Role of Titanium in Ti/SiO₂-Supported Metallocene-based Olefin Polymerization Catalysts. Part 1: Genesis of Active Sites and Catalytic Performance

Performance enhancement of metallocene-based olefin polymerization catalysts can be obtained, among others, by the chemical modification of their support. We investigated a titanated SiO2 (Ti/SiO2) as an improved support material for zirconocene catalysts, which lead to similar to 35 % higher ethylene polymerization yields when compared to the unmodified SiO2-supported metallocene. The improved catalytic performance of the modified catalyst was found to be related to the presence of a Ti-based active site, second to the Zirconocene centers, as well as to a higher Lewis acidity in the titanated supported-MAO, which improved the activation of the Zr-based centers. The Ti active species were generated by reduction of the Ti/SiO2 support with the methylaluminoxane (MAO) co-catalysts, which introduced oxygen vacancies (V-O) and Ti3+ species, as confirmed by probe molecule Fourier Transform Infrared (FT-IR) spectroscopy and UV-Vis Diffuse Reflectance Spectroscopy (DRS). The higher Lewis acidity was linked to 5-coordinated Ti4+, as detected by probe molecules FT-IR spectroscopy.