Skeletal rearrangements of hydrocarbons on "ideal surfaces" (single crystals), "classical" and "inorganic complexes derived" catalysts of platinum

Abstract

Skeletal isomerization and hydrogenolysis of hexanes were studied on single crystal faces of platinum (stepped and low index faces) and on supported mono or bimetallic catalysts prepared by decomposition of organometallic complexes : CHINI, CHATT and hetero polymetallic cluster. The high and low index faces of platinum simulated very well catalysts with large particles (d > 100 Å). Hydrogen induced surface reconstruction. The labeling of hydrocarbon with13C allowed the evaluation of the percentages of cyclic or bond-shift mechanisms in hexanes isomerization. A direct correlation was found between the increase of bond shift mechanism and the nature of the ledges of the stepped surfaces. Single crystals faces of platinum never simulated highly dispersed catalysts (d < 20 Å). On another hand, small particles of platinum were obtained by decomposition of organometallic complexes deposited on alumina. CHINI'S molecular clusters derived catalysts had the same behaviour as classical high dispersed supporter Pt catalysts and showed a correlation between the percentages of small aggregates and the increase of cyclic mechanism. Moreover CHATT and hetero polymetallic clusters derived catalysts were highly selective for demethylation and bond-shift isomerization.