{"492001":{"#nid":"492001","#data":{"type":"news","title":"For this Nanocatalyst, One Atom Makes a Big Difference","body":[{"value":"\u003Cp\u003ECombining 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.\u003C\/p\u003E\u003Cp\u003EAt 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\u2019s no longer true. The shape of nanoscale clusters, they found, can dramatically affect reaction efficiency.\u003C\/p\u003E\u003Cp\u003EWhile 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. Supported by the Air Force Office of Scientific Research and the Department of Energy, the research was reported January 28 in the journal \u003Cem\u003ENature Communications\u003C\/em\u003E.\u003C\/p\u003E\u003Cp\u003E\u201cWe have re-examined the validity of a very fundamental concept on a very fundamental reaction,\u201d said \u003Ca href=\u0022https:\/\/www.physics.gatech.edu\/user\/uzi-landman\u0022\u003EUzi Landman\u003C\/a\u003E, a Regents\u2019 Professor and F.E. Callaway Chair in the \u003Ca href=\u0022http:\/\/www.physics.gatech.edu\/\u0022\u003ESchool of Physics\u003C\/a\u003E at the Georgia Institute of Technology. \u201cWe found that in the ultra-small catalyst range, on the order of a nanometer in size, old concepts don\u2019t hold. New types of reactivity can occur because of changes in one or two atoms of a cluster at the nanoscale.\u201d\u003C\/p\u003E\u003Cp\u003EThe 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.\u003C\/p\u003E\u003Cp\u003EThe 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.\u003C\/p\u003E\u003Cp\u003EBokwon Yoon, a research scientist in Georgia Tech\u2019s Center for Computational Materials Science, and Landman, the center\u2019s director, then used large-scale first-principles quantum mechanical simulations to understand how the size of the clusters \u2013 and their shape \u2013 affected the reactivity. Using their simulations, they discovered that the 9-atom cluster resembled a symmetrical \u201chut,\u201d while the larger clusters had bulges that served to concentrate electrical charges from the substrate.\u003C\/p\u003E\u003Cp\u003E\u201cThat one atom changes the whole activity of the catalyst,\u201d Landman said. \u201cWe 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\u2019t facilitate the reaction, but adding just one atom changes everything.\u201d\u003C\/p\u003E\u003Cp\u003ENanoclusters with 13 atoms provided the maximum reactivity because the additional atoms shift the structure in a phenomena Landman calls \u201cfluxionality.\u201d This structural adjustment has also been noted in earlier work of these two research groups, in studies of clusters of gold which are used in other catalytic reactions.\u003C\/p\u003E\u003Cp\u003E\u201cDynamic fluxionality is the ability of the cluster to distort its structure to accommodate the reactants to actually enhance reactivity,\u201d he explained. \u201cOnly very small aggregates of metal can show such behavior, which mimics a biochemical enzyme.\u201d\u003C\/p\u003E\u003Cp\u003EThe simulations showed that catalyst poisoning also varies with cluster size \u2013 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.\u003C\/p\u003E\u003Cp\u003E\u201cSmall really is different,\u201d said Landman. \u201cOnce you get into this size regime, the old rules of structure sensitivity and structure insensitivity must be assessed for their continued validity. It\u2019s not a question anymore of surface-to-volume ratio because everything is on the surface in these very small clusters.\u201d\u003C\/p\u003E\u003Cp\u003EWhile the project examined only one reaction and one type of catalyst, the principles governing nanoscale catalysis \u2013 and the importance of re-examining traditional expectations \u2013 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.\u003C\/p\u003E\u003Cp\u003E\u201cIt\u2019s a much richer world at the nanoscale than at the macroscopic scale,\u201d added Landman. \u201cThese are very important messages for materials scientists and chemists who wish to design catalysts for new purposes, because the capabilities can be very different.\u201d\u003C\/p\u003E\u003Cp\u003EAlong 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.\u003C\/p\u003E\u003Cp\u003E\u201cWe 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,\u201d Landman added.\u003C\/p\u003E\u003Cp\u003EIn addition to those already named, the research team included first-author Andrew Crampton, Marian Rotzer, Claron Ridge and Florian Schweinberger from the Catalysis Research Center at the Technical University of Munich.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe experimental work has been supported by the European Research Council (ERC) through the advanced research grant (246645-ASC3), and by the DFG through project HE3454\/23-1. Support was also provided by the Air Force Office of Scientific Research (AFOSR) and by grant FG05\u201386ER45234 from the Office of Basic Energy Sciences of the US Department of Energy (DOE). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the sponsors.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Andrew S. Crampton, et al., \u201cStructure sensitivity in the nonscalable regime explored via catalyzed ethylene hydrogenation on supported platinum nanoclusters,\u201d (Nature Communications 2016). \u003Ca href=\u0022http:\/\/dx.doi.org\/10.1038\/ncomms10389\u0022\u003Ehttp:\/\/dx.doi.org\/10.1038\/ncomms10389\u003C\/a\u003E.\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia 30332-0181 USA\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Assistance\u003C\/strong\u003E: John Toon (404-894-6986) (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EResearchers 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.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Researchers have explained why platinum nanoclusters of a specific size range facilitate the hydrogenation reaction used to produce ethane from ethylene."}],"uid":"27303","created_gmt":"2016-01-27 22:51:23","changed_gmt":"2016-10-08 03:20:31","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2016-01-28T00:00:00-05:00","iso_date":"2016-01-28T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"491971":{"id":"491971","type":"image","title":"Nanocatalyst platinum","body":null,"created":"1454083200","gmt_created":"2016-01-29 16:00:00","changed":"1475895248","gmt_changed":"2016-10-08 02:54:08","alt":"Nanocatalyst platinum","file":{"fid":"204473","name":"nanocatalyst_platinum.jpg","image_path":"\/sites\/default\/files\/images\/nanocatalyst_platinum_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/nanocatalyst_platinum_0.jpg","mime":"image\/jpeg","size":974096,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/nanocatalyst_platinum_0.jpg?itok=OmbWZIaY"}},"491981":{"id":"491981","type":"image","title":"One-atom","body":null,"created":"1454083200","gmt_created":"2016-01-29 16:00:00","changed":"1475895248","gmt_changed":"2016-10-08 02:54:08","alt":"One-atom","file":{"fid":"204474","name":"one-atom.jpg","image_path":"\/sites\/default\/files\/images\/one-atom_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/one-atom_0.jpg","mime":"image\/jpeg","size":412615,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/one-atom_0.jpg?itok=vgmch3DS"}},"491991":{"id":"491991","type":"image","title":"Cluster comparison","body":null,"created":"1454083200","gmt_created":"2016-01-29 16:00:00","changed":"1475895248","gmt_changed":"2016-10-08 02:54:08","alt":"Cluster comparison","file":{"fid":"204475","name":"multiple-catalysts.jpg","image_path":"\/sites\/default\/files\/images\/multiple-catalysts_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/multiple-catalysts_0.jpg","mime":"image\/jpeg","size":619521,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/multiple-catalysts_0.jpg?itok=1Z_ioE5s"}}},"media_ids":["491971","491981","491991"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"},{"id":"150","name":"Physics and Physical Sciences"}],"keywords":[{"id":"2506","name":"catalyst"},{"id":"2529","name":"cluster"},{"id":"63631","name":"nanocatalyst"},{"id":"2528","name":"nanocluster"},{"id":"7531","name":"platinum"},{"id":"9180","name":"Uzi Landman"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39531","name":"Energy and Sustainable Infrastructure"},{"id":"39471","name":"Materials"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E404-894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}