Organothermal Synthesis of Ultrafine Ceria Particles and Their Function

在200-300℃下，将具有表层的金属铈尖在2-甲氧基乙醇中反应，然后去除表层的粗二氧化铈颗粒，得到深棕色的透明溶液，该溶液显示为含有粒径为2nm的超细二氧化铈颗粒的胶体溶液（反应在200-250℃）。该粒径是目前合成的最小的二氧化铈颗粒，其粒径随反应温度的升高或反应时间的延长而增大。在低至500℃的温度下，经氧化铈胶体颗粒混凝得到的氧化铈粉末呈现出晶体生长，这是由于超细颗粒具有较大的表面能。由于初级颗粒的凝聚性很强，初级颗粒之间形成的微孔太小，氮分子无法进入。因此，氧化铈粉末的表面积并不像初粒径所期望的那么大。通过添加高分子分散剂或控制混凝剂的离子强度，可以抑制强混凝，制备出大表面积、大孔径的二氧化铈粉体。在大孔径的二氧化铈粉上负载的氧化铝催化剂对苯甲醇的液相氧化具有较高的性能，用类似的反应方法也得到了含有氧化钐和氧化镱的胶体溶液。然而，一些稀土金属对该反应是惰性的。发现稀土金属的反应性与金属的晶体结构有关。对反应活性较低的稀土金属，加入乙酸可促进反应，蒸腾得到相应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