Síntese e aplicações catalíticas de polímeros de coordenação derivados de íons lantanídeos e ligantes arenossulfônicos

Abstract

This work deals with the synthesis and structural characterization of three new coordination polymers derived from lanthanum(III) and neodymium(III) ions with 5-sulfoisophthalic acid, named as Nd-5sis-gel, La-5sis-gel and Nd-5sis, in addition to the synthesis of two other compounds derived from p-sulfobenzoic acid combined with these lanthanide ions named as Nd-psb and La-psb. The compounds were synthesized mainly by solvothermic reactions, which were efficient and with greater reproducibility and by gel crystallization, in which the methodology, despite of favoring the formation of crystals, it was not suitable to security the reproducibility of the syntheses. All the compounds were investigated by spectroscopic techniques of infrared absorption and Raman scattering and elemental analysis of carbon, hydrogen and nitrogen. The crystalline structures for the coordination polymers Nd-5sis-gel, La-5sis-gel and Nd-5sis were determined by single crystal X-ray diffraction, in which a X-ray absorption correction applied to the collected reflections proved to be appropriate for the structural determination of these compounds. Thermogravimetric analysis and X-ray diffraction of polycrystalline materials with temperature variation for the two-dimensional polymer, Nd-5sis, were performed and the results show a thermal stability up to 550 °C, with a slightly increased in weight in oxygen atmosphere after the dehydration process after 150 °C, related to the formation of crystalline phases of neodymium carbonates and oxocarbonate in the structure. Studies on the structural and surface effects were carried out for the Nd-5sis by means of a reaction model with hydrogen peroxide. The formation of the neodymiumhydroperoxide complex on the surface allowed the determination of the amount of sites on the surface of the two-dimensional polymer. Two catalytic tests were also performed for the Nd-5sis as a heterogeneous catalyst in the cycloaddition reactions between glycerol and urea and for the oxidation of linalool. The properties of the coordination polymer allowed getting conversion and selectivity values for the cycloaddition reaction comparable with several catalysts described in the literature and from the experimental data it was possible to set the reaction rate and to estimate the production and consumption rate of glycerol and glycerol carbonate in a catalytic process. The chemical and structural stability of two-dimensional coordination polymer was evaluated up to the fourth cycle of reaction and it was observed that the polymer shows a good catalytic activity after a suitable recrystallization process between one cycle and another of the reaction. The catalytic tests for linalool oxidation show viably good conversion and selectivity values for the reaction. The formation of the neodymium-hydroperoxide complex on the surface was essential to ensure catalytic activity. In addition, the heterogeneity of the reaction was evaluated and the results show that the Nd-5sis acts as a heterogeneous catalyst in the reaction, since the removal of compound, in the oxidation reaction, stops the conversion process. The structural stability of Nd-5sis was evaluated after the first cycle and the results indicate that at the end of the reaction the crystalline structure is preserved.