Influence of different diluents in Pt/Al2O3 catalyst on the hydrogenation of benzene, toluene and o-xylene

The hydrogenation of benzene, toluene and a-xylene was investigated over Pt/Al2O3, diluted by silica, alumina, MgO, US-SSY, HA1MCM-41 and WO3/Al2O3, respectively. The correlation between the nature of diluent and its distribution to the overall aromatic conversion is discussed. The remarkable enhancement of overall aromatic conversion is found over both powdery and granular mixtures of Pt/Al2O3 and the diluent: solid acid (US-SSY, HA1MCM-41) or the n-type semiconductor (WO3), although the diluent is inactive under utilized conditions. For the acid-diluted catalyst, the carbonium ion adsorbed on acid sites could react with the spillover hydrogen, which is delivered through interparticle migration from metal phase; and for the tungsten-diluted one, the coordinated unsaturated tungsten sites (CUS), on which the aromatic molecule could be adsorbed and then hydrogenated by the spillover hydrogen, could be created by the spillover hydrogen, and thus remotely controlled by neighboring platinum centers. The spillover hydrogen is thus responsible for the increase of the overall aromatic conversion. (C) 1998 Elsevier Science B.V. All rights reserved.