Activation of Adsorbed Molecules in Zeolite by Means of Low-temperature Plasma and Photoexcitation

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Zeolite that is a mixed oxide of silica and alumina has an ability of ion-exchange as well as a porosity, and hence, its internal space can be expected to use as a reaction field. Recently, we have reported that the copper ion-exchanged zeolite (ZSM-5 type) interacts strongly with nitrogen molecules even at room temperature, where the monovalent copper ion species (Cu^+) act as adsorption sites. In the present study, we intended to synthesize nitrogen compounds in the zeolite by means of plasma or photoexcitation and to elucidate the state of sites that reacted with nitrogen molecules as well as the reactivity of nitrogen compound formed. We also tried to prepare new catalysts by making use of the internal space of zeilite as a reaction field.Some results obtained are as follows. The copper ion-exchanged zeolites (CuZSM-5) prepared have different ability to adsorb nitrogen molecules, depending on the kind of counter ions involved in the exchanging solution ; the sample prepared by using a solution involving carboxylato (-COO^-) was found to be excellent in adsorption property. It was evident that the nitrogen molecules can be activated by plasma excitation to be adsorbed strongly on the zeolite surface (these species are removed by only treating at 573 K in vacuo). Furthermore, silver ion-exchanged zeolite (AgZSM-5) was also prepared, and by photoexciting it with ultraviolet rays, silver clusters consisting of about ten atoms were formed in the zeolite. It became cleat that the coexistence of such silver clusters and silver ions was necessary and sufficient condition for catalytic reaction (partial oxidation of methane).Two papers including these results have already been published in the scientific journals, and two more papers are submitted to the journals.