Tag Archives: Claron J. Ridge

Producing catalytically active gold nanoparticles at absolute zero

A Sept. 8, 2016 news item on Nanowerk describes research into producing remarkably stable gold nanoparticles with catalytic capabilities (Note: A link has been removed),

An ultra-high-vacuum chamber with temperatures approaching absolute zero—the coldest anything can get—may be the last place you would expect to find gold. But a group of researchers from Stony Brook University (SBU) in collaboration with scientists at the Air Force Research Lab (AFRL) and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have just demonstrated that such a desolate place is ideal for producing catalytically active gold nanoparticles.

A paper describing the first catalyst ever produced using their new method, called Helium Nanodroplet Deposition (HND), was recently published in the Journal of Physical Chemistry Letters (“Development of a New Generation of Stable, Tunable, and Catalytically Active Nanoparticles Produced by the Helium Nanodroplet Deposition Method”).

A Sept. 7, 2016 Brookhaven National Laboratory news release by Alexander Orlov and Karen McNulty Walsh, which originated the news item, describes the work in more detail,

As lead researcher Alexander Orlov of SBU explains, HND works by boiling gold atoms in a vacuum to produce a vapor. The vaporized gold is then “picked up” by an extremely cold jet stream of liquid helium droplets that act to literally strike gold clusters against a solid collector downstream. Upon striking the collector, the liquid helium droplets instantly evaporate releasing helium gas and leaving behind unprecedentedly pure and stable gold nanoparticles.

“This new method to produce active nanoparticles offers unique opportunities to create materials with unprecedented properties to solve energy and environmental problems,” Orlov said.  “Our Brookhaven and AFRL collaborators made it possible for our students to access the most unique facilities in the world, which made all the difference in our research.”

Qiyuan Wu, a graduate student working in Orlov’s laboratory and first author on the paper, performed much of the work to develop the method. Michael Lindsay and Claron Ridge of AFRL provided state-of-the-art facilities at Eglin Air Force Base, one of only a few places in the world with the capabilities required to generate the gold nanoparticles using the new technique. And a team at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, used advanced imaging and characterization tools to study the nanoparticles’ catalytic activity.

Specifically, Brookhaven scientists Eric Stach and Dmitri Zakharov of the CFN and Shen Zhao, then a postdoctoral fellow working under Stach, developed a method to deposit the gold nanoparticles onto a “catalyst support” structure they use for characterizing the stability of other nanomaterials. They then studied the characteristics of the nanoparticles, including their stability under reaction conditions, using the Titan Environmental Transmission Electron Microscope at the CFN. Further characterization by Zhao and CFN staff member Dong Su using aberration-corrected Scanning Transmission Electron Microscopy allowed the SBU researchers to understand how the droplets form.

“This was part of a User project, that morphed into a collaboration,” said Stach, who leads the electron microscopy group at CFN. “It was a very nice study”—and an example of how the Office of Science User Facilities offer not just unique scientific equipment but also scientific expertise that can be essential to the success of a research project.

Nanoparticles are of high research interest due to their improved properties compared to bulk materials. They have revolutionized technologies aimed at improving sustainability such as fuel cells, photocatalysts, and solar panels. The gold nanoparticle catalysts produced in this study are capable of converting poisonous carbon monoxide gas into carbon dioxide gas, an essential reaction that occurs in the catalytic converters of cars to reduce pollution and lower impacts on the environment.

According to Orlov, the HND method is not limited to the production of gold nanoparticles, but can be applied to nearly all metals and can even produce challenging multi-metallic nanoparticles. The technique’s versatility and ability to produce clean and well-defined samples make it a powerful tool for the discovery of new catalysts and studying factors that affect catalyst performance.

The collaboration is currently researching how the parameters of HND can be adjusted to control catalyst performance.

Here’s a link to and a citation for the paper,

Development of a New Generation of Stable, Tunable, and Catalytically Active Nanoparticles Produced by the Helium Nanodroplet Deposition Method by Qiyuan Wu, Claron J. Ridge, Shen Zhao, Dmitri Zakharov, Jiajie Cen, Xiao Tong, Eoghan Connors, Dong Su, Eric A. Stach, C. Michael Lindsay, and Alexander Orlov. J. Phys. Chem. Lett., 2016, 7 (15), pp 2910–2914 DOI: 10.1021/acs.jpclett.6b01305 Publication Date (Web): July 13, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.

When an atom more or less makes a big difference

As scientists continue exploring the nanoscale, it seems that finding the number of atoms in your particle makes a difference is no longer so surprising. From a Jan. 28, 2016 news item on ScienceDaily,

Combining experimental investigations and theoretical simulations, researchers have explained why platinum nanoclusters of a specific size range facilitate the hydrogenation reaction used to produce ethane from ethylene. The research offers new insights into the role of cluster shapes in catalyzing reactions at the nanoscale, and could help materials scientists optimize nanocatalysts for a broad class of other reactions.

A Jan. 28, 2016 Georgia Institute of Technology (Georgia Tech) news release (*also on EurekAlert*), which originated the news item, expands on the theme,

At the macro-scale, the conversion of ethylene has long been considered among the reactions insensitive to the structure of the catalyst used. However, by examining reactions catalyzed by platinum clusters containing between 9 and 15 atoms, researchers in Germany and the United States found that at the nanoscale, that’s no longer true. The shape of nanoscale clusters, they found, can dramatically affect reaction efficiency.

