| This investigation has focused on a variety of factors influencing the kinetics and product distribution of Fischer-Tropsch Synthesis over bulk and supported iron catalysts in a fixed bed reactor.; The activities of the bulk iron catalysts (on a per gram of catalyst basis) decrease in the order: P - Fe(Ox) > P - Fe(Red) > P - K/Fe(Red), F - K/Fe(Red) where: the letters P and F designate the methods of catalyst preparation of precipitation and fusion, Ox and Red indicate the pretreatments of oxidation and reduction, and K denotes promotion with potassium. The higher activity of the oxidized, unpromoted catalyst is attributed to: (1) a lower rate of catalyst deactivation, caused by a lower initial rate of carbon deposition, and (2) a higher surface area. The turnover frequencies of the supported catalysts (based on irreversible H(,2) uptakes) decrease in the order: 11% Fe/TiO(,2) > 20% Fe/Al(,2)O(,3) > 11% Fe/SiO(,2) > 11% Fe/Al(,2)O(,3) > 5% Fe/Y-Zeol > 14% Fe/Mgo. The variation in activity with support is attributed to metal-support interactions. Particle size may also influence activity.; The major products of the catalysts are linear hydrocarbons, principally (alpha)-olefins, (beta)-olefins, and n-paraffins. The production of significant amounts of (beta)-olefins and n-paraffins is due to the readsorption and further reaction of (alpha)-olefins. The readsorbed olefins do not participate in further chain growth.; The CO partial pressure coefficients are dependent on particle size, decreasing towards the coefficients obtained for the bulk iron catalysts as the dispersion decreases. The activation energies are dependent upon the pretreatment and the support used.; Increasing the reduction temperature of the Fe/TiO(,2) catalyst from 300-500(DEGREES)C causes a decrease in the irreversible H(,2) uptake, but causes no change in the values for: (1) the CO uptake, (2) (alpha), or (3) the rate parameters for the C(,1)-C(,5) hydrocarbons. It does however cause an increase in the activation energy and H(,2) partial pressure coefficient for CO(,2) production. (Abstract shortened with permission of author.)... |
