| Nowadays, world energy is supplied by three conventional fossil fuels including oil, coal and natural gas. While the oil resource is using up and coal utilization induces lots of pollution. As a rich and clean resource, natural gas attracts extensive attention, and is expected to play a more important role in the furture. In human energy history, main energy resource changed from wood and coal to oil, and now is turning to natural gas and hydrogen. In this decarbonization process of energy source, future energy will be mainly supplied by hydrogen.Steam methane reforming (SMR) is the main technology for the hydrogen production in recent industry. However, SMR is characterized with complex purification process and high energy consumption. Hence, a new natural gas conversion and hydrogen production technology named chemical-looping steam methane reforming (CL-SMR) was introduced. This technology is based on the chemical-looping concept, and now is becoming a hot research topic in the world.In this paper, CL-SMR technology is systematically studied in order to obtain pure hydrogen and high quality syngas. It includes thermodynamic analysis of metal oxides employed for oxygen carrier, oxygen carrier design and modification, in situ methane reduction study on Ce-Fe oxygen carrier, and CL-SMR performance over Ce-Fe oxygen carrier and its reaction mechanism.Ce-M-O (M=Zr,W,Fe,Ni, Ce molar:M molar=7:3) oxygen carrier selected based on thermodynamic analysis and basic principle were prepared by chemical precipitation method. CeO2, CeO2-ZrO2and CeO2-Fe2O3showed the good performance for selective oxidation of methane and water splitting, as well as CL-SMR. CeO2-ZrO2was found to be more stable with constant products production, while CeO2-Fe2O3shows highest activity and was deemed to be the promising oxygen carrier for CL-SMR.In order to obtained more detail material information, Ce1-xFexO2-d oxygen carrier (x=0,0.1,0.2,0.3,0.4,0.5,0.6, and1) and their synergy between Ce-Fe species were studied by in situ methane reduction. It was found that selective oxidation of methane was favorable at a higher temperature. Pure CeO2showed chemical-looping performance due to well lattice-oxygen releasing capacity. Pure Fe2O3was likely to complete oxidation of methane to CO2. Fe doping of CeO2could enhance the CO selectivity and CH4conversion due to the improvement of oxygen storage capacity, but a higher Fe content could deactivate the CO selectivity. In the in situ methane isothermal reaction, methane was completely oxidized to CO2at the beginning of the reaction, and then selective oxidized to CO at the following reaction. In methane conversion step, synergy between Ce-Fe species was proved to be favorable for selective of methane to syngas, and high-dispersed metallic Fe on the CeO2surface could remarkably enhance the releasing capability of lattice oxygen in material.All Ce1-xFexO2-d oxygen carriers (x=0-0.6) showed pleasing performance for hydrogen and syngas production in CL-SMR process. CeO2was found to be active in methane conversion step and could produce more syngas. Fe addition could improve the active of the water splitting reaction for hydrogen production. Ceo.sFeo.502-d oxygen carrier showed the best performance of all samples, and it also displayed preferable and stable performance in terms of syngas and hydrogen products. A higher methane-reduction time and reaction temperature leaded a higher yield of products, a suitable methane-reduction time is necessary to ensure the quality of products. After redox cycles, surface lattice oxygen was removed and lattice oxygen was transferred to a higher reduction temperature in H2-TPR due to reductive atmosphere and increase of Ce3+in oxygen carrier.In this work, behavior of ceria-based oxygen carrier and their reaction mechanism were thoroughly investigated to obtain a further understanding of Ce-Fe mixed oxides materials. Basic theory of CL-SMR technology based on Ce-Fe complex oxygen carriers was established.
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