Factors Affecting The Structure-directing Effect Of Dipropylamines In The Synthesis Of Open-Framework Aluminophosphates

Zeolites are widely used in catalysis,adsorption and separation due to the diversity of their structures,unique pore structures,excellent thermal stability,and large specific surface areas.In the synthesis of zeolites and related open-framework aluminophosphates,the structure-directing agent plays a critical role which is denoted as the structure-directing effect.It has been demonstrated that the structure-directing effect can be affected by many factors.In this thesis,we investigated the factors affecting the structure-directing effect of di-n-propylamine?DPA?and diisopropylamine?D-iPA?.The main results are summarized as follows:1.The influence of the crystallization temperature on the structure-directing effect of di-n-propylamine was investigated.By heating the initial gel with the molar composition of 1.0Al2O3 : 1.0P2O5 : 1.0DPA : 60H2 O at 135,150,and 200°C,aluminophosphate molecular of VPI-5,mixture of VPI-5 and aluminophosphate molecular sieve of AlPO4-11,and AlPO4-11 were obtained,respectively.The crystallization processes were investigated using X-ray diffraction,elemental analysis,solid-state Magic Angle Spinning Nuclear Magnetic Resonance?MAS NMR?and pH measurement.The results showed that the crystallization temperature can affect the structure-directing effect of di-n-propylamine by altering the type and distribution of the fragments formed in the synthetic system and the starting point of the crystallization,which will determine the structure of the resulting crystals.2.The structure-directing effect of dipropylamine isomers,i.e.,di-n-propylamine?DPA?and diisopropylamine?D-iPA?,was investigated.By heating the initial gels with the molar composition of 1.0Al₂O₃ : 1.0P₂O₅ : 1.2DPA/D-iPA : 75H₂O and 1.0Al₂O₃ : 1.0P₂O₅ : 1.0DPA/D-iPA : 75H₂O at 200°C for 24 h,highly crystalline aluminophosphate molecular sieve AlPO4-11 was obtained.The crystallization processes were investigated using X-ray diffraction,elemental analysis and pH measurement.For the crystallization process of the initial gel with the molar composition of 1.0Al2O3 : 1.0P2O5 : 1.2DPA/D-iPA : 75H2 O,no intermediate phase was formed when the di-n-propylamine was used as the structure-directing agent,whereas intermediate phase of aluminophosphate molecular sieve AlPO4-5 was observed when the diisopropylamine was used as the structure-directing agent.For the crystallization process of the initial gel with the molar composition of 1.0Al2O3 : 1.0P2O5 : 1.0DPA/D-iPA : 75H2 O,intermediate phase of aluminophosphate molecular sieve VPI-5 was formed when the di-n-propylamine was used as the structure-directing agent,whereas intermediate phases of both VPI-5 and AlPO4-5 were observed when the diisopropylamine was used as the structure-directing agent.Theoretical calculation showed that the charge on the protonated di-n-propylamine was different with that on the protonated diisopropylamine.The results indicated that the structure-directing effect of amine can be affected by the molar composition of the initial gel and the fine-tuning of the structure of amine can influence its structure-directing effect.However,such influence is affected by the molar composition of the initial gel.