Shaped eggshell catalyst containing cobalt, use and preparation thereof
A method for the preparation of an eggshell catalyst is described comprising the steps of i) immersing shaped units of an oxidic support having a smallest unit dimension ≧0.5 mm in a solution of cobalt ammine carbonate, ii) heating the solution to a temperature between 60 and 120° C. to precipitate cobalt compounds onto the surface of the shaped units, iii) separating the resulting supported cobalt compounds from the remaining solution, and iv) drying the supported cobalt compounds. The cobalt compounds may be reduced to provide catalysts suitable for the hydrogenation of unsaturated compounds or the Fischer-Tropsch synthesis of hydrocarbons.
1. A method for the preparation of an eggshell catalyst precursor comprising the steps of:
i) immersing shaped units of an oxidic support having a length from 0.5 mm to 50 mm, and a cross sectional width from 0.5 mm to 25 mm in an aqueous solution of cobalt ammine carbonate,
ii) heating the solution containing the immersed shaped units at a heating rate of less than 0.4° C/minute to a temperature between 60 and 120° C. to precipitate cobalt compounds onto the surface of the shaped units,
iii) separating the resulting supported cobalt compounds from the remaining solution, and
iv) drying the supported cobalt compounds to form the eggshell catalyst precursor having a cobalt containing layer with a thickness between 5 and 250 microns; wherein less than or equal to 10 wt. % of the cobalt compounds are precipitated in an unsupported state.
2. The method of claim 1 , wherein the cobalt concentration of the cobalt ammine carbonate solution is greater than 5% wt.
3. The method of claim 1 , wherein the oxidic support comprises silica, titania, or alumina.
4. The method of claim 1 , wherein the oxidic support is gamma alumina or theta alumina.
5. The method of claim 1 , wherein the shaped units are pellets or extrudates with a cross-section that is circular, lobed, or fluted.
6. The method of claim 1 , wherein an oxidising agent is added to the solution of cobalt ammine carbonate to oxidise the Co(II) to Co(III), prior to heating the solution to precipitate the cobalt compounds.
7. The method of claim 1 , wherein the dried catalyst precursor is sieved to remove any unsupported cobalt compounds.
8. The method of claim 1 , wherein the dried supported cobalt compounds are heated at elevated temperatures to convert at least a portion of the cobalt compounds to cobalt oxide.
9. The method of claim 1 , wherein the dried supported cobalt compounds are heated under reducing conditions so that at least part of the cobalt is converted to its elemental form.
10. The method of claim 1 , wherein the cobalt compounds are reduced by passing a hydrogen-containing gas over the catalyst precursor at a temperature in the range 200-600° C. for between 1 and 24 hours at atmospheric or higher pressures up to 25 bar.
11. The method of claim 9 , wherein the reduced catalyst precursor is subsequently passivated with an oxygen containing gas or encapsulated with a barrier coating.
12. The method of claim 1 , wherein the cross sectional width is a diameter.