Study On Mn-doped Aluminum-based Spinel And Its Chemical Chain Reforming Performanc

In the context of the’dual carbon’strategy,there is an urgent need to improve the technology for capturing and utilising the two main greenhouse gases carbon dioxide and methane.Chemical looping dry reforming of methane（CL-DRM）is a technology that simultaneously captures and converts both of these greenhouse gases.The technology uses the lattice oxygen in the catalyst to partially oxidise CH₄ to produce syngas,while using CO₂ to restore the lattice oxygen to the catalyst to reach a cycle,enabling non-contact combustion.The catalyst plays a central role in oxygen transfer and is at the heart of the technology,and the development of catalysts with high activity and cycling stability is the way forward.Spinel is an important activating CL-DRM catalyst,but this catalyst also suffers from:limited oxygen storage capacity and the tendency of single-phase metals to sinter.As redox catalysts assume an important role in the reaction process,redox catalysts with high activity and stability can avoid material sintering and reactor deterioration at high temperatures（800-1000°C）,so redox catalysts with high activity and stability at low temperatures are a hot topic of research in this paper.Therefore,in this paper,metal Mn-doped spinel catalysts were used for the CL-DRM reaction.The effect of the composite catalysts on the performance of the CL-DRM reaction was systematically investigated by using X-ray diffraction,hydrogen programmed warming reduction,high power transmission electron microscopy and X-ray photoelectron spectroscopy for characterization.In this paper,a series of Mn_xNi_1-xAl₂O₄ composite catalysts were prepared by sol-gel method.The effect of Mn doping on the activation performance of spinel methane was investigated,and aluminum-based spinels were initially sieved for the study.The effect of different Mn doping on the activity of Ni Al₂O₄ spinel was explored,and the cycling stability of the catalysts was also analyzed.The results showed that the doping of Mn significantly lowered the reaction temperature and enhanced the reaction activity,but too high a doping amount would lead to a decrease in methane catalytic activity.In the Mn_0.4Ni_0.6Al₂O₄ composite catalyst,the methane conversion was as high as 95.4%with an H₂/CO molar ratio of 9.9 when the Mn doping was 40 wt.%,and the results were stable after 40 cycles,showing excellent cycle stability performance.Mn particles are uniformly dispersed on the surface of Ni Al₂O₄ spinel,Mn effectively adsorbs and activates CO₂,improves oxygen mobility and effectively inhibits and restores agglomeration and sintering in metallic Ni sintering during methane reduction.Enables Ni to be highly dispersed on the catalyst surface,providing an effective active site for methane.The stable structure of spinel effectively improves cycling stability.Enables the catalyst to have good methane activity at low temperatures.Finally,the intermediate process of the reaction was studied to reveal the reaction mechanism.The Mn_0.4Ni_0.6Al₂O₄ composite oxygen carrier with high activity and stability was obtained to achieve low temperature chemical looping CH₄cracking for hydrogen production and CO₂ oxidation,extending the application of the catalyst in low temperature chemical looping processes.