Marjolein Velthoen

PhD Candidate

Employed since: September 2014
Phone: +31 6 22736375
E-mail: M.E.Z.Velthoen (at)
Room: 4th floor study area

Lewis acidity probing methods for polymerization, cracking and hydroprocessing catalysts

Sponsor: Albemarle

This research aims for the development of chemical imaging tools enabling the visualization of Lewis acidic sites in three different catalytic systems: Fluid catalytic cracking (FCC) catalysts, hydroprocessing catalysts (HPC) and metallocene polymerization catalysts. This project is carried out in collaboration with Ara Muñoz Murillo, who works in our group as a postdoc

Metallocenes in combination with methylaluminoxane as a cocatalyst form extremely active catalysts for olefin polymerization. Moreover, the choice of ligand determines the zirconocene symmetry and chirality, leading towards a different tacticity of the resulting polymers.[1] In this catalyst, the zirconocene precursor is believed to be activated by the Lewis acidic sites from the silica-supported methylaluminoxane. The chloride ligands are hereby extracted and partially replaced with methyl groups by the MAO, creating a vacant site for ethylene polymerization, as can be seen in Figure 1.

My project involves the use of micro-spectroscopic techniques in combination with probe molecules to determine the strength and distribution of the Lewis acidic sites on the supported MAO and, subsequently, the distribution of the active zirconocene species with the aim to correlate the results to the catalyst polymerization activity. This micro-spectroscopic study of the solid catalyst builds on previously reported spectroscopic studies of this system in solution.[2] Furthermore, the UV-Vis micro-spectroscopic study of single particles is compared to in-situ UV-Vis DRS measurements during gas phase polymerization reactions.

Figure 1: The zirconocene precursor is activated by the Lewis acidic sites of the silica-supported MAO, yielding the active species for olefin polymerization.

[1] Kaminsky, Catalysis Today 20, 257 - 271 (1994)
[2] D. Coevoet et al., Macromol. Chem. Phys. 199, 1451 - 1457 (1998)