Glue As Catalysis Research Zeolite Crystal And Zeolite Surface Modification

In general, zeolite is synthesized under hydrothermal condition using an amorphous aluminosilicate gel as a starting material. However, sometimes it is observed that the formation of a zeolite phase may be preceded with another phase during the course of zeolite crystallization. This phenomenon, therefore, could be considered to be an alternative synthesis strategy for the hydrothermal conversion of one zeolite into another, i.e., zeolite-zeolite transformation. In fact, this method is of attractive research area, since it may provide information about the crystallization mechanism and also is an outstanding route to obtain a new zeolite which cannot be crystallized by a conventional method.Firstly, steam-assist crystallization method was introduced to study zeolite-zeolite transformation. HCl-treated Y zeolite was used as precursor, studying the transformation rules in certain base and temperature and also studying the conversion products in different temperatures. The results were as followed:The acid-treated Y zeolites were almost amorphous but some short-range-order aluminosilicate species were retained. The acid-treated Y zeolites were recrystallized at150℃with0.3mol/L NaOH solution by steam-assist crystallization method, and pure mordenite zeolite products with the morphology from aggregate of nano-rod to micron-sized crystal were obtained within suitable Si/Al ratio range (3.95-9.75); While with Si/Al ratio below3.95, the products was zeolite ANA and with Si/Al ratio higher than9.75, the products was the mixture of zeolite MOR, MFI and Magadiite. If the temperature was improved, the Si/Al ratio range of obtained pure MOR would be decreased.Secondly, steam-assist crystallization method was used in dealuminum USY zeolite phase conversion. Dealuminum USY zeolite was used as primary zeolite source, the phase transformation was investigated under different TEAOH/SiO2ratios, OH-/SiO2ratios, different Na+sources, and also the course of transformation at different conversion time was studied. The results indicated:when OH-/SiO2ratio was0.416and TEAOH/SiO2ratios were0.3,0.2and0.15separately, their conversion products were all pure*BEA zeolite, what’s more, the structure of*BEA zeolite with TEAOH/SiO2ratios0.3and0.2was hollow structure; while if TEAOH/SiO2ratios were lower to0.1and0.05, the conversion products were mixtures of*BEA and MOR zeolites; but when TEAOH/SiO2ratio was0.1and lower the OH-/SiO2ratio to0.300, the conversion product was pure*BEA zeolite; when NaF, NaCl and Na2SO4 were use as Na+sources, only NaF would obtained pure*BEA zeolite with hollow strcture, while conversion products for NaCl and Na2SO4were mostly*BEA zeolites but mixture with some impurity.At the end of this thesis, ZSM-5zeolite was treated by (NH4)2SiF6solution, in order to form a pure thin layer of Silicalite-1in the surface of ZSM-5zeolite; the influence of different (NH4)2SiF6concentrations, pH values and treating temperatures were studied. The results were as followed:with high temperature, high (NH4)2SiF6concentrations and no control of pH values would cause higher Al-dissolution rate than Si-insertion rate which will cause damage to ZSM-5skeleton and form mesoporous in ZSM-5zeolite; through controlling (NH4)2SiF6concentrations (0.11M), temperature (80℃) and proper pH values, to make the same value of Al-dissolution rate and Si-insertion rate, so as to form a thin layer of Silicalite-1in surface of ZSM-5zeolite. The obtained ZSM-5zeolites can be used in the separation of three xylenes under room temperature.