Experimental study of Nd₂O₃ doped iron-based oxygen carrier for biomass chemical looping steam gasification process

Oxygen carrier (OC) is vital in the biomass chemical looping process because the OC plays the multiple roles of lattice oxygen supply, heat transfer, and catalyst. In the current study, neodymium oxide doped iron-based oxygen carriers (Nd₂O₃-Fe₂O₃ OC) recycled from the Nd-Fe-B sintered magnet waste scraps and experimentally synthesized with various Nd₂O₃ weight ratios were used in the biomass chemical looping steam gasification (BCLSG) process for syngas production. The properties of the fresh and used Nd₂O₃-Fe₂O₃ OCs were characterized using different methods, including XRD, H₂-TPR, and SEM-EDS. Results showed that the activity of Fe₂O₃ was dramatically enhanced by Nd₂O₃ doping due to the formation of NdFeO₃ perovskite oxide in the Nd₂O₃-Fe₂O₃ OCs. The synergistic effect of Nd₂O₃ and Fe₂O₃ could exhibit more oxygen vacancies and enhance the catalytic activity of the OCs. Syngas yields exceeding 0.90 Nm³/kg, an H₂/CO mole ratio around 1.80 and carbon conversion efficiencies above 71% were reached with the Nd₂O₃-Fe₂O₃ OCs during the BCLSG process at 900°C, OC/B = 2:1, and S/B = 0.4. The generation of NdFeO₃ perovskite oxide mitigated the negative effect caused by the outward diffusion of Fe in the OCs, resulting in a stable performance of the Nd₂O₃-Fe₂O₃ OC during the multi-cycle BCLSG process. The recycled Nd₂O₃-Fe₂O₃ OC may be a better choice than the experimental synthesized one because its manufacturing method is more accessible, and does not require additional Nd₂O₃.