Kazuo Soga

Influence of Crystallinity of HZSM-5 Zeolite on Its Dealumination Rate

Abstract To clarify the influence of the crystallinity (structure defect) of zeolites on dealumination behavior, HZSM-5 zeolites synthesized using 1-BuOH and TPABr were dealuminated under a hydrothermal atmosphere. It was found that the dealumination rate of the HZSM-5 zeolite has apparently a third-order dependence upon the number of framework aluminums in the zeolite structure and that, in the case of the lower water vapor pressure, below 10 kPa the dealumination rate of the HZSM-5 zeolite synthesized using 1-BuOH is smaller than that of the zeolite synthesized using TPABr. Taking into account the fact that the peak intensity at ca 3,740 cm −1 assigned to silanol groups is very weak in the spectrum of the HZSM-5 zeolite from 1-BuOH as compared with that from TPABr, this seems to indicate that the dealumination rate strongly depends upon the crystallinity of zeolite, namely, the structure defect. It was also found that the dealumination rates of the HZSM-5 zeolites synthesized using 1-BuOH and TPABr have approximately a second-order and a 1.5-order dependence on water vapor pressure, respectively. Based on the results obtained, a plausible mechanism of the dealumination of HZSM-5 zeolite by hydrothermal treatment was discussed.

Synthesis and functionalization of poly(ethylene‐co‐dicyclopentadiene)

Copolymerizations of ethylene with endo-dicyclopentadiene (DCP) were performed by using Cp2ZrCl2 (Cp = Cyclopentadienyl), Et(Ind)2ZrCl2 (Ind = Indenyl), and Ph2C(Cp)(Flu)ZrCl2 (Flu = Fluorenyl) combined with MAO as cocatalyst. Among these three metallocenes, Et(Ind)2ZrCl2 showed the highest catalyst performance for the copolymerization. From 1H-NMR analysis, it was found that DCP was copolymerized through enchainment of norbornene rings. The copolymer was then epoxidated by reacting with m-chloroperbenzoic acid. 13C-NMR spectrum of the resulting copolymer indicated the quantitative conversion of olefinic to epoxy groups.

Effects of Al/Zr ratio on ethylene-propylene copolymerization with supported-zirconocene catalysts

Abstract Effects of heterogenization parameters on compositional and catalytic properties of Et(Ind) 2 ZrCl 2 supported on silica modified with MAO were evaluated using data on metal loading, catalyst activity in ethylene–propylene copolymerization, and polymer properties. The supported catalysts were prepared according to a 2 3 factorial design for multivariate analysis. The parameters studied were: MAO concentration in impregnation, Et(Ind) 2 ZrCl 2 concentration in grafting, and immobilization temperature for both metallocene and organoaluminum. The grafting solution was monitored by UV–VIS spectroscopy, while the resulting catalyst systems were characterized by inductively-coupled plasma-optical emission spectroscopy (ICP-OES), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS). At high statistical significance, both MAO and Et(Ind) 2 ZrCl 2 concentrations during preparation affected the determination of the final Al/Zr ratio on silica. The catalyst systems were tested in ethylene–propylene copolymerizations using external MAO as cocatalyst. Relationships were observed between (i) catalyst activity and the binding energy of Zr 3d 5/2 electrons and (ii) Al/Zr ratio on silica and the average ethylene incorporation. The polymer samples presented narrow molecular weight distribution, but according to differential scanning calorimetry (DSC), and cross-fractionation chromatography (CFC) data, catalyst systems with given Al/Zr ratios might yield different crystallites, suggesting a plural distribution of chemical composition.

Ethene polymerization with a poly(styrene-co-divinylbenzene) beads supported rac-Ph2Si(Ind)2ZrCl2 catalyst

Poly(styrene-co-divinylbenzene) beads supported rac-Ph 2 Si(Ind) 2 ZrCl 2 was prepared and tested as a catalyst for ethene polymerization using methylaluminoxane (MAO) as a cocatalyst. At a polymerization temperature below 100°C, the catalyst showed pretty high activity to give polyethene beads replicating the shape of the carrier. With increasing polymerization temperature up to 150°C, the catalyst activity increased drastically but the spherical shape of polyethene disappeared due to the melting. From the plots of apparent activity against polymerization temperature, it was suggested that the polymerization below 100°C is more or less controlled by monomer diffusion through the crystalline polyethene films.

Investigation on the polymer particle growth in ethylene polymerization with PS beads supported rac-Ph2Si(Ind)2ZrCl2 catalyst

Abstract The mechanism of polyethylene particle growth was investigated using poly(styrene-co-divinylbenzene) (PS beads) supported rac-Ph2Si(Ind)2ZrCl2 catalyst. From the analysis of the resulting polyethylene particles by SEM (scanning electron microscopy) and EPMA (electron probe microanalysis), it was found that the active species are located on the surface layer of catalyst particles and that the catalytic species are uniformly distributed throughout the polymer particles, whereas the cores of PS beads, which lack a potential active species, were not disintegrated during polymerization. These results suggest that the PS beads supported catalyst also follows the fragmentation and replication process as frequently observed with the MgCl2 supported Ziegler–Natta catalysts.

