The Preparation Of Lanthanum-cerium-based Oxygen Carrier And Its Chemical Chain Reforming Performance

Energy is an important material basis for the progress of human society and economic development.As new energy sources?such as solar,wind and nuclear?cannot replace fossil fuels on a large scale in the short term,the world's energy supply is expected to continue to rely heavily on fossil fuels.Because of its large reserves,clean and efficient,natural gas is bound to replace coal and oil and become the leading energy consumption.In the foreseeable future,the traditional field of power generation and heating will be replaced by new energy,and natural gas will become the raw material for the production of high value-added chemicals.Therefore,the development of natural gas resource utilization technology has become the focus of competing research all over the world.The chemical looping reforming of methane process is a new and efficient methane reforming technology,which combines the partial oxidation of lattice oxygen to syngas and the water splitting to hydrogen?or the CO₂ splitting to co?.In this process,redox metal oxides,known as oxygen carriers,are used as recyclable chemical intermediates for reduction and regeneration to transfer oxygen and energy.Therefore,the design and development of oxygen carrier is the research focus of this technology.However,cerium oxide?Ce O₂?and lanthanum ferrite?La Fe O₃?are the representatives of rare earth based metal oxides.It plays an important role in many key areas related to the sustainable development of national economy,and has attracted the attention of many chemical looping researchers in recent years.In this paper,Ce based and La based oxides will be taken as the research object,and the following research will be carried out from two aspects:developing the macro structure of new oxygen carriers and designing the oxygen carrier system with excellent performance.1.The reaction behavior of Ce-Fe-Zr-O/Mg O monolithic oxygen carrier with many parallel channels in Cl-SMR was studied.Firstly,the best ratio of Ce-Fe-Zr-O and Mg O was selected.The best ratio of Ce-Fe-Zr-O accounted for 40%of the total mass of oxygen carrier.Then,Ce-Fe-Zr-O?40%?/Mg O powder was coated on cordierite honeycomb by slurry coating method to prepare Ce-Fe-Zr-O?40%?/Mg O monolithic oxygen carrier.The cl-smr activities of Ce-Fe-Zr-O?40%?/Mg O monolithic oxygen carriers and pellet oxygen carriers were compared in detail.It is found that the monolithic oxygen carrier has higher activity of methane oxidation and water splitting,which leads to higher methane conversion?from 52.9%to 63.2%?,yield of synthesis gas(2.85 mol·kg^-1)and H₂(1.14 mol·kg^-1).In the long-term stability test,the reaction activity and macro structure of the monolithic oxygen carrier are stable without obvious reduction and breakage.2.A new oxygen carrier of La Ni_xFe_1-xO_3-?with a small amount of Ni doped La Fe O₃was designed.Compared with the standard La Fe O₃ material,at 800?,the first CH₄conversion of La Ni_xFe_1-xO_3-?is twice of the former,reaching 80%,the syngas yield is 5.3mol·kg^-1,the second H₂ yield is 1.83 mol·kg^-1and the CO yield is 2.01 mol·kg^-1,among which the syngas production is the maximum value reported by the non noble metal oxygen carrier at the same temperature.When the temperature rises to 900?,the CH₄conversion is up to 95%.And,it is proved that the existence of Ni not only effectively activated CH₄,but also contributed to the dissociation of CO₂ and O₂.Combined with the analysis of experimental characterization,it is found that there is a strong interaction between Ni and La Fe O₃,which can not only improve the redox ability of oxygen carrier,but also accelerate the overflow of lattice oxygen,promote the deep reduction of La Fe O₃ and improve the utilization of oxygen carrier.In addition,we also found that Ni species can reversibly complete the change from Ni to Ni O in CH₄ and CO₂ atmosphere,which can effectively limit the growth of Ni catalyst,make La Ni_xFe_1-xO_3-?oxygen carrier easily embed and remove lattice oxygen in the redox test,and provide thermodynamic driving force for CH₄partial oxidation and CO₂ or H₂O splitting step,so that it can be maintained high activity and stability in 100 redox cycles test.