Cobalt-based single-atom dehydrogenation catalysts and method for producing corresponding olefins from paraffins using the same
In the present disclosure, a dehydrogenation catalyst in which cobalt in the form of single atom is supported on an inorganic oxide (specifically, silica) support in which an alkali metal in the form of single atom is fixed by alkali metal pretreatment and a method for producing the same, and a method for producing olefins by dehydrogenating corresponding paraffins, specifically light paraffins in the presence of the dehydrogenation catalyst are described.
1. A method for preparing a cobalt single-atom catalyst, the method comprising:
a) preparing a silica-containing aqueous dispersion;
b) dissolving a salt of an alkali metal in the silica-containing aqueous dispersion to give an aqueous dispersion of alkali metal-treated silica;
c) adjusting a pH of the aqueous dispersion of alkali metal-treated silica to at least 10 by adding an ammonium-containing base to the aqueous dispersion to give a pH-adjusted aqueous dispersion of alkali metal-treated silica, wherein at least a part of alkali metal ions are electrostatically adsorbed on the surface of the silica;
d) separately preparing an aqueous solution of a cobalt precursor having an oxidation number of 3+ and adjusting a pH of the aqueous solution of a cobalt precursor to at least 10 by adding a base to the aqueous solution to give a pH-adjusted aqueous cobalt precursor solution;
e) combining the pH-adjusted aqueous dispersion of alkali metal-treated silica with the pH-adjusted aqueous cobalt precursor solution to give an aqueous dispersion in which at least a part of cobalt ions having an oxidation number of 3+ are electrostatically adsorbed on the surface of the alkali metal ion-adsorbed silica;
f) removing an alkali metal and cobalt that are not adsorbed on the surface of the silica from the aqueous dispersion of the cobalt ion, alkali metal ion-adsorbed silica; and
g) heat treating the cobalt ion, alkali metal ion-adsorbed silica resulting from the step f),
wherein the cobalt having an oxidation number of 2+ and the alkali metal having an oxidation number of 1+, respectively, exist in an isolated form of single atom on the silica while the cobalt having an oxidation number of 2+ forms a tetrahedrally coordinated at the three-membered siloxane ring present on the surface of silica,
wherein a content of an alkali metal in the catalyst is in a range of 0.004% to 1% by weight, and
wherein a weight ratio of cobalt (Co)/alkali metal in the catalyst is in a range of 1 to 2000, and wherein the silica is amorphous silica.
2. The method according to claim 1 , wherein a content of silica in the silica-containing aqueous dispersion prepared in the step a) is in a range of 1% to 30% by weight.
3. The method according to claim 1 , wherein the alkali metal is at least one selected from the group consisting of sodium (Na), potassium (K), and cesium (Cs), and
the salt of an alkali metal is at least one selected from the group consisting of a hydroxide, a nitrate, a chloride, a carbonate, and a sulfate of an alkali metal.
4. The method according to claim 1 , wherein a content of the salt of an alkali metal in the step b) is in a range of 0.001% to 3% by weight based on a weight of silica in the aqueous dispersion.
5. The method according to claim 1 , wherein the cobalt precursor in the step d) is a precursor containing a cobalt (Co(III)) complex ion having an oxidation number of 3+, and
a concentration of the cobalt precursor in the aqueous solution of cobalt precursor is in a range of 0.1% to 20% by weight.
6. The method according to claim 5 , wherein Co(NH 3 ) 6 Cl 3 is directly used or a precursor containing a cobalt complex ion, which is obtained by treating at least one cobalt compound selected from the group consisting of Co(NO 3 ) 2 , CoCl 2 , and Co(acac) 3 with ammonia water and performing filtering as the cobalt precursor.
7. The method according to claim 1 , wherein a mixing ratio of the pH-adjusted aqueous solution of cobalt precursor and the pH-adjusted aqueous dispersion of alkali metal-treated silica in the step e) is adjusted so that a content of the cobalt precursor is 1% to 20% by weight based on a weight of silica.
8. The method according to claim 1 , wherein the heat treatment is performed in an oxygen-containing atmosphere under a temperature condition of 250° C. to 1000° C.
9. The method according to claim 1 , further comprising drying the cobalt ion, alkali metal ion-adsorbed silica at 50° C. to 150° C. prior to the step g),
wherein an oxidation number of cobalt ions after drying is partially reduced to 2+.
10. The method according to claim 1 , wherein a content of cobalt in the catalyst is in a range of 0.1% to 10% by weight.
11. The method according to claim 1 , wherein the step e) is performed at a temperature in a range of 10° C. to 40° C.