Porous Liquids for Catalysis

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Porous liquids (PLs) are an exciting new class of counterintuitive porous materials that combine the properties of a microporous solid with the mobility of a liquid. Like their solid counterparts, these liquids with holes have the capability to demonstrate gas uptake and release, and guest selectivity. However, unlike solid porous materials, they could also potentially have unique applications, such as the ability to be pumped around a continuous system facilitating guest loading/unloading steps, or being used as a gas-loaded reaction solvent. Despite this potential, the application of PLs in areas other than gas uptake and selectivity has not been investigated. Recently, we reported the formation of high cavity concentration PLs using porous organic cages (POCs) - discrete molecules containing permanent molecular cavities accessible through windows - and demonstrated their ability to exhibit increased uptake of a range of gases (e.g., CO2, CH4, Xe, SF6) over neat liquids (Nature, 2015, 527, 216; Chem. Sci., 2017, 8, 2640, ChemRxiv, 2021, DOI:10.26434/chemrxiv.14719503.v2). In addition, there have been reports of the use of solutions of cages for catalytic CO2 conversion into cyclic carbonates (Sustainable Energy Fuels, 2019, 3, 2567), and as nanoreactors (Chem. Soc. Rev., 2008, 37, 247). These systems differ from PLs, which are defined as having permanently empty pores that are accessible to guests, due to either guests being in competition with the solvent which occupies the cavities or guest binding being driven by a hydrophobic effect. In this project, we will build on these initial reports and explore different ways of applying PLs in the area of catalysis. This includes the use of gas-loaded PLs as a reusable and controllable external gas source in stoichiometric gas reactions, and as a solvent to carry out lower pressure gas reactions by 'simulating' high gas concentrations that are normally only achieved at higher pressures, and as nanoreactors to catalyse small molecule reactions by confinement. Once we have a thorough understanding of these different methodologies, we will then seek to translate this into a high-throughput workflow with the aim of being able to use PLs to rapidly screen a range of catalytic reactions involving the incorporation of a gas as a reagent.