Immobilization of Zirconocene into Silica Prepared by Non‐Hydrolytic Sol‐Gel Method

Abstract

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.

Catalisadores metalocênicos suportados para a produção de poliolefinas: revisão das estratégias de imobilização

“…90 Entretanto, o encapsulamento em óxidos binários de caréter ácido, tais como SiO 2 -TiO 2 e SiO 2 -WO 3 , exibem boas atividades em concentrações reduzidas de MAO (Al/Zr= 50-500) em comparação com os catalisadores obtidos com suportes super ácidos como a sílica ou a zircônia sulfatada. 91 Nos sistemas obtidos por encapsulamento via rota sol-gel, o ambiente de imobilização é restrito de espaço, devido ao estreito diâmetro de poro (3 nm) e à reduzida área específica (30 m 2 g -1 ).…”

Investigation of silica particle structure containing metallocene immobilized by a sol–gel method

“…The solid was further dried under vacuum for 12 h at room temperature and milled under inert atmosphere (argon) until reaching a diameter of 20-53 lm. A more detailed description of the synthesis methodology and the catalyst characterization can be found elsewhere [17] (Scheme 2).…”

“…Recently, self-assembled porous, hollow silica nanoparticles were conglomerated and used as a novel support for metallocene catalysts [16]. In a fashion similar to using a support for metallocene catalysts, we have proposed the concomitant immobilization of zirconocenes into the silica matrix with the oxide synthesis obtained from a non-hydrolytic sol-gel method [17]. The resulting catalysts were shown to be active for ethylene polymerization with similar activities to those found in Cp 2 ZrCl 2 grafted on commercial SiO 2 .…”

“…The chlorine and ethoxy groups resulting from the initial reactions are reactive for the next condensation reactions. After some time, a three-dimensional oxide network, which is completely amorphous (glassy), is produced [17]. In fact, the complete reaction will seldom be obtained, and therefore, residual groups are expected to be present in the final product.…”

Direct production of ultra-high molecular weight polyethylene with oriented crystalline microstructures

“…Therefore, the choice of the support type and immobilization methodology plays an important role on the performance of metallocenes during the polymerization. In a previous study, we have proposed a methodology for the immobilization of zirconocenes into a silica matrix concomitantly with the SiO 2 synthesis by a non-hydrolytic sol-gel method [8,9]. In this method, the metallocene catalyst is entrapped within the amorphous SiO 2 network formed around the metallocene complex.…”