Synthesis And Characterization Of Fe-Doped Zeolites

Zeolite framework is built exclusively form TO4 tetrahedra (T denotes tetrahedrally coordinated Si or Al), and each TO4 tetrahedron is connected with neighbors by sharing their vertex O atoms. As heterogeneous solid acid catalyst, zeolite has been widely used in petroleum refining, petrochemical industry and fine chemical industry due to their high thermal and hydrothermal stability, shape selectivity, ease separation from products and regeneration. Y zeolite and β zeolite with a three-dimensional network of 12-ring pores as the most important catalytic materials have been widely used in the petroleum refining and fine chemical industries. Y zeolite can be obtained without any structure directing agents, but synthesis of β zeolite should add some agents under the same hydrothermal conditions.To modify surface acidity, introduce new catalytic center, avoid the restriction of microporous material of aluminosilicates in the applications and expand the application of zeolite in redox reaction, it is particularly necessary to introduce other heteroatom, especially the element with redox ability, into zeolite. To investigate the heteroatom effects on zeolite structures and properities, Fe was introduced into the framework of Y zeolite and β zeolite. Zeolite FeY was prepared without any structure direction agents and zeolite Feβ was synthesized by addition of calcined Beta seeds in the starting aluminosilicate gel in the absence of any organic templates. The main results are shown as follows:(1) The synthesis of zeolite FeY and FeP:improving crystallization temperature or prolonging crystallization time accelerates the crystallization rate of zeolites significantly. Crystallinity of zeolite Y and β decreases with the increasing of Fe or Si content in the starting aluminosilicate gel.(2) The Fe-doped content: Higher Fe-doped content FeY and Feβ were successfully synthesized under the optimized synthetic conditions. The results show that improving crystallization temperature, prolonging crystallization time or increasing Fe content in the gel can increase the Fe-doped content. Fe/Si=0.05, the gel aged at room temperature for 12 hours, crystallined at 100 ℃ for 48 h has a higher Fe-doped content (Fe/Si= 0.016) zeolite FeY; Si/Al=20, Fe/Si=0.04, the gel crystallined at 140 ℃ for 6 d, has a higher Fe-doped content (Fe/Si= 0.022) zeolite Feβ.