Abstract:

The chemical looping dry reforming (CLDR ) of methane is an emerging technology for the generation of Fischer-Tropsch ready syngas (H₂/CO≈2) and CO₂ utilization via the circulation of oxygen carriers to temporally or spatially decouple the traditional dry reforming. The successful application of CLDR is strongly dependent upon the oxygen carrier (OC) with excellent performance. Iron-based perovskite (ABO₃) has attracted much attention in the chemical looping reforming process due to its good structural stability and syngas selectivity. Unfortunately, it suffers from low CH₄ activity and poor cyclic stability. The surface catalytic activity and lattice oxygen mobility of OC can be adjusted by doping metal ions at A and B sites, thereby improving the syngas yield and cyclic stability. In this work, the effects of metal substitution at A (Y, La, Pr, Sm ) and B ( Mn, Sn, Zr) sites of AFe_1-x B _x O₃ iron-based perovskite OCs on the potential of CLDR for syngas production were firstly studied by thermodynamic software. It was found that the AFe_1-x B _x O₃ OC with A = La and B = Zr had the best performance. Then, LaFe_0.93Zr_0.07O₃ OC was prepared by sol-gel method. Compared to LaFeO₃ (X_{\mathrm{C}{\mathrm{H}}_{\mathrm{4}}}=62.06%, Y_syn=1.38mmol/g), Zr-doped fresh LaFe_0.93Zr_0.07O₃ OC exhibited much higher methane conversion (94.57 %) and syngas yield (1.97mmol/g), and still remained at high level during 30 redox cycles (93.90%—96.29% and 1.96—2.01mmol/g). During the CO₂ oxidation stage, more CO₂ molecules (0.86mmol/g vs. 1.21mmol/g) could also be stably and efficiently converted into CO without deactivation. The excellent performance of Zr-doped perovskite OC was mainly due to the fact that Zr doping reduced the grain size, caused FeO₆ octahedron distortion and more oxygen vacancies, and enhanced lattice oxygen activity and sintering resistance. This work combining theoretical and experimental research could provide theoretical and experimental insight for the optimal design of oxygen carriers.

Key words: chemical looping dry reforming, perovskite, thermodynamic simulation, oxygen carrier, methane

摘要：

甲烷化学链干重整（CLDR）技术借助载氧体的循环将传统甲烷干重整反应进行时空解耦，可直接获得适合费托合成的合成气（H₂/CO≈2），并实现温室气体CO₂至CO的定向转化，其中，性能优异的载氧体（OC）是CLDR技术成功运行的关键。铁基钙钛矿（ABO₃）具有优良的结构稳定性和合成气选择性，在化学链重整过程中备受关注，但它存在CH₄活性低和循环稳定性差等不足，通过A和B位掺杂可调节载氧体的表面催化活性和晶格氧移动性，进而提高合成气产量和循环稳定性。本工作首先利用热力学软件研究了AFe_1-x B _x O₃铁基钙钛矿载氧体A（Y、La、Pr、Sm）位和B位（Mn、Sn、Zr）金属取代对CLDR制合成气潜力的影响，发现A=La、B=Zr时载氧体性能最佳。之后，采用溶胶-凝胶法制备了LaFe_0.93Zr_0.07O₃载氧体，发现Zr掺杂的新鲜LaFe_0.93Zr_0.07O₃载氧体的甲烷转化率、合成气收率分别由LaFeO₃的62.06%和1.38mmol/g提高至94.57%和1.97mmol/g，且在30次氧化还原循环反应过程中保持稳定（93.90%~96.29%和1.96~2.01mmol/g），在CO₂氧化阶段也能够稳定高效地将更多CO₂分子定向转化为CO（0.69mmol/g vs. 1.21mmol/g），无失活现象，这主要归因于Zr掺杂降低了载氧体的晶粒尺寸，造成了FeO₆八面体畸变和更多的氧空位，增强了晶格氧活性和抗烧结性。本工作结合理论与实验的研究，能够为载氧体的优化设计提供理论和实验依据。

关键词: 化学链干重整, 钙钛矿, 热力学模拟, 载氧体, 甲烷