Impact of A-Site Sr Substitution in LaFeO₃ on Syngas Selectivity During Chemical Looping Dry Reforming of Methane...

La_1-xSr_xFeO₃ (0 ≤ x ≤ 1) perovskite oxygen carriers (OCs) were evaluated for dry reforming of methane (DRM) at 900°C under co-feed and chemical-looping (CL-DRM) configurations. Sr substitution decreased CH₄/CO₂ conversions in co-feed DRM, indicating suppressed intrinsic catalytic activity. In contrast, CL-DRM enhanced CH₄ conversion by LaFeO₃ to ∼75%-79% but promoted carbon deposition and a deviation of the H₂/CO ratio from 2 (2.6). Sr-containing compositions exhibited lower CH₄ conversion but improved carbon balance and syngas selectivity. La_0.7Sr_0.3FeO₃ provided the best compromise, achieving ∼40% CH₄ conversion, an ideal H₂/CO ratio of 2, and a carbon balance above 95%. Sr²⁺ substitution induces Fe⁴⁺/Fe³⁺ charge compensation and modifies the oxygen-defect environment. The improved coke resistance is primarily associated with the suppression of nonselective CH₄ cracking rather than with enhanced oxygen mobility. These findings establish that selective and stable syngas production in CL-DRM is governed not by maximizing oxygen reactivity, but by precisely balancing oxygen exchange kinetics with methane activation.