Hydrogenation of CO

7 Carbon Dioxide Conversion in High Temperature Reactions 

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Goodman D W, Kelley R D, Madey T E and Yates J T Jr 1980 Kinetics of the hydrogenation of CO over a single crystal nickel catalyst J. Catal. 63 226... 

The chemical complex includes the methanol plant, methyl acetate plant, and acetic anhydride plant. The methanol plant uses the Lurgi process for hydrogenation of CO over a copper-based catalyst. The plant is capable of producing 165,000 t/yr of methanol. The methyl acetate plant converts this methanol, purchased methanol, and recovered acetic acid from other Eastman processes into approximately 440,000 t/yr of methyl acetate. 

Steam reforming of CH4 CH4 + H2O = CO + 3H2 NH3 synthesis from the elements Hydrogenation of CO and CO2 to form hydrocarbons (Fischer-Tropsch syndresis)... 

The hydrogenation of CO and C02 on transition metal surfaces is a promising area for using NEMCA to affect rates and selectivities. In a recent study of C02 hydrogenation on Rh,59 where the products were mainly CH and CO, under atmospheric pressure and at temperatures 300 to 500°C it was found that CH4 formation is electrophobic (Fig. 8.54a) while CO formation is electrophilic (Fig. 8.54b). Enhancement factor A values up to 220 were... 

W-Rh IWCRht/oCOMCOljD/VCsHO ,) 193, Si02 Hydrogenation of CO and characterization of catalyst (FTIR. CO chemisorption. TPR. EPR) E)9... 

The reaction mechanism of methanol synthesis is complex since two processes are involved and coupled. Formally, the reaction can be written as the hydrogenation of CO by the overall reaction ... 

Another example of potassium as a promoter is in the hydrogenating of CO to give methanol directly, as mentioned earlier [M. Maack, H. Friis-Jensen, S. Sckerl, J. H. Larsen and I. Chorkendorff Top. Catal. 22 (2003) 161]. Here it works as a promoter for CO hydrogenation, but with conventional methanol synthesis great efforts are made to avoid the presence of alkalis in the catalyst as they tend to ruin the selectivity by promoting the production of higher alcohols, i.e. the surface becomes too reactive. Thus great care has to be exercised to achieve the optimal effects. 

The type catalyst, Pt/Ti02 reduced at 300 C behaves much like Pt/Si02, but reduction at 500°C largely eliminates its capacity for the chemisorption of H2 and hydrogenation while inducing activity for the hydrogenation of CO. Ti suboxide formed by reduction encapsulates the Pt particles. 

In recent years research of possible utility in the production of fine chemicals has increased substantially and in part consequent to government policy. This work has been too variegated to summarize briefly. A flurry of work in the hydrogenation of CO also originated in government policy. It led to the elaboration of our imderstanding of these reactions, but it is not clear that it led to major developments. 

Hydrido(alkoxo) complexes of late transition metals are postulated as intermediates in the transition metal-catalyzed hydrogenation of ketones (Eq. 6.17), the hydrogenation of CO to MeOH, hydrogen transfer reactions and alcohol homologation. However, the successful isolation of such complexes from the catalytic systems was very rare [32-37]. 

As an example, we shall discuss the interstellar synthesis of a compound which is produced on Earth in millions of tons per year methanol. This simplest alcohol was obtained by Robert Boyle in 1661 from the dry distillation of wood. In the molecular clouds of the universe, it is likely that hydrogenation of CO on the surface of dust particles occurs according to the following scheme (Tielens and Charnley, 1997) ... 

However, recently Inderwildi et al.28 showed by density functional theory (DFT) calculations that hydrogenation of CO leading to formyl (oxomethyli-dyne) and subsequent conversion toward CH2 show lower activation barriers than CO dissociation. 

With the recent development of zeolite catalysts that can efficiently transform methanol into synfuels, homogeneous catalysis of reaction (2) has suddenly grown in importance. Unfortunately, aside from the reports of Bradley (6), Bathke and Feder (]), and the work of Pruett (8) at Union Carbide (largely unpublished), very little is known about the homogeneous catalytic hydrogenation of CO to methanol. Two possible mechanisms for methanol formation are suggested by literature discussions of Fischer-Tropsch catalysis (9-10). These are shown in Schemes 1 and 2. 

The formation of metal-oxygen bonds has previously been found to occur for the stoichiometric hydrogenation of CO to methanol with metal hydrides of the early transition metals (20). Moreover, in ruthenium-phosphine catalyzed hydrogenation (with H2) of aldehydes and ketones, metal-oxygen bonded catalytic intermediates have been proposed for the catalytic cycle and in one case isolated (21,22). 

IT -cyclopentad ienyldicar bony 1 cobalt, CpCo(C0)2 This material is active in the hydrogenation of CO to saturated linear hydrocarbons and appears to retain its "homogeneous", mononuclear character during the course of its catalysis. 

The bulk of this review concerns transient experiments on heterogeneous catalysis at atmospheric pressure. After some comments on current methods for doing the experiments, the application of the method will be illustrated by two examples the oxidation of CO over Pt, and the hydrogenation of CO over Fe. 

Methane is also a widely observed by-product,13 which can be produced by hydrogenation of CO ... 

Examples 2-10 are for the hydrogenation of CO to produce CH4. For Example 2, the order and calculated log L values suggest that Step 1 or 6 for hydrogen is the rate-determining step. If it is Step 1, the rate-determining step is the adsorption of H2 on a CO-saturated surface. If it is Step 6, it is a surface reaction between hydrogen and CO, where the surface is saturated with CO but the amount of hydrogen adsorbed corresponds to the linear part of the adsorption isotherm. 

Also of potential interest is the direct hydrogenation of CO to isobutanol as it was practiced by BASF (13-14) or still is done in the German Democratic Republic. Again, a mixture of alcohols is obtained with isobutanol amounting up to 30 % (. The latter one can be dehydrated to isobutene (chemical usage) or converted with methanol to fuel usage (MTBE). 

Table IV shows the reactivities of raw materials and products on a nickel-activated carbon catalyst and the effect of hydrogen on the reactions. When carbon monoxide and hydrogen were introduced into the catalyst, no product was formed. Thus, the hydrogenation of CO does not proceed at all. When methyl iodide was added to the above-mentioned feed, 43% of the methyl iodide was converted to methane. In the presence of methyl iodide small amounts of methane, methanol, and acetic acid were formed from methyl acetate, while small amounts of methane and acetic acid were also formed from acetic anhydride. Hydrogen fed with methyl acetate accelerated the formation of methane and acetic acid remarkably.

Figure 7 shows the results of TPR of CO adsorbed on nickel supported on activated carbon, y-alumina and silica gel, respectively. For Ni/Y Al20 and Ni/Si02/ only CO was desorbed at low temperature and methane (and CO2) were formed at higher temperature. In the case of Ni/A.C., however, almost all of adsorbed CO was desorbed below 150 C. It has been generally accepted that the first step of methane formation by hydrogenation of CO is the dissociation of C-0 bond (Equation 8) (8). The resultant and then react with either hydrogen or CO as... 

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