Defect Sites in H2-Reduced TiO2 Convert Ethylene to High Density Polyethylene without Activator

We show the unprecedented potential of commercially available TiO2 materials reduced in H-2 (H-2-reduced TiO2) in the conversion of ethylene to high density polyethylene (HDPE) under mild conditions (room temperature, low pressure, absence of any activator), with the consequent formation of HDPE/TiO2 composites, which have been characterized by electron microscopy. Combination of UV-vis and IR spectroscopies allows one to demonstrate that ethylene polymerization occurs on Ti4-n defect sites, which behave as shallow-trap defects located in the band gap and, differently from the active sites in the widely used Ziegler-Natta catalysts, do not contain any alkyl (Ti-R) or hydride (Ti-H) ligands. These results represent a step forward the understanding of ethylene polymerization mechanism and open valuable perspectives for commercial TiO2 materials as catalysts for polyethylene production under mild conditions.