Hexaaluminates Supported Cerium Oxide Compound Oxygen Carrier For High Quality Synthesis Gas Production From Chemical-looping Reforming Of Methane

Chemical-looping reforming of methane（CLRM）is a novel CH₄/CO₂ technology for the production of syngas.This technology uses the lattice oxygen of the oxygen carrier instead of the gas phase oxygen to oxidize methane highly selectively to a synthesis gas with a molar hydrogen-carbon ratio of 2,and uses CO₂ to regenerate the lattice oxygen to realize the recycling of the oxygen carrier.Oxygen carrier is the core part of this technology.The cerium oxide（CeO₂）of the fluorite cubic structure has a strong ability to store and release oxygen.Hexaaluminate materials have excellent high temperature stability,adjustable redox properties,and rapid lattice oxygen transport due to their special layered structure.In this paper,the CeO₂ and iron-based hexa-aluminate were compounded for the first time.The CLRM system was used to obtain high-quality synthesis gas.The calcination temperature and cerium loading on the microstructure and CLRM of CeO₂ and iron-based hexaaluminate composite oxygen carrier were investigated.The influence of the performance,and the microstructure of the composite oxygen carrier before and after the CH₄/CO₂ cycle reaction were characterized,and the intrinsic correlation between the structure and the performance was preliminarily established.The effects of calcination temperature（600℃,700℃,800℃,900℃,and 1000℃）on the performance of high-quality synthesis gas from composite oxygen carriers were investigated,and the reaction conditions（space velocity and reaction temperature）were optimized.It is found that when the calcination temperature of CeO₂ and hexaaluminate composite oxygen carrier is 900℃,the strong interaction between will not only reduce the content of surface oxygen,but also increase the mobility of lattice oxygen and the amount of movable lattice oxygen.Increased oxygen and syngas production.Appropriate space velocity(66.7ml·min^-1·g^-1)and reaction temperature（900℃）can greatly increase the CH₄conversion rate and synthesis gas selectivity,which is beneficial to improve the oxygen output and synthesis gas production.The effects of pure CeO₂,iron-based hexaaluminate and cerium oxide loading（Ce/Fe=1:9,3:7,5:5）on the performance and cycle stability of high quality synthesis gas were investigated.The loading of CeO₂ on the surface of iron-based hexaaluminate can not only promote the deeper phase lattice oxygen release of iron-based hexaaluminate,but also increase the selectivity of synthesis gas,and improve the high-temperature cycling stability.When the Ce/Fe molar ratio is 3:7,it has the highest partial oxidation of methane activity,synthesis gas selectivity,oxygen yield（2.3 mmol O atoms）and syngas production（2.5mmol/g）.After repeated CH₄/CO₂ cycles,CeO₂ and hexaaluminate composite oxygen carriers formed a well-stabilized CeAlO₃ perovskite structure during the redox cycle reaction.A small amount of Fe³⁺ entered CeAlO₃ crystal structure to improve the storage/releases of composite oxygen carriers,and partially oxidizes methane activity.