Watching oxidation of bimetallic catalysts in 3D

March 13, 2017

What is the scientific achievement?

Bimetallic alloy nanoparticles are important catalysts, and understanding the ways they oxidize is key to designing materials for high performance.  However, it has been experimentally difficult to observe both the local structure and chemistry during oxidation of multi-component materials.  This work combines multiple advanced electron microscopy techniques to reveal the surprising complex ways these materials undergo oxidation on both exterior and interior surfaces.

Why does this achievement matter?

The 3D reconstruction and real-time imaging information reveals the mechanism of bimetallic particle oxidation, which control and alter morphology of hollow structured metal oxides.

What are the details?

3D evolution of a Ni2Co particle enlarge

Top Row: 3D evolution of a Ni2Co particle before (left), during (middle) and after (right) oxidation. Bottom Row: 3D mapping of oxygen (blue), cobalt (green), and nickel (red) in a fully oxidized nanoparticle.

An understanding of bimetallic alloy oxidation is key to the design of hollow-structured binary oxides and the optimization of their catalytic performance. However, one roadblock encountered in studying these binary oxide systems is the difficulty in describing the heterogeneities that occur in both structure and chemistry as a function of reaction coordinate.  This is due to the complexity of the three-dimensional mosaic patterns that occur in these heterogeneous binary systems. By combining real-time imaging and chemical-sensitive electron tomography, we show that it is possible to characterize these systems with simultaneous nanoscale and chemical detail. We find that there is oxidation-induced chemical segregation occurring on both external and internal surfaces. Additionally, there is another layer of complexity that occurs during the oxidation, namely that the morphology of the initial oxide surface can change the oxidation modality. This work elucidates the pathways that can control the morphology of binary oxide materials.

CFN Capabilities:

The CFN Electron Microscopy Facility was used for collecting 3D reconstruction data and  real-time in-situ and ex-situ images.

Publication Reference

Lili Han1,2, Qingping Meng3, Deli Wang4, Yimei Zhu3, Jie Wang4, Xiwen Du2, Eric A. Stach1, and Huolin L. Xin,1 Interrogation of bimetallic particle oxidation in three dimensions at the nanoscale, Nature Communications 7, 13335 (2016).

10.1038/ncomms13335

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Other internet media: 

Press release: Scientists track chemical and structural evolution of catalytic nanoparticles in 3D
Scientists track chemical, structural evolution of catalytic nanoparticles in 3D

Acknowledgement of Support

This research is supported by the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. L. H. was supported by a scholarship from the China Scholarship Council (CSC) (201406250041). Q. M. and Y. Z. were supported by DOE-BES, Materials Sciences and Engineering Division under Contract DESC0012704.

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