DRIFT study of internal donors in supported Ziegler–Natta catalysts

Abstract

The state of internal donor (ID) in the supported titanium–magnesium (TiCl 4/ID/MgCl 2) catalysts for stereospecific propylene polymerization has been studied by diffuse reflectance infrared spectroscopy (DRIFT). The samples were prepared via interaction of highly dispersed MgCl 2 with different IDs (ethyl benzoate, EB; di- n-butyl phthalate, DBP) and TiCl 4. It was found that the DRIFT spectra of carbonyl groups of IDs adsorbed on MgCl 2 could be best described as a superposition of several overlapping vibration bands from a variety of surface complexes. Within this model the content of individual EB and DBP complexes on the MgCl 2 surface was calculated. In the case of EB, three main complexes were found on the MgCl 2 support in about equal proportions. In the case of DBP, only one of three complexes was preferentially formed. The surface content of both EB and DBP was found to decrease in presence of TiCl 4. At the same time TiCl 4 had influenced the distribution pattern of EB but not DBP complexes. The most likely scenario of competitive adsorption of TiCl 4 and IDs on the MgCl 2 support is discussed. A model describing surface distribution of TiCl 4 on MgCl 2 is proposed for TiCl 4/EB/MgCl 2 and TiCl 4/DBP/MgCl 2 catalysts.