Novel photocatalytic materials for CO2 utilisation

Abstract

The worrying rise in greenhouse gas emissions, in particular of CO2, has led on one hand to the necessity of limiting the consumption of fossil sources on one hand, and on the other to find ways of capturing, storing and utilise this gas. In this perspective, CO2 presents a great potential for the synthesis of the same fuels still deriving from fossil sources and other building block molecules of high value, namely formaldehyde, formic acid, methanol, methane and carbon monoxide. CO2 photoreduction, paired with water-splitting to produce the required protons for the hydrogenation, could represent away of giving value to waste and reintroducing it in the production chain in what could be considered a circular economy. To develop a photocatalytic system allowing both the reactions and being selective for one product, the perovskite BaTiO3 was chosen as a new promising photoactive material, and it was then paired up through impregnation with CuO as a co-catalyst, since the latter had already been proved to have good activity and selectivity towards methane. These materials were then compared with CuO/ZnO and CuO/TiO2, widely investigated in literature for photocatalysis. Materials are characterised through N2 physisorption, DRS, chronoamperometry, SEM-EDX, TEM, XPS, TPD and TGA, to demonstrating their photoactivity and superior potential of impregnated perovskite compared to other materials. Photoactivity is tested both in gas and liquid phase with three different reactors: (a) liquid phase batch reactor under high pressure (University of Milan); (b) batch reactor in gas phase in mild conditions of temperature, irradiance and room pressure (Ca’ Foscari University of Venice); (c) continuous flow gas phase reactor with high irradiance (Heriot-Watt University of Edinburgh). Reaction conditions for CO2 utilisation are optimised by Heriot-Watt University with a Design of Experiment applied to the continuous flow reactor, focusing on the effect of CO2/H2O and irradiance as variables. From the experimental data, it can be proved that CuO/BaTiO3 presents enhanced photoreactivity towards C-based products, leaving many possibilities open for the further optimisation of the material.