Dehydrogenation of cyclohexane on catalysts containing noble metals and their combinations with platinum on alumina support

Abstract

The dehydrogenation of cyclohexane over catalysts containing 0.35 wt% of each of the following metals: Pt, Rh, Re, U, PtIr, PtRh, PtRe and PtU on g-Al2O3 was carried out in a pulsed micro-reactor system at the temperature range 200±5008C. PtRh catalyst was the most active for the dehydrogenation of cyclohexane in the temperature range 250±3508C. The catalyst containing Rh was the most active for hydrogenolysis of cyclohexane to propane due to the higher percentage of d-bond character of Rh. It was found that the introduction of U inhibits the activity of Pt catalyst for the dehydrogenation. The effect of chlorine and fuorine contents (1, 3 and 6 wt%) on the activities of these catalysts were investigated. Optimum halogen content was found to be 3% for dehydrogenation enhancement which may be attributed to improved hydrogen spillover as well as to increased dispersion of the metal in the support. The catalysts containing Ir (3.0% F) and PtU (3.0% F) exhibit some hydroisomerization activity to methylcyclopentane. However, inclusion of chlorine reduces the activity of PtIr whereas both chlorine and fuorine reduce the activity of PtRh-containing catalysts.