Iron-Poor Ferrites for Low-Temperature CO₂ Conversion via Reverse Water–Gas Shift Thermochemical Looping

CO2 utilization via the reverse water-gas-shift (RWGS) reaction for the production of CO and then long-chain hydrocarbons is a potentially scalable method to mitigate rising global CO2 emissions, if appreciable CO yields can be achieved at low reaction temperatures. Here, we report that Fe0.35Ni0.65Ox achieves, to the best of our knowledge, a record high experimentally measured CO yield of 80 mL CO/g(MOx)/cycle at low reaction temperatures (500 ? for both oxidation and reduction steps) in a chemical looping (CL) process. This reported yield is substantially higher than previously reported RWGS-CL metal oxides at 500 ?. We identified the composition of the metal oxide Fe0.35Ni0.65Ox using the Calculation of Phase Diagrams (CALPHAD) methodology to screen and filter through many combinations of metal oxides. We then experimentally tested this Fe0.35Ni0.65Ox metal oxide for chemical looping RWGS and utilized X-ray characterization techniques and CALPHAD to find that a spinel to metallic phase transition gives Fe0.35Ni0.65Ox its noteworthy CO yield and oxygen capacity. We emphasize the importance of thermodynamics calculations and CALPHAD screening to quickly search through the vast design space of metal oxides to greatly reduce the amount of necessary experimentation.