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 H₂ (H₂-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 Ti^4–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.