Selectivity of CO hydrogenation

The addition of certain ionic promoters to ruthenium catalytic solutions has been found to dramatically affect the rate and selectivity of CO hydrogenation. Whereas ruthenium solutions do not otherwise produce ethylene glycol as a significant product (except as its derivatives in in reactive solvents),... 

Catalyst Composition - Effect on Performance. Comparison of catalyst selectivities are best made at equal conversions. It was previously shown that selectivity of CO hydrogenation to oxygenates decreases with increasing conversion. For example, selectivity decreased linearly from 35% at 4% conversion to 20% at 18% conversion for Rh/Al203 catalysts at 250 C.(10)... 

Supported Cu-Pd catalysts have the potential to provide new alternatives to conventional commercial methanol synthesis catalysts (based on the Cu-ZnO-alumina system). Cu-Pd catalysts are also of industrial interest in hydrogenolysis and CO oxidation (Bulatov 1995). To interpret the catalyst behaviour and selectivity, including CO hydrogenation, a fundamental understanding of the structure, surface structure and stability of the phases in this system is required. The Cu-Pd phase diagram indicates that at temperatures greater than 600 °C, Cu... 

As is mentioned in Section 3.4, the use of hydrogen gas as a source of clean energy is gaining attention. Based on the ion selectivity of CSZ, hydrogen gas can be produced by electrolysis of H2O gas. In principle, the reverse reaction of the fuel cell shown in Fig. 3.5, can be used for this purpose, that is, the electrochemical extraction of hydrogen from H2O gas by an external current. In Fig. 3.7 the equipment for the electrolysis of HjO gas, devised by General Electric Co., is shown. 

In presenting the proposed mechanisms of CO hydrogenation reactions, we have omitted detailed examination of any experimental evidence, which can be found elsewhere (70, 71, 74, 76), and have attempted to summarize only select conclusions. It is important to remember that these proposals are still only that, with definitive proof lacking, and that alternative postulations remain viable. Surface bound intermediates have not been conclusively established as to either composition or reactivity. 

Product selectivity in CO hydrogenation is generally shifted by sulfur poisoning in the direction of higher molecular weight products. 

Conclusions. Submonolayer deposits of titania grow on the surface of Rh in the form of two-dimensional islands until a coverage of nearly a monolayer is achieved, at which point some three-dimensional growth of the islands is observed. The titania islands exclude CO chemisorption on Rh sites covered by the titania. The Ti + ions in the overlayer are readily reduced to TP+. This process begins at the perimeter of the islands and extends inwards as reduction proceeds. Titania promotion of Rh enhances the rate of CO hydrogenation by up to a factor of three and increases the selectivity to C2+ hydrocarbons. By contrast, the activity of Rh for the hydrogenolysis of ethane decreases monotonically with increasing titania promotion. 

Our site-time yields were measured on catalyst granules smaller than 0.2 mm in diameter in order to ensure that CO hydrogenation rates were unaffected by diffusion-limited CO and H2 arrival at catalytic sites. Product removal is still slow on such small pellets, but it affects only the selectivity and not the rate of CO hydrogenation reactions. Our site-time yields were measured on catalysts with more than 95% of the Co atoms in a zero-valent state, in order to avoid complicating factors associated with partially reduced Co surfaces. 

Many of the catalysts which are usefiil in Fischer-Tropsch synthesis are also capable of catalyzing the hydrogenation of CO2 to hydrocarbons. Our structure-function studies have shown that it is possible to control the selectivity of CO2 hydrogenation by specific iron-based catalysts to generate yields of C5+ hydrocarbons that are comparable to those produced with conventional CO based... 

TiO on the surface of a bulk metal can increase the rate of CO hydrogenation and selectivity of products relative to the clean metal surface. In the case of Ni, the effects of surface TiO on CO hydrogenation rate can be rationalized in terms of the perturbation in the relative competition between CO and H2 for chemisorption sites. This explanation cannot be generalized to other Group VIII metals. There is circumstantial evidence that a Ti species may be directly involved in the formation of the site on which reaction occurs on other Group VIII metals, but definitive proof and elaboration of the mechanism await future work. 

The reduction of cobalt acetylacetonate with triakylaluminium leads to species composed of zerovalent cobalt and unreduced cobalt species. The exact composition depends upon the Al/Co ratio and the activation process. When we used a catalyst corresponding to a Al/Co = 1, activaded with hydrogen at 180°C, we obtained an increase of the selectivity of the hydrogenation of 2-pentyl-2-nonenal into 2-pentyl-2-nonenol. 

The high selectivity of Co-Br (and Co-Mn-Br) catalysis is explained by the high activity of the Br radical that easily abstracts hydrogen from a deactivated methyl group of / -toluic acid [31]. An alkylperoxy radical, in contrast, cannot... 

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