SURFACE CHEMICAL AND PHYSICAL PROPERTIES OF VARIOUS ACTIVATED CARBON SUPPORTS AND THEIR ROLE IN FISC

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SURFACE CHEMICAL AND PHYSICAL PROPERTIES OF
VARIOUS ACTIVATED CARBON SUPPORTS AND THEIR ROLE
IN FISCHER-TROPSCH SYNTHESIS Wenping Ma, Edwin
L. Kugler and Dady B. Dadyburjor Department of
Chemical Engineering, West Virginia University
Presented at CFFS Annual Technical Meeting,
Pittsburgh PA August 2008
ACKNOWLEDGMENTS USDOE DE-AC22-99FT40540
Cooperative Agreement with Consortium for Fossil
Fuel Science WVU - Steve Carpenter, Liviu Magean
(EDS), Vinod Berry (TEM) USDA Wayne Marshall
(Pecan-, Walnut-based ACs)
__ Current Address CAER, University of Kentucky
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• OUTLINE
• INTRODUCTION

• Background
• Previous work

• RESULTS

• pH of ACs cf. Impurities
• AC morphology by SEM, TEM size, shape of
  impregnated particles by TEM
• N2 Isotherms, BET before / after impregnation
• Temperature-programmed Desorption,
  Temperature-programmed Reduction
• Activity / Selectivity for FTS

• SUMMARY AND CONCLUSIONS

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• INTRODUCTION -- BACKGROUND
• ACs used to support

• noble metals (Pt, Ru, Rh)
• transition metals (Fe, Co, Mo, Cu)

for

• H / DH / Ox
• HDN / HDS
• Hydroformylation, MeOH decomposition

because of

• high surface area, surface texture

• In FT, use of ACs leads to carbon numbers lt 36
  (?)

• O-containing groups anchor, redisperse metals
• Disadvantage small impurities could change
  properties (?)

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• INTRODUCTION PREVIOUS WORK
• Ma et al., Stud. Surf. Sci. 163, 125 (2007)
• Prepr. Petroleum Chemistry
  Division ACS, 50(2), 161 (2005)
• Four AC types

• Peat
• Pecan
• Walnut
• Wood (generic)

• Fe -- Mo Cu K by incipient wetness
• BET, SEM cf Activity, Selectivity, Impurities

• Now More complete analysis

• pH, BET
• SEM, TEM
• TPR, TPD-MS

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RESULTS pH cf. Impurities
AC Type
pH Impurities (O 0.06)
Peat (PT) 9.9 most basic Mg, Al, Si, Ca, Fe,
S Wood (WD) 9.6 Ca, S Pecan (PC) 8.5 - Walnu
t (WN) 8.5 least basic -

• Impurities gt more CO evolved gt basicity

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RESULTS (contd) Surface Morphology by SEM
WD Irregular, Pan-shaped
PT Layered, Slit-shaped
PC WN Honeycomb
structures
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RESULTS (contd) Particle Distribution, Morphology
by TEM
PT WD PC WN

• Particles have different shapes
• Some big particles (100-150 nm) on external
  surface
• dmean(WD) 10-50 nm gt others, 10-30 nm
• More large particles on WD than on other ACs

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RESULTS (contd) BET Before / After Impregnation

• 6 Mo / 15.7 Fe / 0.8 Cu / 0.9 K
• WD - 95 SA is in ?p others - 75 SA in ?p
• Impregnation gt ?p ? 60 (all ACs)
• gt MP PC, WN ? 70 WD
• gt more metal on WD exterior (consistent with
  TEM, SEM)

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RESULTS (contd) BET Before / After Impregnation

• 6 Mo / 15.7 Fe / 0.8 Cu / 0.9 K
• WD - 95 SA is in ?p others - 75 SA in ?p
• Impregnation gt ?p ? 60 (all ACs)
• gt MP PC, WN ? 70 WD
• gt more metal on WD exterior (consistent with
  TEM, SEM)

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RESULTS (contd) BET Before / After Impregnation

