Understanding of the oxygen uncoupling characteristics of Cu–Fe composite oxygen carriers for chemical-looping gasification

A Cu–Fe oxygen carrier (OC) with oxygen uncoupling capability is proposed to be applied in chemical-looping gasification with oxygen uncoupling (CLGOU) technology to increase the gasification rate. Density functional theory analysis shows that a chemical reaction occurs after Cu₄O₄ cluster adsorption onto α - Fe₂O₃ (001) surface. Extension of bond length and transfer of charge indicate the composite oxide has been activated. An optimal molar ratio of 2:1 of CuO to Fe₂O₃ is determined for the preparation the OC and the oxygen transport capacity is determined at 3.65 wt% with a starting oxygen uncoupling temperature is 749.5 °C. The composite OC exhibits good low-temperature oxygen uncoupling characteristics. This OC exhibits stable behaviour and satisfactory oxygen recyclability over 15 consecutive redox cycles at 900 °C / 700 °C oxygen uncoupling and absorbing temperatures. The high stability is corresponding to the calculation result (high adsorption energy of CuO onto Fe₂O₃). And oxygen uncoupling rates are much higher than the lower limit (0.4 wt%/min) for cracking. The chemical phases and surface micromorphology all retain stable after cycles. Using combined Coats-Redfern and Malek method, the oxygen uncoupling kinetic model of Cu–Fe OC is determined as a shrinking core model (m = 3).