【作者】 王燕鸿；

【导师】 王务林； 王军；

【作者基本信息】 天津大学 ， 环境化工， 2008， 博士

【摘要】 本文系统考察了不同方法制备的磷改性氧化铝的结构、表面物理化学性质及热稳定性;开发了磷化铝水解制备体相晶胞改性氧化铝的工艺;研究了磷掺杂对氧化铝结构和性能的影响;对磷的化学环境与氧化铝性能之间的关系及磷对活性氧化铝的改性机理进行了探讨。通过浸渍法和凝胶法,调变磷的引入方式,合成了颗粒表面改性（GI）,表层改性（GP）,内核改性（PG）和颗粒体相改性（G）四个系列磷改性氧化铝。利用低温N2吸附、XRD、FTIR及Zeta电位仪等手段研究了氧化铝的孔织构、晶型、表面酸碱性、表面电性及高温（水热）稳定性。结果表明:在氧化铝中引入磷可以提高氧化铝的高温热稳定性,其中以5 wt%的磷改性效果最佳;1000℃以下,浸渍法制备的GI样品具有最佳抗烧结性能;1000℃以上,凝胶法制备的G样品具有较好的热稳定性;用浸渍法和凝胶法在氧化铝中引入磷,使γ-Al₂O₃表面出现Br?nsted位,同时降低了表面碱性。采用磷化铝水解法制备体相晶胞磷改性氧化铝,开发了创新的氧化铝合成工艺,考察了工艺条件对活性氧化铝性能的影响,并进行了工艺优化。通过HRTEM、XRD、原位DRIFT、NMR等手段系统研究了该改性氧化铝的性能及结构。结果显示:水解法制备氧化铝具有良好的高温热稳定性,α相变温度提高到1300℃,体相晶胞中“锚定”的1 wt%左右的磷是其稳定的根本原因。磷在水解及煅烧过程中从-3价变至+5价,增加了氧化铝中的阴离子空位,从而提高了氧化铝的表面碱性。通过NMR、XRD、DRIFT等手段,研究磷在氧化铝中的赋存方式,考察磷对活性氧化铝的稳定作用机理。实验证明:磷在氧化铝中分布越均匀、结合越牢固,其稳定作用越强;磷的不同引入方式改变了氧化铝中铝离子的配位情况,六配位铝离子越多,活性氧化铝越稳定。磷在氧化铝表面以无定型态存在,改变了氧化铝表面羟基的数量及性质,抑制了氧化铝的脱羟基烧结和颗粒长大,提高了其热稳定性;磷在氧化铝体相以单磷酸盐形式存在,抑制了铝离子的体相扩散,从而提高了氧化铝的α相变温度。此外,在水蒸汽环境中,Al-OH被不易脱除的P-OH取代,故氧化铝的水热稳定性大幅提高。更多还原

【Abstract】 The structural physical and chemical properties of surface as well as thermal stability of phosphorus modifiedγ-alumina were investigated. A novel producedure, aluminium phosphide （AlP） hydrolysis method was developed to synthesize phosphorus crystal littice modified alumina. The effect and mechanism of phosphorus dopant on the alumina structure and thermal properties was studied. Finally, the interaction between chemical environment of phosphorus and alumina properties and mechanism of thermal stable of phosphorus in alumina were explored.Four series aluminas, GI （surface modified）, GP （shell modified）, PG （core modified） and G （particle bulk modified） samples, were synthesized by impregnation and gel method through change the introduced ways of phosphorus into alumina. The nitrogen adsorption, XRD, FTIR etc. technique were used to determine the pore texture, crystallography, acid/base properties, IEP and high thermal or hydrothermal stability. The results showed that the alumina, with 5 wt% phosphorus, has the best thermal stability. Below 1000℃, GI sample has better stability to resist sintering; when calcination temperature was higher than 1000℃,G sample performs higher phase transformation temperature. The Br?nsted acid appeared on the alumina surface when phosphorus doped alumina as well as the surface base decreased.The aluminium phosphide hydrolysis was used to synthesize the crystal lattice modified alumina, which is a new process to produce active alumina. The influence of procedure parameters of AlP hydrolysis on alumina performance was investigated and optimized. The properties and structure of the alumina was studied using HRTEM, XRD, in situ DRIFT, NMR, XPS and EDS. It was showed that theαphase transformation temperature of the alumina was enhanced to 1300℃, due to 1 wt% phosphorus anchored in the crystal lattice of alumina. Valence of phosphor changed from -3 to +5 during calcination, which increased the anions vacancies and enhanced the surface base.The location and chemical environment of phosphorus in alumina was studied using NMR, XRD, EDS and DRIFT techniques and related to the properties of alumina. Additionally, the mechanism of thermostable of phosphorus was explored. It was proved that the more homogeneous of phosphorus in alumina and the stronger interaction between P and alumina, the more stable of alumina was; additionally, the coordination of Al3+ ions might be changed with the introduced ways of phosphorus to alumina, which can modified the stability of alumina. Octahedral Al³⁺ ions can improve the thermal stability of active alumina. Phosphorus, as form of amorphous phosphate on the surface of alumina, can modify the amounts and nature of surface hydroxyl groups, which inhibited the dehydroxyl sintering and prevent the particles growth inhibited the decrease of surface area; phosphorus, as mono-phosphate, in the bulk of alumina, prevented the Al3+ ions diffusion in the bulk, which enhanced the alumina phase transformation temperature. Furthermore, the hydrothermostability of alumina was improved effectively, due to the Al-OHs of particles surface was replaced by P-OHs, which was more difficult to remove than Al-OHs.更多还原