(684e) Perovskite Oxides for Low Temperature Carbon Dioxide Conversion Towards Hydrocarbon Generation

Carbon dioxide is the primary cause towards global warming and climate change. Carbon dioxide reduction thus, demands acute attention. Though carbon capture and sequestration (CCS) routes for CO₂ reduction attracted sufficient investment in the recent years, its scale of operation (about 35 Mtpa, in early 2017) is far below the CO₂ emissions (about 35 Gtpa, in 2015). Thus, it is imperative to spend efforts on repurposing CO₂ for hydrocarbon generation. Amongst the different routes of CO₂ conversion, solar energy based options like solar photocatalytic or solar thermochemical cycles (STC) garnered a lot of interest. Photocatalysis can be a low temperature process, however extreme low rates of conversion makes it unsuitable for industrial application. STC can achieve superior rates of CO₂ conversion, but at the cost of high temperatures of operation (more than 1000 °C). Reverse water gas shift – chemical looping (RWGS-CL) presents the benefits of these processes without facing their limitations. It can operate at low temperatures of about 500 °C with even better CO₂ conversion rates.

Mixed metal oxides like perovskite oxides (ABO₃) are the main vehicles of conversion of CO₂ to CO via RWGS-CL process. RWGS-CL is essentially a two-step process in which the perovskite oxide is first reduced under hydrogen to its oxygen deficient form (ABO_3-δ). In the second step, CO₂ is converted over these oxygen vacant materials while the materials regain their stoichiometric forms. Since oxygen vacancy formation is the most crucial factor that drives this process, DFT‑calculated oxygen vacancy formation energy (E_vac) presents an appropriate descriptor for the process. This E_vac is largely dependent on the material composition and perovskite oxides are capable of accommodating different elements in their crystal structure. Hence, perovskite oxides present the perfect platform for tuning the oxygen vacancy formation characteristics of a material. We hence, undertook a screening process to predict different perovskite oxide with CO₂ conversion capabilities. Based on our DFT calculation we predicted several earth abundant materials which can prove worthy of our purpose. CO₂ conversion capability of these predicted materials was tested via temperature programmed experiments. Lanthanum and calcium based materials revealed unprecedented CO formation yields and rates. Detailed investigation of the effect of composition tuning of lanthanum and calcium based materials has been done to optimize the CO₂ conversion performance of these materials.