FischerTropsch synthesis via ruthenium supported on hybrid alumina xerogels

1
Fischer-Tropsch synthesis via ruthenium
supported on hybrid alumina xerogels

• Gregory C. Turpin, Edward M. Eyring, Ronald J.
  Pugmire, and Richard D. Ernst

2
Original goals

• Hybrid alumina xerogel supports
• High density (1 g/cm3)
• Enhanced physical attributes
• Enhanced chemical attributes
• High-activity catalyst loading
• Ru
• Most active FT catalyst
• Suitable when activity is at premium relative to
  cost1
• Ru is highly recoverable from spent catalysts

1. As of July 26, 2007 390/oz,
www.platinum.matthey.com
3
New FT reactor

• Newly constructed reactor with integrated gc
• GC1
• TCD and FID detector
• Sampling valves and injection ports (split and
  splitless) for each detector
• 1/2 year of nearly flawless operations

1. www.srigc.com
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Alumina xerogels

• Synthesized similarly to alumina aerogels,1 but
  without supercritical drying
• Uses off-the-shelf reagents
• Suitable for other metal chloride hydrates
• Dried by evaporation, followed by calcination at
  600 C2

• Satcher, J. H, Jr. et al. Chem. Mater. 2005, 17,
  395.
• 5 C/min ramp, 4 h soak, 10 sccm flowing air

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Mechanistic detail gel formation
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Hybrid alumina xerogels

• 595 (MAl) mole ratio alumina xerogel hybrids
  have been prepared
• Replace mole fraction of AlCl3.6H2O with hydrated
  metal chloride or nitrate
• Zr, La, Ce
• Are expected to cogel within the alumina
  framework
• And may provide physical strength
• Zn, Ba
• Zn and Ba are are expected to deposit
  superficially
• Are promoters for Ru catalysts1
• Drying and calcination identical as alumina-only
  xerogels

1. Hansen, T. W. et al. Science 2001, 294, 1508.
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BET surface areas alumina xerogels

• Metals that condense (Zr, La, and Ce) with
  aluminum lower the surface of the support
• Metals that do not condense (Ba and Zn) increase
  the surface area

• Variation represents the standard deviation of
• multiple measurements, not any errors.

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Attrition resistance?

• ASTM 5757-95
• 50 g sample
• We are developing a 1 g jet-cup test
• jet cup test has been shown to correlate well
• with the ASTM 5757-95 test1

1. Goodwin, J. G., Jr et al. Ind. Eng. Chem.
Res. 2000, 39, 1155.
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Ru incorporation

• Gas-phase incorporation of bis(2,4-dimethylpentadi
  enyl) ruthenium
• Halide-free
• Stable, easily synthesized
• Solvent-free incorporation
• Yields very highly dispersed Ru
• Alumina xerogel incorporations at high vacuum1
  and 50 C

1. Approximately 10-3 torr.
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TPR1 support effects

• Silica-Ru interactions much weaker than
  alumina-Ru interactions
• Alumina aerogel calcined at a lower temperature,
  leaving more surface hydroxyl groups, which
  interact with the Ru

• All TPR experiments to 800 C at a heating rate
  of
• 10 C/min, with diluted hydrogen (10 H2 in Ar).

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TPR calcination1 effects
RuO2
300 C calc.

• Clustered RuO2 lt170 C
  SMSI2-RuO2 gt380 C
• Higher temperature calcination promotes RuO2
  agglomeration

1. Calcination at indicated temperature for 4 h,
achieved with a heating rate of 1 C/min and
with a 10 sccm air flow 2. SMSI strong
metal-support interaction
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TPR loading effect

• 2 Ru, 6 Ru
• Current limitation of gas-phase incorporation
  method

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TPR hybrid alumina xerogel

• Zirconia hybrid is similar to alumina xerogel
• Ceria is H2 active

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FT reaction conditions

• Fixed-bed, single-pass
• 240 C, 100 psig
• 15 sccm CO, 30 sccm H2, and 10 sccm Ar
• 4000 10000 h-1 space velocity1
• Permanent gases analyzed on a 5 Å molecular sieve
  column by TCD2
• Methane analyzed on a silica gel column by FID
• Heavy hydrocarbons condensed and analyzed
  off-line on a DB-5MS column by FID

• Space velocity calculated at STP and with total
  gas flow.
• XCO calculated by comparing ArCO at zero
  conversion.

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FT results calcination effects

• Highest activity without calcination, with a
  reasonable methane selectivity
• Imcomplete calcination (at 100 C and 200 C)
  may leave refractory organic residuals
• Agglomerated Ru (300 C) appears to favor methane

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FT results Ru loading

• 2 and 6 have similar activity based on Ru
• 6 has unusually high methane selectivity

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FT results hybrid alumina xerogels

• Zirconia hybrid offers similar activity and
  methane selectivity to alumina only
• Ceria hybrid is unfavorable with respect to
  methane selectivity, as well as overall activity

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FT results methane production

• For all Ru catalysts,1 converges to a lower,
  steady-state production of methane
• Likely correlating with a controlled
  agglomeration to a small cluster

1. Results shown for 2 Ru on alumina xerogel, no
calcination.
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FT results - conclusions

• Very highly dispersed Ru is mostly a methanation
  catalyst
• A threshold size1 for Ru is critical for
  productive FT activity with a low methane
  selectivity
• Gas-phase incorporation yields very highly
  dispersed Ru, but agglomeration occurs in situ
• Ce hybrid has pronounced methanation activity
• Ru on alumina xerogels produces 4060
  aolefinn-parrafin ratio

• Postulated at 3-7 nm Abrevaya, H et al. Catal.
  Lett. 1990, 7, 183.

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Hybrid supports - conclusions

• Waiting for attrition resistance testing
• Readily synthesized by the current gelation
  method (gel initiation by propylene oxide)

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Future Directions

• Better understanding and optimization.
• Very high loadings with newest generation of
  reactor designs (microchannel design)?
• Highly efficient heat removal
• i.e. Velocys, Inc.1
• Unprecedented activity per unit volume?

1. www.velocys.com
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Acknowledgements

• Financial support from the Consortium for Fossil
  Fuel Science through our financial sponsors, the
  U.S. Department of Energy and the U.S. Department
  of Defense
• Mr. Eric Fillerup (University of Utah) with
  assistance with nitrogen desorption and TPR
  measurements