Metal-organic frameworks based in zinc and aluminium as heterogeneous catalysts to oleic acid esterification

Abstract

The recurring environmental problems of the use of fossil fuels have encouraged the search for fuels from clean and renewable sources that can minimize the emission of greenhouse gases. In this sense, biodiesel has been highlighted in the market of fuels. The production of industrial biodiesel based on homogeneous alkaline catalysis presents technical requirements that directly impact on its cost of production. Researchers have sought to develop heterogeneous catalysts as an alternative to this process. Metal-Organic Frameworks, MOFs, are a class of promising materials for catalytic processes, as they result from the combination of organic and inorganic materials, which gives them properties such as high porosity, ordered structure and structural flexibility. Thus, the focus of this study was to synthesize and characterize MOFs containing zinc and aluminum oxides, prepared by the hydrothermal method, and immobilize them in the silica network, aiming to increase their thermal and chemical stability. The physicochemical characterization of the materials confirmed the formation of MOFs, indicating that the synthesis method was reproducible and efficient. The catalytic tests indicated that the non-immobilized material MOF-Al/Zn presented higher catalytic activity in the esterification of oleic acid, however it showed leaching of the active species. However, the immobilization of this material on silica resulted in a stable catalyst, being possible to reuse it without significant loss of the catalytic activity. The immobilization of Metal-Organic Frameworks on silica networks has shown to be a promising option for the synthesis of an active and efficient heterogeneous catalyst for esterification reactions of oleic acid.