Specific Adsorption of Dinitrogen Molecule at Room Temperature in Zeolite Nanospace

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There are some net charges in the lattice of zeolites due to the presence of aluminum atoms in the zeolite lattice, and the compensating cations, typically sodium ions, are required to balance the anionic framework charges. Some cations are easily exchanged for sodium cations. It is well known that copper ions are exchanged non-stoichiometrically in zeolite and this excessively copper ion-exchanged zeolite has high catalytic activity for the direct decomposition of nitric oxides. We found another interesting property that this excessively copper ion-exchanged zeolite, which was evacuated at 873 K in vacuo, strongly adsorbs dinitrogen molecules at room temperature. It seems conceivable that copper ion-exchanged zeolite could represent new and promising candidates for the development of heterogeneous system capable of dinitrogen separation, fixation, and activation.In this study, the adsorption properties of copper ion-exchanged mordenite for dinitrogen molecules were examined at 298 K t … More hrough XAFS,ESR,and IR measurements, and also by using CO as a probe molecule. As a result, it is evidenced that the Cu (I) site, which was formed by the evacuation of the sample at 873 K in vacuo, is active site for dinitrogen adsorption. It is also found that two active sites for CO adsorption are present in copper ion-exchanged zeolite : the one gives the band at 2159 cm^<-1> in the IR region and the other at 2151 cm^<-1> for CO molecule adsorbed on copper ion-exchanged mordenite. The strong adsorption of dinitrogen molecules occurs on the site giving the latter band for CO adsorption. The adsorption heat data also supports the presence of two active sites for CO adsorption. These results lead to the conclusion that dinitrogen molecules are adsorbed on amorphous Cu (I) sites which was formed from dimeric Cu (II) species by heat treatment. the change of the state of copper ion in mordenite due to the heat treatment and subsequent rehydration at 300 K was also investigated. These processes can be interpreted by assuming a disproportionation reaction of cuprous ions formed in the evacuation process to Cu (II) and Cu (0). Less