First Principles Simulations of Surface Modified TiO2 for CO2 Activation

Abstract

Replacing liquid fossil fuels with renewable fuels produce from water and CO2 is a key challenge for the 21st century. This is linked with both the increase in world energy demand and the climate emergency. Two potential technologies than will alleviate these issues are replacing liquid fuels with hydrogen for transport and capturing & converting CO2 produced in industrial process to useful chemicals with the former integrated with CO2 capture to drive conversion to e.g. methanol or C2 compunds. If these process are further driven by solar energy or other renewable energy, then the processes will be fully renewable.In this presentation we describe our work on density functional theory simulations of modifications to TiO2 rutile and anatase surfaces by nanoclusters of metal oxides and explore the possibility for these heterostructures to promote CO2 activation and reduction. We show that modifying TiO2 with metal oxides produces stable heterostructures with potential band gap reduction towards the visible region of the electromagnetic spectrum, while these structures also promote charge localisation and oxygen vacancy formation. #for CO2 conversion we identify oxide modifiers to TiO2, namely CuOx, Bi2O3, CeO2 and Cr2O3 that can activate or even directly dissociate CO2 to CO. Low loadings of Cu appear to be most favourable for CO2 activation by promoting reduction of the TiO2 substrate; the electrons released by reduction are transferred to CO2 to give a carboxyl species which is an important intermediate in hydrogenation of CO2. Bi2O3 species are able to adsorb and activate CO2, producing a range of adsorbed species, but upon reduction can promote electron transfer to form a carboxyl or break a C-O bond and produce CO. Key aspects appear to be the presence of active sites as a result of oxide reduction, the presence of reduced cations and the electronic structure of the modifiers. Comparison with experimental results will also be presented.