Many efforts have been made in order to investigate catalyst under relevant working conditions. Indeed, the action of a chemical potential has to be considered when describing the state of a catalyst and recent studies have demonstrated that the catalyst surface evolves dynamically under reaction conditions.^1,2 In order to complement in-situ spectroscopic tools, such as near-ambient X-ray photoelectron spectroscopy (NAP-XPS), with visual information about the active surface structure, we have implemented in-situ scanning electron microscopy (SEM) for the observation of dynamic processes at the µm to nm scale.³

By coupling in-situ SEM with mass spectroscopy measurements we are able to relate structural dynamics at the surface of metal catalysts to changes in the gas phase composition. Under specific conditions, oscillatory behavior of the catalyzed chemical reactions was observed for the case of polycrystalline nickel and copper foils. These self-sustained oscillations can be utilized to assist the identification of kinetic mechanisms⁴ and provide insight in the active and inactive state of the catalyst. Figure 1. demonstrates the dynamic behavior of the Ni foil surface during hydrogen oxidation reaction at 600°C. The active state in the oscillatory reaction is dominated by the presence of metallic Ni, while the formation of NiO coincides with a decrease in the catalytic activity. Overall, it will be outlined how the implementation of complementary in-situ SEM and mass spectroscopy techniques can enrich our understanding of the dynamic behavior of active catalyst and how it complements spatially integrated spectroscopic data that is recorded under similar conditions.

Figure 1. Self-sustained oscillations during hydrogen oxidation over a Ni foil at 0.3 mbar with a hydrogen/oxygen ratio of 7:1. The SEM images correspond to the different points in the oscillation as indicated in the mass spectrum profile. During the active state of an oscillation (A), the Ni foil exhibits a smooth metallic surface. In the low-active state (B), the surface of the Ni foil is covered by an oxide layer.

References

[1]T. Lunkenbein et al., Angew. Chem. Int. Ed. 2015, 127, 15, 4627-4631

[2] S. Piccinin et al., Phys. Rev. Lett. 2010, 104, 035503

[3] Z. J. Wang et al., ACS Nano., 2015, 9, 1506-1519

[4] V. V. Kaichev et al., Surf. Sci., 2013, 609, 113-118

Figures:

Figure 1. Self-sustained oscillations during hydrogen oxidation over a Ni foil at 0.3 mbar with a hydrogen/oxygen ratio of 7:1. The SEM images correspond to the different points in the oscillation as indicated in the mass spectrum profile. During the active state of an oscillation (A), the Ni foil exhibits a smooth metallic surface. In the low-active state (B), the surface of the Ni foil is covered by an oxide layer.

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EMC Abstracts - https://emc-proceedings.com/abstract/structural-dynamics-of-copper-and-nickel-substrates-during-redox-reactions-studied-by-in-situ-sem/