Unraveling the Catalytic Synergy between Ti3+ and Al3+ Sites on a Chlorinated Al2O3: A Tandem Approach to Branched Polyethylene

An original step-by-step approach to synthesize and characterize a bifunctional heterogeneous catalyst consisting of isolated Ti3+ centers and strong Lewis acid Al3+ sites on the surface of a chlorinated alumina has been devised. A wide range of physicochemical and spectroscopic techniques were employed to demonstrate that the two sites, in close proximity, act in a concerted fashion to synergistically boost the conversion of ethylene into branched polyethylene, using ethylene as the only feed and without any activator. The coordinatively unsaturated Al3+ ions promote ethylene oligomerization through a carbocationic mechanism and activate the Ti3+ sites for the traditional ethylene coordination polymerization.