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In this paper we present two different techniques for the preparation of single site heterogeneous catalyst. The first method consists in the impregnation of a solution of the organometallic compound in MCM41. The second method intends to establish the in situ synthesis of the complex within the solid's pores by the reaction of the organic ligand with the metal cation previously introduced in the support. The direct deposition of the organometallic complex in the support resulted in an active catalyst which gives polyethylene with the same microstructure as the one obtained with the related homogeneous systems. The heterogeneous catalysts obtained by reaction of the ligand with the metal already present in the support showed a lower catalytic activity. [ABSTRACT FROM AUTHOR]

The polymerization of ethylene in the presence of vanadium catalysts supported on zeolite NaY, HY and charcoal was examined. The catalysts were prepared by the incipient wetness method and characterized by a variety of techniques to determine the oxidation state of the vanadium species inside the zeolite. In all the catalysts that were prepared vanadium is not in a single oxidation state. These catalysts were active in the polymerization of ethylene with activities of the order of magnitude 105 gPE/molV.[M].h for the zeolite catalysts and 103 gPE/molV.[M].h for the charcoal systems. No polymer could be obtained in the absence of alkylaluminum or aluminoxane in the experimental conditions used. The kinetics of ethylene polymerization reactions using the vanadium catalysts was studied. A kinetic model based on a proposed mechanism for these reactions was used to fit the experimental data. The application of this model resulted in very good fittings and the kinetic rate constants of each elementary step could be estimated. Since the polyethylene that was produced is closely bound to the zeolite catalysts, the thermal and mechanical properties of the PE/zeolite composites were measured, indicating that the presence of zeolite improved the mechanical properties of the polymers produced. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the catalytic degradation of high and low density polyethylenes, using catalysts based on transition metals supported on zeolite Y, is analysed using simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). The results obtained in the catalytic degradation are compared with those that were obtained in the purely thermal degradation. The transition metals used, vanadium, zirconium and nickel, supported on NaY or HY were studied since they were found to be active, although with different degrees of efficiency, for ethylene polymerization, which is, in a way, the reverse reaction of the one we are interested in. It was found that they are also able to promote the degradation process of polyethylene, also with varying efficiencies. A kinetic model capable to describe the performance of the catalytic degradation, and which has already been used to analyse its thermal degradation, has been applied. Fitting this model to the experimental results obtained by TG and DSC made it possible to estimate several kinetic parameters and to gain some insight into the processes involved. [Copyright &y& Elsevier]