Ethylene (co)polymerization with supported-metallocenes prepared by the sol–gel method

Four supported metallocenes prepared by the sol‐gel method were tested by ethylene homopolymerization and in ethylene/1-hexene copolymerization. The effects of Al/Zr ratio, polymerization temperature and cocatalysts were evaluated. Catalyst A2, produced by TEA and MAO treatments showed the highest activity (180 £ 10 3 kg PE/mol Zr h 21 ) among the tested systems at Al/Zra 1000. A2 showed thermal stability on polymerization performed at a temperature as high as 1208C. All the systems exhibited activity in the presence of common alkylaluminum (TMA, TEA, TIBA). Comonomer effect was observed in the copolymerization of ethylene with 1-hexene, where the comonomer incorporation is about 7 mol%. SAXS measurements of the employed xerogel suggested a weakly branched polymeric texture. Metal content in the resulting polymers showed extremely low levels of Zr. q 2001 Elsevier Science Ltd. All rights reserved.

Synthesis of a dinuclear ansa-zirconocene catalyst having a biphenyl bridge and application to ethene polymerization

Abstract A novel dinuclear ansa-zirconocene catalyst ( μ -C 12 H 8 {[SiPh(Ind) 2 ]ZrCl 2 } 2 ) ( I ) was prepared by a Wurtz coupling reaction between two equivalent of bisindenylphenylchlorosilane and one equivalent of 4,4′-dibromobiphenyl in THF at reflux temperature for 12 h, followed by a successive reaction with ZrCl 4 ·2THF in THF at −78°C. Polymerization of ethene was conducted in a 300 cm 3 glass reactor equipped with a stirrer at 40, 60, 80 and 100°C using MAO or Ph 3 C[B(C 6 F 5 ) 4 ] as cocatalyst and toluene as the solvent. The catalyst ( I ) gave linear polyethene with a broader molecular mass distribution (MMD) in a much higher yield as compared to the corresponding mononuclear catalyst derived from [Ph 2 Si(Ind) 2 ]ZrCl 2 ( II ). The apparent activity increased monotonously from 40°C up to 100°C. The replacement of MAO with Ph 3 C[B(C 6 F 5 ) 4 ] gave polyethene with a higher molecular weight.

Supported metallocenes using inorganic–organic hybrid xerogels

Abstract Four metallocene catalysts were prepared using two indenyl-containing aerogels as supports, treated under different conditions (triethylaluminum (TEA), methylaluminoxane (MAO) and butyllithium). The catalysts were characterized by complementary spectroscopic techniques: ultraviolet–visible spectroscopy (UV–Vis), X-ray photoelectronic spectroscopy (XPS), matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF-MS), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The highest metal content (1.32 mmol Zr/g-cat.) was achieved in the case of xerogel treated with TEA prior to metallocene synthesis. After MAO leaching, such content is reduced to 0.82 mmol-Zr/g-cat., exhibiting the highest activity in ethylene polymerization among the four developed catalysts. A relationship between catalyst activity and binding energy of Zr 3d 5/2 core level could be evidenced. The most active catalyst system showed a better Zr distribution, being the catalyst grain covered by aluminum cocatalyst. Depth profile monitoring by XPS measurements showed that, in fact, MAO leaches the zirconocene low binding energy species, being deposited in the uttermost surface of the grains.

Realumination of dealuminated HZSM-5 zeolites by acid treatment and their catalytic properties

Abstract Effects of acid treatment variables on the realumination efficiency for realumination of dealuminated HZSM-5 zeolite (reinsertion of non-framework aluminums into the zeolite framework) were investigated using 27Al MAS NMR and nitrogen adsorption. Among various mineral acids employed, HCl solution was the most effective for the realumination. The realumination efficiency was also studied, evaluating the change in the cracking activity of cumene. The cumene cracking activity of the realuminated HZSM-5 zeolite was comparable to that of the parent zeolite, whose framework SiO2/Al2O3 ratio was the same as that of the realuminated zeolite. From the results obtained, it was found that no structural degradation of HZSM-5 zeolite crystals takes place during the acid treatment and that som of the non-framework aluminums in dealuminated HZSM-5 zeolites are reinserted into the framework.

Indenyl-silica xerogels: new materials for supporting metallocene catalysts

Abstract Inorganic–organic hybrid xerogels bearing indenyl groups on their surfaces have been synthesised by the sol–gel method. The hybrid xerogels were obtained by hydrolysis and polycondensation of bisindenyldiethoxysilane (Ind 2 Si(OEt) 2 ) and tetraethoxysilane, TEOS (Si(OEt) 4 ) under two different conditions. Chemical structure was investigated by ultraviolet spectroscopy (UV–VIS), transmittance (FT-IR) and diffuse-reflectance (DRIFTS) infrared spectroscopy, magic angle spin nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Xerogel texture and structure were analysed by nitrogen sorption based on the Brunauer–Emmett–Teller (BET) method, X-ray diffraction spectroscopy (XRD), and natural scanning electron microscopy (N-SEM). Under our experimental conditions, in alkaline milieu and 1:3 indenyl/TEOS ratio, a xerogel with higher indenyl content, but nonporous and showing agglomerate patterns was produced (xerogel I). Spherical particles of diameter about 6–8xa0μm where obtained in the absence of catalyst, using 1:5 indenyl/TEOS ratio, higher temperature and shorter reaction time (xerogel II). Xerogel II was used as support for heterogeneous metallocene catalyst synthesis. The resulting catalyst presented high Zr content (0.68xa0mmol Zrxa0g cat −1 ) and high catalyst activity (40×10 3 xa0kg PExa0mol −1 xa0Zrxa0h −1 ) in ethylene polymerisation.