Core-shell particles with catalytic activity
The present invention pertains to novel core-shell particles comprising a core of iron oxide and a shell of cobalt oxide, characterized in that they are spherical with a number average diameter, as measured by TEM, of between 1 and 20 nm. This invention is also directed to their uses in the manufacture of a catalyst, and to the method for preparing these particles, by precipitating cobalt oxide onto magnetite or hematite particles which are themselves precipitated from Fe(III) and optionally Fe(II) salts.
1. A method for the preparation of spherical core-shell particles, comprising the successive steps of:
(a) preparing an aqueous solution comprising a ferric salt, at a temperature of less than 50° C.;
(b) adding at least one base to said aqueous solution, so as to obtain a suspension of iron oxide particles having a pH value of from 10 to 14;
(c) washing the suspension;
(d) adding a strong acid to the washed suspension to peptize the washed suspension;
(e) reacting at least one base with said peptized suspension, until the pH reaches a value from 10 to 14, at a temperature of from 50 to 95° C.;
(f) adding a cobalt salt to the heated suspension in order to obtain spherical particles having a core of iron oxide and a shell comprising cobalt oxide.
2. The method according to claim 1 , characterized in that the aqueous solution comprising the ferric salt further includes a ferrous salt in a molar ratio of Fe(III) to Fe(II) of 2:1, whereby the iron oxide particles are magnetite particles.
3. The method according to claim 1 , characterized in that the ferric salt is ferric nitrate, ferric chloride or ferric hydroxide.
4. The method according to claim 2 , characterized in that the ferrous salt is ferrous nitrate, ferrous chloride or ferrous hydroxide.
5. The method according to claim 1 characterized in that the cobalt salt is cobalt nitrate, cobalt chloride or cobalt sulphate.
6. The method according to claim 1 , characterized in that the strong acid is nitric acid or hydrochloric acid.
7. The method according to claim 3 , characterized in that the ferric salt is ferric chloride.
8. The method according to claim 4 , characterized in that the ferrous salt is ferrous chloride.
9. The method according to claim 5 , characterized in that the cobalt salt is cobalt nitrate.