| Research Abstract |
In this research project, we have tried to construct a Fourier-transform microwave spectrometer, which is suitable for the determination of the structure of active sites in a certain catalytic reaction. First of all, we reformed our old wave-guide type spectrometer into Fourier-transform type. But the sensitivity did not improved as expected, and is not enough for our original project purpose. Accordingly, we changed our plan, and took a Favlli-Perror type resonance cavity spectrometer. We made ultra-vacuum vessel which contains 25 cm diameter miller for microwave reflection, and obtained the desired sensitivity. Now, we are trying to extend our methods for some new probe molecules such as methanol, acetaldehyde, methyl amine and acetonitrile. We prepare the deuterated compounds, and determine the assignments of the rotational spectra of deuterated species. methanol and acetaldehyde are very important products in CO hydrogenation, and the structure for their active site are still under
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debate. On the other hand, carbon-nitrogen bond is easily broken up on metal catalysts. So it is important to clarify the structure of active site for C-N bond breaking and formation. To this purpose, it is valuable to take methyl amine and acetonitrile as probe molecules.
We also investigated the structure sensitivity of the supported metal, metal oxide, carbide, and nitride catalysts, by employing C3H6-D2 and C3H6-C3D6 hydrogen exchange processes as probe reactions. The reaction mechanism as well as reaction intermediates were discussed by analyzing propene-dl molecules by microwave spectroscopy. It is concluded that over metal catalysts, hydrogen exchange of propene in the presence of hydrogen, proceeds through the associative mechanism, whereas in the absence of hydrogen through dissociative mechanism. On the contrary, over metal oxide or metal carbide catalysts, both associative and dissociatve mechanisms are operating independently, irrespective of the presenc eor absence of hydrogen. Over metal nitride catalysts, the situation was completely different and gaseous hydrogen seems to accelerate the dissociative hydrogen exchange process, too. Less
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