Synergistic improvements in stability and performance of the double perovskite-type oxides La2−xSrxFeCoO6 for chemical looping steam methane reforming

Abstract

Chemical looping steam methane reforming (CL-SMR) is a potential route to efficiently co-produce syngas and hydrogen. Development of oxygen carrier with high activity, good recyclability, strong resistance to carbon deposition and excellence capacity for steam splitting is highly desired for this process. The article investigated a novel and unique structure of double perovskite-type oxides La1−xSrxFeCoO6 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) as oxygen carrier. XRD, XPS and H2-TPR technologies were adopted to characterize the physical and chemical properties of them. Meanwhile, isothermal reactions and cyclic redox reactions were carried out in a fixed-bed reactor to determine the influences of Sr-substitution on the reactivity of La1−xSrxFeCoO6. XRD results confirmed the formation of double perovskite crystal structure for all the samples, while substitution of Sr induced a certain degree of Fe/Co disorder generating oxygen vacancies and/or higher oxidation states of metal cations. Synergistic interactions between surface metal ions, such as Fe4+/Fe5+ with Co3+ which were detected by XPS, strongly enhance the reducibility of oxygen carriers. Three zones including total oxidation of methane by surface oxygen, partial oxidation of methane by lattice oxygen and carbon deposition were divided. Among the six samples with different substitution of Sr, La0.6Sr0.4FeCoO6 exhibited the best oxygen transport ability, thermal stability, as well as capacity for hydrogen generation. A stable CH4 conversion at ∼90% with desired H2/CO ratio at 2.0–2.5 in the methane reduction stage, and an average hydrogen yield at ∼5.9mmol/g oxygen carrier with ∼93.8% of hydrogen concentration in the steam oxidation stage were obtained during twenty successive redox reactions, which made them very attractive for the purpose of chemical looping partial oxidation of carbon fuel in real applications.