包头混合轻稀土催化材料的制备及催化性能研究
摘要
本文用改进沉淀法制备了包头稀土催化剂,通过掺杂Y、Dy、Tb和Mn对该催化剂进行改性处理。用X衍射仪、激光粒度仪、比表面积测试仪、扫描电子显微镜和透射电子显微镜等手段对所制备催化剂进行了表征,并利用密度泛函的方法对催化剂掺杂前后进行了机理计算。
通过测定催化剂的比表面积,研究了沉淀剂的浓度、稀土硝酸盐浓度、反应温度、滴加速度及搅拌速度等沉淀条件对催化剂比表面积的影响,找出了制备该催化剂的最佳工艺条件。利用DTA/TG对催化剂样品前驱体的热分解行为进行了动力学分析,结果表明其前驱体热分解反应符合D3模型,活化能为62.939 kJ·mol~(-1),指前因子A=1.184×10~3s~(-1),动力学方程为:dα/dt=1.776×10~3exp[-62.939×10~3/(RT)]·(1-α)~(2/3)[1-(1-α~(1/3)]~(-1)。
由X射线衍射图谱看出,掺杂改性前后包头稀土催化剂基本属于立方晶系,萤石结构。通过对比表面积、粒度及透射电镜照片分析,未掺杂改性的颗粒内部分布大量空隙,随焙烧温度增加,内部空隙消失,颗粒大小有所增大,比表面积减小;掺杂Y、Dy、和Tb后粒度变小,比表面积增大,抗高温老化性能,提高,H2-TPR还原温度向低温方向移动,但掺杂Mn元素后,抗老化性能不好,催化性能改善不明显。
依据平面波展开的第一性原理赝势法,研究了包头稀土催化剂掺杂前后的电子结构。结果表明Zr掺杂LaCePrO后在高能带中出现大量由Zr 3d和O 2p贡献的自由载流子电子,增加了Ce离子变价的几率,改善了催化环境。同时,计算了掺杂Y、Dy、Tb和Mn后的LaCePrZrO的电子结构,发现掺杂Y、Dy和Tb后可使体系内部具有更多活跃电子,增加了固溶体中Ce3+和Ce4+之间的变价几率,这样会增加该固溶体中氧负离子的流动性,改善催化环境,提高了催化性能和催化活性,但掺杂Mn却减少了体系中氧负离子的流动性,所以其还原性能没有很好改善。
In this paper, Baotou rare earth mineral catalyst was prepared by precipitation method. It doped Y, Dy, Tb and Mn for modification the catalyst of property. The catalyst property was characterized by X-ray diffraction, laser particle size analyzer, specific surface area, scanning electron microscopy and transmission electron microscopy. Catalytic mechanism was calculated by DFT methods.
Preparation of the optimum conditions was concluded by measuring specific surface area of catalyst to study the concentration of the precipitant, the concentration of rare earth nitrate, reaction temperature and stirring speed. The DTA / TG were used to study the catalyst precursor of the thermal decomposition kinetic analysis. The results showed thermal decomposition reaction in line with the D3 model, the activation energy is 62.939 kJ·mol~(-1), pre-exponential factor A = 1.184×10~3s~(-1), kinetic equation: dα/ dt = 1.776×103exp [-62.939×10~3 / (RT)]·(1-α)~(2/3)[1 - (1-α)~(1/3)]~(-1).
Crystal structure of Baotou rare earth catalyst is cubic crystal system, fluorite structure by measuring X-ray diffraction. Morphology of non-doped catalyst is a large number of particles within the distribution of the gap. But, when the calcination temperature increased, the internal gap disappears and particle size has increased and specific surface area decreased. Doped Y, Dy, and Tb sample have small particle size, large specific surface area, H2-TPR reduction temperature shifted to lower temperature, and anti-aging properties of high temperature better than non-doped sample.But the Mn-doped sample is not good at anti-aging properties of high temperature and can not improve the catalytic properties of catalyst obviously.
We are based on plane wave expansion of the first principles pseudopotential method to study the before and after doping of rare-earth catalyst electronic structure. The results show that the Zr-doped high-energy band in the emergence of a large number of Zr 3d and O 2p contributions to the free carrier electronics, an increase of Ce ions of the probability of price change. At the same time, the calculation of the doped Y, Dy, Tb and Mn in LaCePrZrO of the electronic structure found that doping Y, Dy and Tb will take more active system of internal electronics, an increase of solid solution of Ce3+ and Ce4+ between the probability of price change, which will increase the solid solution in the mobility of oxygen ions to improve the catalytic environment, and improve the catalytic properties and catalytic activity, but Mn-doped system has reduced the mobility of oxygen ions, the restore performance improvement is not very good.
