Please see the attached article

Hello Nastaran, it seems to me an interesant question. I think the easy way to do it is to reduce the oxide to cerium and treat it with concentrated nitric acid. Any other way I thik will be more complicate. Check this article (It is in Portuguese but the diagrams are easy to understand).

http://www.scielo.br/pdf/ce/v47n301/a0947301.pdf

I hope it will be useful.

Greetings

Cathodic electrodeposition of cerium based oxide ....Please ref: Hamlaoui and others 2008.

Nastaran Dayani

It depends wether you mean trivalent or tetravalent cerium. For trivalent cerium, you can just add cerium oxide or cerium carbonate to hot dilute nitric acid until the mixture stays cloudy. Then you filter off unreacted cerium oxide or carbonate and evaporate the filtrate at elevated temperature until it becomes viscous. Crystal of hydrated cerium nitrate will form upon standing at room temperature. For cerium carbonate, you can just take an aqueous solution of cerium trichloride and add a solution of sodium carbonate. Cerium carbonate will form as a somewhat slimy white precipitate. This can be isolated by filtration, thorough washing with water and drying in air.

Ilustre Frank T. Edelmann Frank, Ce++++ é mais estável, então CeO_2 seria muito ideal, mas acho que deve reagir em um conversor catalítico com uma base forte (exemplo, de um metal M++) para obter Ce(OH)_4 e isso será facil neutralizar com HNO_3 (concordo contigo Jorge Gonzalez Gonzalez) para obter Ce(NO_3)_4