NEWS OF THE WEEK SCIENCE
COMPUTATIONAL CATALYSIS Theoretical study validates decades-old assumption and advances rational design
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ICTURE RESEARCHERS WORK-
ing busily at industrial cata lyst development and what comes to mind? Benchtop reac tors and laboratory-scale gas man ifolds, most likely But thanks in part to a new study that image may change as investigators begin huntingfornew and effective cat alysts using computers. Scientists in Denmark have shown that computational meth ods can be used to determine rel ative catalytic activities among a group of transition metals. The study advances rational ap proaches to catalyst design and verifies a 70-year-old empirical chemistry axiom. The investigation was con ducted by Jens K. Norskov, a physics professor at Technical University of Denmark, Lyngby and graduate students Ashildur Logadottir and Thomas H. Rod [J. Catalysis, published online, http:/AvwwideaHbrarycom/links/ doi/10.1006/jcat.2000.3087].The team also includes Danish scien tists at the University of Aarhus and at catalyst manufacturer Haldor Topsoe. Chemists studying reaction kinetics commonly invoke a sim plifying assumption, which states that, for agiven chemical reaction, the activation energy and reaction energy are related linearly The Bronsted-Evans-Polanyi rule provides a direct way to relate changes in activation energy to changes in bonding characteris tics, such as bond strength. J. W (Hans) Niemantsverdriet, a professor in the department of chemistry and chemical engi neering at Eindhoven University of Technology the Netherlands, HTTP://PUBS.ACS.ORG/CEN
explains that the Bronsted-EvansPolanyi rule is used, among other areas, in modeling studies of het erogeneous catalytic reactions to compare related systems that dif fer, for example, in reactant cov erage or catalyst surface structure. The Norskov group's paper validates the "clever but unproven assumption" for an important class of surface reactions on a number of surfaces, Niemants verdriet says. "This elegant result has great significance." Using industrial ammonia syn thesis as a test case, Norskov and coworkers incorporate the Bron
sted-Evans-Polanyi relation and a microkinetic model in a density functional theory computation and show that it is possible to calculate catalytic activities as a function of nitrogen binding strength. The group compares the activities of several transition metals, including ruthenium, iron, copper, palla dium, and others, and finds that iron and ruthenium are predicted to generate the highest rates of reaction. The finding agrees with experimental observation. In addition to ranking catalysts by reaction rate, the theoretical method also provides a quantita tive way to distinguish candidate materials by differences in elec tronic and geometrical properties. "We are reaching a point where calculations can be used broadly to determine relative reactivities of various catalysts," Norskov says. "That gives us a real opportunity to use computation as an important input in catalyst design."—MITCH JACOBY
E N V I R O N M E N T
Lead Reporting Change Delayed
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•he Environmental Protection Agency has delayed until April 17 a new rule that requires more facilities, including chemical plants, to file Toxics Release Inventory (TRI) reports on lead. The delay is a result of a directive from President George W. Bush to review rules issued near the end of the Clinton Administration (C&EN, Jan. 29, page 12). The rule, which was to take effect Feb. 16, requires TRI reporting for facilities that use or release at least 100 lb of lead per year. Previously, the reporting threshold for lead was the same as for most other TRI materials: 25,000 lb for chemicals manufactured at a facility and PAPERWORK 10,000 lb for substances used by a plant. EPA Estimated additional TRI lowered the reporting threshold because it clas reports for lead sifies lead as a persistent bioaccumulative toxic. The American Chemistry Council hopes EPA Other Electrical will use the 60-day delay to review the scientific 27% uipment 36% basis for the rule, says Michael Walls, counsel Chemicals for the trade group. Industry argues that EPA 5% should not classify lead as highly bioaccumula tive. Also, since lead levels in the environment have decreased in recent years, EPA lacks a Electric health or environmental reason to lower the TRI utilities reporting threshold, Walls says. Primary 6% Bulk To change the new TRI reporting threshold for metals petroleum 20% lead, EPA would have to issue a proposal, accept 6% public comment on it, then issue a new rule. Additional reports = 9,813 This formal process generally takes 18 months SOURCE: Environmental Protection Agency at a minimum.—CHERYL HOGUE
C&EN
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FEBRUARY
26, 2001
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