Application of Ni–Spinel in the Chemical-Looping Conversion of CO₂ to CO via Induction-Generated Oxygen Vacancies

We demonstrate the technical feasibility of a novel and efficient method for the valorization of CO 2 produced by the reverse water gas shift reaction (rWGS), while using an extruded NiFe 2 O 4 as catalyst and self-controlled heating medium induced by magnetic heating. First, oxygen vacancies (δ) were generated by flowing an Ar/H 2 mixture over the catalyst for 1 h at ca. 400 °C. Then, an Ar/CO 2 mixture was flowed over the activated catalyst (NiFe 2 O 4-δ ) in similar conditions, leading to CO generation and oxygen restocking. We study the impact of heating method (conventional or induction), gas feeding, and number of cycles on the catalyst performance. We show that the catalyst retains activity during multiple cycles (1.37 ± 0.07 μmol/g of NiFe 2 O 4 ) but slowly reduces upon H 2 exposure. Extensive catalyst characterization suggests that (Ni,Fe) clusters forming on the surface of the Ni–ferrite nanoparticle result from the segregation of metal atoms recruited from octahedral sites of the Ni–ferrite. Such change in the chemistry and structure of the catalyst has a profound impact on the activity of the catalyst and the total CO production. Induction heating excelled in thermally activating the catalyst in a short time; however, it suffers from an uneven distribution of the temperature along the bed, which led to the reduction of overheated zones of the catalyst bed. Finally, simultaneous feeding of H 2 and CO 2 allowed a higher production of CO when compared to chemical looping, up to 7.74 ± 0.67 μmol/g of NiFe 2 O 4 in a 1-h experiment.