Chemical looping reforming of CH₄ in the presence of CO₂ using ilmenite ore and NiO-modified ilmenite ore oxygen carriers

In this paper, a naturally occurring ilmenite ore and the same ore modified with NiO were employed as oxygen carriers for chemical looping reforming of CH4 for syngas production. The reactivity of the oxygen carriers and the syngas selectivity with CH4-based feedstocks were quantitatively examined in a fixed-bed reactor in the presence of CO2. The results showed that calcined ilmenite ore partially oxidizes CH4 to syngas and the reactivity of the calcined ilmenite can be greatly improved by a redox activation treatment. With the reaction of CH4 and calcined ilmenite, there is an initial period in which CH4 is fully oxidized via the reduction of Fe3+ to Fe2+ containing species; while subsequently, CH4 is partially oxidized leading to the reduction of Fe2+ to Fe-0 containing species. However, the presence of CO2 in the feedstock stops any iron-containing species reduction beyond Fe2+, which is a critical reaction for syngas production. In order to permit syngas production in the presence of CO2, a NiO-modified ilmenite ore oxygen carrier was developed and evaluated, largely eliminating the negative effect of CO2. Consequently, syngas was successfully produced through partial CH4 oxidation in the presence of CO2. We have attributed this phenomenon to the catalytic effect of the metallic Ni or FeNi alloys generated during oxygen carrier reduction by CH4, which converted CO2 and CH4 into CO and H-2 via dry reforming. Additionally, the incorporation of NiO within ilmenite ore significantly improved the reactivity of the ilmenite-based oxygen carrier. We believe that this dual-function catalyst-modified oxygen carrier will enable CH4-based syngas generation through both chemical looping reforming and dry-reforming processes simultaneously, ultimately allowing for syngas production in combination with CO2 utilization.