Performance Study Of Cerium-based Oxygen Carriers In Chemical Chain Reforming

Chemical looping methane reforming coupled with CO₂reduction process was a very promising technology.This technique was mainly divided into two steps.Firstly,the lattice oxygen of the oxygen carrier partially oxidized methane to CO and H₂.And then,CO₂was used as the oxygen source to regenerate the oxygen carriers,with the production of CO.This process not only converted and utilized CH₄but also achieved the purpose of CO₂reduction.The design and construction of oxygen carriers with high activity and stability was the key factor to realize this technology.The cerium-based oxygen carrier could be used as an oxygen carrier for chemical looping methane reforming coupled with CO₂reduction process due to its unique structural characteristics and excellent oxygen storage and release performance.In the chemical looping methane reforming coupled with CO₂reduction process,pure CeO₂oxygen carrier owned high carbon deposition resistance,but the reactivity was relatively lower.However,doping Ni/Zr ions into CeO₂could improve the reactivity of CeO₂.In this paper,the Ni/Zr-doped cerium-based oxygen carriers were successfully prepared by the co-precipitation method and the reactivity of chemical looping methane reforming coupled with CO₂reduction was studied.The physical and chemical properties of oxygen carriers were characterized by XRD,BET,XPS and CH₄-TPR techniques.The reactivity of CeO₂,Ce_1-xNi_xO_yand Ce_xZr_yNi_1-x-yO_zoxygen carriers in the chemical looping methane reforming coupled with CO₂reduction process was systematically investigated.In addition,the influence of the calcination temperature on the reactivity of the oxygen carriers was also deeply explored.It was found that the Ce_1-xNi_xO_yseries of oxygen carriers exhibited good oxygen transport capacity and high reactivity in the chemical looping methane reforming coupled with CO₂reduction process.The CH₄conversion and CO₂conversion of oxygen carriers gradually increased with the increase of Ni contents.Among them,Ce_0.2Ni_0.8O_yand Ce_0.4Ni_0.6O_yoxygen carriers owned high CH₄conversion and CO₂conversion.It was also found that the calcination temperature had a very important influence on the structural properties of the Ce_0.2Ni_0.8O_yoxygen carrier.Compared with the samples calcined at other temperatures,the Ce_0.2Ni_0.8O_ysample calcined at850 ? exhibited good structural stability,higher oxygen vacancy concentration and oxygen storage and release.After twenty redox cycles,it still had better reactivity and cycle stability.In summary,850 ? was the most appropriate calcination temperature for Ce_0.2Ni_0.8O_yoxygen carrier.Ce_xZr_yNi_1-x-yO_zoxygen carriers showed good reactivity and carbon deposition resistance in chemical looping methane reforming coupled with CO₂reduction.The degree of methane cracking with Ce_0.4Zr_0.2Ni_0.4O_zoxygen carrier exhibited the highest carbon deposition resistance.After twenty redox cycles,the syngas production and CO₂conversion of Ce_0.4Zr_0.2Ni_0.4O_zoxygen carrier dropped slightly.The results showed that Ce_xZr_yNi_1-x-yO_zoxygen carriers owned high cycle stability.