Microstructure Evolution of a Co/MnO Catalyst for Fischer‐Tropsch Synthesis Revealed by In Situ XAFS Studies

Abstract

Co−Mn catalysts have long been considered as a promising catalyst for Fischer‐Tropsch synthesis (FTS). However, the promotional role of Mn and its interaction with Co remain unclear and controversial. In situ characterization of the structural change of FTS catalysts is a powerful way to reveal the reaction mechanisms. Nevertheless, there are significant difficulties because of the harsh reaction conditions. Here, the microstructure evolution of Co/MnO catalysts during FTS is monitored by in situ X‐ray absorption fine structure (XAFS) spectroscopy under real FTS atmosphere up to 6 bar for the first time. Combined with in situ X‐ray diffraction (XRD), ex situ high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and H2 chemisorption characterizations, we reveal that the metallic Co liberated from Mn1−xCoxO during FTS leads to activity enhancement. The presence of Mn improves the Co dispersion. However, an initial association of Mn with the Co phase hampers the cobalt reducibility. We also find that increasing the reaction pressure enhances the oxygen dissociation on the Mn surface, which leads to an increased number of exposed Co sites and consequent FTS activity improvement.

Efficient Decomposition of Ozone at Room Temperature by Cobalt-Organic ZIF-67 Nanostructure and Its Derivatives

“…There is a major peak located at 1.45 Å, which corresponds to the Co−O coordination shell. 55 The major peak at 2.1 Å corresponding to the metallic shell of Co−Co indicates the presence of metallic Co, which is consistent with the results of XANES. Among them, CoMn− NC has the highest Co−Co peak, which indicates that it contains the greatest number of Co in nanoparticles.…”

“…More detailed local structural information about Co atoms was obtained from the k 2 -weighted χ­( k )-function EXAFS spectra, as shown in Figure (b). There is a major peak located at 1.45 Å, which corresponds to the Co–O coordination shell . The major peak at 2.1 Å corresponding to the metallic shell of Co–Co indicates the presence of metallic Co, which is consistent with the results of XANES.…”

Full life cycle characterization strategies for spatiotemporal evolution of heterogeneous catalysts

“…identified species, including CoO, Co2C, and cobalt-supported compounds [32]. Thus, dynamic structure characterization of Co nanoparticles under working conditions, such as sintering, dispersion, and oxidation (caused by water), has attracted interest even though this involves great challenges under harsh conditions [33,34].…”