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First look inside nanoscale catalysts shows ‘defects’ are useful

11/01/2017

Study in leading science journal Nature validates hypothesis that atomic defects are essential to catalytic reactivity

Using one of the world’s brightest light sources to peer inside some of the world’s smallest particles, scientists have confirmed a longstanding hypothesis: that atomic disorder or “defects” at the edges of nanoparticles is what makes them effective as chemical change agents.

The process by which a change agent, or catalyst, accelerates a chemical reaction is key to the creation of many materials essential to daily life, such as plastics, fuels and fertilizers. Known as catalysis, this process is a basic pillar of the chemical industry, making chemical reactions more efficient and less energy-demanding, and reducing or even eliminating the use and generation of hazardous substances.

Although catalysts have been used in industry for more than a century, scientists have yet to observe how their structure impacts their effectiveness as change agents. That’s because catalysts are typically tiny metallic nanoparticles made of precious metals such as Platinum, Palladium or Rhenium. The extreme smallness that makes nanoparticles such effective catalysts also makes it hard to see how they work.

If scientists could peer inside individual nanoparticles’ chemical reactions at a nanoscopic level, they would gather a treasure of useful knowledge for the design of improved catalysts to address the pressing energy needs of the 21st century.

That type of knowledge may now be close at hand, thanks to new research published January 11 in the journal “Nature”. In the new study — led by Dr. Elad Gross from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem, and Prof. F. Dean Toste from the College of Chemistry at University of California, Berkeley, and Chemical Science Division at Lawrence Berkeley National Laboratory — researchers directly observed for the first time how metallic nanoparticles, used as catalysts in numerous industrial processes, activate catalytic processes.

Using a light source one million times brighter than the sun, the researchers were able to observe chemical reactivity on single Platinum particles similar to those used as industrial catalysts. What they found is that chemical reactivity primarily occurs on the particles’ periphery or edges, while lower reactivity occurs at the particles’ center.

The different reactivity observed at the center and edges of Platinum particles corresponds to the different properties of the Platinum atoms in the two locations. The atoms are mostly flat at the center, while they’re corrugated and less-ordered at the edges. This disorderly or “defective” structure means that Platinum atoms at the edges are not totally surrounded by other Platinum atoms, and will therefore form stronger interactions with reactant molecules. Stronger interactions can activate the reactant molecules and initiate a chemical reaction that will transform the reactant molecule into a desired product.

The research findings validate a well-known hypothesis in the world of catalysis, which correlates high catalytic reactivity with high density of atomic defects. It also shows, for the first time, that the enhanced reactivity of defected sites can be identified at the single-particle level.

“Our findings provide insights about the ways by which the atomic structure of catalysts controls their reactivity. This knowledge can direct the design of improved catalysts that will make chemical process greener, by decreasing the amount of energy that is consumed in the process and preventing the formation of unwanted, potentially hazardous, products,” said Dr. Elad Gross, from the Institute of Chemistry and the Center for Nanoscience and Nanotechnology at the Hebrew University of Jerusalem.

To peer into individual nanoparticles, researchers focused a bright infrared beam generated in a synchrotron source (Advanced Light Source, Lawrence Berkeley National Laboratory) into a thin probe with an apex diameter of 20 nanometers. The probe acts as an antenna, localizes the infra-red light in a specific range, and by that provides the capabilities to identify molecules which reside on the surface of the catalytic nanoparticles. By scanning the particles with the nanometric probe while it is being radiated by the infrared light, the researchers were able to identify the locations and conditions in which chemical reaction occurs on the surface of single particle.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

PHOTO: http://media.huji.ac.il/new/photos/hu170110_nano.tif - Chemical reactivity was identified on the surface of single Platinum nanoparticles, which are similar to the particles which are used as catalysts in various industrial processes. The chemical reactivity was measured by focusing a bright infrared beam into the apex of a thin tip with a diameter of 20 nm that monitored the chemical reactivity on the particle’s surface. (Credit: Hebrew University of Jerusalem)

CITATION: Chung-Yeh Wu, William J. Wolf, Yehonatan Levartovsky, Hans A. Bechtel, Michael C. Martin, F. Dean Toste, & Elad Gross. High-spatial-resolution mapping of catalytic reactions on single particles. Nature, Advance Online Publication (AOP) on January 11, 2017. doi:10.1038/nature20795. Paper will be online at http://dx.doi.org/10.1038/nature20795.

- Dov Smith

First look inside nanoscale catalysts shows ‘defects’ are useful
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Asian Religious Leaders Discuss Peace, Environment With Israeli Counterparts at Hebrew University's Truman Institute

13/09/2016

A delegation of Asian religious leaders visited the Hebrew University of Jerusalem today to hold a day of discussions at the Harry S. Truman Research Institute for the Advancement of Peace. The leaders met with their Israeli counterparts from religion and academia to exchange ideas on issues ranging from the advancement of peace to the protection of environment.

