(26a) Selectivity of Ring-Contraction Products in the Hydroisomerization of Methylcyclohexane

The hydroisomerization of alicyclic compounds (e.g., methylcyclohexane) attracts the interests of researchers due to high demand for clean fuels, which can maintain high octane numbers while decreasing aromatic content. The composition of the products from skeletal isomerization of hydrocarbon is principally dependent on the shape selectivity and the acid strength of the acid catalyst, as well as the hydride transfer step. Experiments were conducted at 533 K in the presence of hydrogen at a total pressure of 2 MPa over bare and Pt-supported zeolitic and non-zeolitic solid acid supports. The products obtained under these conditions were mainly those from the methylcyclohexane ring-contraction (RC), that is, isomers consisting of 1,1-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethylcyclopentanes, and trans-1,2-dimethylcyclopentane, and ethylcyclopentane. It was found that the acid strength plays an essential role in defining the product distribution due to the relative stability of the different carbenium ion intermediates. In addition to the acid strength, the shape selectivity of the catalysts was seen to be important in determining the RC product distribution. Interestingly, the high rate of hydride transfer was seen to greatly influence the selectivity of RC isomers over all zeolitic supports, but much less on non-zeolitic supports, such as tungstated zirconia.