NEWS OF THE WEEK FROM T H E ACS
MEETING
ORIGIN OF GOLDS CATALYTIC ACTIVITY Two atomic layers are key to the catalytic activity of nanoscale gold
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N T H E BULK, GOLD IS ESSEN-
tially inert. But in nanostructuredform,the noble metal can be a surprisingly good catalyst. Researchers may have just uncovered the secret of the element's high catalytic activity In a talk at the ACS national meeting in Philadelphia, chemistry professor D. Wayne Goodman of Texas A&M University described experiments that identify a gold structure that is two atomic layers thick as the form of the metal responsible for gold's ability to catalyze the oxidation of carbon monoxide to an unprecedented degree.The study addresses questions regarding catalytic reaction mechanisms and eventually may lead to more active commercial catalysts. Scientists have been interested in gold's potential for catalyzing CO and propylene oxidation and other reactions since the unexpected discovery by Japanese researchers several years ago that nanometer-sized gold clusters LIFE
supported on metal oxides such asTi0 2 exhibit high catalytic activity for certain reactions. Several research teams have tried to uncover the origin of the nanostructured metal's unique reactivity The results have prompted debate in the catalysis community, with researchers questioning the role of particle thickness and shape, metal oxidation state, and interactions with the oxide support material. Now, some of those questions have been answered. Using vapor deposition methods, Goodman and postdoc MingShu Chenprepared model catalysts and used them to study CO oxidation, a reaction relevant to fuel-cell processes and similar to propylene oxidation. The catalysts, which feature structures that were challenging to prepare and verify experimentally, consist of atomically ordered monolayer and bilayer films ofgold that cover aTi0 2 support. The precise arrangement of gold atoms in the model sys-
tems eliminates particle shape and direct interactions withTL02 as factors in the catalytic reaction mechanism. Goodman reported that the bilayer gold catalyst is more than 10 times more active for CO oxidation than the monolayer form and that reactivity decreases when gold coverage exceeds two atomic layers. In addition, the reaction proceeds roughCATALYTIC ly 50 times faster on the POWERHOUSE Chemists bilayer catalyst than it prepared monolayer (bottom does on Au/Ti0 2 catastructure) and bilayer films lysts prepared via conof gold atoms (yellow and ventional synthesis red) on titania (purple = Ti; methods [Science, pub- oxygen not shown). They lished online Aug. 26, found that a specific twohttp://dx.doi.org/10.ll layer gold structure (top) 26/science.ll02420}. catalyzes CO oxidation with "These results say exceptional activity. that titania is activating gold through an electronic effect—by making gold slightly electron rich— rather than by titania interacting with {CO and oxygen] directly at the gold-titanium interface," Goodman asserted. The two-layer structure readily lends itself to examination by computational methods, he added. "The theoreticians have already begun calculating."—MITCH JACOBY
SCIENCES
Clariant Pushes Microreactors For Pharmaceuticals
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number of firms are looking into microreactors to produce fine chemicals, but Clariant Pharmaceuticals, a unit of Swiss specialty chemicals maker Clariant, is in an all-out push to develop the modular gram-scale devices to make pharmaceutical intermediates and active pharmaceutical ingredients. The company will be using experience with the technology gained over three years and formalized in January with the establishment of the Clariant Competence Center MicroReaction Technology. C3MRT's facilities in Frankfurt, Germany, include two microreactor pilot plants and a dedicated laboratory. The use of parallel microreactor modules makes it possible to turn out kilogram or even ton quantities of a product, Clariant says. C3MRT's mission is to custom-synthesize a wide range of molecules for Clariant's various units. Even so, Ralf Pfirmann,
HTTP://WWW.CEN-ONLINE.ORG
global pharmaceutical market management director, says, "Use of microreactors in pharmaceutical synthesis has the potential to deliver molecules at much better yields, with higher selectivities, and with economics heretofore not possible." Christian Wille, who is responsible for technical development, believes that microreactor process development "can be done once with the knowledge that it will be effective through the life cycle of a compound, eliminating the risk of encountering unmakeable compounds at the large scale." Other firms, such as Degussa, have begun to consider commercial use of microreactor technology. And earlier this year, Sigma-Aldrich installed and began to evaluate a microreactor system at its R&D facility in Buchs, Switzerland (C&EN, July 5, page 18).-MARC REISCH
C&EN
/ AUGUST
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