The delegation included representatives of the Buddhist, Hindu, Jain, Shinto, Sikh, Taoist and Zoroastrian faiths, from countries including China, India, Japan, Myanmar, South Korea and Taiwan.

The meeting opened with a prayer and meditation session, followed by discussions about safeguarding the ecology of planet earth in the industrial age, and the role of religious leadership in peacemaking.

Bawa Jain, Secretary General of the World Council of Religious Leaders, said: "Participants in this conference are leaders of forty percent of the world's population, with over three billion followers. That this day took place, and at the Truman Institute, is natural because the Institute is a meeting place where politics, religion and culture come together."

The meeting was part of "Ancient Traditions, Contemporary Realities: A Meeting of Israel-Asia Faith Leaders," a first-of-its kind conference organized by the Israeli Foreign Ministry, the American Jewish Committee and the World Council of Religious Leaders. 

Asian Religious Leaders Discuss Peace, Environment With Israeli Counterparts at Hebrew University's Truman Institute
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Bees Diversify Diet to Take the Sting Out of Nutritional Deficiencies

13/04/2016
New research shows that honey bees forage for a diet that balances their colony’s specific nutritional deficits

While pesticides and pathogens pose clear threats to honey bee health, the need of bee colonies for balanced nutrition is gaining increasing appreciation. As colonies are kept in agricultural areas for crop pollination, they may encounter nutritional deficits when foraging predominantly on one pollen source. In California almond orchards for instance, 1.6 million colonies are kept every year, despite the risk of low floral diversity, which can reduce the life expectancy of bees.

In light of the challenge that agricultural intensification poses for pollinator habitats, Dr. Harmen Hendriksma and Prof. Sharoni Shafir from the Hebrew University of Jerusalem report that honey bee colonies are astoundingly resilient to nutritional stress. In new research reported in the journal Behavioral Ecology and Sociobiology, they found that bees can shift their foraging effort towards resources that complement nutritional deficits.

The research was conducted at the B. Triwaks Bee Research Center, Department of Entomology, The Robert H. Smith Faculty of Agriculture, Food and Environment, at the Hebrew University of Jerusalem.

In their experiment, eight honey bee colonies were kept in screened enclosures and fed pollen substitute diets that were deficient in particular essential amino acids. Subsequently, the bees were tested for their dietary choice, between the same diet previously fed, a different diet that was similarly deficient, or a diet that complemented the deficiency. The foragers preferred the complementary diet over the same or similar diets.

This result indicates that honey bee colonies not only attempt to diversify their diet, but that they bias their foraging effort towards a diet that specifically balances nutritional deficits of the colony. How bees perceive and evaluate nutrient composition needs further elucidation. This new-found ability of honey bees to counter deficient nutrition contributes to mechanisms that social insects use to sustain homeostasis at the colony level.

“This research indicates that honey bee colonies strive to balance their nutrition if appropriate floral resources are available. Bee colonies can benefit by this type of resilience when food options are sparse, for instance at certain sites or in seasons of dearth. Since alternative floral resources can help bees to balance their nutritional needs, this should serve as an incentive for everyone to plant flowers, wherever and whenever they can,” said Dr. Harmen Hendriksma.

“Our research with bees continues to reveal their remarkable abilities. Honey bee colonies must maintain a balanced diet for optimal health, and bee foragers seem to have evolved the sophisticated ability to bias their efforts towards finding food that balances the colony’s nutritional deficiencies. In so doing they remind us that in nutrition, as in many other things, maintaining the proper balance is key,” said Prof. Sharoni Shafir.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

VIDEO 1: https://youtu.be/WqbDrAJjRkQ - Honey bee workers in this video hover over feeding dishes with different diets. While flying, bees may distinguish differences by sight and by scent. Here, bees were given a choice between 34 different diets. Notably, protein content was found least explanatory for their choice behavior, while their preference was best explained by the foods color intensity and caloric contents (please see the supplements to the paper).  (Video credit: Harmen P Hendriksma)

VIDEO 2: https://youtu.be/YyTKbRd2uWQ - Honey bee workers in this video are collecting diet from feeding dishes. Bees touch the diet with their antennas, their feet, and mouth parts. Bees have receptors on these body parts, and it is likely that bees are probing the diet for taste, smell and texture. (Video credit: Harmen P Hendriksma)

FUNDING: The research was funded jointly by a grant from the BBSRC, NERC, the Wellcome Trust, Defra, and the Scottish Government under the Insect Pollinators Initiative (grant no: BB/I000968/1), and with partial support from the Orion Foundation.

REFERENCE: Harmen P. Hendriksma , Sharoni Shafir. Honey bee foragers balance colony nutritional deficiencies. Behavioral Ecology and Sociobiology. April 2016, Volume 70, Issue 4, pp 509-517.  doi:10.1007/s00265-016-2067-5 (link: http://link.springer.com/article/10.1007/s00265-016-2067-5)

Bees Diversify Diet to Take the Sting Out of Nutritional Deficiencies
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