| In this study, carbon blacks, activated carbons, graphitized carbon, and molecular sieve glassy carbons were used to prepare a number of supported iron catalysts. All catalysts were characterized by CO chemisorption and x-ray diffraction measurements to determine average iron crystallite sizes. Magnetization measurements were made on representative samples to estimate metal particle sizes which were compared to the aforementioned values. The catalytic properties of carbon-supported iron were then determined for the CO hydrogenation reaction at 101 kPa using a differential, plug-flow reactor.;Both H(,2) and CO chemisorption on carbon-supported iron were dependent on metal particle size. Large iron crystallites around 30 nm, supported on graphitized Vulcan 3 carbon, exhibited H(,2) and CO chemisorption behavior essentially identical to that determined for unsupported bulk iron, and indicated little if any influence of the graphitic carbon support on the chemisorption properties of large iron crystallites. However, on small iron particles, H(,2) chemisorption was activated and saturation was not achieved even at 473 K. In addition, CO isobars between 195 and 473 K showed that a maximum in uptake occurred at 300 K which inferred the possibility of iron subcarbonyl formation on these small crystallites. For all crystallite sizes, CO chemisorption at 195 K is an accurate measure of iron surface area, while H(,2) adsorption at 373 K is also applicable for large iron particles.;Magnetization measurements on an Fe/Carbolac-1 catalyst revealed the presence of superparamagnetic iron, and application of the Langevin equation indicated the presence of (TURN)3 nm iron particles. This was in excellent agreement with chemisorption and x-ray diffraction estimates. An Fe/V3G catalyst was ferromagnetic, as expected for 30 nm iron particles.;Highly active carbon-supported iron catalysts can be prepared provided no sulfur is present in the carbon. On a gram iron basis, the activities of iron supported on common carbons were consistently higher than any previously reported activities for CO hydrogenation. The use of carbon molecular sieve supports, however, did not provide any favorable changes in activity or selectivity compared to amorphous carbons. The catalytic behavior of large iron crystallites supported on graphitized Vulcan 3 carbon was similar to that of alumina-supported on graphitized Vulcan 3 carbon was similar to that of alumina-supported iron with a similar meta particle size, indicating little effect of the graphitic carbon support on the catalytic properties of large iron crystallites. Kinetic parameters such as activation energies and partial pressure dependencies did not vary significantly among all these catalysts. Kinetic parameters such as activation energies and partial pressure dependencies did not vary significantly among all these catalysts. However, the highly dispersed carbon-supported iron catalysts had turnover frequencies an order of magnitude lower than large iron particles, higher olefin/paraffin ratios, and better activity maintenance. This study confirms that CO hydrogenation over iron is a structure sensitive reaction, presumably because of lower surface concentrations of hydrogen on small crystallites caused by inhibited H(,2) chemisorption.;Highly dispersed iron (very small crystallites) catalysts were prepared using high surface area amorphous carbons such as Carbolac-1 (950 m('2) g('-1)). All three experimental techniques indicated that average metal particle sizes for these highly dispersed iron catalysts were less than 4 nm. This represents the first report of a successful effort to prepare highly dispersed iron catalysts using an aqueous impregnation technique. |
