Shaped dehydrogenation catalysts and process for converting paraffins to corresponding olefins, using same
Disclosed herein are a dehydrogenation catalyst having single-atom cobalt loaded on a silica-based, shaped support, a preparation method therefor, and a method for preparing an olefin by dehydrogenating a corresponding paraffin, particularly light paraffin in the presence of the dehydrogenation catalyst.
1. A method for preparation of a cobalt-based, shaped single-atom catalyst, the method comprising the steps of:
combining a silica binder and a silica powder for support material in an aqueous medium to prepare a molding paste;
molding the paste into a silica-based, molded support;
contacting the silica-based, molded support with an alkali metal salt in an aqueous medium to form an alkali metal-treated, silica-based, molded support, before or after which pH adjustment is made with a base, wherein at least a part of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based, molded support;
contacting the alkali metal-treated, silica-based, molded support with an aqueous solution of a cobalt precursor to form a cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the cobalt precursor being adjusted in pH by adding a base thereto, with the cobalt precursor having an oxidation number of 3+, wherein at least a part of the cobalt ions having an oxidation number of 3+ is electrostatically adsorbed on the alkali metal-treated, silica-based, molded support; and
thermally treating the cobalt- and alkali metal-containing silica-based, molded support such that cobalt having an oxidation number of 2+ and alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single-atom on the silica-based, molded support,
wherein the cobalt having an oxidation number of 2+ is tetrahedrally coordinated at a three-membered siloxane ring present on the surface of the silica-based, molded support.
2. A method for preparation of a cobalt-based, shaped single-atom catalyst, the method comprising the steps of:
combining a silica binder and a silica powder for support material in an aqueous medium to prepare a molding paste;
molding the paste into a silica-based, molded support;
contacting the silica-based, molded support with an alkali metal salt in an aqueous medium to form an alkali metal-treated, silica-based, molded support, before or after which pH adjustment is made with a base, wherein at least a part of the alkali metal ions are electrostatically adsorbed on the surface of the silica-based, molded support;
contacting the alkali metal-treated, silica-based, molded support with an aqueous solution of a cobalt precursor to form a cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the cobalt precursor being adjusted in pH by adding a base thereto, with the cobalt precursor having an oxidation number of 3+, wherein at least a part of the cobalt ions having an oxidation number of 3+ is electrostatically adsorbed on the alkali metal-treated, silica-based, molded support;
contacting the cobalt- and alkali metal-containing, silica-based, molded support with an aqueous solution of a second cobalt precursor to form a second cobalt- and alkali metal-containing, silica-based, molded support, the aqueous solution of the second cobalt precursor being adjusted in pH by adding a base thereto, with the second cobalt precursor having an oxidation number of 3+ to form a second cobalt- and alkali-metal-containing silica-based molded support; and
thermally treating the second cobalt- and alkali metal-containing silica-based, molded support such that cobalt having an oxidation number of 2+ and alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single-atom on the silica-based, molded support,
wherein the cobalt having an oxidation number of 2+ is tetrahedrally coordinated at a three-membered siloxane ring present on the surface of the silica-based, molded support.
3. The method of claim 2 , further comprising a step of thermally treating the cobalt- and alkali metal-containing silica-based, molded support, prior to the step of forming the second cobalt- and alkali metal-containing silica-based, molded support.
4. The method of claim 1 , wherein the silica powder for support material is amorphous silica.
5. The method of claim 4 , wherein the amorphous silica comprises wet (hydrated) silica.
6. The method of claim 1 , wherein the silica binder is colloidal silica.
7. The method of claim 1 , wherein a weight ratio of the silica binder to the silica powder for support material ranges from 1:0.1 to 1:10.
8. The method of claim 1 , wherein the step of preparing a molding paste comprises:
preparing (i) a silica binder-containing lubricant emulsion or (ii) a silica binder-containing aqueous dispersion; and
combining the silica binder-containing lubricant emulsion or the silica binder-containing aqueous dispersion with the silica powder for support material,
wherein the silica binder-containing lubricant emulsion or the silica binder-containing aqueous dispersion contains the silica binder at a content of 10 to 60% by weight.
9. The method of claim 8 , wherein the silica binder-containing lubricant emulsion contains the lubricant at a content of 0.1 to 20% by weight.
10. The method of claim 1 , wherein the silica-based, molded support has at least one shape selected from the group consisting of a cylinder, a granule, a pellet, a tablet, a sphere, and a trilobe.
11. The method of claim 1 , wherein alkali metal is at least one selected from the group consisting of sodium (Na), potassium (K), and cesium (Cs), and
the alkali metal salt is at least one selected from a hydroxide, a nitrate, a chloride, a carbonate, and a sulfate of the alkali metal.
12. The method of claim 1 , wherein the step of forming an alkali metal-treated, silica-based, molded support employs the silica-based, molded support in an amount of 1 to 30% by weight, based on the weight of the aqueous medium, and
the alkali metal salt in an amount of 0.001 to 3% by weight, based on the weight of the silica-based, molded support in the aqueous medium.
13. The method of claim 1 , wherein the base in the step of forming an alkali metal-treated, silica-based, molded support is an ammonium-containing base and is used to adjust the pH to at least 9.
14. The method of claim 1 , wherein the cobalt precursor in the aqueous solution is a precursor comprising a complex ion of cobalt having an oxidation number of 3+(Co (III)), and is contained at a concentration of 0.1 to 20% by weight.
15. The method of claim 1 , wherein the cobalt precursor in the step of forming the cobalt- and alkali metal-containing silica-based, molded support is used in an amount of 1 to 100% by weight, based on the weight of the silica molded support.
16. The method of claim 1 , wherein the thermal treatment is carried out at a temperature of 250 to 700° C. in an oxygen-containing atmosphere.
17. The method of claim 1 , wherein the cobalt-based, shaped single-atom catalyst contains cobalt and alkali metal at a content of 0.5 to 3% by weight and 0.00001 to 1% by weight, respectively, with the weight ratio of cobalt(Co)/alkali metal ranging from 1 to 1000.