Silica-alumina catalyst support, catalysts made therefrom and methods of making and using same
View Patent ↗This invention relates to catalysts comprising a catalytic metal deposited on a composite support with well-dispersed chemical “anchor” species acting as nucleation centers for catalytic metal crystallites growth. The catalysts have the advantage that the average catalytic metal crystallite size can be controlled by the molar ratio of catalytic metal to chemical “anchor,” and is not limited by the porous structure of the support. A preferred embodiment comprises a cobalt-based catalyst on a silica-alumina support made by a co-gel method, wherein its average pore size can be controlled by the pH. The alumina species in the support most likely serve as chemical “anchors” to control the dispersion of cobalt species, such that the average cobalt crystallite size can be greater than the average pore size.
1. A catalyst comprising:
a porous composite support comprising a first element and a second element with a molar ratio of the first element to the second element between about 3:1 and about 1,000:1, wherein the first element comprises silicon, titanium, zirconium, thorium, cerium, aluminum, boron, oxides thereof, or any combination thereof and wherein the second element comprises aluminum, titanium, zirconium, tungsten, molybdenum, sulfate, boron, gallium, scandium, oxides thereof, or any combination thereof; and
a catalytic metal comprising catalytic metal crystallites deposited on said porous composite support, wherein the catalytic metal comprises cobalt, iron, ruthenium, nickel, or combinations thereof and wherein the catalytic metal comprises between about 10 and about 40 wt. % of the total catalyst weight and further wherein the catalytic metal average crystallite size is between about 6 nm and about 25 nm;
wherein the support is made in a manner effective in distributing species of said second element amongst species of said first element;
wherein the porous composite support has an average pore size between 5 nm and 40 nm a surface area of between about 275 and about 600 m 2 /g;
wherein the porous composite support is made by a sol-gel method and the sol-gel method comprises: mixing a compound of the first element and a compound of the second element under conditions effective for providing a homogeneous hydrogel comprising the molar ratio of the first element to the second element; aging the hydrogel; and treating the hydrogel to form the porous composite support, wherein the treating comprises drying and calcining in air;
wherein the catalyst has a molar ratio of said catalytic metal to said second element between about 2:1 and about 1,000:1;
wherein species of said second element serve as nucleation centers for said catalytic metal crystallites; and
wherein the catalyst further comprises a promoter selected from the group consisting of silver, boron, ruthenium, rhenium, palladium, platinum, or any combination thereof.
2. The catalyst according to claim 1 wherein the first element comprises silica, and the second element comprises alumina.
3. The catalyst according to claim 2 wherein the porous composite support has a silica-to-alumina molar ratio between about 30:1 and about 500:1.
4. The catalyst according to claim 1 wherein the first element comprises zirconia, and the second element comprises titania.
5. The catalyst according to claim 1 wherein the first element comprises silica, and the compound of silica is sodium silicate; and wherein the second element comprises alumina, and the compound of aluminum is sodium aluminate.
6. The catalyst according to claim 1 wherein the catalytic metal is active for the synthesis of hydrocarbons from a mixture of hydrogen and carbon monoxide.
7. The catalyst according to claim 1 wherein the catalytic metal comprises cobalt.
8. The catalyst according to claim 7 wherein the second element is alumina.
9. The catalyst according to claim 8 wherein the catalyst has a cobalt-to-alumina molar ratio between about 5:1 and about 300:1.
10. The catalyst according to claim 8 wherein the catalyst has a cobalt-to-alumina molar ratio between about 10:1 and about 150:1.
11. The catalyst according to claim 1 wherein the porous composite support has an average pore size between about 5 nm and about 20 nm.
12. The catalyst according to claim 1 wherein the porous composite support has a surface area between about 300 and about 600 m 2 /g.
13. A Fischer-Tropsch catalyst comprising:
an amorphous silica-alumina support having an average pore size and a molar ratio of silica to alumina between about 3:1 and about 1,000:1 and wherein the amorphous silica-alumina support has an acidity index greater than about 6 and less than about 129; and
cobalt crystallites with an average crystallite size deposited on said support, wherein the average crystallite size is greater than the average pore size of the support, and wherein the catalyst has a molar ratio of cobalt to alumina between about 2:1 and about 1,000:1;
wherein the cobalt comprises between about 5 and about 40 wt. % of the total catalyst weight and the average cobalt crystallite size is between about 6 nm and about 25 nm;
wherein the average pore size of the amorphous silica-alumina support is between about 5 nm and about 20 nm and further wherein the amorphous silica-alumina support has a surface area between 260 and 600 m 2 /g;
wherein the catalyst further comprises which comprises between about 0.001 and about 10 wt. % of the total catalyst weight, and wherein the promoter comprises silver, boron, ruthenium, rhenium, palladium, platinum, or any combination of two or more thereof.
14. The catalyst according to claim 13 wherein the silica to alumina molar ratio is from about 30:1 to about 500:1.
15. The catalyst according to claim 13 wherein the silica to alumina molar ratio is from about 40:1 to about 400:1.
16. The catalyst according to claim 13 wherein the catalyst has a molar ratio of cobalt to alumina between about 5:1 and about 300:1.
17. The catalyst according to claim 13 wherein the catalyst has a molar ratio of cobalt to alumina between about 10:1 and about 150:1.
18. The catalyst according to claim 13 wherein the amorphous silica-alumina support comprises low acidity silica-alumina.
19. The catalyst according to claim 13 wherein the support is homogeneous with respect to silica and alumina.