n-octane reforming over alumina-supported Pt, Pt-Sn and Pt-W catalysts

Pt, Pt-Sn and Pt-W supported on gamma-Al2O3 were prepared and characterized by H-2 chemisorption, TEM, TPR, test reactions of n-C-8 reforming (500 C-d egrees), cyclohexane dehydrogenation (315 C-degrees) and n-C-5 isomerizatio n (500 degrees C), and TPO of the used catalysts. Pt is completely reduced to Pt-0, but only a small fraction of Sn and of W oxides are reduced to met al. The second element decreases the metallic properties of Pt (H-2 chemiso rption and dehydrogenation activity) but increases dehydrocyclization and s tability. In spite of the large decrease in dehydrogenation activity of Pt in the bimetallics, the metallic function is not the controlling function o f the bifunctional mechanisms of dehydrocyclization. Pt-Sn/Al2O3 is the bes t catalyst with the highest acid to metallic functions ratio (due to its lo wer metallic activity) presenting a xylenes distribution different from the other catalysts. The acid function of Pt-Sn/Al2O3 is tuned in order to inc rease isomerization and cyclization and to decrease cracking, as compared t o Pt and Pt-W.