Organothermal Synthesis of Ultrafine Ceria Particles and Their Function

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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