• 6 Mo / 15.7 Fe / 0.8 Cu / 0.9 K
• WD - 95 SA is in ?p others - 75 SA in ?p
• Impregnation gt ?p ? 60 (all ACs)
• gt MP PC, WN ? 70 WD
• gt more metal on WD exterior (consistent with
  TEM, SEM)

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RESULTS (contd) BET Before / After Impregnation

• 6 Mo / 15.7 Fe / 0.8 Cu / 0.9 K
• WD - 95 SA is in ?p others - 75 SA in ?p
• Impregnation gt ?p ? 60 (all ACs)
• gt MP PC, WN ? 70 WD
• gt more metal on WD exterior (consistent with
  TEM, SEM)

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RESULTS (contd) Nitrogen Adsorption Isotherms
Before Impregnation
After Impregnation

• All are Type I
• Inflection points, (P/Po) 0.002 ? 0.008
  dpore ?
• dP/dV (not shown) gt maxima all at 3.5 3.7 nm

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RESULTS (contd) Temperature-Programmed Desorption
of AC Ar, RT-915?C, 10?C/min

• Small broad peak at 700?C MS gt CO2 (lt acidic
  groups)
• MS gt CO 800?C (lt neutral basic)

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RESULTS (contd) Temperature-Programmed Desorption
of AC Ar, RT-915?C, 10?C/min
AC Total Area CO/CO2 PT
25,900 49 WD 18,500
8.5 PC 40,200
52 WN 32,900 33

• Small broad peak at 700?C MS gt CO2 (lt acidic
  groups)
• MS gt CO 800?C (lt neutral basic)
• CO / CO2 gtgt 1 gt Basic groups predominate
• WD should be ??, cf. pH measurements
• but Tmax 700?C, probably too low

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RESULTS (contd) Temperature-Programmed Desorption
of Impreg Catalyst Ar, RT-915?C, 10?C/min
Mo/Fe/Cu/K/AC after reduction at 400?C

• Same peak positions as AC alone
• CO2 peak ??, CO peak ?
• Metals increase oxidations

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RESULTS (contd) Temperature-Programmed
Reduction H2 / Ar, RT-915?C, 10?C/min
Mo/Fe/Cu/K/AC

• PT has 3 peaks, others have 4
• Fe2O3 ? Fe3O4 ( ? FeO) ? Fe MoO3 ? MoOx
• Tpeak for PT 50?C higher than others
  (interactions ? )

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RESULTS (contd) Temperature-Programmed
Reduction H2 / Ar, RT-915?C, 10?C/min
Mo/Fe/Cu/K/AC
AC Actual H2 Theor H2 Reduction PT 4.34
6.22 69.8 WD 5.08
81.8 PC 4.91
79.0 WN 4.67
75.1

• PT has 3 peaks, others have 4
• Fe2O3 ? Fe3O4 ( ? FeO) ? Fe MoO3 ? MoOx
• Tpeak for PT 50?C higher than others
  (interactions ?)
• Quantitatively, Reduction lowest for PT
• Reduction highest for WD lt external metals ?

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RESULTS (concluded) Activity and Selectivity for
FTS over Mo/Fe/Cu/K/AC 320?C, 300 psig, H2/CO
0.9, 3Nl/gcat/h, TOS50-70 h
AC XCO, C1 C2-4 C5 PT
77 11 41 48 WD 38
14 55 31 PC 90 15
32 52 WN 59 15 35
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SUMMARY OF RESULTS
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SUMMARY OF RESULTS
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SUMMARY OF RESULTS
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SUMMARY OF RESULTS (?)
Ma parameter C A x B where A fraction
of BET SA of impreg catalyst present in large
pores B fraction of BET SA lost from large
pores of support after impregnation gt Amount of
metal in large pores left after impregnation (?)
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CONCLUSIONS

• AC basicity helps keep CH4 down
• -- stronger interactions with metal?
• TPD (CO CO2) correlates well with selectivity
• Large particles on external surface (WD) hurt
  activity and selectivity
• Degree of reduction (TPR) does not correlate
  well with activity or selectivity
• Activity correlates with amount of metal in
  large pores left after impregnation (?)
• Deactivation a factor in AC choice