SKELETAL REARRANGEMENT REACTIONS OF HEXANES ON PT3TI POLYCRYSTALLINE CATALYSTS

Reactions of hexanes have been performed on a Pt3Ti intermetallic polycrystalline sample placed in a cell housed within an ultrahigh-vacuum apparatus where the surface can be monitored before and after the reactions by Auger electron spectroscopy (AES). The catalytic results show that Pt3Ti is very sensitive to experimental pretreatments, due to changes in surface composition. The main results obtained with the Pt3Ti compound are (i) low catalytic activities, (ii) formation of highly dehydrogenated products (benzene), and (iii) formation of homologation products, whereas no carbonaceous deposits are observed. These results can be explained by considering that there is no or little hydrogen chemisorption. The homologation reactions require the presence of bimetallic Pt]Ti sites where titanium can be slightly oxidized. These bimetallic sites are also responsible for the large amounts of benzene obtained with Pt3Ti (or "Pt3TiOx"). The fact that Pt3Ti (or "Pt3TiOx") has low hydrogen chemisorption ability suggests the participation of such a compound in strong metal-support interaction (SMSI) phenomena. Nevertheless, the catalytic behavior observed on a clean surface is different from that obtained on a supported Pt/TiO2 catalyst in the SMSI state. © 1990.