HYDROTHERMAL SYNTHESIS OF ZEOLITE-LIKE IRON AND ZINC PHOSPHATES AND ITS APPLICATION IN THE METHANOL CONVERSION

摘要

The reactions in R-ZnO(Fe_2O_3)-P_2O_5-H_2O system (where R is an organic or an inorganic base) under the hydrothermal conditions have been investigated. The products of reactions have been characterized by X-ray diffraction, thermogravimetric and differential thermal analyses, IR-spectroscopy and elemental analysis. The influence of synthesis conditions (temperature, time, composition of initial mixture, nature and concentration of base) on the crystallization of zinc and iron phosphates has been studied. It has been established that zeolite-like KZnPO_4·1.5H_2O with hexagonal unit cell parameters a=18.14 A and c=8.504 A, is formed in the presence of KOH. Three-dimensional framework consists of strictly alternating ZnO_4- N PO_4-tetrahedra. For compensation of negative charge of the framework the cations of potassium are located in the channels of it. In the presence of triethanolamine and low concentrations of alkaline cations the synthetic analogue of hopeite-mineral is crystallized either in the individual form or in the association with zinc phosphates of alkaline cations. A new three-dimensional microporous iron phosphate Fe_2H_3(PO_4)_3·(EtOH)_3N was obtained by hydrothermal synthesis in the presense of triethanolamine in the form of transparent elongated crystals of light green colour. The symmetry is orthorhombic with unit cell parameters a=9.61 A; b=8.64 A and c=14.19 A. The catalytic properties of zinc and iron phosphates have been investigated in methanol conversion. Iron phosphate is active in the formation of dimethyl ether, while zinc phosphates depending upon their composition leads to formation of dimethyl ether, lower olefins or formaldehyde.