Síntesis innovadora de materiales híbridos y su impacto en la valorización de CO2

Abstract

On September 25, 2015, the United Nations adopted 17 global goals to ensure future prosperity and global well-being. Among these goals, number 13 "Climate Action" stands out, in which said organization strongly calls for the decrease and reduction of CO2 emissions as the main greenhouse gas. This is the framework for this doctoral thesis, through which a series of hybrid materials have been developed that have been used as catalysts in a reaction to trap CO2 and valorize it. Metal-Organic Frameworks (MOF) are characterized by their exceptional porosity, which arises from the combination of organic and inorganic components within a crystalline structure. These hybrid materials possess well-defined and highly accessible pores, making them attractive for a wide range of applications. This characteristic, as well as their high thermal and moderate chemical stability, make them potential candidates for use as catalysts. However, not all MOFs exhibit such good properties or show good electrical conductivity or sufficient handling properties to be used as catalysts. For this reason, in this PhD thesis we have developed new ways of MOF synthesis from metal substrates that open new opportunities to create MOFs in an efficient and viable way for the industry. In addition, an innovative procedure of defect induction in MOFs post-synthesis has also been carried out with the aim of improving their catalytic properties. The materials we have prepared in this thesis have been tested as catalysts in the cycloaddition of CO2 with epichlorohydrin. This is a reaction that does not involve the reduction of the carbon atom in CO2, but a fixation of the CO2 by the epoxide, which implies a much lower energy input. In this PhD thesis it has been observed that the induction of defects in the MOF structure brings about an improvement in the catalytic activity in the reaction. In addition, it has also been studied that a different morphology of the MOF crystals and a different distribution of planes present on the external surface of the MOF also significantly affect the stability of the crystal. Finally, it should be noted that, despite what is reported in the literature, ZIF-67, one of the most commonly used MOFs as a catalyst in the cycloaddition of CO2 with epichlorohydrin, is not stable in the reaction. It was observed that the stability of such MOF is influenced by the amount of exposed {100} planes, which are unstable in the reaction conditions and are the cause of the leaching of cobalt and organic species that truly catalyzes the reaction.