Supported precious metal catalysts via hydrothermal deposition
View Patent ↗A process for making a catalyst having precious metal nanoparticles deposited on a support includes first providing an aqueous dispersion of support particles. A pre-treatment slurry is prepared by mixing the aqueous dispersion of support particles with a water-soluble precious metal precursor and a reducing agent. The pre-treatment slurry is hydrothermally treated at a temperature in the range of from about 40° C. to about 220° C. for a time sufficient to deposit precious metal nanoparticles on the surface of the support particles, the precious metal nanoparticles having an average particle size less about 50 nm.
1. A process for making a catalyst having precious metal nanoparticles deposited on a support, the process comprising the following steps:
(a) preparing a slurry of an aqueous dispersion of support particles, a water-soluble precious metal precursor, and a reducing agent; and
(b) hydrothermally treating the slurry in a sealed system by heating the slurry to a temperature in a range of from about 40° C. to about 220° C. at autogenic pressure for a time sufficient to deposit precious metal nanoparticles, in a metallic form, onto at least a portion of a surface of the support particles, the precious metal nanoparticles having an average particle size less than about 50 nm.
2. The process of claim 1 , wherein the support particles comprise a particulate metal oxide.
3. The process of claim 2 , wherein the particulate metal oxide is particulate titanium dioxide.
4. The process of claim 3 , wherein the titanium dioxide is primarily in the anatase form.
5. The process of claim 1 , wherein the precious metal precursor is selected from the group consisting of metal precursors of gold, palladium, platinum and silver.
6. The process of claim 1 , wherein the precious metal precursor comprises a metallic gold precursor, and wherein the particle size of the resulting metallic gold nanoparticles is controlled, in part, by heating the slurry to a temperature in the range of from about 50° C. to about 130° C. in the step for hydrothermally treating.
7. The process of claim 6 , wherein the precious metal precursor is selected from the group consisting of sodium tetrachloroaurate, potassium tetrabromoaurate, hydrogen tetranitroaurate and combinations thereof.
8. The process of claim 6 , wherein the reducing agent is selected from the group consisting of ethanol, iso-propanol, butanediol and combinations thereof.
9. The process of claim 1 , wherein the precious metal precursor comprises a metallic platinum precursor, and wherein the particle size of the resulting metallic platinum nanoparticles is controlled, in part, by heating the slurry to a temperature in the range of from about 50° C. to about 150° C. in the step for hydrothermally treating.
10. The process of claim 9 , wherein the precious metal precursor is selected from the group consisting of hexachloroplatinic acid, sodium tetrachloroplatinate, platinum sulfate and combinations thereof.
11. The process of claim 9 , wherein the reducing agent is selected from the group consisting of ethanol, iso-propanol, butanediol and combinations thereof.
12. The process of claim 1 , wherein the precious metal precursor comprises a metallic palladium precursor, and wherein the particle size of the resulting metallic palladium nanoparticles is controlled, in part, by heating the slurry to a temperature in the range of from about 50° C. to about 180° C. in the step for hydrothermally treating.
13. The process of claim 12 , wherein the precious metal precursor is selected from the group consisting of palladium chloride, sodium tetrachloropalladate, palladium sulfate and combinations thereof.
14. The process of claim 12 , wherein the reducing agent is selected from the group consisting of sodium tetrahydridoborate, sodium hypophosphite and combinations thereof.
15. The process of claim 1 , wherein the precious metal precursor comprises a metallic silver precursor, and wherein the particle size of the resulting metallic silver nanoparticles is controlled, in part, by heating the slurry to a temperature in the range of from about 50° C. to about 200° C. in the step for hydrothermally treating.
16. The process of claim 15 , wherein the precious metal precursor is selected from the group consisting of silver nitrate, silver perchlorate, silver sulfate and combinations thereof.
17. The process of claim 15 , wherein the reducing agent is selected from the group consisting of ethanol, iso-propanol and combinations thereof.
18. The process of claim 1 , wherein the slurry further comprises a particle size controlling agent selected from the group consisting of stearic acid, oleic acid, linoleic acid and combinations thereof.
19. The process of claim 1 , wherein the slurry further comprises a dispersant.
20. The process of claim 1 , further comprising the steps of:
(c) filtering the hydrothermally treated slurry; and
(d) calcining the filtered support particles having the metallic precious metal nanoparticles deposited thereon.
21. A method for controlling the particle size and effective surface area of supported catalytic precious metal nanoparticles, the method comprising:
(a) preparing a slurry of an aqueous dispersion of support particles, a water-soluble precious metal precursor, and a reducing agent; and
(b) hydrothermally treating the slurry in a sealed system by heating the slurry to a predetermined temperature in a range of from about 40° C. to about 220° C. at autogenic pressure for a time sufficient to deposit precious metal nanoparticles, in a metallic form and having a preselected particle size, onto at least a portion of a surface of the support particles, the temperature determined based on the precious metal and the selected particle size.