Conversion of methylcyclohexane over Ir/H-β zeolite in the presence of hydrogen

We studied the conversion of methylcyclohexane into dimethylpentanes in the presence of hydrogen, catalyzed by Ir supported on H-β zeolites with different Si/Al ratios. Ir/H-β catalysts with a high Si/Al ratio (Si/Al = 75 or 150) showed activity in promoting both ring-contraction (from six-membered to five-membered rings) on the acidic sites of H-β and ring-opening on Ir metal sites, resulting in high activity and selectivity toward dimethylpentanes. In contrast, Ir/H-β catalysts with a low Si/Al ratio were less active in ring-opening on the Ir metal sites, which resulted in the high selectivity for dimethylcyclopentanes. In the conversions of methylcyclohexane, 2-methylhexane, and 2,4-dimethylpentane, the dependence of the conversion rate on W/F values demonstrated that, for the highly active and selective Ir/H-β catalyst with Si/Al = 75, methylcyclohexane was first transformed into dimethylcyclopentanes on the acidic sites, followed by ring-opening on the Ir sites to form dimethylpentanes and methylhexanes. The skeletal isomerization of methylhexanes into dimethylpentanes over this catalyst was very slow under the reaction conditions studied.