Pr doped CeO2 for chemical looping air separation at ultra-low temperatures

Abstract

Chemical looping air separation (CLAS) represents a promising approach to use thermal energy for high-purity oxygen production. CeO2 represents a class of material that uncouples oxygen using thermal energy, but the required temperature is usually very high (>1400 °C). This limits the potential use for CeO2-based materials in CLAS. This study reports a Pr doped CeO2 oxygen sorbents for chemical looping air separation at ultra-low temperatures. The as-formed Ce1-xPrxO2 solid solution can uncouple oxygen effectively, achieving a redox oxygen capacity of 0.88 wt% at isothermal condition as low as 500 °C. The redox oxygen capacity can be further enhanced to 1.63 wt% in temperature-swing cycles between 400 °C and 900 °C. Moreover, oxygen partial pressure-swing cycles show that the Ce1-xPrxO2 solid solution maintains 95% of its redox oxygen capacity at oxygen partial pressure as low as 0.02 atm, indicating its potential applications in oxygen separation from diluted air. DFT calculations and other physio-chemical characterizations indicate that Pr doping can effectively reduce the oxygen vacancy formation energy, and gaseous oxygen is uncoupled when Pr4+ and Ce4+ are reduced in the Ce1-xPrxO2 solid solution. Overall, this study highlights the novel performance of CeO2 with Pr doping and could offer insights into CeO2 modification strategies for thermal chemical applications.