Transient kinetic studies of partial oxidation of CH4
Transient kinetic studies of partial oxidation of CH4
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CH4部分氧化的瞬态动力学研究
DOI：
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
E. Ruckenstein
中科院分区：
文献类型：
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作者：
Y. Hu;E. Ruckenstein
采用脉冲瞬态分析法研究了甲烷在Ni/La_2 O_3催化剂上低温（450-700°C）、常压、停留时间为3.8ms的氧化动力学。瞬态响应曲线表明，CO2的产生比CO的产生延迟，因此CO是主要产物，随后才由CO产生CO2。CH 4/O2脉冲期间催化剂表面C和O物种的产生以及CO的脱附比CO的产生快得多;因此，表面碳物质和表面O物质之间的反应构成了速率控制步骤。在新鲜还原的催化剂上，以He为载气，在45 μ l的CH_4/O_2（2/1）的小脉冲下，获得了高的CH_4转化率和几乎100%的CO选择性;在未还原的催化剂上，CH_4转化率和CO选择性较低。还原态催化剂表面被氧化后，CH 4转化率和CO选择性降低。结果表明，催化剂还原后得到的Ni原子构成了甲烷部分氧化反应的活性中心。得出的结论是，CH 4的转化取决于其解离，而CO的选择性在很大程度上取决于O物种结合到催化剂的强度。在还原的催化剂上，O物质难以氧化，因为它们与Ni原子的强结合，CO变成CO2，而在未还原的催化剂（其含有Ni氧化物）上，氧物质容易氧化，因为它们被弱吸附，CO变成CO2。
The kinetics of methane oxidation over Ni/La2O3at low temperatures (450–700°C), atmospheric pressure, and a residence time of 3.8 ms was studied by the pulse-transient analysis method. The transient response curves revealed that CO2generation is delayed in comparison to that of CO, hence that CO is the primary product and CO2is only subsequently generated from CO. The generation of C and O species over the surface of the catalyst during CH4/O2pulses and the desorption of CO were much faster than the generation of CO; hence the reaction between the surface carbon species and the surface O species constitutes the rate-controlling step. High CH4conversions and almost 100% CO selectivities were obtained for small pulses of 45 μlof CH4/O2(2/1) over freshly reduced catalysts, with He as the carrier gas; over the unreduced catalyst the CH4conversion and CO selectivity were low. The experimental data also indicated that the CH4conversion and CO selectivity decreased when the surface of the reduced catalyst was oxidized. The results demonstrated that Ni atoms, obtained by the reduction of the catalyst, constitute the active sites in CH4partial oxidation. One concludes that the CH4conversion depends on its dissociation, whereas the CO selectivity is largely dependent on the strength of O species binding to the catalyst. Over the reduced catalyst, the O species oxidize with difficulty, because of their strong binding to Ni atoms, CO to CO2, whereas over the unreduced catalyst (which contains Ni oxide), the oxygen species easily oxidize, because they are weakly adsorbed, CO to CO2.