通过测定催化剂的比表面积,研究了沉淀剂的浓度、稀土硝酸盐浓度、反应温度、滴加速度及搅拌速度等沉淀条件对催化剂比表面积的影响,找出了制备该催化剂的最佳工艺条件。利用DTA/TG对催化剂样品前驱体的热分解行为进行了动力学分析,结果表明其前驱体热分解反应符合D3模型,活化能为62.939 kJ·mol~(-1),指前因子A=1.184×10~3s~(-1),动力学方程为:dα/dt=1.776×10~3exp[-62.939×10~3/(RT)]·(1-α)~(2/3)[1-(1-α~(1/3)]~(-1)。
由X射线衍射图谱看出,掺杂改性前后包头稀土催化剂基本属于立方晶系,萤石结构。通过对比表面积、粒度及透射电镜照片分析,未掺杂改性的颗粒内部分布大量空隙,随焙烧温度增加,内部空隙消失,颗粒大小有所增大,比表面积减小;掺杂Y、Dy、和Tb后粒度变小,比表面积增大,抗高温老化性能,提高,H2-TPR还原温度向低温方向移动,但掺杂Mn元素后,抗老化性能不好,催化性能改善不明显。
依据平面波展开的第一性原理赝势法,研究了包头稀土催化剂掺杂前后的电子结构。结果表明Zr掺杂LaCePrO后在高能带中出现大量由Zr 3d和O 2p贡献的自由载流子电子,增加了Ce离子变价的几率,改善了催化环境。同时,计算了掺杂Y、Dy、Tb和Mn后的LaCePrZrO的电子结构,发现掺杂Y、Dy和Tb后可使体系内部具有更多活跃电子,增加了固溶体中Ce3+和Ce4+之间的变价几率,这样会增加该固溶体中氧负离子的流动性,改善催化环境,提高了催化性能和催化活性,但掺杂Mn却减少了体系中氧负离子的流动性,所以其还原性能没有很好改善。
In this paper, Baotou rare earth mineral catalyst was prepared by precipitation method. It doped Y, Dy, Tb and Mn for modification the catalyst of property. The catalyst property was characterized by X-ray diffraction, laser particle size analyzer, specific surface area, scanning electron microscopy and transmission electron microscopy. Catalytic mechanism was calculated by DFT methods.
Preparation of the optimum conditions was concluded by measuring specific surface area of catalyst to study the concentration of the precipitant, the concentration of rare earth nitrate, reaction temperature and stirring speed. The DTA / TG were used to study the catalyst precursor of the thermal decomposition kinetic analysis. The results showed thermal decomposition reaction in line with the D3 model, the activation energy is 62.939 kJ·mol~(-1), pre-exponential factor A = 1.184×10~3s~(-1), kinetic equation: dα/ dt = 1.776×103exp [-62.939×10~3 / (RT)]·(1-α)~(2/3)[1 - (1-α)~(1/3)]~(-1).
Crystal structure of Baotou rare earth catalyst is cubic crystal system, fluorite structure by measuring X-ray diffraction. Morphology of non-doped catalyst is a large number of particles within the distribution of the gap. But, when the calcination temperature increased, the internal gap disappears and particle size has increased and specific surface area decreased. Doped Y, Dy, and Tb sample have small particle size, large specific surface area, H2-TPR reduction temperature shifted to lower temperature, and anti-aging properties of high temperature better than non-doped sample.But the Mn-doped sample is not good at anti-aging properties of high temperature and can not improve the catalytic properties of catalyst obviously.
We are based on plane wave expansion of the first principles pseudopotential method to study the before and after doping of rare-earth catalyst electronic structure. The results show that the Zr-doped high-energy band in the emergence of a large number of Zr 3d and O 2p contributions to the free carrier electronics, an increase of Ce ions of the probability of price change. At the same time, the calculation of the doped Y, Dy, Tb and Mn in LaCePrZrO of the electronic structure found that doping Y, Dy and Tb will take more active system of internal electronics, an increase of solid solution of Ce3+ and Ce4+ between the probability of price change, which will increase the solid solution in the mobility of oxygen ions to improve the catalytic environment, and improve the catalytic properties and catalytic activity, but Mn-doped system has reduced the mobility of oxygen ions, the restore performance improvement is not very good.
引文
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