Breaking the Stoichiometric Limit in Oxygen-Carrying Capacity of Fe-Based Oxygen Carriers for Chemical Looping Combustion using the Mg-Fe-O Solid Solution System
Qianwenhao Fan, Chuande Huang, Shibo Xi, Yong Yan, Jijiang Huang, Syed Saqline, Longgang Tao, Yihu Dai, Armando Borgna, Xiaodong Wang, Wen Liu
Abstract
The performance of oxygen carriers contributes significantly to the efficiency of chemical looping combustion (CLC), an emerging carbon capture technology. Despite their low cost, Fe2O3-based oxygen carriers suffer from sintering-induced deactivation and low oxygen-carrying capacity (OCC) during CLC operations. Here, we report the development of a sintering-resistant MgO-doped Fe2O3 oxygen carrier with an optimal composition of 5MgO·MgFe2O4, which exhibits superior cyclic stability and an OCC of 0.45 mol O/mol Fe (2.25 mmol O/gsolid), exceeding the widely accepted OCC limit of 0.167 mol O/mol Fe (2.08 mmol O/gsolid) of unmodified commercial Fe2O3. This result distinguishes this report from all past studies, in which efforts to enhance the cyclic stability of Fe-based oxygen carriers would always result in dilution of the OCC. The capacity enhancement by MgO is attributed to the unique mixtures of MgxFe1–xO (halite) and Mg1–yFe2+yO4 (spinel) solid solutions, which effectively reduce the exergonicity for the reduction from Fe3+ to Fe2+, while preventing any irreversible structural transformations during the redox process. This hypothesis-driven oxygen carrier design approach provides a new avenue for tailoring the lattice oxygen activities of oxygen carriers for chemical looping applications.