Geometric causes of the methylcyclopentane ring opening selectivity over Pt/NaY catalysts

The hydrogenolytic ring opening of methylcyclopentane (MCP) is catalyzed by Pt and other transition metals. The relative rates of cleaving each of the five CC bonds depend on both chemical and geometric factors. Two preparations of Pt in NaY show different patterns of ring opening products, which are possibly related to the geometry of Pt particles inside the zeolite supercage. If the Pt particles are smaller than the cages, MCP molecules are adsorbed on the Pt particle, but rollover is sterically hindered. In this situation n-hexane formation is reduced. If the Pt particle is larger, 3-methylpentane is formed in larger-than-statistical quantities, which may be due to a preferred orientation of the impinging molecule. Ring opening is suppressed by benzene or cyclohexene, i.e., products of the simultaneous ring expansion in catalysts containing an acidic function besides platinum.