铁基钙钛矿氧载体甲烷化学链制合成气过程研究

Catalytic conversion of methane to syngas (CO+H2) is a critical step for the industrial gas-to-liquid (GTL) technologies. Chemical looping partial oxidation (CLPO) represents a novel methane-to-syngas route, which shows the advantages of high security and low energy consumption. The key issue for CLPO process lies in the selection of suitable oxygen carriers (OCs), among which the iron based materials have received particular attention due to their good performance in methane activation and environmental benign feature. However, they still suffer from severe coke deposition and low durability when the Fe cations are deeply reduced to metallic Fe0. In this proposal, Fe-based perovskite oxides are employed as OCs in terms of the outstanding oxygen mobility and structural compatibility. By adjusting the redox property via metal substitution, it is supposed to realize a structure evolution from homogenous perovskite phase to Fe0@metal oxides with core-shell structure in methane atmosphere, which would be helpful to suppress the carbon deposition and improve the cycling stability. As an alternative agent to O2, the H2O-CO2 mixture will be introduced to regenerate the core-shell structured intermediate to homogenous perovskite structure with the production of syngas. Various characterization techniques (e. g. 57Fe Mössbauer spectroscopy, HRTEM) will be employed to study the structure evolution, chemical state of Fe species and the mobility of lattice oxygen with the aim to establish a structure-reactivity correlation. In addition, combined with the kinetic study and DFT calculations, the reaction mechanism of CLPO of methane over Fe-based perovskite catalysts will be proposed, which can provide theoretical guidance for developing more efficient oxygen carriers for the CLPO process.

甲烷催化转化为合成气是工业中天然气制液体燃料的重要中间步骤。化学链部分氧化（CLPO）作为一种新型甲烷制合成气工艺，具有低能耗、安全等优点，其关键是氧载体。铁基氧载体因有较好的CH4活化能力、环境友好而备受关注，但仍面临深度还原（至零价Fe0）易积碳、循环稳定性不足的难题。本申请以铁基钙钛矿为氧载体，利用其结构可镶嵌性及晶格氧移动性实现CH4气氛中原位形成Fe0@氧化物核壳结构中间体，抑制积碳生成并提高氧载体循环稳定性。以H2O-CO2混合物取代O2，研究核壳中间体对氧化再生气氛的普适性，实现氧化过程中合成气的制备，拓展合成气来源。借助57Fe穆斯堡尔谱等表征研究核壳中间体的形成机制，系统考察铁基钙钛矿氧载体的微观结构、Fe化学状态和晶格氧移动性与甲烷CLPO性能间的内在关联。进一步结合动力学研究和密度泛函理论计算，揭示铁基氧载体的催化本质，为开发高效CLPO氧载体提供理论指导。

将甲烷催化转化为合成气是工业中天然气制备制液体燃料的重要中间步骤。化学链部分氧化技术（CLPO）作为一种新型甲烷转化工艺，其关键是高效氧载体的设计。铁基氧化物作为最具应用前景的氧载体之一，具有环境友好、成本低的优势，但其在载氧能力、甲烷活化性能及合成气选择性方面仍无法满足实际应用需求。本申请利用钙钛矿材料的高温稳定、结构兼容性强的特性，通过调变其氧化还原性能及反应过程中的氧载体微观形貌变化显著提高了其抗积碳性能。在此基础上，进一步通过结构助剂和电子助剂的修饰，调变氧载体中Fe-O键相互作用及催化剂表面氧物种种类，显著改善了甲烷反应活性和反应选择性。本课题结合多种表征、动力学研究及理论计算，从基础角度深入研究了氧载体的构效关系和反应机制，进而为开发高效CLPO用材料提供了理论基础。