Although the Mn promoter has been widely demonstrated to be beneficial to promoting the adsorption and dissociation of CO and therefore increasing the selectivity to light olefins in Fe-based FTS, it also brings about a negative effect on the catalytic activity due to its strong interaction with Fe oxides. In this study, Fe oxide was directly dispersed on a synthesized mesoporous spherical-like MnO_x support and further doped with Ag nanoparticles to investigate its impact on the FTS reaction. XRD and H₂-TPR characterization confirmed that Mn and Fe tend to form an FeMn solid solution over a 10 wt% Fe/MnO_x catalyst. As expected, a small amount of Ag doping on it could remarkably increase the catalytic activity by 1–5 times and even the selectivity to light olefins; this could be attributed to easier reduction of the Fe oxide, Mn oxide and FeMn solid solution due to the hydrogen (H) spillover generated by Ag as the reduced metallic Fe favors the formation of active Fe carbide and more O vacancies in MnO_x facilitate CO adsorption and the rapid removal of dissociated O atoms on Fe carbide. Furthermore, the FTS activity related to the H spillover was intensively investigated over the MnO_x-supported catalysts with different impregnation sequences of Ag and Fe, and over the hybrid 10Fe/MnO_x and 1Ag/MnO_x catalysts with particle and powder mixing in order to regulate the distance between Fe and Ag. It was found that the primary and secondary ways of H spillover are involved in the promoted reduction process, which was illustrated by XRD, H₂-TPR, H₂-TPD and CO-TPD characterization combined with catalytic results. The secondary spillover exhibited a much milder effect on the reduction promotion with a farther distance of Fe and Ag. Compared with the co-impregnated 1Ag10Fe/MnO_x catalyst, the sequential impregnation of Ag and Fe onto the MnO_x support, named the 10Fe/1Ag/MnO_x catalyst, showed higher catalytic activity, which might be due to less formation of FeMn solid solution resulting from firstly introduced Ag on MnO_x. Interestingly, both Ag-doped and Ag-free 10Fe/MnO_x catalysts showed a rapid increase in CO conversion after several tens of hours of stable reaction and the CO conversion can reach 80–90% after a 100 hour test, and the possible reason for this was discussed based on HAADF-STEM observations of spent catalyst samples.

中文翻译：

---

负载的 Fe掺杂的Fe / MnO _x催化剂可显着提高费-托合成过程中的催化活性†

尽管已广泛证明Mn促进剂有利于促进CO的吸附和解离并因此提高基于Fe的FTS中对轻烯烃的选择性，但由于与Mn的强相互作用，它也会对催化活性产生负面影响。铁的氧化物。在这项研究中，Fe氧化物直接分散在合成的介孔球形MnO _x载体上，并进一步掺杂Ag纳米颗粒以研究其对FTS反应的影响。XRD和H ₂ -TPR表征证实，Mn和Fe倾向于在10 wt％Fe / MnO _x上形成FeMn固溶体。催化剂。不出所料，少量的Ag掺杂可以显着提高催化活性1至5倍，甚至对轻烯烃的选择性。这可能归因于由于Ag产生的氢（H）溢出，Fe氧化物，Mn氧化物和FeMn固溶体的还原更容易，因为还原的金属Fe有利于形成活性Fe碳化物，而MnO _x中更多的O空位有利于CO吸附并快速去除碳化铁上解离的O原子。此外，在不同的Ag和Fe浸渍顺序的MnO _x担载的催化剂上以及在10Fe / MnO _x和1Ag / MnO _x杂化物上深入研究了与H溢出有关的FTS活性。将催化剂与颗粒和粉末混合以调节Fe和Ag之间的距离。发现X射线衍射，H ₂ -TPR，H ₂ -TPD和CO-TPD表征以及催化结果表明，H溢出的主要和次要方式参与了促进的还原过程。Fe和Ag的距离越远，二次溢出对还原的促进作用就越温和。与共浸渍的1Ag10Fe / MnO _x催化剂相比，将Ag和Fe顺序浸渍到MnO _x载体上，称为10Fe / 1Ag / MnO _x催化剂显示出较高的催化活性，这可能是由于在MnO _x上首次引入Ag导致形成的FeMn固溶体较少。有趣的是，经过数十小时的稳定反应后，掺银和不含银的10Fe / MnO _x催化剂均显示出CO转化率快速增加，经过100小时的测试后，CO转化率可达到80-90％，这可能是由于基于HAADF-STEM对废催化剂样品的观察，对此进行了讨论。