New Chemical Instrument Uses Advanced Missile Technology

The instrument will be used to create vast databases of chemical catalysts, says Jochen Lauterbach, a Purdue assistant professor of chemical engineering.

He has applied the technique to the growing field of combinatorial chemistry, in which scientists use automated equipment to systematically create and test thousands of chemical samples in about the same amount of time it would have taken to test one sample with more conventional methods.

The new system developed at Purdue can analyze many samples within seconds. It is nearly 5,000 times faster than other technology in screening samples of catalysts that react with liquids, and at least 20 times faster in screening catalysts that react with gas, such as those used in catalytic converters for automotive exhaust systems and in numerous manufacturing processes.

The system, a novel application of infrared imaging, is detailed in an article in the May/June issue of the Journal of Combinatorial Chemistry, published by the American Chemical Society. The paper, which is the first to describe the system, appeared originally in the online version of the publication on March 15.

The new "rapid-scan Fourier transform infrared imaging system" designed and built by Lauterbach's team analyzes chemical samples in a range of infrared light that is invisible to the human eye. This light reveals the unique infrared signature that corresponds to a specific chemical, its so-called molecular fingerprint. The fingerprint identifies the molecules that have been absorbed onto the catalyst's surface, information that can be used to understand the molecular mechanisms in the reactions for each catalyst.

At the heart of the system is a recently declassified infrared-detection technology that was developed for heat-seeking missiles. The Purdue engineers mated the detector with an optical design, which they created from scratch with infrared lenses. The configuration of lenses in the instrument provides a large field of view, which means that many samples can be analyzed at the same time, says Lauterbach, whose team has been working on the system since 1998.

The instrument will speed up the analysis of samples used in combinatorial chemistry, where thousands of tiny plastic beads about the width of a human hair are coated with different catalysts. All of the beads, each bearing its own individual catalyst, are tested simultaneously in the same experiment. Then they are analyzed, one at a time, with laboratory equipment such as a mass spectrometer, a gas chromatograph or an infrared microscope to see how well they worked.

"This is very time-consuming if you want to screen 10,000 beads," Lauterbach says, noting that his instrument can screen hundreds of catalysts simultaneously in 15 seconds. "This is really going to make an impact."

Unlike some conventional techniques, the Purdue instrument carries out the analysis without destroying the samples, an advantage for researchers trying to conduct follow-up work with certain samples that show promise.

Lauterbach also is using the instrument to screen "gas-solid" catalysts for the eventual development of better automotive catalytic converters, devices that change the primary pollutants in car exhaust into less harmful compounds.

In gas-solid catalysis, a gas stream – the car's exhaust – flows over a solid catalyst typically made out of three metals: platinum, palladium and rhodium. The effectiveness of such catalysts are known to change drastically depending on small variations in the concentrations of the metals. But systematically screening tens of thousands of possible formulations is daunting.

"For three metals alone, you have thousands of different combinations of metal concentrations in this catalyst that you need to look at," Lauterbach says, noting that better catalysts will be needed to meet more stringent automotive emissions standards, especially for diesel-powered vehicles and equipment.

In addition to speeding up the screening process, the instrument is more sensitive than conventional equipment, so it will be used to reveal the molecular mechanisms involved in gas-solid catalysis. "And with that information, we can create a database, which we can use for the actual design of new catalysts," Lauterbach says.

Engineers are trying not only to find more effective versions of existing gas-solid catalysts, but also to develop catalysts made of less costly metals than platinum, palladium and rhodium. Besides its role in automotive pollution control, gas-solid catalysis is critical for many types of large-scale chemical manufacturing operations, including the processing of fertilizers, textiles, plastics and petroleum products. Just a slight improvement in a catalyst's efficiency translates into millions of dollars in manufacturing savings.

The next step in the research will be to use the technique in the actual search for better catalysts, Lauterbach says.

The research has been funded by the National Science Foundation.