Nature of the Active Centers of In-, Zr-, and Zn-Aluminosilicates of the ZSM-5 Zeolite Structural Type

Resumo

In-, Zr-, and Zn- containing elementoaluminosilicates of ZSM-5 zeolite structural type are synthesized by means of hydrothermal crystallization from alkaline alumina–silica gels. Based on the data of structural morphological studies on the samples, it is established that introducting metals into the zeolite structure leads to the formation of particles different in morphology and elemental composition. Studies of the electronic state of active centers in elementoaluminosilicates (E-AS) show that Zn²⁺ and In³⁺ cations are associated with oxygen ions in zeolite channels with bonding energies inherent in their oxides. The high value of Zn 3d bonding energy explains the stability of zinc ions in the Zn-AS structure with no formation of clusters under heating the sample by an electron microscope beam. The isomorphic substitution of Al³⁺ ions in the zeolite crystal lattice by Zr⁴⁺ and In³⁺ ions, despite the relatively low Zr 3d and In 3d bonding energies, also results in the stability of Zr-AS and In-AS systems. It is found that the aggregation of Zr and In into oxide clusters is observed only under strong heating with the electron beam after the destruction of the zeolite channel structure.