In^(3+)掺杂CeO_2的固溶度及其储氧能力

SOLID SOLUBILITY AND OXYGEN STORAGE CAPABILITY OF In^(3+)-DOPED CeO_2

以(CH_2OH)2和H_2O的混合溶液为溶剂,Ce(NO_3)_3?6H_2O和In(NO_3)_3?4.5H_2O分别为Ce和In源,采用溶剂热法在200℃下合成了前驱体,再经500℃焙烧2 h制备了In^(3+)掺杂的CeO_2粉末.通过研究一系列In^(3+)的添加浓度,得出In^(3+)掺杂CeO_2中In^(3+)的固溶度为1%(摩尔分数).In^(3+)掺杂对CeO_2形貌的影响不大,固溶In^(3+)前后的CeO_2颗粒形貌均为层状结构,但当In^(3+)的添加量高于固溶度时,出现了细碎的第二相颗粒.In^(3+)饱和掺杂浓度时CeO_2粉末的比表面积高于未掺杂的CeO_2,达到100 m2/g,当In^(3+)的添加量大于等于3%时比表面积有所下降.In^(3+)添加量对储氧能力的影响为:首先,In^(3+)的引入能够明显降低CeO_2的低温还原峰温度;其次,当In^(3+)的添加量为饱和浓度1%时,CeO_2的低温储氧能力由未掺杂的3.6×10-4mol/g提高到4.4×10-4mol/g;当In^(3+)的浓度大于等于3%时,试样的低温储氧能力先有所下降,随后趋于稳定.不同In^(3+)添加量CeO_2粉末的晶格常数、氧空位浓度、比表面积和低温储氧能力都在1%In^(3+)固溶度的位置出现了转折.低温储氧能力与比表面积和氧空位浓度都有关联,是二者综合作用的结果.

CeO_2 is an important rare earth oxide and can be used in automotive exhaust three- way catalysts on the basis of its oxygen storage capability. Ion doping is an effective method to enhance the oxygen storage capability of CeO_2. And when doping a cation whose size is smaller than Ce4 ＋and valence is lower than ＋4, it tends to evolve more defects. It is known that defects play important roles in enhancing the oxygen storage capability of CeO_2. Therefore, In ion was selected as a dopant cation which matches above two factors of size and valence. In this work, a series of CeO_2 with different content ofIn^（3＋）were synthesized via a two-step process. The precursor was synthesized by a solvothermal method at 200 ℃ using a mixture solvent of（CH2OH）2and H_2O, as well as Ce（NO_3）_3·6H2O and In（NO_3）_3？4.5H_2O as Ce and In sources, respectively. CeO_2 was obtained after the precursor was calcined at 500 ℃ for 2 h in air. It was found that the solid solubility of In3＋in CeO_2 was 1%（molar fraction）.The doping of 1%In3 ＋in CeO_2 almost had no impact on the morphology of multilayered structure. However, a second phase of small particles appeared and there were some changes of the morphology of multilayered structure when the concentration of In3＋increased further. The specific surface area of the 1%In3＋solid solution was 100 m2/g,which was th highest among all the samples, and undoped CeO_2（92 m2/g） ranked second. When the content of In3＋was above the solid solubility, i.e., 1%In3＋, the specific surface area decreased. The low temperature oxygen storage capability could be improved from 3.6×10- 4mol/g for undoped CeO_2 to 4.4×10- 4mol/g for 1%In3 ＋-doped CeO_2.When the In3＋content was greater than or equal to 3%, the low temperature oxygen storage capability decreased at the beginning, and then almost no change. Lattice parameter decreased and the concentration of Ce3 ＋and oxygen vacancy increased by the doping of In3＋. Moreover, lattice parameter, the specific surface area, concentration of oxygen vacancy and low temperature oxygen storage capacity could mark a turning point for 1%In3＋. It could be found that the low temperature oxygen storage capability was in relation to both the specific surface area and the concentration of oxygen vacancy of CeO_2. In addition, the low temperature reduction peaks shifted towards lower temperatures with the addition of In3＋.