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

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, Fe 2 O 3 -based oxygen carriers suffer from sintering-induced deactivation and low oxygen-carrying capacity (OCC) during CLC operations. Here, we report the development of a sinteringresistant MgO-doped Fe 2 O 3 oxygen carrier with an optimal composition of 5MgO•MgFe 2 O 4 , which exhibits superior cyclic stability and an OCC of 0.45 mol O/mol Fe (2.25 mmol O/g solid ), exceeding the widely accepted OCC limit of 0.167 mol O/mol Fe (2.08 mmol O/g solid ) of unmodified commercial Fe 2 O 3 . 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 Mg x Fe 1−x O (halite) and Mg 1−y Fe 2+y O 4 (spinel) solid solutions, which effectively reduce the exergonicity for the reduction from Fe 3+ to Fe 2+ , 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.

Dicalcium ferrite: A chemical heat pump in integrated carbon capture and chemical looping combustion for the steel industry

“…Inert supports do not form mixed phases, and therefore the iron oxide has the same phase transitions as pure iron oxide, for example, ZrO2 [40] and MgAl2O4 [41]. Some support materials form mixed oxides or solid solution phases with the iron oxides and alter the equilibrium of the phase transitions, e.g., TiO2 [42], Al2O3 [43], MgO [44,45], and CaO [24,25]. The mixed oxides of calcium and iron have previously been suggested as looping materials [24,25,36,37,[46][47][48].…”

Subsurface A-site vacancy activates lattice oxygen in perovskite ferrites for methane anaerobic oxidation to syngas

“…Tuning the oxygen activity in metal oxides offers opportunities to manufacture prospective catalysts for reactions proceeding via the Mars−van Krevelen mechanism 1 – 3 . However, it was usually found that the oxides with high oxidizing capability display low selectivity, and vice versa, which poses huge obstacle for designing an efficient redox catalyst 4 , 5 . The perovskite oxides (structural formula: ABO 3 ) has attracted particular attention in redox cycling reactions due to their capacity to accommodate different cations in single perovskite matrix 6 – 8 .…”

Asymmetric coordination activated lattice oxygen in perovskite ferrites for selective anaerobic oxidation of methane

“…23 For example, simple iron oxides (e.g., Fe 2 O 3 and Fe 3 O 4 ) are reactive towards methane conversion, but total combustion is preferred over these OCs due to high oxygen mobility. [24][25][26][27][28] Comparably, when conning iron cations into a perovskite matrix (structural formula: ABO 3 ), a syngas selectivity of more than 90% can be obtained at the expense of reactivity, which was attributed to the lowered oxygen activity with high oxygen vacancy formation energy (e.g., 4.54 eV for LaFeO 3 ). 29 To this end, extensive effort has been made with the aim of breaking such scaling relations.…”