The Synthesis And Charaterization Of Heteroatom-Substituted Aluminophosphate Molecular Sieves By Microwave Irradiation

Zeolitic materials with regular microporous structures and large surface areahave been extensively used in many industrial processes such as catalysis, adsorptionand separation, etc. Aluminophosphate molecular sieves （AlPO₄-n） are one of theimportant families of microporous materials, which have been extensively studied dueto their rich structural architectures and important applications in catalysis, absorptionand separation. Particularly, heteroatom-substituted aluminophosphate molecularsieves have exhibited special redox and catalytic properties because of the creation ofacid sites and redox centers, as well as photoluminescence properties, electronicconductivity and magnetic properties.In order to meet the needs of industrial production, people begin to pay moreattention to the synthesis of molecular sieves with special structure and properties.Compared with the conventional synthetic methods, microwave assisted synthesishas unique “microwave effects”:（i） time reducing and consequently energyconsumption decreasing;（ii） the uniform structure and versatile of composition forthe products. Therefore, the microwave-assisted synthesis method has been widelyused in the synthesis of inorganic microporous materials.This thesis is focused on the synthesis and characterization ofheteroatom-substituted aluminophosphates molecular sieves prepared undermicrowave-assisted and hydrothermal or solvothermal conditions. Main achievementsare as follows:1. Copper-substituted aluminophosphate molecular sieves CuAPO-5have been synthesized by using tetraethyl ammonium hydroxide as the template undermicrowave conditions. The product has been characterized by X-raydiffraction （XRD）, composition analysis, thermogravimetric analysis （TGA）,nitrogen adsorption measurements NH₃-TPD, and so on. Uniqueinterspersed morphology of the as-synthesized product can be clearlyobserved by the scanning electron microscopy （SEM）. The test of NH₃-TPDanalysis shows that the product has weak aciding, indicating potentialapplications in catalysis. We also studied the influence of various factors onthe synthesis, for example, reaction temperature, heating method, the kind ofhetero atoms, and the amount of hetero atoms, the solvent and the influenceof the microwave power.2. MAPO-34（M=Co, or Zn） and AlPO-34have been synthesized by usingdiethylamine as the template in the solvothermal system, under microwaveirradiation and conventional heating, respectively. AlPO-34crystallizes inthe space group P-1（No.2） with a=9.1887（15）, b=9.2025（15）, c=9.2881（15）, α=87.548o, β=79.031o, γ=87.895o, Z=2. The frameworkis constructed by the strict alternation of AlO₄tetrahedra, AlO₄F2hexahedran and PO₄tetrahedra. In each asymmetric unit, there are6independent crystallographic positions: three crystallographicallyindependent P atoms, and three distinct Al sites. ZnAPO-34crystallizes inthe space group R-3（No.148） with a=13.8218（4）, b=13.8218（4）, c=15.1159（7）, Z=18. The framework is based on the strict alternation ofMO4（M=Al, Zn） and PO₄tetrahedra to form an anionic [M₁Al₂（PO₄）3]1-framework. Charge neutrality is achieved by extra-framework protonateddiethylamine cations. It contains three-dimensional8-ring channels runningin the direction perpendicular to the [001] direction. The protonateddiethylamine molecules reside in the8-ring channels to balance the chargeof the framework, actually the diethylamine reside in the cha-cage with2.0template cations per cage. The framework of AlPO-34and ZnAPO-34canalso be described as a three-periodic net with higher symmetry. The intrinsic symmetry of this underlying net, as determined by Systre software, is R-3mwith one T site. The vertex symbols for the T site in the net of theframework is4·4·4·8·6·8. This three-periodic net is carried by a uniquenatural tiling with the transitivity of （1442）. There are two different tiles inthis tiling with the face symbols [4⁶.6²] and [412.6².86]. The signature of thistiling is [4⁶.6²]+[412.6².86]. The occupancies of Zn and Al with0.25to0.75were suggested by the ICP analyses. The product has been characterized byTGA, scanning electron microscopy, infrared spectroscopy, nitrogenadsorption, CPMAS¹H→¹³C NMR, and so on. And we have discussedthe influence of the synthesis method, the solvent amount, reaction time andthe power of the microwave synthesis.3. Under microwave condition, cobalt-substituted aluminophosphate molecularsieves CoAPO-5and CoAPO-34have been synthesized by usingtriethylamine as the template, triethylene glycol and water as the solvent.The influence of water amount in the mixed solvent has been investigated bydifferent heating methods. Compared with the conventional heating method,the influence of the solvent under microwave irradiation is much stronger,which may be due to the polarity of the system. Based on our work, the highpolarity solvent is conducive to generate the dynamics stable phase AFI, andthe low polarity one is more favorable for the existence of thermodynamicstable phase CHA. Notably, if the alcohol is used as the only solvent, theproduct is an amorphous phase, which indicates that a small amount of wateradded to the reaction systems is unambiguously involved in thecrystallization of the molecular sieves, which promoting both the nucleationand the crystal growth process in the microwave condition. This resultprovides a new route for rapid synthesis of molecular sieves with specialstructures and properties.In summary, this thesis is mainly focused on investigating the variety of reactionconditions on the phase selectivity of the product in microwave assisted synthesis ofheteroatom-substituted aluminophosphate molecular sieves. The results can help us to better understand their growth mechanism which may provide new methods andideas to realize the controlable synthesis of molecular sieves with special structureand properties.