| RESEARCH |
MANY INDUSTRIAL catalytic processes are based on chemical reactions that occur in the interior of zeolites, a family of porous aluminosilicate-type compounds. Yining Huang, a chemistry professor at the University of Western Ontario, London, Ontario, reported on studies of interactions between porous hosts and various types of molecules contained within the pores and interior channels of support materials. Huang noted that Fourier transform (FT) Raman spectroscopy is well suited to studying the behavior of guest molecules in zeolites because zeolites tend to produce weak Raman signals, which simplifies the job of detecting molecules adsorbed inside of them. In addition, by exciting vibrational transitions with near-IR laser light (1,064 nm), the FT Raman method reduces the fluorescence interference typically associated with zeolites. Drawing on examples of 1,4-dichlorocyclohexane and other dichlorinated compounds, Huang showed that the vibrational method can be used to distinguish between various conformational isomers of adsorbed molecules even at room temperature. That ability is noteworthy, he explained, "because molecular conformation affects adsorption, diffusion, and the subsequent chemistry of adsorbed molecules." The FT Raman method is also useful for interrogating chemical reactions and other types of processes that take place in zeolites. For example, Huang showed that the technique can be used to probe dimerization of Mn(CO)5Br by detecting metal-metal bond formation. It also can distinguish between the three types of sites at which benzene adsorbs in zeolite ZSM-5. |
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