IR Imager Uses Missile Technology
Michael D. Wheeler
WEST LAFAYETTE, Ind. -- A form of infrared imaging developed by the military for heat-seeking missiles is helping researchers rapidly identify catalysts that could improve chemical manufacturing processes and pollution-control systems. The imaging technique could pave the way for the simultaneous testing of thousands of chemicals in the time it would take to test one sample with more conventional methods.
For years, scientists have sought to better understand and evaluate "gas/solid" catalysts. These materials are important in the development of catalytic converters, for instance, where a gas stream -- the car's exhaust -- flows over a catalyst typically made of three metals: platinum, palladium and rhodium. The catalysts' effectiveness can vary dramatically depending on even small variations in the concentrations of these metals and additional promoter materials. Conventional methods that use mass spectrometers or gas chromatographs can be painstakingly slow and inefficient for evaluating catalyst performance.
Jochen Lauterbach, an assistant professor of chemical engineering, heads a team at Purdue University that developed a rapid-scan Fourier transform infrared (FTIR) imaging system to analyze chemical samples. The mid-IR system (sensitive between 10,000 and 900 cm21 reveals the infrared signature that distinguishes each chemical, its molecular fingerprint. This fingerprint identifies the molecules that have been absorbed onto the catalyst's surface or that are present in the gas stream, and it can be used to understand the catalyst's molecular reactions.
"Our goal was to be able to analyze multiple samples for truly parallel screening [of combinatorial libraries] simultaneously, and, in order to get chemically sensitive information, you almost have to go to the mid-IR," Lauterbach said.
He and his colleagues mated the infrared-detection technology with a rapid-scan FTIR spectrometer and an optical setup created with infrared lenses. They also developed a reactor and a gas-phase screening array for studying libraries of catalysts.
Jochen Lauterbach (left) and Gudbjorg Oskarsdottir of Purdue University work with the infrared imaging instrumentation developed by Lauterbach's team to speed up the screening of chemical catalysts. Photo by David Umberger, courtesy of Purdue News Service.
"We have several home-built optical setups for different spatial resolutions and fields of view," he said. "The entire system, however, is based on off-the-shelf lenses. The system is very flexible and can be easily adapted to new sampling geometries in transmission, attenuated total reflection and reflection-absorption geometries."
The Purdue team has performed a number of experiments on combinatorial gas/solid catalysis and has focused its attention on automotive exhaust catalysis, among other processes. Lauterbach said the new technique also could have a dramatic effect on the growing field of combinatorial chemistry and could enable the creation of vast databases of chemical catalysts. He claims that the system can screen catalysts that react with liquid up to 5000 times faster and screen those that react with gas 20 times faster. The technique also is nondestructive and more sensitive than traditional instruments.
Details of the work appear in the May/June issue of the Journal of Combinatorial Chemistry, published by the American Chemical Society.
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