Ca2Fe2O5: A promising oxygen carrier for CO/CH4 conversion and almost-pure H2 production with inherent CO2 capture over a two-step chemical looping hydrogen generation process

Chemical looping hydrogen generation (CLHG) is a promising technology for high-purity hydrogen production with inherent CO2 separation. The selection of a high-performance oxygen carrier capable of being reduced and oxidized over multiple redox cycles against deactivation is a key issue for CLHG technology. In this work, a two-step chemical looping hydrogen generation (TCLHG) process is proposed by using a novel calcium ferrite, Ca2Fe2O5, as an oxygen carrier which is synthesized with applied a citric acid assisted sol gel method. The experimental results indicate that the reduced oxygen carrier achieves one-step oxidation from Fe to Fe3+ by using steam as an oxidizing agent. Thus, higher yields of hydrogen could be generated compared with Fe2O3. The fresh and reacted Ca-Fe based oxygen carriers were characterized using different methods such as XRD, SEM/EDS, TEM, N-2 adsorption, H-2-TPR, XPS, and Mossbauer spectroscopy test etc. The oxygen release and storage capacity, cyclic stability, and carbon deposition characteristics of the Ca-Fe based oxygen carriers were investigated using TGA and a fixed bed reactor with multicycles of CO/CH4 reduction and H2O/O-2 oxidation. Ca2Fe2O5 is proved to be a more stable formation of the calcium ferrite compounds and a promising oxygen carrier for TCLHG process which shows perfect reducibility, oxidation activity, and cyclic stability. The existence of Ca appears to perform a significant effect on the Fe3+ reduction and Fe oxidation and the reduction from Fe3+ to Fe was concluded to be a simple one-step reaction.