High selectivity syngas generation by double perovskite oxygen carriers La2Fe2-xCoxO6 for chemical looping steam methane reforming

The generation of high-quality syngas combined with high-purity hydrogen is an essential challenge in the chemical looping steam methane reforming (CL-SMR) process, in which the design of oxygen carriers (OCs) is crucial. In this study, La₂FeBO₆ (BCr, Ni，Co) and La₂Fe_2-xCo_xO₆ (x = 0.2, 0.4, 0.6, 0.8, 1.0) double perovskites have been investigated as OCs in the CL-SMR process. Various analytical techniques (BET, XPS, XRD, H₂-TPR, Raman.) have been deployed to characterize the OCs' specific surface area, crystal structure, and surface oxygen species. The fixed-bed experiments revealed that the Cr-modified perovskite had the lowest reactivity, which was attributed to the creation of LaCrO₃ limiting the oxygen release rate of the OC. Meanwhile, Ni doping exhibited the maximum methane conversion (99.15 %), but it resulted in more carbon deposition due to methane cracking, and its carbon deposition was four times than that of Co doping. Whereas, the Co doped double perovskite OCs showed excellent overall performance, in which La₂Fe_1.8Co_0.2O₆ (L₂F_1.8Co_0.2) exhibited the optimum CO selectivity (90.72 %), H₂ selectivity (96.91 %), and H₂ purity (96.84 %), as well as the lowest carbon deposition. Moreover, the L₂F_1.8Co_0.2 also exhibited outstanding stability in 10 cycles, and it could be a prospective material for CL-SMR, enabling the simultaneous generation of high-quality syngas and high-purity hydrogen.