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December 22, 2003

UCSD Insight Into One of the Holy Grails of Chemistry
May Permit the Design of Better Catalysts for Fuel Refinement

By Sherry Seethaler

Snapshots of a catalytic process in action taken by researchers at the University of California, San Diego provide important information for the first time about the chemical action of catalysis, and could have implications for improving the energy efficiency and environmental safety of the reactions involved in the refinement of the hydrocarbons in petroleum.

The study, to be published in the December 24th issue of the Journal of the American Chemical Society, reports the structure of a uranium-based model catalyst designed in the laboratory of UCSD assistant professor of chemistry and biochemistry Karsten Meyer. Although the model was designed two years ago, this is the first time the researchers were able to gain precise information about the orientation of the atoms constituting the model and how the hydrocarbon reactant molecule is activated by it. They accomplished this using X-ray crystallography, a technique in which X-rays are passed through crystals of a molecule, accurately revealing the locations of the atoms.

“Catalysts have been developed to facilitate reactions of hydrocarbons, but it has been more like alchemy because until now we didn’t know how this was working,” says Meyer. “Using X-ray crystallography, we have been able to show exactly how the atoms
in the reactant molecules and catalyst interact, and this information could make it possible to design super-effective catalysts for these reactions.”

Molecular model of catalyst with
uranium atom shown in pink.
Credit: Ingrid Castro-Rodriguez, UCSD

Catalysts of the sort modeled by Meyer are valuable in the production of more useful fuels from methane. During oil refinement, large quantities of methane are produced, but because methane is a gas, highly flammable and difficult to store, it must be converted into something else to make it a useful fuel. So methane, the smallest hydrocarbon, is put through a series of chemical reactions, requiring high temperature and pressure, to remove hydrogen and link multiple carbons together to build larger molecules.

An understanding of how catalysts facilitate the removal of the hydrogen from the carbon in these types of reactions has been so elusive that in 1996 chemists listed it as one of the Holy Grails of chemistry. But it is not solely a matter of academic interest according to Meyer, as better catalysts for this process could save tremendous amounts of energy and reduce the level of pollutants produced.

As molecules react to form new molecules, they rapidly transition through a highly unstable intermediate compound. Catalysts work by stabilizing this intermediate compound, and this reduces the amount of energy that needs to be put in to make the reaction occur.

The catalytic model designed by the Meyer group consists of an atom of uranium in the center surrounded by three large cyclic groups of atoms. The researchers selected uranium for the center of the catalyst because, as the heaviest naturally occurring element, it is large, electron rich, and able to do many different chemical reactions. X-ray crystallography revealed that a group of atoms in the model compound provides a
pocket around the top of the uranium atom in which the hydrocarbon molecule is altered by contact with the uranium atom.

“The catalyst provides a platform for the reactant as well as a rim around the platform that helps to orient the reactants and provide the right environment for the reaction,” explains Meyer.

These new findings provide a snapshot of how modern catalysts work and open possibilities to create a new generation of efficient tools to form and modify carbon-carbon bonds from limited natural resources, such as natural gas and raw oil. As Meyer points out, this is important not only in transportation and electricity generation, but also in the development of products derived from natural resources.

“Natural gas, raw oil, and fuel is a limited natural resource that we simply burn away; not only with very inefficient cars and power plants but also with inefficient catalysts that produce our daily medicine and supplements,” says Meyer. “If we run out of oil the worst part is not that we have to walk again, but that we don't get our daily dose of drugs, such as blood pressure and cancer curing medicine.”

The other UCSD researchers involved with this project were Ingrid Castro-Rodrigeuz, the first author on the paper; Hidetaka Nakai; Peter Gantzel; and Lev Zakharov and Arnold Rheingold. The study was supported by a grant from the American Chemical Society.

Media Contacts: Sherry Seethaler (858) 534-4656

Comment: Karsten Meyer (858) 822-4247

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