Synthesis And Crystallization Of-CLO Zeotype Extra-large Pore Aluminophosphate Zeolites By Dry Gel Method

Due to its special pore size,the Extra-large pore zeolites have great advantages and application prospects in chemical operation such as macromolecular catalysis,adsorption and separation.At present,precious metals such as germanium and gallium are widely used as skeleton atoms in their synthesis,which leads to the problems of high synthesis cost and unstable structure after removing the template.In recent years,the synthesis of Extra-large pore aluminophosphate zeolites by ionothermal method also has some problems,such as high synthesis cost and unclear crystallization mechanism.The dry gel method has the advantages of low cost,simple operation,high yield,and easy to study the crystallization process of zeolite.Therefore,the synthesis and crystallization mechanism of-CLO zeotype Extra-large pore aluminophosphate zeolites by dry gel method were studied in this paper.Aluminophosphate zeolites with different structures were synthesized by using tetramethylammonium,tetraethylammonium,tetrapropylammonium and tetrabutylammonium hydroxide as templates in dry gel synthesis system.It was found that the topological structure of crystallization products was related to the structure of quaternary ammonium hydroxide template,in which tetraethyl ammonium cation could guide the formation of-ClO structure.In addition,the formation of-CLO structure is also influenced by the gel chemistry of quaternary ammonium base,water and fluorine concentration.The crystallization process of AlPO-CLO zeolites synthesized by dry gel method with tetraethylammonium hydroxide as template was studied.The structure information of the synthesized products with different crystallization time,such as the coordination of skeleton atoms and the position of template,were characterized by FT-IR,NMR,Raman and other characterization methods.It was found that there were many double four ring(d4r)units in the initial dry gel.With the crystallization time increasing,d4r first self-assembled around the template to form lta cage,Then lta cage and d4r self assemble around the template to form clo cage and super cage,and finally form-CLO Extra-large pore structure.The-CLO silicoaluminophosphate Extra-large pore zeolites SAPO-CLO was synthesized by dry gel method.The substitution of silicon atom makes the molecular sieve have certain acidity,and its activity in propylene oligomerization is significantly improved.The reaction product is mainly propylene dimer C6,and the catalyst deactivates rapidly due to carbon deposition.