Deoxygenation of coal bed methane on LaCoO3 perovskite catalyst: the structure evolution and catalytic performance

Abstract

A series of perovskite-type LaBO₃ (B = Fe, Co, Mn, and Ni) materials have been studied as catalysts for coal bed methane (CBM) deoxygenation. Among them, LaCoO₃ shows the best catalytic performance and stability, O₂ could be completely eliminated by CH₄ to produce CO₂ and H₂O in the range of 400–720 °C, and the complete deoxidization could be maintained at temperatures of 400, 500, 600, and 660 °C for 100 h. Furthermore, the structure of LaCoO₃ could transform from perovskite to Co/La₂O₃ through La₂CoO₄/LaCoO₃ and La₂CoO₄/Co₃O₄ during the process of CBM deoxygenation. The results of H₂-TPR and O₂-TPO showed the perovskite LaCoO₃ is like a smart catalyst, whereby the Co species could reversibly move into and out of the perovskite structure depending on the temperature and reaction atmosphere. When Co species exist in an oxidised state (Co₃O₄, La₂CoO₄ and/or LaCoO₃), the CH₄ in CBM is completely oxidized by O₂ to produce CO₂ and H₂O, the results of isotopic tracer experiments and pulse reaction demonstrate that the reaction follows the Mars–van Krevelen mechanism. However, the preferred products of the CBM deoxygenation reaction are CO and H₂ on Co/La₂O₃ through partial oxidation of CH₄. With the structure transforming from Co/La₂O₃ to LaCoO₃ after reoxidation by O₂, the activity of CBM deoxygenation could be recovered.