Organothermal Synthesis of Ultrafine Ceria Particles and Their Function

在2-甲氧基乙醇中，2 0 0~30 0℃反应2 0 0~30 0℃，去除表层产生的粗大CeO2颗粒，得到深棕色透明溶液，该溶液为胶体溶液，含有2 nm左右的CeO2超细颗粒(反应时间2 0 0~2 5 0℃)。该粒子是合成的CeO_2粒子中最小的，因此脂肪，粒子的大小随着反应温度的升高或反应时间的延长而增大。用凝聚法制备的CeO_3胶体粒子在500℃时出现晶体生长，这是由于超细粒子具有较大的表面能所致。由于初级颗粒的凝聚作用很强，初级颗粒之间形成的微孔太小，氮气分子无法进入。因此，CeO_2粉末的比表面积并不像预期的一次粒子大小那样大。通过添加聚合物分散剂或控制凝聚剂的离子强度来抑制强凝聚，可制得大比表面积、大孔径的氧化铈粉末。以大孔CeO_2粉末为载体的Au催化剂对苯甲醇的液相氧化具有较高的催化性能，同样的反应过程也得到了含Sm、Yb氧化物的胶体溶液。然而，一些稀土金属对该反应是惰性的。稀土金属的反应性与金属的晶体结构有关。对于活性较低的稀土金属，加入冰醋酸促进了反应，得到了相应的金属氧化物或氢氧化物的胶体溶液

The reaction of cerium metal tips having the superficial layer in 2-methoxyethanol at 200-300℃ followed by the removal of coarse ceria particles originating from the superficial layer yielded a dark brown clear solution, which was shown to be a colloidal solution containing ultrafine particles of ceria with a particle size of 2 nm ( reaction at 200-250℃.) This particle size is the smallest of the ceria particles synthesized thus fat The particle size increased with the increase in the reaction temperature or with prolonged reaction time. The ceria powder obtained by coagulation of the ceria colloidal particles showed crystal growth at as low as 500℃, which was concluded to be due to the large surface energy of ultrafine particles. Since the coagulation of the primary particles was so strong that micropores formed between the primary particles were too small to be accessed by nitrogen molecules. Therefore, surface area of the ceria powder was not so large as expected from the primary particles size. Strong coagulation was prohibited by the addition of polymer dispersant or by controlling the ionic strength of the coagulant, and ceria powder with large surface area and large pore size could be prepared. Aruthenium catalyst supported on the ceria powder having large pore size had quite a high performance for liquid phase oxidation of benzylalcohol, Colloidal solutions containing samarium and ytterbium oxides were also obtained by the similar reaction procedure. However, some rare earth metals were inert for the reaction. The reactivity of the rare earth metals was found to be connected with the crystal structure of the metals. For the rare earth metals with low reactivity, addition of acetic acid promoted the reaction and transpired colloidal solution of the corresponding metal oxide or hydroxide was obtained