonated dioxopentamine macrocycles have been found to display very low oxidation potentials Nin/Nira in aqueous solution (about 0.24-0.25 V vs. SCE at 25 °C and 0.5 M Na2S04). Air oxidation of the same complexes in aqueous solution yields 1 1 NiL-02 adducts (5 = 1) which are better formulated as superoxo complexes, NimL-02 (Scheme 56). The activation of Ni-bound oxygen is such that it attacks benzene to give phenol.2855... 

In a potentially significant development in CO reduction chemistry, Rathke and Feder (88h) have found that HCo(CO)4 serves as a catalyst for conversion of CO/H2 mixtures to MeOH and HCOOMe under forcing conditions (300 atm, 200°C), albeit at very slow rates. An activation energy of 40.7 kcal/mol was obtained, and a scheme based on formyl radical chemistry was proposed. While the latter seems premature, the fact that reduction products were observed in the absence of cluster compounds brings into question the necessity of such a structural arrangement. 

Hydroformylations. The hydroformylation of vinyl acetate was run at 6 to 7 atm with a 44 56 CO/H2 mixture at 80°-100°C using benzene as a solvent and an 8 x 10"4M concentration of rhodium and a 3.45M concentration of vinyl acetate. The ratio of ligand to metal was varied from 1 to 6 and the best results were obtained only at high ratios. 

Here, the chosen domain for our case study is on-board hydrogen production to supply pure H2 to a fuel cell in an electrical car. Among the sequential catalytic reactions that take place for H2 production, the hydrogen purification units are located downstream, after the primary reforming of hydrocarbons into a CO-H2 mixture or Syngas units. They consist of Reaction (1) the water-gas shift (WGS) reaction and Reaction (2), the selective or preferential oxidation of CO in the presence of hydrogen (Selox). 

In the production of syngas, the following reactions are usually undesired. The desired reaction is the production of CO/H2 mixtures according to... 

Slaugh has claimed that a catalyst consisting of MoSi2 has resistance to sulphur.130 This material gave 20% conversion of CO + H2 mixture (1 3) at 500-600 °C and the conversion was >2% after 90 min of H2S treatment. Other transition metal silicides (e.g., ZrSi, WSi2) were tested for methanation but had no activity. 

In this respect it should be said that even open faces such as the (210) and the stepped (001) surface do not dissociatively adsorb CO at 25-125°C (97). This suggests that unsupported Pd is a rather poor methanation catalyst. Under 1 atm total pressure in a CO + H2 mixture, the Pd black catalyst (210-nm crystallites) produces methane but, here again, the activity level is about two times lower than that of Pd/Si02 catalysts (4.6-nm Pd particle size), and about two orders of magnitude less active than Pd/ A1203 catalysts (4.8-nm Pd particle size) (98). It therefore seems that the effect of dispersion here is not pronounced with respect to the support effect. Silica, as an inert support, does not influence the activity of Pd to the same extent as does more the acidic alumina. 

The growth of filamentous carbon along with the gas phase product analysis has been used to determine the influence of sulfur on the iron catalyzed decomposition of carbon containing gas mixtures at 600°C. Pretreatment of the metal in H2S was found to initially suppress the reactions leading to carbon deposition from the decomposition of CO/H2 mixtures. After a short time the activity was restored to approximately the same level as that exhibited by an unadulterated iron powder, suggesting that most of the sulfur atoms were being removed from the surface. The small residual fraction of adatoms did, however, induce modifications in the structural characteristics of the filamentous carbon deposit and also altered the reactivity pattern of the iron towards decomposition of a CO/C2H4/H2 mixture. 

Poisoning of transition metals by sulfur is a serious problem encountered in many industrial processes [1-4]. In the Fisher-Tropsch synthesis of hydrocarbons from CO/H2 mixtures, the presence of a few ppm volume ratio of a sulfur containing gas can have a drastic effect on the life time of an iron catalyst [1]. On the other hand, a partial and well controlled treatment of a metal by sulfur can result in desirable effects, particularly with regard to the manipulation of catalyst selectivity for certain reactions [5]. 

Chinchen GC, et al. Mechanism of methanol synthesis from CO2/CO/H2 mixtures over copper/zinc oxide/alumina catalysts - use of 14C-labeled reactants. Appl Catal. 1987 30(2) 333-8. 

With Cu a slight preoxidation shortens the induction period which otherwise accompanies the reaction with CO / H2 mixtures on well reduced catalysts [58 ]. 

This ligand reacts with [Rh(nbd)2]BF4 to form 10-LXXVIII, which under reaction conditions reacts with the CO/H2 mixture to form the actual catalyst. The latter is thought to be 10-LXXIX. 

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