Atomically dispersed platinum-group metal-free catalysts and method for synthesis of the same
Atomically dispersed platinum-group metal-free catalyst and method for synthesizing the same. According to one embodiment, the catalyst is made by a method in which, in a first step, a metal oxide/zeolitic imidazolate frameworks (ZIF) composite is formed by combining (i) nanoparticles of an oxide of at least one of iron, cobalt, nickel, manganese, and copper, (ii) a hydrated zinc salt, and (iii) an imidazole. Then, in a second step, the metal oxide/ZIF composite is thermally activated, i.e., carbonized, to form an M-N—C catalyst. Thereafter, the M-N—C catalyst may be mixed with a quantity of ammonium chloride, and then the M-N—C/NH 4 Cl mixture may be pyrolyzed. The foregoing NH 4 Cl treatment may improve the intrinsic activity of the catalyst. Then, a thin layer of nitrogen-doped carbon may be added to NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD). Such CVD treatment may improve the stability of the catalyst.
1. A method of preparing a catalyst, the method comprising the steps of:
(a) incorporating nanoparticles of a metal oxide into a zeolitic imidazolate frameworks (ZIF) nanocrystal to form a metal oxide/ZIF composite, wherein the metal oxide comprises an oxide of at least one metal that is selected from the group consisting of iron, cobalt, nickel, manganese, and copper and wherein the nanoparticles are ultrafine nanoparticles having an average size of about 5 nm; and
(b) then, pyrolyzing the metal oxide/ZIF composite to form an M-N—C catalyst.
2. The method as claimed in claim 1 wherein the metal oxide comprises Fe 2 O 3 nanoparticles.
3. The method as claimed in claim 1 wherein the ZIF is selected from the group consisting of ZIF-7, ZIF-8, and ZIF-11.
4. The method as claimed in claim 1 wherein the ZIF is ZIF-8.
5. The method as claimed in claim 1 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature of at least about 500° C.
6. The method as claimed in claim 1 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature of at least about 700° C.
7. The method as claimed in claim 1 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature in the range of about 700° C.-1100° C. for about 1 hour in an Ar gas environment.
8. The catalyst prepared by the method of claim 1 .
9. A method of preparing a catalyst, the method comprising the steps of:
(a) incorporating nanoparticles of a metal oxide into a zeolitic imidazolate frameworks (ZIF) nanocrystal to form a metal oxide/ZIF composite, wherein the metal oxide comprises an oxide of at least one metal that is selected from the group consisting of iron, cobalt, nickel, manganese, and copper;
(b) then, pyrolyzing the metal oxide/ZIF composite to form an M-N—C catalyst;
(c) then, mixing a quantity of the M-N—C catalyst with a quantity of NH 4 Cl; and
(d) then, pyrolyzing the M-N—C/NH 4 Cl mixture.
10. The method as claimed in claim 9 wherein the M-N—C is Fe—N—C.
11. The method as claimed in claim 10 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of up to 10:1.
12. The method as claimed in claim 11 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of 3:1.
13. The catalyst prepared by the method of claim 12 .
14. The catalyst prepared by the method of claim 11 .
15. The method as claimed in claim 9 further comprising, after pyrolyzing the M-N—C/NH 4 Cl mixture, adding carbon species or nitrogen-doped carbon species to the NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD).
16. The method as claimed in claim 15 wherein the carbon species or nitrogen-doped carbon species are added as a surface layer having a thickness ranging from a monolayer up to about 1 nm.
17. The method as claimed in claim 15 wherein the M-N—C is Fe—N—C and wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of up to 10:1.
18. The method as claimed in claim 17 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of 3:1.
19. The catalyst prepared by the method of claim 18 .
20. The catalyst prepared by the method of claim 17 .
21. The catalyst prepared by the method of claim 15 .
22. The catalyst prepared by the method of claim 9 .
23. A method of preparing a catalyst, the method comprising the steps of:
(a) combining (i) nanoparticles of a metal oxide, wherein the metal oxide comprises an oxide of at least one metal that is selected from the group consisting of iron, cobalt, nickel, manganese, and copper, and wherein the nanoparticles are ultrafine nanoparticles having an average size of about 5 nm, (ii) a hydrated zinc salt, and (iii) an imidazole to form a metal oxide/ZIF composite; and
(b) then, pyrolyzing the metal oxide/ZIF composite to form an M-N—C catalyst.
24. The method as claimed in claim 23 wherein the metal oxide comprises Fe 2 O 3 .
25. The method as claimed in claim 23 wherein the hydrated zinc salt comprises zinc nitrate hexahydrate.
26. The method as claimed in claim 23 wherein the imidazole comprises 2-methylimidazole.
27. The method as claimed in claim 23 wherein the combining step comprises preparing a first solution and a second solution, the first solution comprising the metal oxide and the hydrated zinc salt in methanol and the second solution comprises the imidazole in methanol, and then mixing the first solution and the second solution.
28. The method as claimed in claim 23 wherein the metal oxide/ZIF composite comprises an Fe 2 O 3 @ZIF-8 composite.
29. The method as claimed in claim 23 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature of at least about 500° C.
30. The method as claimed in claim 23 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature of at least about 700° C.
31. The method as claimed in claim 23 wherein the pyrolyzing step comprises heating the metal oxide/ZIF composite at a temperature in the range of about 700° C.-1100° C. in an Ar gas environment.
32. A method of preparing a catalyst, the method comprising the steps of:
(a) combining (i) nanoparticles of a metal oxide, wherein the metal oxide comprises an oxide of at least one metal that is selected from the group consisting of iron, cobalt, nickel, manganese, and copper, (ii) a hydrated zinc salt, and (iii) an imidazole to form a metal oxide/ZIF composite;
(b) then, pyrolyzing the metal oxide/ZIF composite to form an M-N—C catalyst;
(c) mixing a quantity of the M-N—C catalyst with a quantity of NH 4 Cl; and
(d) then, pyrolyzing the M-N—C/NH 4 Cl mixture.
33. The method as claimed in claim 32 wherein the M-N—C is Fe—N—C.
34. The method as claimed in claim 33 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of up to 10:1.
35. The method as claimed in claim 34 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of 3:1.
36. The catalyst prepared by the method of claim 35 .
37. The catalyst prepared by the method of claim 34 .
38. The method as claimed in claim 32 further comprising, after pyrolyzing the M-N—C/NH 4 Cl mixture, adding carbon species or nitrogen-doped carbon species to the NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD).
39. The method as claimed in claim 38 wherein the carbon species or nitrogen-doped carbon species are added as a surface layer having a thickness ranging from a monolayer up to about 1 nm.
40. The method as claimed in claim 39 wherein the M-N—C is Fe—N—C and wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of up to 10:1.
41. The method as claimed in claim 40 wherein the quantities of Fe—N—C catalyst and NH 4 Cl are mixed together in a mass ratio of NH 4 Cl to FeNC of 3:1.
42. The catalyst prepared by the method of claim 41 .
43. The catalyst prepared by the method of claim 40 .
44. The catalyst prepared by the method of claim 38 .
45. The method as claimed in claim 38 wherein the carbon species or nitrogen-doped carbon species are added to the NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD) of a ZIF.
46. The method as claimed in claim 45 wherein the carbon species or nitrogen-doped carbon species are added to the NH 4 Cl-treated M-N—C catalyst by chemical vapor deposition (CVD) of ZIF-8.
47. The catalyst prepared by the method of claim 32 .