Abstract
The catalytic dehydrogenation of perhydro-dibenzyltoluene (H18-DBT) to dibenzyltoluene (DBT) on a Pt/Al2O3 catalyst was investigated using H-1 NMR spectroscopy and GC-MS. It has been found that the dehydrogenation of a cyclohexyl ring of H18-DBT is very rapid and that Hx-DBT species with partially dehydrogenated rings can be neglected. Four different dehydrogenation pathways of H18-DBT to DBT, based on the ring dehydrogenation sequence were considered, including side-middle-side order, middle-side-side order, side-side-middle order, and statistical dehydrogenation with no ring preference. The H18-DBT dehydrogenation proceeds with a high preference for the side-middle-side (SMS) sequence of ring dehydrogenation. Steric hindrance leads to one of the side rings of H18-DBT dehydrogenating first. Subsequent adsorption of the H12-DBT with one side ring dehydrogenated, via the phenyl ring on the Pt surface is more stable and stronger than that of the cyclohexyl ring, causing the middle ring to be more accessible to the Pt sites and to undergo dehydrogenation. Finally, the remaining side ring is dehydrogenated to complete the SMS dehydrogenation pathway.