Performance optimization of Ca2Fe2O5 oxygen carrier by doping different metals for coproduction syngas and hydrogen with chemical looping gasification and water splitting

Abstract

This work focused on the potential effects of different metals (Co/Al/Ni/Ce) on the chemical looping performance of brownmillerite-structured Ca2Fe2O5 for syngas and hydrogen production. Oxygen carriers (OC) were prepared by the sol-gel method. The presence of NiO and CeO2 phases in fresh Ca2Fe2O5 samples indicated that Ni and Ce were not fully doped into the brownmillerite structure. The oxides of Al and Co were not detected in the fresh Ca2Fe2O5 sample, indicating that the Al and Co were doped into the brownmillerite structure. The introduction of Ni and Co decreased the reduction temperature and increased the reduction rate of OC. However, the increase in reactivity with Ni-modified OC is mainly due to the high reactivity of the NiO phase. The presence of Al and Ce inhibited the reduction of Ca2Fe2O5 and decreased the oxygen transport capacity, which is beneficial for syngas production but leads to a lower H2 production in the steam reactor (SR). The Co-modified Ca2Fe2O5 exhibited better resistance to carbon deposition and increased the H2 production in SR. When the ratio of Ca:Fe:Co equals 2:1.5:0.5, the formation of Ca2Co0.5Fe1.5O5 exhibited the highest hydrogen yield and purity of 10.92 mmol/g OC and 99.32%, respectively. In addition, the Ca2Co0.5Fe1.5O5 showed almost stable reactivity over the 5 reaction cycles.