Surface Carbonaceous Deposits as Activity and Selectivity Influencing Species in Ring-Opening Reactions of Propylcyclobutane Catalyzed by Pt/SiO₂

Active site formation in the hydrogenative ring opening of propylcyclobutane over Pt/SiO₂ was investigated in a static reactor, mainly at 373 K. Changes in the ring-opening rates and selectivities on variously treated catalyst are described. Three types of treatment were applied: repeated runs with (i) only evacuation or (ii) inter-run reduction (H₂, 473 K, 0.5 h), or (iii) prepoisoning of the catalyst with propylcyclobutane at 373 K or 673 K. The observed (in some cases dramatic) increase in selectivity towards the formation of heptane (1,2 CC bond scission) is interpreted in terms of the formation of a metal-carbonaceous deposit interface where the deposit provides an anchoring site for the adsorption of the propyl side-chain and the ring opens on the clean Pt atoms. Changes in activity due to the various treatments are also discussed.