Xiang Yizhi, Kovarik Libor, Kruse Norbert
Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA, 99164, USA.
Dave C. Swalm School of Chemical Engineering, Mississippi State University, Mississippi State, MS, 39762, USA.
Nat Commun. 2019 Sep 2;10(1):3953. doi: 10.1038/s41467-019-11836-z.
While cobalt-based catalysts have been used in industrial Fischer-Tropsch synthesis for decades, little is known about how the dynamics of the Co-CoC phase transformation drive their performance. Here we report on the occurrence of hysteresis effects in the Fischer-Tropsch reaction over potassium promoted Co/MnO catalyst. 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-CoC phase transformation. The conclusions are supported by High Resolution Transmission Electron Microscopy which identifies the Co-CoC transformation, MnO layered topologies at low H/CO partial pressure ratios, and MnO at high such ratios.
虽然钴基催化剂已在工业费托合成中使用了数十年，但对于Co-CoC相变的动力学如何驱动其性能却知之甚少。在此，我们报道了在钾促进的Co/MnO催化剂上费托反应中滞后效应的出现。当在从整体还原到碳化条件之间来回改变氢/一氧化碳分压时，反应速率以及对链增长的石蜡和末端官能化产物（醛、醇、烯烃）的选择性均表现出双稳态。虽然一氧化碳转化率和对官能化产物的选择性遵循顺时针滞后，但对石蜡的选择性表现出逆时针行为。原位X射线衍射表明，活性/选择性双稳态是由Co-CoC相变驱动的。高分辨率透射电子显微镜证实了Co-CoC转变、低H/CO分压比下的MnO层状拓扑结构以及高该分压比下的MnO，从而支持了这些结论。
