Fischer-Tropsch synthesis catalytic measurements

ICP) measurements. The catalytic performance of the nanocatalysts was finally tested in the Fischer-Tropsch synthesis carried out in a fixed bed reactor. The obtained results were compared with literature data of commercially used Fischer-Tropsch catalysts. 

According to the International Union of Pure and Applied Chemistry (IUPAC O)) the turnover frequency of a catalytic reac tion is defined as the number of molecules reacting per active site in unit time. The term active sites is applied to those sites for adsorption which are effective sites for a particular heterogeneous catalytic reaction. Because it is often impossible to measure the amount of active sites, some indirect method is needed to express the rate data in terms of turnover frequencies In some cases a realistic measure of the number of active sites may be the number of molecules of some compound that can be adsorbed on the catalyst. This measure is frequently used in the literature of the Fischer-Tropsch synthesis, where the amount of adsorption sites is determined by carbon monoxide adsorption on the reduced catalyst. However, it is questionable whether the number of adsorption sites on the reduced catalyst is really an indication of the number of sites on the catalyst active during the synthesis, because the metallic phase of the Fischer-Tropsch catalysts is often carbided or oxidized during the process. 

The strength of interaction of hydrocarbons with metallic surfaces serves as a probe to investigate the role of desorption and adsorption of these species in a variety of catalytic reactions (Table XXIX). Ostrovskii and Medvedkova (242) used calorimetry and gas chromatography to measure heats of adsorption of C4-C8 hydrocarbons over Co before and after use in Fischer-Tropsch synthesis. For the fresh samples, the adsorption of aliphatic hydrocarbons was reversible, and the initial heat of adsorption increased with increasing chain length of the adsorbate. It appeared that the saturated hydrocarbons were adsorbed with the C—C bond axis parallel to the surface, and the contributions from the CH3 and CH groups were calculated as cHj = -4.63 and mol". With these values, the experimental... 

The effect of water on the Fischer-Tropsch synthesis over alumina-supported cobalt catalysts has been studied using isotopic transient kinetic methods (SSITKA) in combination with steady-state measurements. Water has been introduced to the catalytic system as a pretreatment procedure as well as under reaction conditions. The SSITKA results showed a decrease in the number of active surface sites, but no change in the specific site activity. 

In a collaborative effort with Dr. B. T. Heaton from the Iftiiverslty of Rent at Canterbury, England, we have recently applied this technique W to measure spectra of rhodium carbonyl clusters under high pressure of CO and H2. In connection with the efforts by the petrochemical Industry to find catalytic syntheses which use CO and H. there is increasing evidence that transition metal carbonyl clusters are Involved in the catalytic synthesis of ethylene glycol and in the Fischer Tropsch and related reactions. 

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