Interzeolite Conversion And Solvent-free Synthesis For SSZ-13 Zeolite

SSZ-13,a CHA-type aluminosilicate zeolite,has a three-dimensional pore system with ellipsoidal large cages（6.7?×10?）that are accessible by 8-membered ring windows（3.8?×3.8?）.It has widely used in conversion of methanol-to-olefins（MTO）and selective catalytic reduction of NO_x with NH₃（NH₃-SCR）since it has ordered channel,good thermal stability,more surface Br?nsted acid center and exchangeable cations.Generally,SSZ-13 can be synthesized directly in alkali and fluoride medium under hydrothermal conditions in the presence of structure-directing agent（SDA）N,N,N-trimethyladamantammonium cation（TMAda⁺）at relatively long times（3²1 days）and wide temperature range（120¹80℃）.However,the expensive SDAs and the long crystallization time increase the synthetic cost.Hence,it makes sense to develop a fast,efficient and environmentally friendly synthetic route.In this paper,A zeolite could be efficiently and rapidly converted into SSZ-13,and crystallization processes of LTA-CHA interzeolite conversion at different temperatures were investigated.Also,SSZ-13 was prepared by using low-cost and green choline chloride as SDA,and the factors of synthesis were optimized.The following results were obtained by XRD,SEM,FT-IR,N₂ sorption isotherm,etc.（1）SSZ-13 with good performance can be prepared rapidly and efficiently via interzeolite conversion from low cost and easy available A zeolite.The zeolite yield could reach 91.0%,and the crystallization time was greatly shortened.It takes only 5 h at 180℃to completely crystallize.The interzeolite conversion process includes two steps:the dissolution of A zeolite and the generation of SSZ-13 zeolite.Notably,the two steps are simultaneous at lower temperature while SSZ-13 crystallizes quickly after A zeolite has almost completely dissolved at higher temperature.Catalytic test in NH₃-SCR shows that copper exchanged CHA（Cu-SSZ-13）exhibits comparable catalytic properties to those of Cu-SSZ-13 obtained from the conventional methods.（2）H₂O plays an important role in the process of solvent-free synthesis of SSZ-13,which not only can strengthen the mass transfer,but also can adjust the alkalinity to promote the depolymerization of the silicon species in the system.The suitable H₂O/SiO₂ is the key to the solvent-free synthesis of SSZ-13,and the form of addition of H₂O has no direct effect.（3）Choline chloride does not show a structure-directing role in the scope of the ratios studied in this paper.When a small amount of TMAdaOH or DMECHABr is added into choline chloride to form a dual template system,SSZ-13 with high crystallinity can be successfully synthesized.At this time,choline chloride is likely to exist in the cage of SSZ-13as filler.