Hybrid Layered Double Hydroxides for CO2 Conversion to Useful Chemicals

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Carbon dioxide (CO2) levels in the atmosphere have risen to over 400 ppm, as a result of human activities including the extraction and burning of fossil fuels for energy, and in the manufacture of a range of products in everyday life. In order to transition to net zero and keep temperature rises below the 1.5oC target of the Paris Agreement, two approaches are proposed - reduction in emissions through renewable sources of energy, and removal of CO2 from the atmosphere. Upon removal from the atmosphere, CO2 can be stored or used as a feedstock in chemical synthesis, for example for polymers or methanol.The concept of the methanol economy was proposed by George A. Olah in the 1990s. Methanol is the simplest alcohol, composed of only one carbon atom, and can be used as a clean fuel, emitting only CO2 and water, and much smaller amounts of other toxic gases or soot compared to the combustion of fossil fuels. Methanol is currently produced from syngas, generated by reforming natural gas, over a metal catalyst at relatively high temperatures and pressures. However, alternative, more sustainable methods are currently being pursued. If methanol can be synthesised from captured CO2 and renewable hydrogen, this whole process becomes carbon neutral. In addition, methanol is a useful feedstock to the chemical industry to produce a range of more complex molecules, and is also used as a solvent. This is reflected in the global production of methanol, which reached 85 million tonnes in 2018, enough to fill an Olympic swimming pool every twelve minutes.Layered double hydroxides (LDHs) are a class of ionic solid with a structure based on that of the naturally occurring mineral hydrotalcite. They are made of positively charged layers, which allows a range of negatively charged ions to be inserted in the interlayer space. The ability to vary the elements in the layered structure and the chemicals that can be inserted between means their properties can be tailored by researchers towards specific applications. These can range from adsorption to plastic additives to vehicles for drug delivery.LDHs are also able to be used as catalysts, materials which speed up a chemical reaction, or enable it to occur in the first place. Recently, LDHs have been used to catalyse the addition of hydrogen gas to carbon dioxide, producing methanol, however with low overall yield. This project aims to synthesise more LDH materials incorporating different metals, which will be tested for the catalytic hydrogenation of carbon dioxide to produce methanol. Compared to previous work in this area, these will aim to have improved CO2 conversion and selectivity, and therefore increased overall methanol yield.This project falls within the EPSRC manufacturing the future and physical sciences themes.