Catalisadores para síntese do butadieno a partir do etanol: composição e o tipo de preparo

Abstract

For some years now, the Chemical Industry has been seeking greater sustainability, with emphasis on replacing fossil raw materials with renewable ones in the generation of chemical products and intermediates. Brazil is the second largest producer of ethanol in the world, which is mainly used as a fuel and additive to gasoline. Ethanol can be considered a different platform molecule, as from it is possible to generate several drop-in compounds, in a reaction step using multifunctional catalysts.Butadiene (BD) is one of these substances, and stands out for being widely used by the Automotive Industry, in the production of various types of materials, especially synthetic rubbers. Currently, this olefin is produced as a co-product of ethylene production from naphtha cracking. Thus, the conversion of ethanol to butadiene has attracted the interest of several research groups.In fact, the challenge is to develop active, selective and stable catalysts that enable the production of butadiene from ethanol on an industrial scale. In this context, the objective of this study is to compare the performance of ZnTa/SiO2, ZnZr/SiO2 and ZnHf/SiO2 catalysts in the synthesis of butadiene from ethanol and also to determine the catalyst preparation technique that is capable of generating the most active systems and selective to the olefin of interest. The two most promising catalysts in this set were prepared using different techniques and were evaluated by standard and isoconversion catalytic tests and characterized by TPD-NH3, TPD-CO2, TPSR-ethanol, XRD, UV-Vis and XPS techniques. The results reveal that all the synthesized catalysts are promising for the reaction in question, especially the ZnZr/SiO2 synthesized from dry impregnation in two stages, with intermediate calcination, which shows the greatest selectivity for butadiene, showing that this catalyst, despite not being the most active is the most selective to BD. It was found that Zn plays a central role in this synthesis, as it minimizes the formation of ethylene and promotes the generation of BD. It was found that Hf catalysts have isolated atoms, clusters and Hf oxide, while Zr catalysts have clusters and Zr oxide. Finally, it was suggested that the nature of the metal seems more relevant to the behavior of the catalyst than the species involved.