Catalysts are the pacesetters of the chemical industry, speeding reactions that are vital to the manufacture of a host of products such as drugs, synthetic fibers and plastics. Now researchers at the Weizmann Institute of Science have found that a catalyst's performance can be dramatically improved by adjusting the structural orientation of its molecules.
When used in solution, catalysts interact with surrounding molecules in a random, free-floating "mess." The Weizmann study, published in the December 21 issue of Science, shows that when all the molecules of a soluble catalyst are neatly arranged so that they are held close to one another and point in a particular direction, catalytic efficiency jumps by a factor of 140.
With at least 20 percent of the gross national product of the United States dependent on industrial processes involving catalysts, improving catalytic performance may have a major economic impact. The new study's findings may also have important implications for basic research in such areas as supramolecular chemistry and coordination chemistry.
The study was conducted by postdoctoral fellow Dr. Karl Toellner and staff scientist Dr. Ronit Popovitz-Biro under the guidance of Prof. David Milstein of the Organic Chemistry Department and Prof. Meir Lahav of the Materials and Interfaces Department.
The scientists worked with a soluble rhodium- complex catalyst. The chemical industry uses similarsoluble metal-based catalysts, called homogenous catalysts, to produce millions of tons of chemicals annually. The researchers compared the performance of the rhodium complex when its molecules were arranged in two different ways. In the first case, the catalyst's molecules floated about randomly in solution; in the second, they were arranged in "tidy" rows on a glass plate. This is the first time that such a comparative experiment has been performed.
Not only was the "tidy" version of the catalyst more efficient, it was also more selective, making it easier to control chemical reactions. When added to a solution containing acetone and butanone, which are nearly identical in chemical composition, it only catalyzed acetone's reaction with hydrogen to produce isopropanol. In contrast, its "messy" counterpart did not distinguish between acetone and butanone and catalyzed reactions with both.
According to Prof. Milstein, the differences probably arise because the molecules of the uniformly-oriented catalyst "cooperate" with one another, although it's not yet clear how.
Weizmann Institute researchers are currently seeking to explain their findings and are extending their studies to other catalytic reactions.
This work has opened a new avenue of research into how catalysts' structure affects their activity.
ADDITIONAL INFORMATION
Prof. Lahav holds the Margaret Thatcher Chair of Chemistry and Prof. Milstein, the Israel Matz Chair in Organic Chemistry. This research was funded in part by the Minerva Foundation, the Israel Science Foundation and the German-Israeli Foundation.
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