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Rh/SiO_2催化剂上甲烷部分氧化制合成气的反应机理

ISSN号：0253-9837
期刊名称：《催化学报》
时间：0
分类：O643[理学—物理化学;理学—化学]
作者机构：[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
相关基金：国家重点基础研究发展计划（973计划,2010CB732303）; 国家自然科学基金（20873111,20923004,21033006）; 教育部创新团队项目（IRT1036）; 福建省重大科技专项（2009HZ0002-1）

作者：温在恭[1], 李虎[1], 翁维正[1], 夏文生[1], 黄传敬[1], 万惠霖[1]

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

中文摘要：

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Ra-man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1ms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.

英文摘要：

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：H2 18O：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.