Effect of promoters on benzene hydrogenation over fused iron catalysts

Abstract

The hydrogenation of benzene to cyclohexane is a structure-insensitive reaction which, at atmospheric pressure, is thermodynamically favoured at temperatures below 550 K. The Group VIIIA metals are the most active catalysts for this reaction; studies prior to the 1960s showed zero (or very low) activity for iron. Badilla-Ohlbaum et al. reported the first thorough kinetic study of the reaction over a 7.95 mass% Al{sub 2}O{sub 3}-promoted fused iron catalyst; a rate maximum was observed at 443 K and the authors suggested that the rate-determining step was the surface reaction of adsorbed benzene with adsorbed hydrogen. Vannice and co-workers have reported the activities of the kinetic data over a series of supported iron catalysts. Rate maxima were observed near 473 K; activities were roughly one order of magnitude less than that reported by Badilla-Ohlbaum et al. under similar conditions. While it is apparent that the catalytic activity of iron for this reaction is too low to be of industrial significance, it was of interest to know to what extent the difference in the rates is due to chemical promotion. To this end, the activities of four multiply promoted ammonia synthesis catalysts were compared with that of a precipitated iron in anmore » effort to determine the effect of acidic and basic promoters on the reaction rate.« less