Rate and selectivity hysteresis during the carbon monoxide hydrogenation over promoted Co/MnOx catalysts
Rate and selectivity hysteresis during the carbon monoxide hydrogenation over promoted Co/MnOx catalysts
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DOI：
10.1038/s41467-019-11836-z
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发表时间：
2019-09
影响因子：
16.6
通讯作者：
Y. Xiang;L. Kovarik;N. Kruse
中科院分区：
文献类型：
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作者：
Y. Xiang;L. Kovarik;N. Kruse
虽然钴基催化剂在工业费托合成中已经使用了几十年，但人们对Co-Co2C相变的动力学如何驱动它们的性能知之甚少。本文报道了钾促进的Co/MnOx型催化剂上Fischer-Tropsch反应的滞后效应。当氢气/一氧化碳分压从总体还原到碳化条件来回变化时，反应速率和对链长链烷烃和端基官能化产物(醛、醇、烯烃)的选择性都表现出双稳态。一氧化碳转化率和官能化产物选择性表现为顺时针滞后，而烷烃选择性表现为逆时针行为。原位X射线衍射表明，催化剂的活性/选择性双稳态是由Co-Co2C相变驱动的。高分辨电子显微镜证实了Co-Co2C相变、低H2/CO分压比下的Mn5O8层状拓扑和高H2/CO分压比下的MnO。
While cobalt-based catalysts have been used in industrial Fischer-Tropsch synthesis for decades, little is known about how the dynamics of the Co-Co2C phase transformation drive their performance. Here we report on the occurrence of hysteresis effects in the Fischer-Tropsch reaction over potassium promoted Co/MnOxcatalyst. Both the reaction rate and the selectivity to chain-lengthened paraffins and terminally functionalized products (aldehydes, alcohols, olefins) show bistability when varying the hydrogen/carbon monoxide partial pressures back and forth from overall reducing to carbidizing conditions. While the carbon monoxide conversion and the selectivity to functionalized products follow clockwise hysteresis, the selectivity to paraffins shows counter-clockwise behavior. In situ X-ray diffraction demonstrates the activity/selectivity bistability to be driven by a Co-Co2C phase transformation. The conclusions are supported by High Resolution Transmission Electron Microscopy which identifies the Co-Co2C transformation, Mn5O8layered topologies at low H2/CO partial pressure ratios, and MnO at high such ratios.