Chemical looping reforming with water splitting (CLRWS) for syngas and hydrogen coproduction using the ternary metal-oxides (Ca-Fe-Cu–O) as oxygen carriers

Abstract

In this work, chemical looping reforming with water splitting (CLRWS) using ternary metal oxides (Ca-Fe-Cu–O) as oxygen carrier (OC) was investigated for syngas and hydrogen coproduction. The introduction of Cu into the Ca-Fe-O system results in the formation of the main crystalline phases, which include Ca2Fe2O5, CuFe2O4, and a small amount of CaO. The presence of Cu enhances the oxygen transfer capacity (OTC) and reduces the reduction temperature of Ca-Fe-O oxides. When the ratio of Ca:Cu:Fe equals 0.5:0.5:2, the Ca0.5Cu0.5Fe2O4 exhibited the highest hydrogen yield and purity of 9.15 mmol/(g OC) and 96.80 %, respectively. The syngas yield, purity and fuel conversion were 66.48 mol/L, 74.76 % and 83.12 %, respectively. It can be attributed to the suitable ratio of brownmillerite Ca2Fe2O5 and the spinel CuFe2O4 in Ca0.5Cu0.5Fe2O4. The crystal phases of Ca2Fe2O5 and CuFe2O4 exhibit a synergistic effect in the Ca-Fe-Cu–O system, the formation of CuFe2O4 enhances the lattice oxygen activity, while the brownmillerite-structured Ca2Fe2O5 inhibits the sintering and agglomeration of CuFe2O4 due to the morphology effect. The Ca0.5Cu0.5Fe2O4 showed almost stable reactivity after 10 cycles.