Novel polymers of intrinsic microporosity for heterogeneous base-catalysed reactions (HBC-PIMs)

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Catalysts play a crucial role in chemistry, as they increase the rate of reaction by lowering the activation energy, allowing the formation of compounds that otherwise will not form promptly. Typical examples are the production of ammonia, which is a process that needs to be catalysed by iron, or the production of biofuels. The improvements of catalytic processes not only help chemists and engineers to increase the efficiency of reactions, but also to reduce waste products, generating a massive environmental impact. This is especially true if we can design and synthesise new catalysts that produce alternative fuels in a more efficient way. This will be beneficial from both the economic and the social point of view, as we can reduce the cost of sustainable fuels and, at the same time, the exploitation of natural resources such as fossil fuel. The two most common catalysed reactions are known as homogeneous, where the catalyst can be dissolved in the media, and heterogeneous, where it is insoluble. Homogeneous catalysts are sometimes more active but their separation and reutilisation requires more energy and effort, whereas the heterogeneous ones are easily removed and recycled from the reaction by simple filtration. They can be further classified as acid, neutral or basic (alkaline), according to the nature of their active sites (i.e. where the catalytic reaction happens). Although alkaline catalysed reactions have been less investigated than their acidic counterparts, in recent years they have become more attractive as they are suited for the efficient production of biodiesel, as a sustainable and renewable source of fuel. This research project will focus on the design and synthesis of novel basic heterogeneous catalysts based on Polymers of Intrinsic Microporosity (PIMs). PIMs are materials with porosity arising from the inefficient packing of their polymeric structure in the solid state, which leaves voids of nano-dimensions. They can be used for a wide range of applications, including gas separation, gas storage and catalysis. Porosity represents a great advantage for a heterogeneous catalyst, as it forces the reaction to occur in a close environment, such as the surface of a pore, forcing the components of the reaction to be in much closer contact. Because of this advantage, PIMs have been previously used in heterogeneous catalysis but only by incorporating in the material active metal ions, which is not ideal as the presence of the metal makes them more expensive and less environmentally friendly. Recently, I introduced and patented a new class of PIMs based on a core known as Tröger's base (TB). They combine the high porosity of PIMs with the presence of two basic (alkaline) nitrogens. Attempts have been made to use TB cores by grafting them into pre-made polymeric materials, but this procedure leads to loss of catalytic material (known as leaching) during its recycling from the reaction media. I recently reported the synthesis of a network (insoluble) PIM exclusively made exclusively via TB formation, which showed great potential for heterogeneous catalysis, especially because the active site (TB) is an integral part of the material, and not simply grafted onto it. The project aims to the synthesis of new TB-PIMs to be used to catalyse biomass conversion (i.e., from waste biomass to make sustainable fuels) along with other environmentally and commercially important reactions. The improved production of biodiesel is not the only significant reaction where these novel polymers can be employed. The polymers will also be tested for the conversion of by-product created during the biodiesel synthesis into more reactive compounds, and for the conversion of CO2 into more useful products. Last but not the least, the polymers can be further turned into new materials for more efficient anion-exchange resins, a class of materials that can be used for purification of water and removal toxic metal from liquid waste.