Pt-Ir/Al2O3 catalysts for the ring opening of naphthenes. Performance as a function of time

The catalytic performance of a Pt-Ir/Al2O3 catalyst for the selective ring opening of decalin was studied as a function of time. Fresh and used catalysts were evaluated with the reaction tests of cyclohexane dehydrogenation and cyclopentane hydrogenolysis to assess the metal function properties. The transformation of decalin was used as a test reaction for the ring opening of naphthenes. For this test the yield to ring contraction products passed through a maximum at intermediate values of conversion while yields to dehydrogenation, ring opening, and cracking products increased with conversion. Coke deposition also increased with reaction time but its distribution on the metal and acid sites did not change. Coke was more toxic for hydrogenolysis than for de/hydrogenation and therefore the products ratio of (ring opening)/(dehydrogenation) decreased at end of the reaction. Higher yields to dehydrogenated products produced a higher coke deposition while high activity in both hydrogenolysis and dehydrogenation favored the ring opening reaction.