Catalyst preparation method
A method for preparing a catalyst comprising (i) preparing a calcined shaped calcium aluminate catalyst support, (ii) treating the calcined shaped calcium aluminate support with water, and then drying the support, (iii) impregnating the dried support with a solution containing one or more metal compounds and drying the impregnated support, (iv) calcining the dried impregnated support, to form metal oxide on the surface of the support and (v) optionally repeating steps (ii), (iii) and (iv) on the metal oxide coated support. The method provides an eggshell catalyst in which the metal oxide is concentrated in an outer layer on the support.
1. A method for preparing a catalyst comprising:
(i) preparing a calcined shaped calcium aluminate catalyst support by forming a calcium aluminate cement powder, optionally with additional alumina and/or lime, into a desired shape, curing the cement and subsequently calcining the shaped support by heating to between 500 and 1400° C. in air for between 1 and 16 hours,
(ii) prior to impregnating the calcined shaped support with a solution containing one or more metal compounds, treating the calcined shaped calcium aluminate support with water, said water being essentially free of salts, and then drying the support,
(iii) impregnating the dried support with the solution containing one or more metal compounds and drying the impregnated support,
(iv) calcining the dried impregnated support, to form metal oxide on the surface of the support, and
(v) optionally repeating steps (ii), (iii) and (iv) on the metal oxide coated support.
2. A method according to claim 1 wherein the support is alkalised by impregnation with a solution of an alkali prior to the calcination.
3. A method according to claim 1 wherein the support is in the form of a shaped pellet, extrudate or granule.
4. A method according to claim 3 wherein the support is in the form of a cylindrical pellet having between 1 and 12 holes extending there-though.
5. A method according to claim 1 wherein the treatment of the shaped calcium aluminate support with water is by immersion or spraying with water.
6. A method according to claim 5 wherein the treatment with water is by immersing the shaped support in water for a period of between 1 and 120 minutes at a temperature in the range 10-95° C.
7. A method according to claim 1 wherein the support drying step is performed at a temperature in the range 25-250° C.
8. A method according to claim 1 wherein the impregnation solution comprises one or more transition metals.
9. A method according to claim 1 wherein the metal concentration in the impregnating solution is in the range 100-300 g metal/liter.
10. A method according to claim 1 wherein the metal impregnation step is performed at temperatures in the range 50-90° C.
11. A method according to claim 1 wherein steps (ii), (iii) and (iv) are repeated until the metal oxide content of the calcined material is in the range 2-25% wt.
12. A method according to claim 1 wherein one or more promoter compounds are impregnated into the dried support or the metal oxide coated support.
13. A method according to claim 1 wherein the calcination of the impregnated support is performed at a temperature in the range 250-850° C.
14. A method according to claim 1 , wherein the metal oxide is a reducible metal oxide, further comprising the steps of reducing the metal oxide to elemental form with a hydrogen-containing gas mixture.
15. A method according to claim 1 wherein the impregnation solution comprises one of more transition metals selected from the group consisting of chromium, manganese, nickel, cobalt, iron, copper and zinc.
16. A method according to claim 1 wherein the impregnation solution comprises one of more transition metals selected from the group consisting of nickel, cobalt, iron and copper.