Unsteady-state direct partial oxidation of methane to synthesis gas in a fixed-bed reactor using AFeO3 (A = La, Nd, Eu) perovskite-type oxides as oxygen storage
Unsteady-state direct partial oxidation of methane to synthesis gas in a fixed-bed reactor using AFeO3 (A = La, Nd, Eu) perovskite-type oxides as oxygen storage
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DOI：
10.1021/jp063490b
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发表时间：
2006-11-16
影响因子：
3.3
通讯作者：
Hao, Zheng Ping
中科院分区：
文献类型：
--
作者：
Dai, Xiao Ping;Li, Ran Jia;Hao, Zheng Ping
在固定床反应器上，研究了无氧条件下，在AFeO（3）（A = La，Nd，Eu）氧化物上甲烷直接部分氧化制合成气的一种新的顺序氧化还原循环反应。采用溶胶-凝胶法制备了氧化物样品，并利用X射线衍射（XRD）和X射线光电子能谱（XPS）技术对样品进行了表征。XRD分析表明，在1173 K下煅烧的AFeO（3）（A = La，Nd，Eu）氧化物均为单相钙钛矿。CH 4-TPSR/MS和连续反应实验表明，AFeO（3）（A = La，Nd，Eu）氧化物作为唯一的氧化剂，主要提供氧物种，其氧化剂来源于晶格氧而非气态氧，在无气态氧的条件下，能够高选择性地氧化CH 4生成合成气。就材料经济性和用于合成气形成的氧物种的量而言，LaFeO 3样品在这些用于合成气生产的测试的AFEO（3）氧化物中表现出最佳性能。不同温度下的脉冲实验表明，LaFeO 3与CH 4反应过程中氧的迁移速率受反应温度的影响较大，随着温度的升高，氧的迁移速率增大，有利于高温下CH 4的选择性氧化。通过连续反应实验和脉冲实验确定了这两种氧物种，并用XPS进行了证实。甲烷可以通过消耗晶格氧选择性地转化为合成气，并且在适当的反应条件下通过顺序的氧化还原循环在催化剂表面上不发生一般的碳质沉积物。甲烷选择氧化制合成气的性能可以通过使用气态分子氧的再氧化来恢复; LaFeO 3氧化物在氧化还原气氛中保持相对高的催化活性和结构稳定性。
Direct partial oxidation of methane to synthesis gas on AFeO(3) (A = La, Nd, Eu) oxides by a novel sequential redox cyclic reaction in the absence of gaseous oxygen was investigated over a fixed-bed reactor. These oxides were prepared by the sol-gel method and characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. XRD analysis showed that all AFeO(3) (A = La, Nd, Eu) oxides, calcined at 1173 K, are single-phase perovskites. The CH4-TPSR/MS and continuous reaction experiments indicated that the AFeO(3) (A = La, Nd, Eu) oxides provide mostly oxygen species, as the sole oxidant originated from lattice oxygen instead of gaseous oxygen, which can oxidize CH4 to synthesis gas with high selectivity in the absence of gaseous oxygen. In terms of material economics and the amount of oxygen species for synthesis gas formation, the LaFeO3 sample exhibits the best performance among these tested AFeO(3) oxides for synthesis gas production. The pulse experiments at different temperatures showed that the rate of oxygen migration during the CH4 reaction with LaFeO3 is strongly affected by the reaction temperature, and increases with rising temperature, which is favorable to much more CH4 selective oxidation at high temperature. The two types of oxygen species are identified by experiments of continuous reactions and pulses, and confirmed by XPS. Methane can be converted selectively to synthesis gas by consumption of lattice oxygen, and general carbonaceous deposits on the catalyst surface do not occur under the appropriate reaction conditions by sequential redox cycles. The performance of selective oxidation of CH4 to synthesis gas can be recovered by reoxidation using gaseous molecular oxygen; the LaFeO3 oxide maintains relatively high catalytic activity and structural stability in redox atmospheres.