Hydrothermal incorporation of Ce(La) ions into the framework of ZSM-5 by a multiple pH-adjusting co-hydrolysis

Abstract

Ce and La incorporated ZSM-5 zeolitic materials with different metal loadings were synthesized via the multiple pH-adjusting procedures involving a co-hydrolysis of TEOS (tetraethyl-orthosilicate) with rare earth salts under a strong acidic condition, a further gelation under a weak acidic condition, and a final basic hydrothermal crystallization. Thus obtained Ce(La)-ZSM-5, as well as Ce or La ion-exchanged ZSM-5 samples, were characterized by XRD, SEM, TG, UV–vis, 29Si MAS NMR, FT-IR, N2-physisorption, and elemental analysis. The characterizations provide systematic and complementary evidences to demonstrate the incorporation of Ce(La) ions into the tetrahedral sites of ZSM-5 framework. The upper limits of the rare earth loadings in the synthesis gel and the final product are ca. 50 and 70 of the molar ratio of Si/Ce(La), respectively. It is observed that the synthesized Ce(La)-ZSM-5 zeolites possess an unusual morphology of microspheres that are assembled by numerous cubic prism-shaped nanocrystallines.