Specific Adsorption of Dinitrogen Molecule at Room Temperature in Zeolite Nanospace

由于沸石晶格中铝原子的存在，沸石晶格中存在一些净电荷，并且需要补偿阳离子（通常是钠离子）来平衡阴离子框架电荷。有些阳离子很容易与钠离子交换。众所周知，铜离子在沸石中是非化学计量交换的，这种过度铜离子交换的沸石对一氧化氮的直接分解具有很高的催化活性。我们还发现了另一个有趣的性质，这种铜离子交换过度的沸石，在873 K真空中抽真空，在室温下强烈吸附二氮分子。可以想象，铜离子交换沸石为开发具有二氮分离、固定和活化功能的非均相体系提供了新的、有前途的候选材料。本研究以CO为探针分子，通过XAFS、ESR和IR测试，研究了铜离子交换丝光沸石在298 K t下对二氮分子的吸附性能。结果表明，样品在873 K真空中抽离形成的Cu (I)位点是吸附二氮的活性位点。还发现铜离子交换沸石中存在两个CO吸附活性位点：一个在红外区产生2159 cm^<-1>的条带，另一个在铜离子交换沸石上吸附CO分子产生2151 cm^<-1>的条带。二氮分子的强吸附发生在给CO吸附后一个波段的位置。吸附热数据也支持两个CO吸附活性位点的存在。这些结果表明，二氮分子被吸附在由二聚体Cu （II）通过热处理形成的无定形Cu (I)位点上。研究了丝光沸石在300k下热处理和复水化后铜离子状态的变化。这些过程可以通过假设在排气过程中形成的铜离子对Cu （II）和Cu(0)的歧化反应来解释。少

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