Unveiling the Dance of Atoms: The Intricate Dynamics of Gold Nanoclusters in Catalysis

Understanding the active site at an atomic level is of great importance when designing a catalyst. Here, the evolution of atomically precise noble metal nanocluster catalyts is studied under the water-gas shift reaction.
Published in Chemistry and Materials
Unveiling the Dance of Atoms: The Intricate Dynamics of Gold Nanoclusters in Catalysis
Like

Share this post

Choose a social network to share with, or copy the shortened URL to share elsewhere

This is a representation of how your post may appear on social media. The actual post will vary between social networks

In the ever-growing quest for greener energy solutions, hydrogen has emerged as a promising candidate, boasting high energy content and potential for clean fuel production. Among the various methods, the water-gas shift (WGS) reaction stands out. However, achieving efficient WGS catalysts requires a deep understanding of catalyst structures at the atomic level.

Ligand-protected metal nanoclusters have recently captured the spotlight, offering atomic precision, well-defined structures, and unique molecular-like properties. In our recent paper, we studied the dynamic behavior of platinum and copper dopants within gold nanoclusters supported on ceria catalysts, with a focus on their role in the WGS reaction.

We  synthesized and characterized four types of nanoclusters: monometallic Au, bimetallic CuAu, PtAu, and trimetallic CuPtAu nanoclusters (Figure 1), which were then supported on ceria and tested as catalysts in the WGS reaction.

Structure of the (doped) nanoclusters based on reported crystal structures.
Structure of the (doped) nanoclusters based on reported crystal structures.

The first suprise came with the results of the catalytic activity. Bimetallic PtAu (and CuAu) clusters outperformed their trimetallic counterparts, showing increased activity and selectivity. The dance of these atoms continued through multiple catalytic runs, with PtAu clusters demonstrating remarkable stability compared to their trimetallic counterparts.

Catalytic activity of the nanocluster catalysts (pretO 2 and pretH 2) in the water-gas shift reaction from RT to 300 °C
Catalytic activity of the nanocluster catalysts in the WGS reaction from RT to 300 °C.

Furtermore, high-resolution transmission electron microscopy (HRTEM) studies provided a glimpse into the atomic world of these nanoclusters. The subnanometric size and excellent dispersion of Au clusters on ceria support remained unchanged even after the WGS reaction, showcasing the stability of these catalysts.

. HRTEM images of the nanocluster catalysts as prepared (fresh) and after the WGS reaction (used).
HRTEM images of the nanocluster catalysts as prepared (fresh) and after the WGS reaction (used).

Using operando X-Ray absorption fine sturcture spectroscopy (XAFS), we were able visualize the movement of the dopants during the catalytic process. Now picture this: as we subjected our catalysts to pretreatment and the WGS reaction, copper decided to take a journey. It migrated, forming clusters on the ceria support. On the other hand, platinum showed off its moves by creating single-atom active sites on the gold cluster surface. The result? Enhanced catalytic performance. 

While the XAFS analysis was anything but trivial, we were able to unravel this mysterious ballet of atoms and display it in the following Figures. 

 a , b XANES spectra at Au L 3-edge of the nanocluster catalysts a before the reaction (without pretreatment) and b after WGS reaction (used); c EXAFS R-Space of the catalysts after both pretreatments (pretO 2 and pretH 2) in dotted lines and after WGS reaction (solid lines)
 a,b XANES spectra at Au L3-edge of the nanocluster catalysts a before the reaction (without pretreatment) and b after WGS reaction (used); c EXAFS R-Space of the catalysts after both pretreatments (pretO2 and pretH2) in dotted lines and after WGS reaction (solid lines).

Espacially the extended X-Ray absorption fine structure spectroscopy (EXAFS) seen in Figure 4c already hints at some unexpected changes. The Au-Au coordination number (CN) increases after the WGS rreaction from 6 to 7-8 for the bimetallic and even to 10 for the trimetallic clusters. But we cannot yet say anything for certain.

This is where the Cu-K edge analysis comes into play. Looking at the X-Ray absorption near edge structure spectroscopy (XANES) study in Figure 5, the dance of the copper atoms starts to gain more clarity. The strong interaction of the dopants with the ceria surface can be seen. 

XANES spectra at Cu K-edge of the nanocluster catalysts before the reaction (without pretreatment) and after WGS reaction (used)
XANES spectra at Cu K-edge of the nanocluster catalysts before the reaction (without pretreatment) and after WGS reaction (used).

To fully understand the performance, the EXAFS of the Cu-K edge is needed. Here, an increase in the CN of Cu-Cu is visible, which further coroborates the aforementioned affirmations. But to see this, as well as an equally interesting operando DRIFTS study of these nanoclusters, we invite you to read the paper linked at the top of this post.

To conclude, finding new energy sources is of great importance for the future of the world we live in and hydrogen is a great candidate. The WGS shift reaction is a great way to produce it, but a deep understanding of the catalyst is needed to fully maximize its efficiency. Understanding the intricate dynamics of the dopants in these nanoclusters, thus unveiling the dance of these atoms helps us on our way to design an increasingly effective catalyst.

Please sign in or register for FREE

If you are a registered user on Research Communities by Springer Nature, please sign in

Follow the Topic

Materials Chemistry
Physical Sciences > Chemistry > Materials Chemistry
Heterogeneneous Catalysis
Physical Sciences > Chemistry > Materials Chemistry > Catalytic Materials > Heterogeneneous Catalysis
Spectroscopy
Physical Sciences > Chemistry > Physical Chemistry > Spectroscopy

Related Collections

With collections, you can get published faster and increase your visibility.

Plasmon-mediated chemistry

This collection aims to cover a comprehensive range of topics related to plasmon-mediated chemical reactions.

Publishing Model: Open Access

Deadline: Jan 31, 2024

Coacervation in systems chemistry

This Guest Edited Collection aims to bring together research at the intersection of systems chemistry and coacervation. We welcome both experimental and theoretical studies.

Publishing Model: Open Access

Deadline: Dec 31, 2023