FeO₆ Octahedral Distortion Activates Lattice Oxygen in Perovskite Ferrite for Methane Partial Oxidation Coupled with CO₂ Splitting

Abstract

Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C–H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO6 octahedra in La1–x Ce x FeO3 (x = 0, 0.25 0.5, 0.75, 1) orthorhombic perovskites for the promotion of lattice oxygen activation. By combined electrical conductivity relaxation measurements and density functional theory calculations studies, this paper describes the enhancement of FeO6 octahedral distortion in La1–x Ce x FeO3 promoting their bulk oxygen mobility and surface oxygen exchange capability. Consequently, La0.5Ce0.5FeO3 with the highest FeO6 distortion achieves exceptional syngas productivity of ∼3 and 8 times higher than LaFeO3 and CeFeO3, respectively, in CH4 partial oxidation step with simultaneous high CO2 conversion (92%) in the CO2-splitting step at 850 °C. The results exemplify the feasibility to tailor the active lattice oxygen of perovskite by modulating the distortion of BO6 in ABO3, which ultimately influences their reaction performance in chemical looping processes.

Aerobic oxidative CC bond cleavage of aromatic alkenes by a high valency iron-containing perovskite catalyst

“…7,8 Moreover, perovskite oxides and related materials have received significant attention as substitutes for noble metal catalysts because of their unique stability, compositional and structural varieties, and controllable physicochemical properties. 9,10 However, catalysis over multicomponent perovskites with cornersharing BO 6 octahedra has mainly been investigated for gasphase reactions (CO/CH 4 /NO oxidation), 10,11 and reports on liquid-phase organic reactions are limited. Therefore, we have focused on the liquid-phase catalysis of hexagonal perovskites with unique face-sharing octahedral units based on high valency metal species.…”

Recent Advances of Oxygen Carriers for Chemical Looping Reforming of Methane

“…Zhang et al. fine‐tuned the local structure of lattice oxygen in La 1‐x Ce x FeO 3 via the substitution of trivalent Ce 3+ ions for La 3+ in order to eliminate the effect of crystal structure type of perovskite on reactive performance [48a] . It was found that the distortion degree of FeO 6 octahedra in La 1‐x Ce x FeO 3 (x=0, 0.25 0.5, 0.75, 1) orthorhombic perovskites could be tuned by altering the Fe−O bond‐length variance and La 0.5 Ce 0.5 FeO 3 with the maximum distortion of FeO 6 octahedra (Figure 10(a)) possessed the lowest oxygen vacancy formation energy (ΔE f,vac ) (Figure 10(b)), oxygen migration barrier (E m ) (Figure 10(c)) and improved CH 4 activation ability as well as surface reactivity of lattice oxygen, which accounted for its best CH 4 conversion, syngas selectivity and yield, and redox stability (Figure 10(d–f)).…”

“… (a) FeO 6 octahedra distortion calculated by the equation (, where R av is the average bond length, and R i is the individual bond length of Fe−O in FeO 6 octahedra); (b) Calculated (DFT+U) oxygen vacancy formation energy (ΔE f,vac ); (c) Calculated (DFT+U) oxygen migration energy (E m ); (d) The redox performance of La 1‐x Ce x FeO 3 (x=0, 0.25 0.5, 0.75, 1) redox catalysts in the CH 4 partial oxidation step; (e) Durability test of La 0.5 Ce 0.5 FeO 3 for 40 continuous redox cycles at 850 °C; (f) Proposed reaction mechanism over La 1‐x Ce x FeO 3 (x=0, 0.5, 1) redox catalysts [48a] . Reproduced with permission from Ref.…”

Intensification of Chemical Looping Processes by Catalyst Assistance and Combination

“…It is still a challenge to control selectivity in partial oxidation of methane by lattice oxygen of metal oxides. Zvang et al present the finding that distortion of FeO6 octahedra in La1-xCexFeO3 perovskites positively affects the surface oxygen exchange capability and mobility of bulk oxygen [73]. The distortion of the FeO6 octahedra can be promoted due to the difference between Ce-O and La-O bond lengths.…”