Defect Sites in H2-Reduced TiO2Convert Ethylene to High Density Polyethylene without Activator

Abstract

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 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.