Catalyst for synthesizing carbon nanotube and method of synthesizing carbon nanotube

1. A catalyst for synthesizing a carbon nanotube, including:

a support containing a metal, the metal including aluminum; and

an active metal impregnated on the support, the active metal including cobalt and manganese,

wherein a surface molar ratio of the active metal relative to the metal of the support is 40% or less of a bulk molar ratio of the active metal relative to the metal of the support, wherein the surface molar ratio is an average molar ratio of the active metal measured within a thickness of 10 nm from an outermost surface of the catalyst, and the bulk molar ratio is an average molar ratio of the active metal throughout the catalyst, and

wherein the surface molar ratio of the active metal is in a range from 0.03 to 0.06 relative to aluminum in the support, and the bulk molar ratio of the active metal is in a range from 0.15 to 0.29 relative to aluminum in the support.

2. The catalyst according to claim 1 , wherein the surface molar ratio of the active metal is in a range from 10% to 30% of the bulk molar ratio of the active metal.

3. The catalyst according to claim 1 , wherein the surface molar ratio is represented by Equation 1 below:

aluminum (Al): cobalt (Co): manganese (Mn)=1 :x 1 :y 1  [Equation 1]

wherein in Equation 1, 0.02≤x1≤0.04, 0.01≤y1≤0.02.

4. The catalyst according to claim 3 , wherein, in Equation 1, 0.0200≤x1≤0.0375, 0.0130≤y1≤0.0189.

5. The catalyst according to claim 1 , wherein the bulk molar ratio is represented by Equation 2 below:

aluminum (Al): cobalt (Co): manganese (Mn)=1 :x 2 :y 2  [Equation 2]

wherein in Equation 2, 0.08≤x2≤0.15, 0.07≤y2≤0.14.

6. The catalyst according to claim 1 , wherein the active metal consists of cobalt and manganese.

7. A method of synthesizing a carbon nanotube, comprising:

preparing a support containing a metal, a cobalt precursor and a manganese precursor;

mixing the support, the cobalt precursor and the manganese precursor with changing molar ratios to form a catalyst knead;

performing a thermal treatment on the catalyst knead to form the catalyst of claim 1 for synthesizing a carbon nanotube; and

forming a carbon nanotube using the catalyst.

8. The method according to claim 7 , wherein, in the formation of the catalyst knead, the cobalt precursor and the manganese precursor are mixed so that a surface molar ratio of cobalt and manganese relative to the metal in the support is less than a bulk molar ratio of cobalt and manganese relative to the metal in the support.

9. The method according to claim 8 , wherein the support includes an aluminum oxide, and

the surface molar ratio and the bulk molar ratio of the catalyst are represented by Equation 1 and Equation 2, respectively:

aluminum (Al): cobalt (Co): manganese (Mn)=1 :x 1 :y 1  [Equation 1]

wherein in Equation 1, 0.02≤x1≤0.04, 0.01≤y1≤0.02,

aluminum (Al): cobalt (Co): manganese (Mn)=1 :x 2 :y 2  [Equation 2]

wherein in Equation 2, 0.08≤x2≤0.15, 0.07≤y2≤0.14.

10. The method according to claim 7 , wherein performing the thermal treatment includes:

drying the catalyst knead at a temperature in a range from 100° C. to 150° C.; and

calcinating the dried catalyst knead at a temperature in a ranging from 400° C. to 600° C.

11. The method according to claim 7 , wherein forming the carbon nanotube includes a chemical vapor deposition or a chemical vapor synthesis.

12. The method according to claim 7 , wherein the cobalt precursor includes cobalt nitrate or a hydrate thereof, and the manganese precursor includes manganese nitrate or a hydrate thereof.