Catalysis Letters 8 (1991) 37-44 37 OLEFINS POLYMERIZATION ON TITANIA AND TITANIA-SUPPORTED RHODIUM M.J. HOLGADO and V. RIVES * Dpto. de Qulmica Inorgdnica, Universidad de Salamanca, Facultad de Farmacia, Av. Campo Charro, s/n, 37007-Salamanca, Spain Received 6 July 1990; accepted 20 October 1990 Olefins polymerization, Rh/TiO2 catalysts, titania, rhodium The adsorption of ethene and propene on titania and titania-supported rhodium has been studied, observing a continuous adsorption even after 24 h. The samples have been reduced at 623 or 773 K, but no difference was observed, whichever the reduction temperature or the presence of rhodium, on the amount of gas adsorbed per unit of surface area of the solid. A study of the polymerization has been done following the "equal reactivity hypothesis", and it has been concluded that the role played by the rhodium particles is to facilitate adsorption of the gaseous molecule, that is then transfered to the surface of the support, where it polymerizes. 1. Introduction Although formation of Ti 3+ species has been claimed as one of the factors involved in developing of Strong Metal-Support Interactions (SMSI) when noble metals are supported on titania [1], very little attention has been paid to polymerization processes that may compete with hydrogenation of unsaturated hydrocarbons on these materials. We have recently reported [2] that upon adsorption at room temperature of ethene or propene on a Rh/TiO 2 catalyst, its reaction depends on the simultaneous presence of hydrogen: in the presence of hydrogen total hydrogenation to ethane or propane, respectively, takes place, while in the absence of this gas a polymerization reaction takes place. Such a polymerization process is here studied assuming a Flory mechanism. 2. Experimental Preparation of the catalyst has been described elsewhere [3]. Briefly, it consists of Rh supported (2.5% w/w) on titania (P-25, from Degussa, ca. 50 mZ/g) and 9 J.C. Baltzer A.G. Scientific Publishing Company