Isomerization of 13C labeled hexanes on Pt/Al 2O 3 and on “organometallic cluster derived” catalysts; effect of the metal particle size

Abstract

Skeletal isomerization of 2-methylpentane (2-MP) and hydrogenolysis of methylcyclopentane (MCP) have been studied over a series of Pt/Al 2O 3 and “cluster derived” (CD) catalysts of high dispersions. 13C labeling allowed estimation of the relative contributions of cyclic mechanisms in isomerization. High resolution electron microscopy was used jointly to determine the metal particle size distributions. In the isomerization of 2-MP to 3-MP the relative amount of selective cyclic mechanisms increases with the percentage of surface or length particles ( d ⩽ 10 Å) whatever the catalyst used. In the isomerization of 2-MP to n-hexane for catalysts having the same mean size of particles, the CD catalysts show differences in selectivity compared to the classical Pt/Al 2O 3 catalysts. The observed particle size effect could be explained by changes in electronic or geometrical factors, especially it is proposed that the electronic rather than the geometrical one should be considered in the case of the “organometallic cluster derived” catalysts.