Fe-based Perovskite As Oxygen Carriers For Chemical Looping Dry Reforming

Chemical looping dry reforming（CLDR）of methane,different from the conventional dry reforming of methane（DRM）,represents a new technology for upgrading the methane and carbon dioxide separately to syngas（mixture of H₂ and CO）and carbon monoxide through two semi-reactions instead of the continuous reaction.Such process can effectively inhibit the reverse water gas shift reaction and catalyst carbon deposition.The key to this process lies in the selection of sutable oxygen carrier.Perovskite composite oxide（ABO₃）has the advantages of flexible composition,good oxygen mobility and high temperature stability,which enables this material showing outstanding reactivity and stability in various heterogeneous reactions,especially under high temperature conditions.These unique properties make the perovskite material possess the potential to be an excellent oxygen carrier.In the first part of the thesis,a series of Ni/LaFeO₃（1%-5wt%）oxygen carriers with different Ni loading were prepared by impregnation method,and the corresponding CLDR performance was studied.It was found that the oxygen carrier can achieve 98%methane-to-syngas selectivity and 100%CO₂-to-CO selectivity.Besides,synergistic effect between Ni and LaFeO₃ oxygen carrier was observed that increase of nickel loading effectively promotes the activation of methane and carbon dioxide,significantly accelarating the reaction rate.However,sintering of Ni particles during redox reactions leads to degradation of the overall CLDR performance.In the second part of the thesis,we demonstrate a novel of Ni embeded perovskite（Nióperovskite）composite material as oxygen carrier for CLDR reaction.Such intimate structure enhances the synergy between the active Ni and the perovskite-type oxygen reservoir,leading to rapid phase transformation between Nióperovskite and Ni-Fe alloyóperovskite during redox reactions.Thus,methane conversion up to 97%with CO selectivity above 99%（H₂/CO ratio of 2）and nearly complete CO₂conversion can be achieved.In addition,the Ni and Ni-Fe alloy nanoparticles were well confined in the“nest”constructed by the perovskite oxides throughout the reactions,which restained the sintering the Ni.This material can maintain the reaction performance over 80cycles,revealing the outstanding redox stability.