Cobalt-molybdenum sulfide catalyst materials and methods for stable alcohol production from syngas
The present invention provides methods and compositions for the chemical conversion of syngas to alcohols. The invention includes catalyst compositions, methods of making the catalysts, and methods of using the catalysts including techniques to maintain catalyst stability. Certain embodiments teach compositions for catalyzing the conversion of syngas into products comprising at least one C 1 -C 4 alcohol, such as ethanol. These compositions generally include cobalt, molybdenum, and sulfur, and avoid metal carbides both initially and during reactor operation.
1. A method for making a cobalt-molybdenum-sulfide composition, said method comprising the steps of:
(i) dissolving ammonium dimolybdate, [NH 4 ] 2 [Mo 2 O 7 ], in aqueous ammonia, thereby producing a molybdate solution;
(ii) combining hydrogen sulfide with at least some of said molybdate solution, thereby producing a tetrathiomolybdate solution comprising [MoS 4 ] 2− ;
(iii) combining a Co(II) solution with at least some of said tetrathiomolybdate solution to form a first precipitate within a suspension;
(iv) combining sulfuric acid with at least some of said suspension, to form a second precipitate;
(v) filtering said second precipitate, wherein said filtering removes a portion of water present in said second precipitate, thereby creating a filter cake;
(vi) thermally processing said filter cake to produce a calcined material comprising cobalt, molybdenum, and sulfur;
wherein at least some of said cobalt and some of said sulfur are present as a cobalt-sulfur association, and wherein the molar ratio of sulfur to cobalt (S:Co) in the association is at least 1.2, said molar ratio S:Co calculated after assuming all of said molybdenum is present as MoS 2 .
2. The method of claim 1 , wherein said molar ratio S:Co is at least 1.5.
3. The method of claim 2 , wherein said molar ratio S:Co is at least 2.0.
4. The method of claim 1 , wherein step (vi) includes drying said filter cake in a substantially inert environment to produce a dried material and calcining said dried material to produce said calcined material.
5. The method of claim 1 , further comprising combining said calcined material with a base promoter selected from the alkali or alkaline earth series, thereby producing a base-promoted catalyst.
6. The method of claim 5 , wherein said base promoter comprises potassium.
7. The method of claim 5 , further comprising reacting syngas over said base-promoted catalyst to produce at least one C 1 -C 4 alcohol.
8. The method of claim 7 , wherein said at least one C 1 -C 4 alcohol is ethanol.
9. The method of claim 7 , further comprising co-feeding methanol in an amount in equilibrium with said syngas.
10. The method of claim 7 , further comprising co-feeding methanol at less than an amount in equilibrium with said syngas.
11. A catalyst composition comprising Mo, Co, and S, said composition produced according to a process that includes the steps of:
(i) dissolving ammonium dimolybdate, [NH 4 ] 2 [Mo 2 O 7 ], in aqueous ammonia, thereby producing a molybdate solution;
(ii) combining hydrogen sulfide with at least some of said molybdate solution, thereby producing a tetrathiomolybdate solution comprising [MoS 4 ] 2− ;
(iii) combining a Co(II) solution with at least some of said tetrathiomolybdate solution to form a first precipitate within a suspension;
(iv) combining sulfuric acid with at least some of said suspension, to form a second precipitate;
(v) filtering said second precipitate, wherein said filtering removes a portion of water present in said second precipitate, thereby creating a filter cake;
(vi) thermally processing said filter cake to produce a calcined material comprising cobalt, molybdenum, and sulfur,
wherein at least some of said cobalt and some of said sulfur are present as a cobalt-sulfur association, and wherein the molar ratio of sulfur to cobalt (S:Co) in the association is at least 1.2, said molar ratio S:Co calculated after assuming all of said molybdenum is present as MoS 2 .
12. The catalyst composition of claim 11 , wherein said catalyst composition includes MoS 2 and CoS 2 in intimate contact.
13. The catalyst composition of claim 11 , wherein said molar ratio S:Co is at least 1.5.
14. The catalyst composition of claim 13 , wherein said molar ratio S:Co is at least 2.0.
15. The catalyst composition of claim 11 , further comprising a base promoter selected from the alkali or alkaline earth series.
16. The catalyst composition of claim 15 , wherein said base promoter comprises potassium.
17. A catalyst composition comprising Mo, Co, and S, said composition produced according to a process that includes the steps of:
(i) dissolving ammonium dimolybdate, [NH 4 ] 2 [Mo 2 O 7 ], in aqueous ammonia, thereby producing a molybdate solution;
(ii) combining hydrogen sulfide with at least some of said molybdate solution, thereby producing a tetrathiomolybdate solution comprising [MoS 4 ] 2− ;
(iii) combining a Co(II) solution with at least some of said tetrathiomolybdate solution to form a first precipitate within a suspension;
(iv) combining sulfuric acid with at least some of said suspension, to form a second precipitate;
(v) filtering said second precipitate, wherein said filtering removes a portion of water present in said second precipitate, thereby creating a filter cake;
(vi) thermally processing said filter cake to produce a calcined material comprising cobalt, molybdenum, and sulfur,
wherein at least some of said cobalt and some of said sulfur are present as a cobalt-sulfur association, and wherein the molar ratio of sulfur to cobalt (S:Co) in the association is at least 1.2, said molar ratio S:Co calculated after assuming all of said molybdenum is present as MoS 2 , and
wherein step (vi) includes drying said filter cake in a substantially inert environment to produce a dried material and calcining said dried material to produce said calcined material.
18. The catalyst composition of claim 17 , wherein said molar ratio S:Co is at least 1.5.
19. The catalyst composition of claim 18 , wherein said molar ratio S:Co is at least 2.0.
20. The catalyst composition of claim 17 , further comprising a base promoter selected from the alkali or alkaline earth series.