Insights into the role of A/B-site substitution in chemical looping gasification of cotton stalk for enhanced syngas production over La-Co-O based perovskite oxygen carriers

Biomass chemical looping gasification (BCLG) is an emerging technology for efficient and clean utilization of cotton stalk (CS) to produce high-quality syngas. Among various oxygen carriers, perovskite oxides are holding an ever-increasing position in BCLG due to their unique structural properties and compositional flexibilities. However, research on perovskite-type oxygen carriers mostly focused on Fe-based oxides, and there is little in-depth investigation of Co-based perovskite and the role of A/B site substitution in the BCLG process. Herein, the LaCoO₃ perovskite is selected as the basic oxygen carrier, and Sr, Fe are further doped on the A/B-site to form LaCo_1-xFe_xO₃ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) and La_1-ySr_yCoO₃ (y = 0, 0.2, 0.4, 0.6, 0.8) series. Effects of perovskite type, gasification temperature, steam volume fraction and oxygen carrier mass fraction of the BCLG performance are investigated. Results indicate that La_0.6Sr_0.4CoO₃ and LaCo_0.2Fe_0.8O₃ exhibit enhanced syngas production with the maximum of 1.304 m³/kg and 1.188 m³/kg, respectively, and outstanding cyclic stability at optimal reaction conditions. Further characterizations including H₂-TPR, XPS and EPR analysis reveal that Sr substitution facilitate the formation of oxygen vacancies and adsorbed oxygen species, while Fe doping leads to the increasing concentration of oxygen vacancies and surface lattice oxygen species. Combined with the experimental and characterization results, it is deduced that the oxygen vacancies which promote the adsorption of reactants and accelerate the migration of bulk lattice oxygen, play the key role in the enhanced BCLG performance.