TEAOH-TMABr-Al2O3-SiO2-H2O体系中小晶粒offretite沸石的合成研究

The traditional route for the synthesis of zeolites is in the system of M2O-Al2O3-SiO2-H2O or M2O-organic template-Al2O3-SiO2-H2O (M2O: Na2O, K2O or Li2O), in which inorganic alkali is necessary. Recent advances in zeolite synthesis have centered on high silica zeolite systems or have employed exotic templates. However, low Si/Al ratio zeolites are particularly attractive because they can offer high acid site density for catalytic applications and greater ion-exchange capacity in addition to compositional diversity for separation processes. Blackwell reported their discovery of two new zeolite materials UZM-4 and UZM-5, synthesized at low Si/Al ratio by using the combination of two of the most common organic templates, tetramethylammonium and tetraethylammonium ions. This exploits a new approach for novel zeolites synthesis. Offretite was first described by Gonnard and has relatively large pores of 0.67 nm running in the c-direction. It has been synthesized by several methods, such as in the system containing tetramethylammonium (TMA), Na+, K+ or p-dioxane and alkaline cations as well. Offretite synthesized by using only the combination of two organic templates (TEAOH, TMABr) has not yet to be reported. In this paper, small crystalline offretite was synthesized in a TEAOH/TMABr mixed template system at a typical synthesis composition of 12TEAOH∶ TMABr∶Al2O3∶13.5SiO2∶240H2O, and at crystallization temperature of 423 K within 7 days. The samples were characterized by XRD, SEM and IR. The catalytic properties of offretite were investigated in the alkylation of benzene with propene. These results showed that the dosage of TEAOH directly affects the crystalline phase and size of the product. Compared with TMABr, TEAOH played a more important role in the crystallization. With increasing the dosage of TMABr, zeolite Beta is obtained. The catalytic properties of H-offretite are superior in benzene alkylation reaction.