催化学报

催化学报 ›› 2012, Vol. 33 ›› Issue (7): 1183-1190.DOI: 10.3724/SP.J.1088.2012.20208

• 研究论文 • 上一篇    下一篇

Rh/SiO2 催化剂上甲烷部分氧化制合成气的反应机理

温在恭, 李虎, 翁维正a, 夏文生, 黄传敬, 万惠霖b   

  1. 厦门大学固体表面物理化学国家重点实验室, 醇醚酯化工清洁生产国家工程实验室, 化学化工学院化学系, 福建厦门 361005
  • 收稿日期:2012-02-04 修回日期:2012-03-20 出版日期:2012-06-21 发布日期:2012-06-21

Reaction Mechanism for Partial Oxidation of Methane to Synthesis Gas over Rh/SiO2 Catalyst

WEN Zaigong, LI Hu, WENG Weizhenga, XIA Wensheng, HUANG Chuanjing, WAN Huilinb   

  1. State Key Laboratory of Physical Chemistry of Solid Surfaces, National Engineering Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, China
  • Received:2012-02-04 Revised:2012-03-20 Online:2012-06-21 Published:2012-06-21

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摘要： 采用原位 Raman 光谱技术, 在原料气中的 O2 未完全耗尽的条件下, 对 CH4 部分氧化制合成气反应的 Rh/SiO2 催化剂床层前部贵金属物种的化学态以及由 CH4 解离所生成的碳物种进行了表征. 在此基础上采用脉冲反应和同位素示踪技术, 比较了 CH4 的部分氧化及其与 H2O 和 CO2 的重整等反应对催化剂床层氧化区内 CO 和 H2 生成的相对贡献, 并将实验结果与 Raman 光谱表征结果进行了关联. 结果表明, 在 600 °C 下将还原后的 4% Rh/SiO2 催化剂切入 CH4:O2:Ar = 2:1:45 原料气, 催化剂床层前部未检测到铑氧化物的 Raman 谱峰, 但可清晰检测到源于 CH4 解离的碳物种; 在 700 °C 和接触时间小于 1 ms 的条件下, 催化剂床层的氧化区内已有大量 CO 和 H2 生成, 在相同的实验条件下, CH4 与 H2O 或 CO2 重整反应对氧化区内合成气生成的贡献则很小; 以 CH4:16O2:H218O:He = 2:1:2:95 为原料气的同位素示踪实验结果表明, 在原料气中 16O2 未完全耗尽的情况下, 反应产物中 C16O 的含量占 CO 生成总量的 92.3%, 表明 CO 主要来自 CH4 的部分氧化反应. 上述结果均表明, 在 O2 存在下 Rh/SiO2 催化剂上 CO 和 H2 可以通过 CH4 直接解离和部分氧化机理生成.

关键词: 铑, 甲烷部分氧化, 合成气, 脉冲反应, 原位拉曼光谱, 同位素示踪

Abstract: The partial oxidation of methane (POM) for the production of synthesis gas over Rh/SiO2 catalyst was investigated by in situ Raman spectroscopy characterization, continuous flowing and pulse reaction evaluation focusing on the reaction mechanism of synthesis gas formation in the oxidation zone, i.e., the catalyst zone where O2 is still available in gas phase. It was found that when a flow of CH4:O2:Ar = 2:1:45 at 600 °C was passed through the pre-reduced 4% Rh/SiO2 catalyst, no bands associated with rhodium oxide could be detected on the catalyst by Raman spectroscopy. While Raman bands related to carbon species that originated from methane dissociation could be detected at the catalyst oxidation zone under working conditions. The results of pulse reaction of POM as well as steam reforming and CO2 reforming of methane at 700 °C with a contact time less than 1 ms over the catalyst indicate that the formation of CO and H2 is mainly resulted from the direct partial oxidation of CH4 while the steam reforming and CO2 reforming reactions play only a minor role in the oxidation zone of the catalyst bed. The pulse reaction with an isotopic gas mixture of CH4:16O2:H218O:He = 2:1:2:95 over the Rh/SiO2 catalyst further indicated that the C16O percentage was higher than 92% of the total CO produced in the reaction. Based on these results, the conclusion, that the major reaction responsible for synthesis gas formation in the oxidation zone of Rh/SiO2 catalyst bed is the pyrolysis of methane on reduced rhodium sites to form hydrogen and carbon adspecies followed by the coupling of two surface hydrogen atoms to H2 and partial oxidation of surface carbon species to CO, is suggested.

Key words: rhodium, partial oxidation of methane, synthesis gas, pulse reaction, in situ Raman spectroscopy, isotope tracing