| Nowadays,research and development(R&D) of zeolite related materials are still in bugeoning in the field of material chemistry.Due to the selective N2&O2 adsorption properties of zeolites,many works focused on the employment of zeolites for N2&O2 adsorption.As the advancement of pressure swing adsorption(PSV) technology and adsorption theory in recent years,R&D of functionalized zeolite for gas adsorption turns to be a pressing issue.In this dissertation,hydrothermal synthesis of zeolites using kaolin as raw material has been studied in details.The effects of synthesis conditions to the crystallization of zeolites have been analyzed by using X-ray powder diffraction(XRD);also the rules of crystallization and phase transformation have been investigated.Furthermore,a series of functionalized zeolites have been prepared through modulating of offset cations in zeolite extraframeworks.The parameters for evaluating the as-prepared zeolites,such as crystal phase,specific surface area and N2&O2 adsorption capacity,have been obtained and analyzed systematically by XRD,surface area and porosity analyzer and so on.In addition,the great effects of zeolite framework type and the properties of offset cation in zeolite extraframworks to the N2&O2 adsorption performance of zeolites have been explored.The main results are as follows.1.Several kinds of zeolites have been synthesized hydrothermally from kaolin,a natural clay mineral.Without adding silica and alumina source,NaX,NaP and SOD zeolites have been produced.The binary crystallization phase diagram has been proposed for interpretation of the rule of crystallization and phase transformation.We also studied the decisive role of reducing the initial SiO2/Al2O3 molar ratio to the final products by adding Al source.The analysis of the crystallization conditions of NaA zeolite shows that low initial SiO2/Al2O3 molar ratio is propitious to the generation of zeolies.The crystallization rules of NaP zeolite have also been studied when adding Si source,which indicates that the high initial SiO2/Al2O3 molar ratio fits for the formation of NaP zeolite.2.The offset cations modification of as-synthesized NaA zeolite has been carried out, and two novel zeolites(NaMgA and NaCoA) with fine N2 adsorption properties at 25℃have been obtained.For NaMgA,the key factor for the high adsorption capacity and selectivity is the strong Van der Waals interaction between Mg2+ cations and nitrogen molecules.The Mg2+ cation plays a significant role in the N2 adsorption process.NaCoA also has a high N2 adsorption capacity and selectivity,but this is assigned to theπ-complexation between Co2+ cations and nitrogen molecules.The deduction ofπcomplexation is also supported by the high Langmuir and Virial constants,high heat of adsorption calculated by Clausius-Clapeyron equation and the characteristic IR adsorption band of M-N≡N.3.The offset cations modification of as-synthesized NaX zeolite has been carried out, also the N2&O2 adsorption behaviors at 25℃have been investigated.After Li+,Ca2+,Ag+ and Mn2+ cations exchange modification,X zeolite exhibits outstanding N2 adsorption capacities.Moreover,the differences of adsorption properties between X and A zeolites should be attributed to the structural variation of the zeolite frameworks.4.The offset cations modification of ANA(1D channels) and MOR(2D channels) zeolites have also been executed for evaluating the gas adsorption properties at 25℃.ANA zeolite series show extremely low N2&O2 adsorption capacities,interalated with the framework structure and the pore size.The modifacated MOR zeolite exhibits an increase in gas adsorption capacity compared to the parent zeolite,but still a little less than those of NaA and NaX zeolites with 3D pore structures.For MOR type,SiO2/Al2O3 molar ratio and pore structure should be the main factors influencing the gas adsorption capacities.
|
PDF Full Text Request