Ruthenium hydrocarbon distribution

TI Non-Flory product distributions in Fischer - Tropsch synthesis catalyzed by ruthenium, cobalt. and iron KW Fischer Tropsch synthesis hydrocarbon distribution. Flory kinetics carbon monoxide hydrogenation, chain growth carbon monoxide hydrogenation, ruthenium catalyst carbon monoxide hydrogenation, cobalt iron catalyst hydrocarbon distribution IT Hydrocarbons, preparation... 

Ruthenium is known to catalyze a number of reactions, including the Fischer-Tropsch synthesis of hydrocarbons (7) and the polymerization of ethylene (2). The higher metal dispersions and the shape selectivity that a zeolite provides has led to the study of ruthenium containing zeolites as catalytic materials (3). A number of factors affect the product distribution in Fischer-Tropsch chemistry when zeolites containing ruthenium are used as the catalyst, including the location of the metal (4) and the method of introducing ruthenium into the zeolite (3). 

Tailoring of the product distribution is possible by a limitation of chain growth by pore size. This has been demonstrated by Ballivel Tkatchenko and Tkatchenko using zeolite catalysts. Ruthenium, iron or cobalt metal particles in Y-zcolilc supcrcagcs were prepared by thermal decomposition of the carbonyls. These metal-zeolite catalysts give selective formation of )- hydrocarbons [471. 

Iron-ruthenium bimetallic catalysts have also received considerable attention as interesting catalysts in Fischer-Tropsch synthesis [115,116]. It has been reported that the Fe-Ru alloy system results in catalysts that are more stable than monometallic iron catalysts [117], and that the hydrocarbon product distribution in CO hydrogenation can easily be modified when changing the relative proportions of the two metals [118]. 

Production of Higher-Molecular-Weight Hydrocarbons. Kinetics, Surface Science, and Mechanisms The hydrogenation of carbon monoxide over iron, cobalt, and ruthenium surfaces produces a mixture of hydrocarbons with a wide range of molecular-weight distribution. Most of the hydrocarbons produced are normal paraffins however, olefins and alcohols in smaller concentrations are also obtained. 

Recent studies of the CO—H2 reaction on ruthenium surfaces have also shown the importance of readsorption on the metal catalyst surface. The presence of a multiple-step reaction that proceeds via the readsorption of the initial products provides opportunities for altering the product distribution by using several different catalysts simultaneously in the reaction mixture. By physical mixing of two catalysts, for example, experimental conditions can be realized where the olefins readsorb and further react on the other catalyst instead of on the iron catalyst surface. This way the product distribution can be changed to obtain molecules that are more desirable than the saturated straight-chain hydrocarbons. Chang and Silvestri [132] and Lechthaler and co-workers [133] have reported on a process that converts CO and... 

Influence of the Zeolite on the Product Distribution. When a less acidic support was used for ruthenium, better activity was found under methanation conditions. Using the same argument, under F. T. conditions a higher selectivity for formation of higher hydrocarbons is expected when a less acidic support is used. In this respect, pertinent data are given over RuX and Y zeolites in Table V. The X zeolite is known to be less acidic than the Y zeolite. There is indeed a definite influence of the zeolite matrix in the indicated direction higher products are formed over zeolite X. 

Finally, we mentioned at the beginning that alterations in product selectivity represent our major interest. Table IV shows product distributions for both series of catalysts. As expected, the selectivity shift toward higher molecular weight products with increasing iron content is apparent, with methane formation dropping to 40 mol% in some cases. However, we find not only an enhancement in selectivity to heavier hydrocarbons, but also a pronounced increase in the olefin parafiBn ratios when alloy compositions with Ru Fe ratios between 1/2 and 2 are formed. The production of olefins is enhanced compared with either ruthenium-only or iron-only catalysts. In the case of catalyst Ch in Table V, 45 mol%... 

---