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 CO2 produced by the reverse water gas shift reaction (rWGS), while using an extruded NiFe2O4 as catalyst and self-controlled heating medium induced by magnetic heating. First, oxygen vacancies (delta) were generated by flowing an Ar/H-2 mixture over the catalyst for 1 h at ca. 400 degrees C. Then, an Ar/CO2 mixture was flowed over the activated catalyst (NiFe2O4-delta) 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 mu mol/g of NiFe2O4) 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 CO2 allowed a higher production of CO when compared to chemical looping, up to 7.74 +/- 0.67 mu mol/g of NiFe2O4 in a 1-h experiment.

Automated summary

In this study, a novel method using extruded NiFe2O4 catalyst and magnetic heating for CO2 valorization was demonstrated. The impact of heating method, gas feeding, and cycles on catalyst performance was investigated. Induction heating was found to efficiently activate the catalyst in a short time, but suffered from uneven temperature distribution.