While the study investigated only platinum nanoclusters and the ethylene reaction, the fundamental principles may apply to other catalysts and reactions, demonstrating how materials at the very smallest size scales can provide different properties than the same material in bulk quantities. …

“We have re-examined the validity of a very fundamental concept on a very fundamental reaction,” said Uzi Landman, a Regents’ Professor and F.E. Callaway Chair in the School of Physics at the Georgia Institute of Technology. “We found that in the ultra-small catalyst range, on the order of a nanometer in size, old concepts don’t hold. New types of reactivity can occur because of changes in one or two atoms of a cluster at the nanoscale.”

The widely-used conversion process actually involves two separate reactions: (1) dissociation of H2 molecules into single hydrogen atoms, and (2) their addition to the ethylene, which involves conversion of a double bond into a single bond. In addition to producing ethane, the reaction can also take an alternative route that leads to the production of ethylidyne, which poisons the catalyst and prevents further reaction.

The project began with Professor Ueli Heiz and researchers in his group at the Technical University of Munich experimentally examining reaction rates for clusters containing 9, 10, 11, 12 or 13 platinum atoms that had been placed atop a magnesium oxide substrate. The 9-atom nanoclusters failed to produce a significant reaction, while larger clusters catalyzed the ethylene hydrogenation reaction with increasingly better efficiency. The best reaction occurred with 13-atom clusters.

Bokwon Yoon, a research scientist in Georgia Tech’s Center for Computational Materials Science, and Landman, the center’s director, then used large-scale first-principles quantum mechanical simulations to understand how the size of the clusters – and their shape – affected the reactivity. Using their simulations, they discovered that the 9-atom cluster resembled a symmetrical “hut,” while the larger clusters had bulges that served to concentrate electrical charges from the substrate.

“That one atom changes the whole activity of the catalyst,” Landman said. “We found that the extra atom operates like a lightning rod. The distribution of the excess charge from the substrate helps facilitate the reaction. Platinum 9 has a compact shape that doesn’t facilitate the reaction, but adding just one atom changes everything.”

Here’s an illustration featuring the difference between a 9 atom cluster and a 10 atom cluster,

A single atom makes a difference in the catalytic properties of platinum nanoclusters. Shown are platinum 9 (top) and platinum 10 (bottom). (Credit: Uzi Landman, Georgia Tech)

A single atom makes a difference in the catalytic properties of platinum nanoclusters. Shown are platinum 9 (top) and platinum 10 (bottom). (Credit: Uzi Landman, Georgia Tech)

The news release explains why the larger clusters function as catalysts,

Nanoclusters with 13 atoms provided the maximum reactivity because the additional atoms shift the structure in a phenomena Landman calls “fluxionality.” This structural adjustment has also been noted in earlier work of these two research groups, in studies of clusters of gold [emphasis mine] which are used in other catalytic reactions.

“Dynamic fluxionality is the ability of the cluster to distort its structure to accommodate the reactants to actually enhance reactivity,” he explained. “Only very small aggregates of metal can show such behavior, which mimics a biochemical enzyme.”

The simulations showed that catalyst poisoning also varies with cluster size – and temperature. The 10-atom clusters can be poisoned at room temperature, while the 13-atom clusters are poisoned only at higher temperatures, helping to account for their improved reactivity.

“Small really is different,” said Landman. “Once you get into this size regime, the old rules of structure sensitivity and structure insensitivity must be assessed for their continued validity. It’s not a question anymore of surface-to-volume ratio because everything is on the surface in these very small clusters.”

While the project examined only one reaction and one type of catalyst, the principles governing nanoscale catalysis – and the importance of re-examining traditional expectations – likely apply to a broad range of reactions catalyzed by nanoclusters at the smallest size scale. Such nanocatalysts are becoming more attractive as a means of conserving supplies of costly platinum.

“It’s a much richer world at the nanoscale than at the macroscopic scale,” added Landman. “These are very important messages for materials scientists and chemists who wish to design catalysts for new purposes, because the capabilities can be very different.”

Along with the experimental surface characterization and reactivity measurements, the first-principles theoretical simulations provide a unique practical means for examining these structural and electronic issues because the clusters are too small to be seen with sufficient resolution using most electron microscopy techniques or traditional crystallography.

“We have looked at how the number of atoms dictates the geometrical structure of the cluster catalysts on the surface and how this geometrical structure is associated with electronic properties that bring about chemical bonding characteristics that enhance the reactions,” Landman added.

I highlighted the news release’s reference to gold nanoclusters as I have noted the number issue in two April 14, 2015 postings, neither of which featured Georgia Tech, Gold atoms: sometimes they’re a metal and sometimes they’re a molecule and Nature’s patterns reflected in gold nanoparticles.

Here’s a link to and a citation for the ‘platinum catalyst’ paper,

Structure sensitivity in the nonscalable regime explored via catalysed ethylene hydrogenation on supported platinum nanoclusters by Andrew S. Crampton, Marian D. Rötzer, Claron J. Ridge, Florian F. Schweinberger, Ueli Heiz, Bokwon Yoon, & Uzi Landman.  Nature Communications 7, Article number: 10389  doi:10.1038/ncomms10389 Published 28 January 2016

This paper is open access.

*’also on EurekAlert’ added Jan. 29, 2016.