Comparison of the catalytic properties of H2-reduced Pt/MoO3 and of Pt/zeolites for the conversions of pentane and heptane

The catalytic properties of H-2-reduced Pt/MoO3 for the isomerization of pentane and heptane were compared to those of Pt/zeolites. H-2-reduced Pt/MoO3 was more active for pentane isomerization than PL/Hbeta and Pt/USY. In contrast, the heptane isomerization activity decreased in the following order: Pt/Hbeta > H-2-reduced Pt/MoO3 > Pt/USY. All of the catalysts gave negative kinetic orders toward hydrogen in both pentane and heptane isomerization. The reaction order toward pentane was positive in all cases. The reaction order toward heptane on H-2-reduced Pt/MoO3 was found to be -0.3, whereas those on Pt/Hbeta and Pt/USY were zero and positive, respectively. These results indicate that heptane was more strongly adsorbed on H-2-reduced Pt/MoO3, resulting in the low heptane isomerization activity. Adsorption studies showed that interaction of heptane with the surface of H-2-reduced Pt/MoO3 was hindered, probably by its porous structure. We suggest from these results that the low catalytic activity of H-2-reduced Pt/MoO3 for heptane isomerization can be caused by steric effects as well as by the strong adsorption of heptane. (C) 2003 Elsevier Science B.V. All rights reserved.