Hydroconversion of n-heptane: a comparative study of catalytic properties of Pd/Sulfated Zr-pillared montmorillonite, Pd/Sulfated zirconia and Pd/γ-alumina

The hydroconversion of n-heptane on 1 wt.% palladium supported on sulfated zirconium pillared montmorillonite (PdZMS) under isothermal and isobar conditions (P-HC = 7.99 kPa and PTTot = 101.3 kPa) is studied. The catalyst activity of PdZMS is compared to those obtained on 1 wt.% palladium supported on gamma-alumine (PdAl) and on sulfated zirconia (PdZS). The PdZMS catalyst develops an intermediary catalytic behavior between that of PdAl and that of PdZS and shows a very important isomerization selectivity at 300-330 degreesC. The monobranched isomers are the major reaction products formed on this catalyst and suggest a classical bifunctional mechanism. On the PdAl catalyst, it is rather a metallic mechanism charaterized by hydrogenolysis on Pd particles (demethylation reaction) and by a bond shift isomerization occurring through a cyclic intermediate. On the PdZS catalyst, a high selectivity in cracking products (propane and butane) suggests a mechanism involving a cyclopropanic protonated intermediate, followed by a p-scission attributed to the strong acidity of the sulfated zirconia. (C) 2003 Published by Elsevier B.V.