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Berkeley Scientists Bring MRI/NMR to Microreactors

 

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Sciences Division and the Glenn T. Seaborg Professor of Chemistry at UC Berkeley, a team of researchers that included chemists Louis Bouchard and Scott Burt have developed a technique in which parahydrogen-polarized gas is used to make an MRI signal strong enough to provide direct visualization of the gas-phase flow of active catalysts in packed-bed microreactors. This work, the first application of gas-phase MRI to microfluidic catalysis, shows that parahydrogen-enhanced MRI can be used to track gases and liquids in microfluidic devices as well as in the void spaces of a tightly packed catalyst reactor bed.

“This is the first time hyperpolarized gas has been used to directly study catalytic reaction products on such a small scale and without the use of tracer particles or gas,” says Bouchard. “It opens the door for future studies of heterogeneous catalysis in which all the unique benefits of MRI, such as velocimetry and spatially dependent quantities, are available.”

Adds Burt, “Furthermore, our results indicate that our approach to using parahydrogen can be extended to other chemical reactions beyond hydrogenation, which significantly broadens the impact and potential use of our technique.”

Pines, Bouchard and Burt are the co-authors of a paper published in the January 25, 2008 edition of the journal Science, describing this research. The paper is entitled: “NMR Imaging of Catalytic Hydrogenation in Microreactors with the Use of para-Hydrogen.” Other co-authors of this paper were Sabieh Anwar, who is a former member of Pines’ research group now at Lahore University, Pakistan, and Kirill Kovtunov and Igor Koptyug, from the International Tomography Center, Novosibirsk, Russia, who are experts in catalysis and the use of MRI to study catalytic processes.

Commenting on the Science paper, Jeffrey Reimer, who chairs the UC Berkeley Chemical Engineering Department, said, “The spatial and temporal distribution of reactants and products in heterogeneous systems has not been visited by researchers in recent years owing to the lack of quantitative measures in situ. So while the sophistication of mathematical modeling of such systems proceeds at the rate at which computational power increases, the relevance of such models is dubious since they cannot be compared with measurements other than bulk properties of temperature, conversion, etc. The methods and data presented in this paper portend a new era of measurement, modeling, and design for more efficient reactors.”

Since nearly all manufacturing processes that involve chemistry start with a catalytic reaction, there is a premium on the design of new and better catalysts and catalytic reactors. This is especially true for the growing field of microfluidic chip technology. MRI and nuclear magnetic resonance (NMR), its sister technology, are among the most powerful analytic tools known to science and could be immensely valuable for characterizing catalytic reactors and reactions in microfluidic devices. However, the low sensitivity of conventional MRI/NMR techniques has limited their applicability to microscale catalysis research.