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Reduced anatase TiO 2 is used as an alternative support for TiCl 4 , leading to good results in the polymerization of ethylene and propylene with isotacticity above 80%. However, due to the low concentration of active sites, approximately 1 wt% of active titanium, the system leads to low productivity. With the objective of increasing the amount of active sites and the productivity, a catalytic system with a high surface area was developed. The synthesis consists in the chemical vapor deposition, known as Atomic Layer Epitaxy (ALE), of TiCl 4 onto a silica surface. The deposited titanium is then transformed into anatase by heating between 300 and 500 °C. The synthesis of the catalyst is carried out by chemical reduction of the oxide with n -butyl lithium and heterogenization of TiCl 4 . The amount of supported TiO 2 was, on average, 13 mg TiO 2 (g SiO 2 ) −1 . The content of active titanium was 23 μmol Ti(III) (g cat) −1 . Two resonance peaks for Ti(III) ( g = 1.98 and g = 1.96) in the EPR spectrum suggest the presence of two different active species on the catalyst surface. The catalyst was tested in the polymerization of ethylene in the liquid and in the gas phase, leading to productivities of 140 and 120 g PE (g cat) −1 , respectively. The polymers presented a melting point of 137 °C, molar masses around 3000 kg mol −1 and crystallinities between 49 and 69%. |
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