260157 Thermal Decomposition of K-Comosx Catalyst Precursors: Effects On Catalyst Morphology and Performance

Wednesday, October 31, 2012
Hall B (Convention Center )
Jesse E. Hensley1, Martin Menart2 and Kellen Costelow1, (1)National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, (2)National Bioenergy Center, National Renewable Energy Laboratory

Cobalt molybdenum sulfide-type mixed alcohol catalysts were synthesized via calcination of precipitated bulk sulfides and studied with temperature programmed decomposition analysis. Precursors containing aqueous potassium were also considered. Precipitates thermally decomposed in unique events which released ammonia, CO2, and sulfur. Higher temperature treatments led to more crystalline and less active catalysts in general with ethanol productivity falling from 203 to 97 g-(kg-cat)-1-h-1 when the calcination temperature was increased from 375 to 500C. The addition of potassium to the precursor led to materials with crystalline potassium sulfides and good catalytic performance. In general, less potassium was required to promote alcohol selectivity when added before calcination. At calcination temperatures above 350 C, segregated cobalt sulfides were observed, suggesting that thermally decomposed sulfide precursors may contain a mixture of molybdenum and cobalt sulfides instead of a dispersed Co-Mo-S type of material.

Table 1. Catalyst thermal history, surface area, and elemental analysis

Elemental composition (atom %)

Catalyst

Max. decomp. T (C)

Dwell time @ max. T (min)

K added

BET surface area (m2-g-1)

Co

Mo

S

K

Ratio

S:(Mo+Co)

1

500

60

N

16.7

8.5

26.1

65.4

0

1.9

2

475

15

N

11.7

8.8

22.7

68.5

0

2.2

3

375

45

N

21.1

9.1

23.1

67.8

0

2.1

4

475

15

Y

8.4

9.8

18.3

64.4

7.5

2.3

5

380

60

Y

37.4

7.9

22.4

63.9

5.8

2.1

Figure 1. Performance of catalysts 1-5 in Table 1. Green = ethanol, purple = propanol, blue = methanol. Data was collected at 325 C, pCO = pH2 = 4.8 MPa, 6000 NTPL-(kg-cat)-1-h-1.


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