Studying restructuring in bimetallic catalysts using in-situ transmission electron microscopy

Bimetallic nanoparticles are gaining attention in the field of catalysis, exhibiting strongly enhanced activity and selectivity compared to their monometallic counterparts. The synergy is achieved by mixing a very active metal (normally Pd or Pt) with a less active metal (Au), that slows the reaction rate and provides selectivity to the system. However, atomic distribution inside a nanoparticle is dynamic and it can drastically change under catalytical reaction conditions, such as high temperatures or exposure to different gases.

In this work, we aim to correlate restructuring in bimetallic nanoparticles with their catalytical performance. For this, we make use of in situ transmission electron microscopy (in situ TEM), which with modified TEM sample holders allows imaging with the presence of gas at atmospheric pressure [1]. Using Energy Dispersive X-Ray Analysis (EDX), we can monitor the position of the elements in a single nanoparticle and determine the redistribution kinetics.

These kinds of studies will help us corroborate structure-function relations in bimetallic catalysts. For example Pd is known to segregate to the surface under an oxidative atmosphere, which increases hydrogenation activity since surface palladium is necessary for H2 dissociation [2]. Likewise, core shell structures in Au@Pd nanorods have been found to be more active in the butadiene selective hydrogenation than their monometallic counterparts, by having more Pd in the surface [3].

During my PhD, I will be watching atomic restructuring in well-defined bimetallic nanoparticles upon exposure to common reaction gases using in situ TEM. Since the catalytical properties of the particles can vary depending on the surface composition, gaining knowledge on how the surface composition changes upon different gas exposures, will help us to design switchable catalysts that catalyze different reactions depending on the pretreatment they received.

REFERENCES

[1]         L. I. van der Wal, S. J. Turner, and J. Zecevic, “Developments and advances in in situ transmission electron microscopy for catalysis research,” Catal. Sci. Technol., vol. 11, no. 11, pp. 3634–3658, 2021, doi: 10.1039/D1CY00258A.

[2]         M. Luneau et al., “Enhancing catalytic performance of dilute metal alloy nanomaterials,” Commun. Chem., vol. 3, no. 1, pp. 1–9, 2020, doi: 10.1038/s42004-020-0293-2.

[3]         J. E. S. van der Hoeven et al., “Unlocking synergy in bimetallic catalysts by core–shell design,” Nat. Mater., vol. 20, no. 9, pp. 1216–1220, Sep. 2021, doi: 10.1038/s41563-021-00996-3.