Catalysts for fischer-tropsch synthesis on cobalt/phosphorus-aluminum oxide and preparation methods thereof
The present invention relates to a cobalt/phosphorus-alumina catalyst in which cobalt is supported as an active component on a phosphorus-alumina support wherein phosphorus is supported on alumina surface. With a bimodal pore structure of pores of relatively different pore sizes, the catalyst provides superior heat- and matter-transfer performance and excellent catalytic reactivity. Especially, when Fischer-Tropsch (F-T) reaction is performed using the catalyst, deactivation by the water produced during the F-T reaction is inhibited and, at the same time, the dispersion and reducing property of cobalt and other active component are improved. Therefore, the cobalt/phosphorus-alumina catalyst for F-T reaction in accordance with the present invention provides good carbon monoxide conversion and stable selectivity for liquid hydrocarbons.
1. A cobalt/phosphorus-alumina catalyst for a Fischer-Tropsch reaction in which cobalt is supported on a support as an active component,
the catalyst including cobalt (Co) supported on a phosphorus-alumina support in which the phosphorus (P) is supported on an alumina surface, the phosphorus having 0.05 to 20 wt % per 100 wt % of the alumina and the cobalt having 5 to 40 wt % per 100 wt % of the phosphorus-alumina support, and the catalyst having a bimodal pore structure with pores of a relatively smaller size PS 1 and pores of a larger size PS 2 , wherein the pore sizes PS 1 and PS 2 are;
1 nm ≦PS 1 ≦25 nm; and
25 nm <PS 2 ≦150 nm.
2. The cobalt/phosphorus-alumina catalyst as claimed in claim 1 , wherein the catalyst has a specific surface area of 120 to 400 m 2 /g.
3. The cobalt/phosphorus-alumina catalyst as claimed in claim 1 , wherein a proportion of volume PV 1 of the smaller pores to volume PV 2 of the larger pores, or PV 1 /PV 2 , is maintained at 0.5 to 2.0.
4. A method for preparing the cobalt/phosphorus-alumina catalyst of claim 1 comprising the steps of:
mixing an aluminum alkoxide solution dissolved in an alcohol-based organic solvent, organic carboxylic acid having a pKa value of 3.5 to 5, and water;
heating the mixture at 80 to 130° C. to prepare a boehmite sol and drying;
baking the same at 400 to 700° C. to prepare γ-alumina having a specific surface area in a range from 300 to 800 m 2 /g;
supporting a phosphorus precursor on the γ-alumina;
baking at 300 to 800° C. to prepare a phosphorus (P)-alumina support having a specific surface area in a range from 200 to 500 m 2 /g;
supporting a cobalt precursor on the phosphorus-alumina support; and
baking at 300 to 800° C. to prepare a cobalt/phosphorus-alumina catalyst having a bimodal pore structure with pores of a smaller size PS 1 and pores of a larger size PS 2 , wherein the pore sizes PS 1 and PS 2 are:
1 nm ≦PS 1 ≦25 nm; and
25 nm <PS 2 ≦150 nm.
5. The method as claimed in claim 4 , wherein the phosphorus precursor is a compound selected from the group consisting of phosphoric acid (H 3 PO 4 ), phosphorus oxychloride (POCl 3 ), phosphorus pentoxide (P 2 O 5 ), phosphorus trichloride (PCl 3 ), and mixtures thereof.
6. The method as claimed in claim 4 , wherein the phosphorus-alumina support has 0.05 to 20 wt % of phosphorus supported per 100 wt % of alumina.
7. The method as claimed in claim 4 , wherein the cobalt precursor is a compound selected from the group consisting of a nitrate salt, an acetate salt, a chloride salt, and mixtures thereof.
8. The method as claimed in claim 4 , wherein 5 to 40 wt % of cobalt is supported per 100 wt % of the phosphorus-alumina support in the cobalt/phosphorus-alumina catalyst.