Atomic Scale Stability of Tungsten–Cobalt Intermetallic Nanocrystals in Reactive Environment at High Temperature

Abstract

Catalyst design plays vital roles in structurally relevant reactions. Revealing the catalyst structure and chemistry in the reactive environment at the atomic scale is imperative for the rational design of catalysts as well as the investigation of reaction mechanisms, while in situ characterization at the atomic scale at high temperature is still a great challenge. Here, tracking intermetallic Co 7 W 6 nanocrystals with a defined structure and a high melting point by environmental aberration-corrected transmission electron microscopy in combination with in situ synchrotron X-ray absorption spectroscopy, we directly present the structural and chemical stability of the Co 7 W 6 nanocrystals in methane, carbon monoxide, and hydrogen at temperatures of 700−1100 °C. The evidence is in situ and in real time with both atomic scaled resolution and collective information. The results are helpful in revealing the mechanism of structural-specified synthesis of single-walled carbon nanotubes. This research offers an example of systematic investigation at the atomic scale on catalysts under reactive conditions. Such catalysts presenting high structural stability may also find applications in other structure-specific synthesis.

Carbon-Involved Near-Surface Evolution of Cobalt Catalyst during Reaction: An in-situ Study

“…We assigned atomic columns to hcp-Co [0001] and Co 3 C phases accordingly (Fig. 4b), which con rms again the co-existence of Co and Co 3 C. A t of two dimensional (2D) Gaussians to the intensity of distribution of the atomic columns was used to acquire the precise column coordinates, which improved the resolution to sub-angstrom 38,46 . The perpendicular layer spacings were determined locally from those tted coordinates and then averaged for each shell (d 12 , d 23 , d 34 ...) ( Supplementary Fig.…”

“…Techniques based on aberration-corrected environmental transmission electron microscope (AC-ETEM) [34][35][36][37][38][39][40] have shown to be a powerful tool for the investigation of such process at atomic spatial and high temporal resolution. With the help of in-situ imaging, the nucleation process of carbon nanotubes on both liquid and solid catalysts were recorded 25,29,35,[41][42][43] .…”

Precise Synthesis of Carbon Nanotubes and One‐Dimensional Hybrids from Templates†

“…This is no carbon dissolving induced structural change, which was clearly evidenced by aberration‐corrected ETEM and synchrotron X‐ray absorption spectroscopy (Figure 7e–j). [ 118 ] More importantly, besides the high stability of catalysts, the low symmetry atomic structures of Co 7 W 6 intermetallic compound with unique W and Co arrangements ensure the structural match between catalyst facet and end rims of a ( n , m ) SWCNT (Figure 7a, d). With this strategy, the (12,6), (16,0), and (14,4) SWCNTs with the purity of 79%—97% were synthesized from Co 7 W 6 catalysts under optimized conditions, respectively (Figure 7b, c).…”

Atomic origins of the strong metal–support interaction in silica supported catalysts

“…Here, we report the unequivocal finding of SMSI in industrially relevant Co/SiO 2 model catalyst where SiO 2 migrated onto Co nanocrystals and the SMSI originated from the interfacial reduction induced SiO 2 -Si-Co structure, by employing the state-of-the-art aberration-corrected environmental transmission electron microscopy (ETEM) 18,26,[57][58][59][60][61][62][63][64] combined with in-situ electron energy loss spectroscopy (EELS), 65,66 thus providing the direct visualization and chemical evolution at atomic scale. The dynamic evolution of interface accompanied by the interfacial Si-Co alloying were also investigated in this SMSI system.…”