Solar-driven chemical looping reforming of methane over SrFeO_3-δ-Ca_0.5Mn_0.5O nanocomposite foam

Strontium ferrite (SrFeO_3-δ) is a very attractive oxygen transfer agent for chemical looping reactions and hydrogen-rich syngas generation. Dispersing SrFeO₃ in a medium such as Ca_0.5Mn_0.5O could enhance the activity and cyclability. In this study, SrFeO_3-δ-Ca_0.5Mn_0.5O (30 wt% SrFeO_3-δ) nanocomposite with a reticulated foam structure was explored as the oxygen carrier for chemical looping reforming of methane in a solar tubular reactor. The foam nanocomposite was prepared by a hard-templating method. The performance was investigated at temperatures of 850–1000 °C and methane flowrates of 25–250 STP mL/min, and the oxidative gas was either CO₂ or H₂O in the oxidation step. In the reduction step of 27 successive redox cycles, the production rate of CO changed marginally and CO yield maintained at about 1.9 mmol/g, even though sintering occurred. The productivity of H₂ decreased first and then tended to be stable at 3.8 mmol/g (i.e., twice the CO yield) as the cycling number increased (the average oxygen storage capacity of the material was ∼1.95 mmol/g). Microscopic and X-ray diffraction investigations suggested that the element distribution pattern and crystalline phase of the foam nanocomposite remained almost unchanged after 27 redox cycles, confirming material stability. The maximum solar-to-fuel efficiency for the foam nanocomposite was 5.68%, which was 21.4% higher than that for the powder nanocomposite. To increase syngas productivity and solar-to-fuel efficiency, it is required to conduct the reforming reaction at high temperatures and methane flowrates. However, the energy upgrade factor will decrease as methane flowrate increases.