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Summary: Concomitant immobilization of zirconocene (Cp 2 ZrCl 2 ) into a silica matrix was performed during the SiO 2 synthesis through non-hydrolytic sol-gel method. Two different routes, varying the SiCl 4 :Si(OEt) 4 ratio were evaluated in terms of zirconocene content and catalyst activity in ethylene polymerization, using methylaluminoxane (MAO) as cocatalyst. The catalysts were characterized by Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy and X-ray dispersive spectroscopy. The zirconocene content laid between 0.60 and 1.02 wt.% Zr/SiO 2 , depending upon the components ratio employed in the sol-gel synthesis. Catalyst grains presented of irregular shape (20-100 mm size) and zirconocene distribution was not uniform. Both routes led to supported catalysts active in ethylene polymerization. Catalyst activity was intermediate between that exhibited by the homogeneous and the grafted zirconocene on silica. Resulting polyethylenes presented narrow molecular weight distribution and molecular weight slightly higher than that observed in the case of polymer produced with the homogeneous system.

IntroductionZiegler-Natta catalysts are largely employed in industrial processes for the polymerization of α-olefins in order to produce materials, such as polyethylenes and polypropylenes. The main constituents of such catalysts are Ti and V, which are responsible for the catalytic activity, as a result of the immobilization of compounds, such as TiCl4 or VCl3, onto MgCl2 or SiO2 supports. 1 Catalyst properties and metal content are dependent on some experimental parameters, such as the order of catalyst addition to the support, the grafting time and temperature, the molar ratio among the catalyst and the cocatalyst (aluminum compounds, such as tributylaluminum). These parameters may affect the catalyst performance in the polymerization reaction as well as the properties of the attained polymers. Therefore, the catalyst metal content is an important parameter for evaluating the catalyst performance in terms of the activity, which is defined as the capacity of the catalyst to convert the feedstock into products. The activity is expressed as the ratio of the attained product by the mass of the catalyst, which is expressed as moles of metal. The determination of the metal content in catalysts can be carried out by various techniques, 2 but and in the case of Ziegler-Natta (ZN) catalysts, Ti and V are usually determined by molecular absorption spectrometry after reactions with H2O2 and H2SO4 and measurements at 410 nm and 450 nm, respectively.3-8 The major drawbacks of this technique are a low sampling throughput and high sample handling. In some studies, Ti or V was also determined by flame atomic absorption spectrometry (FAAS) 9-11 and inductively coupled plasma atomic emission spectrometry (ICP OES). 12 In the case of FAAS, the limit of detection (LOD) is not very good, since V and Ti may form compounds that are not completely destroyed in the flame, while in the case of ICP OES, the persistence of such compounds would be very unlikely due to the plasma temperature. However, despite the fact that ICP OES seems to be an appropriate technique, it has not usually been employed in ZN catalysts analysis.It is claimed that the major drawbacks of the above-mentioned techniques are the need for metal extraction from the bulk of the sample matrix, or sample decomposition with an acidic solution (acid digestion) prior to the analyte measurement. These procedures may be tedious, time-consuming and engender some systematic errors due to poor analyte extraction efficiency and solubility. It is expected that such problems may be overcome by using direct analysis techniques, which allow the analysis of solid samples without any analyte extraction or decomposition.Many techniques can provide direct metal determination in catalysts, differing in the measurement principle. Particularly in the case of the Ziegler-Natta catalyst, one can mention metal content determination by X-ray fluorescence spectrometry (XRF), 13,14 X-ray photoelectron spectroscopy (XPS), [12][13][14][15] and Rutherford backscattering spectrometry (RBS). 16,17 ...