Organotemplate-free Synthesis Of ZSM-34 Zeolite And Its Analogue Containing Framework Heteroatoms In The Presence Of Zeolite L Seeds Solution

Zeolites, especially aluminosilicates are regarded as the most important heterogeneous acid catalysts in industry due to their large surface area, high adsorption capacity, uniform and intricate channels, high thermal and hydrothermal stabilities, and well-defined micropores with excellent shape-selectivity in catalysis. In the early of the synthesis, aluminosilicate zeolites such as A, X, Y are normally prepared under hydrothermal conditions in the presence of inorganic cations such as sodium. However, mordern synthesis methodologies for synthesizing aluminosilicate zeolites ususally require the use of organic templates called structure-directing agents (SDAs) that rationally direct the assembly pathway and ultimately fill the pore space. For example, aluminosilicate zeolites of Beta, ZSM-5, and MWW are successfully synthesized from the use of tetraethylammonium, tetrapropylammonium, and hexamethyleneimine, respectively. To obtain zeolites with open pores, SDAs in the zeolites are generally removed by calcination at high temperature, which results in both the consumption of energy and the production of harmful gases for polluting the air. Additionally, the use of expensive organic templates also increase the cost of zeolite catalysts, which strongly hinders the wide applications in industry.To solve the problems brought with organic templates, the scientists are trying to recyle these organic templates in the synthesis of aluminosilicate zeolites. For example, partially recyling and fully recylcing organotemplate synthesis of Beta and MFI zeolites have been successfully performed from ion-exchange and disassembled-reassembled routes. The alternative route for solving these problems is to synthesize these zeolites without using organic templates (organotemplate-free synthesis), and the first example is successful to synthesize ZSM-5 zeolite a long time ago. Recently, several aluminosilicate zeolites such as ECR-1 and Beta have been successfully synthesized in the absence of organic templates. Aluminosilicate zeolite ZSM-34, another example, is originally synthesized in the presence of organic templates such as choline [(CH3)3NCH2CH2OH] and diamines (NH2CnH2nNH2, n=4, 6, 8, 10). In this work, we will show the organotemplate-free synthesis of ZSM-34 from an assistance of zeolite L seeds solution.In chapter two, organotemplate-free route for synthesis of aluminosilicates zeolite ZSM-34 from an assistance of zeolite L seeds solution have been extensively investigated. The amount of zeolite L seeds solution and the ratio of SiO2/Na2O play important roles during the preparation process. Amorphous product is obtained in the absence of zeolite L seeds solution, while ZSM-34 zeolite is formed after the addition of a small amount of zeolite L seeds solution; additionally, crystallization rate increases with the amount of zeolite L seeds solution, but too large amounts of zeolite L seeds solution would result in the formation of zeolite L in the final product. Furthermore, the ratio of SiO2/Na2O in the starting gels should be controlled carefully. Too large amounts of Na2O would lead to the formation of PHI zeolite and too few would result in the formation of MOR zeolite.It has been reported that heteroatoms-substituted zeolites strongly influence their catalytic properties. For example, the presence of framework Ga in zeolite is favorable for catalytic aromatization of propane; ZSM-5 zeolite containing framework Fe is catalytically active for benzene hydroxylation with nitrous oxide; ZSM-5 containing framework B is a very active and selective catalyst for the vapor-phase Beckmann rearrangement of cyclohexanone oxime toε-caprolactam. ZSM-34 zeolite is an intergrowth of offretite (OFF) and erionite (ERI) zeolites containing zeolitic building units of cancrinite (CAN) cages, and its pore size (5.2 ?) is smaller than that of ZSM-5 (5.6 ?). This feature has attracted much attention in the expectation of selective catalysis for conversion from methanol to ethylene and propylene, which are important chemicals for the polymer industry. Consequently, the organotemplate-free synthesis route is applied for heteroatoms-substituted ZSM-34, looking forwards to their excellent properties in catalytic conversion from methanol to ethylene and propylene.In chapter three, organotemplate-free and in-situ synthesis of ZSM-34 analogue containing framework heteroatoms (B, Ga, Fe) have been successfully achieved in the presence of zeolite L seeds solution. We demonstrate here the detailed results of synthesis and characterization of ZSM-34 analogue. Similar to aluminosilicate zeolite ZSM-34, the significant influence on the synthesis of these analogue are the amount of zeolite L seeds solution and the ratio of SiO2/Na2O, which related to crystallization rate and final products. Furthermore, the ratio of SiO2/M2O3 (M: heteroatoms) should be varied in a suitable area for purity of products. By the way of NMR and UV-vis, the heteroatom species are confirmed to be tetrahedral coordinated sites, indicating that they had been essentially incorporated into the framework of ZSM-34 zeolites. Significantly, the nitrogen adsorption isotherms of ZSM-34 zeolite and its analogue all exhibit typical Langmuir adsorption, confirming existence of open pores in these as-synthesized samples without calcination at high temperature.The acidity of H-ZSM-34, H-B-ZSM-34 and H-Ga-ZSM-34 zeolites has been characterized by NH3-TPD. All of the samples have showed weak acidic sites and strong acidic sites, which offers them great opportunity as solid acidic catalysts in industry. As a typical example, methanol-to-olefin (MTO) reaction was chosen to test their catalytic properties. The results show that the selectivity of propylene and ethylene in these zeolites is totally larger than 80%, superior to H-ZSM-5 at less than 30%.In chapter four, a great deal of work has been performed to investigate the hydrothermal synthesis of microporous framework stannosilicates, and a series of products have been obtained successfully, some of them with novel microporous crystal structure included. Moreover, we have illustrated that the final products could be influenced by many factors, such as SiO2/SnO2, pre-activation, pH, ionic effect (such as F-, K+), crystallization temperature and so on. Interestingly, Sn species in stannosilicate framework are six-coordinative number, and play an important role in the synthesis of this kind of microporous materials.