Propriedades catalíticas de aluminossilicatos funcionalizados com propilaminas

Abstract

In this work, the functionalization with aminopropyl-trimethoxysilane (APTMS) of aluminosilicates precursors of the Na-LTA zeolite was explored in the synthesis of basic catalysts for the Knoevenagel condensation. The functionalization of zeolite H-MFI and its amorphous and semicrystalline precursors, amorphous aluminosilicates with different Si/Al ratios in the protonic form, and also of zeolite H-BEA, were evaluated for the synthesis of catalysts with acid-base properties for deacetalization of benzaldehyde dimethylacetal followed by Knoevenagel condensation. Regarding the functionalization of the Na-LTA zeolite and its precursors, the functionalized solids prepared with shorter hydrothermal treatment times were more active in the reaction due to the greater anchoring capacity of propylamine, since they have a higher content of surface silanols. In addition, the amorphous Na-LTA zeolite precursors were more active, due to the greater accessibility of the catalytic sites before the closure of the structure. Functionalization proved to be a simple and efficient strategy to increase the activity of purely sodium aluminosilicates in Knoevenagel condensation. In the case of the functionalization of zeolite H-MFI and its precursors, it was observed that greater selectivity to the Knoevenagel condensation product (a step that occurs in the basic site) is achieved for materials with a greater amount of amorphous solid. Once again, this result was attributed to the greater amount of amine anchored in these solids. When varying the Si/Al ratio of the amorphous aluminosilicates, a tendency towards a decrease in the activity of the acid sites was observed in solids with a higher fraction of Al, which was explained by the increase in the protonation of the nitrogen atoms derived from the APTMS as it increased the acidity of the solid used in the functionalization. The zeolite H-BEA functionalized with APTMS showed the highest yield of acrylate product among all catalysts tested in the acid-base catalyzed series reaction. Its better performance was attributed to the high acidity combined with a large amount of amine anchored due to the high concentration of external silanols in this material.