Defect Sites in H<sub>2</sub>‑Reduced TiO<sub>2</sub> Convert Ethylene to High Density Polyethylene without Activator
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Abstract
We show the unprecedented potential
of commercially available TiO<sub>2</sub> materials reduced in H<sub>2</sub> (H<sub>2</sub>-reduced
TiO<sub>2</sub>) 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/TiO<sub>2</sub> 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<sup>4–<i>n</i></sup> 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 TiO<sub>2</sub> materials as catalysts
for polyethylene production under mild conditions
