The importance of good neighbors of nanoparticles for catalysis

03. November 2020 ((Nanowerk News) Are you affected by your neighbors? This is what nanoparticles are like in catalysts.

New research from the Swedish Technical University of Chalmers published in the professional journals Advances in science and Communication with nature (“Copper catalysis under operando conditions – bridging the gap between the investigation of individual nanoparticles and the averaging in the catalyst bed”) shows how the closest neighbors determine how well nanoparticles function in a catalyst.

“The long-term goal of research is to identify ‘super particles’ in order to contribute to more efficient catalysts in the future. In order to use the resources better than today, we also want as many particles as possible to be active and take part in the catalytic reaction at the same time, “says research director Christoph Langhammer from the Department of Physics at Chalmers University of Technology.

Neighborhood collaboration for catalysis. First, a series of copper nanoparticles is isolated in a gas-filled nanotube. The researchers then use light to measure how they affect each other by turning oxygen and carbon monoxide into carbon dioxide. The long-term goal of the research is to find a resource-efficient “neighborhood cooperation” in which as many particles as possible are catalytically active at the same time. (Image: David Albinsson / Chalmers University of Technology)

Imagine a large group of neighbors gathered to clean up a shared courtyard. They went to work and each contributed to the group work. The only problem is that not everyone is equally active. While some are working hard and efficiently, others are strolling around, chatting and drinking coffee. If you just look at the bottom line, it is difficult to know who worked the most and who just relaxed. To determine this, you would need to monitor each person throughout the day. The same applies to the activity of metallic nanoparticles in a catalyst.

Finding more effective catalysts through neighborly collaboration

Several particles within a catalyst influence the effectiveness of the reactions. Some of the particles in the crowd are effective while others are inactive. However, the particles are often hidden in different “pores”, similar to a sponge, and are therefore difficult to examine.

To see what really happened in a catalyst pore, the researchers at Chalmers University of Technology isolated a handful of copper particles in a transparent glass nanotube. If several are gathered in the small gas-filled tube, it can be examined which particles do what and when under real conditions.

What happens in the tube is that the particles come into contact with an incoming gas mixture of oxygen and carbon monoxide. When these substances react with one another on the surface of the copper particles, carbon dioxide is produced. It’s the same reaction that occurs when exhaust fumes are cleaned in a car’s catalytic converter, except that they often use particles of platinum, palladium, and rhodium to break down toxic carbon monoxide instead of copper. However, since these metals are expensive and scarce, researchers are looking for more resource-efficient alternatives.

“Copper can be an interesting candidate for the oxidation of carbon monoxide. The challenge is that copper tends to change itself during the reaction and we need to be able to measure what state of oxidation a copper particle is when it is most active in the catalyst with our nanoreactor, which mimics a pore in a real catalyst, this is now possible, “says David Albinsson, postdoctoral fellow at the Department of Physics in Chalmers and lead author of two scientific articles recently published in Science Advances and Nature Communications.

Anyone who has seen an old copper roof or statue will recognize how the red-brown metal soon turns green after contact with air and pollutants. Something similar happens with the copper particles in the catalytic converters. It is therefore important that they work together effectively.

“What we have now shown is that the oxidation state of a particle can be dynamically influenced by its closest neighbors during the reaction. The hope is therefore that we can ultimately save resources with the help of optimized neighborly cooperation in a catalyst, ”says Christoph Langhammer, professor at the Physics Department in Chalmers.