| Supported and unsupported iron catalysts were used for a kinetic study of benzene hydrogenation. Supports used were silica, alumina, various carbons, and boron- and potassium-doped carbons. The catalytic properties for benzene hydrogenation were determined at 1 atm using a differential plug-flow reactor, and the effects of the support and iron particle size were investigated.;From the comparison of CO chemisorption results with x-ray diffraction and BET results, it was found that CO chemisorption at 195 K occurred in the bridged-form and provided accurate estimates of iron particle sizes. H(,2) chemisorption was found to be an activated process, and H(,2) uptakes were considerably lower compared to CO uptakes. Most of the catalysts exhibited similar kinetic behavior in a temperature range of 393-513 K: activity maxima occurred near 473 K, reaction orders in hydrogen pressure were near three regardless of temperature, reaction orders in benzene pressure increased from -1 to near zero with temperature, and apparent activation energies in the temperature range of 393-453 K were 22 (+OR-) 5 kcal mole('-1). A Langmuir-Hinshelwood kinetic model, in which associative benzene adsorption and competitive adsorption betwen H(,2) and benzene were assumed, provided a reasonable fit of the data over wide ranges of reaction conditions and gave physically reasonable kinetic parameter values. The activity maximum was explained by a decrease in benzene concentration on the iron surface as temperature increased. Effects on catalytic properties due to the support of iron particle size were not marked. The most apparent observations were that benzene hydrogenation over iron was a structure insensitive reaction and that carbon-supported iron catalysts had the best activity maintenance. |
