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ICCDU-9 Kingston, July 11, 2007
CHEMRAWN-XVII and ICCDU-IX Conference
onGREENHOUSE GASESMitigation and Utilization
Adsorption of CO2 over MgAl-complex oxide
Xin Fu Wei Wei Yuhan Sun
State Key Laboratory of Coal Conversion
Institute of Coal Chemistry Chinese Academy of
Science
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Emission of CO2

• Carbon dioxide is the most important of the
  greenhouse gases and is currently responsible for
  60?of the enhanced greenhouse effect.
• The concentration of CO2 in the atmosphere has
  increased rapidly from 1744 to 2005. Therefore,
  it is necessary to develop an available
  technology for the reduction of the emissions of
  CO2 into the atmosphere.

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Solving main strategies at present
CO2 capture, utilization or sequestration
CO2 capture is very important step.
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Main CO2 capture technology in industry

• Chemical and physical absorbent method- LIQUID
  ABSORBENTS
• Main absorbents organic amines
  (MEA?DEA?MDEA?DIPA?
• 
  DGA?TEA, etc.),
• low
  temperature methanol, propylene carbonate,etc.
• Drawbacks energy required equipment
  corrosion solvent degradation

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Stable solid absorbents might mitigate these
problems
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Properties of CO2
CO2 capture is both important and possible due to
two potential activation sites by solid absorbents
C- Lewis Acid O- Lewis Base
CO2 could be chemically absorbed when the solid
absorbents have corresponding two activation
sites.
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The present work

• Based on our the previous work about MgAl-complex
  oxide, we proposed the MgAl-complex oxide acted
  as a potential CO2 basket to storage and
  capture.
• The adsorption behavior of CO2 over the material
  was investigated by means of TPD and in situ
  FTIR.

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Experimental equipment
FT-IR of CO2 adsorption In situ FTIR spectra is
used to illustrate the states of desorbed CO2
species on the surface of the samples

• CO2-TPD
• CO2-TPD is used to study the amount of surface
  basic sites on samples.

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CO2 adsorption on MgO in different temperature
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From top to bottom, 298 k, 373k, 473k, 553K, 673K

• The band at 1221cm-1 was assigned to bicarbonate
  species,1596cm-1 and 1391cm-1 were associated to
  bidentate carbonate species, 1491cm-1 and
  1393cm-1 were assigned to monodentate carbonate
  species.
• With the temperature increasing, the peak for
  bicarbonate disappeared gradually up to 200?,and
  the peak for bidentate carbonate gradually
  decreased.

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CO2 TPD on MgO
423K
474K
553K
CO2-TPD
Bicarbonate species, bidentate carbonate species
and monodentate carbonate species correspond to
423 K, 474 K and 553 K, respectively.
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Adsorbed CO2 Surface Species over metal oxide

• For the metal oxide,
• The surface hydroxyl groups can react with CO2 to
  form bicarbonate species.
• The acid-base pairs can reacted with CO2 to form
  bidentate carbonate species
• The oxygen cavity can reacted with CO2 to form
  monodentate carbonate species

Bicarbonate species(1615-1630cm-1,1225cm-1)
Bidentate carbonate species (1600-1670cm-1,1280-13
10cm-1)
Monodentate carbonate species(1420-1540cm-1,1330-1
390cm-1)
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• Recently, Anand et al1 also reported that MgO
  showed an adsorption capacity of 8.8mg/g at 400?.
  This adsorbents suffered from either low
  CO2capacities or high desorption temperatures.
• In order to decrease temperature of CO2
  desorption, a series of MgAl-complex oxides were
  developed by our group.

(1) Anand, M. Hufton, J. Mayorga, S. Nataraja,
S. Sircar, S.Gaffney, T. APCI report for DOE,
1995.
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CO2 adsorption on Mg/Al 3
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From top to bottom, 25?, 100?, 200?, 300?, 400?
The band at 1653cm-1 and 1224cm-1 were
assigned to bicarbonate species, 1569cm-1 was
associated to bidentate carbonate species,
1418cm-1 was assigned to monodentate carbonate,
indicating that there are three main kinds of
adsorption sites with different strengths of
basicity.
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CO2 adsorption on Mg/Al 2
From top to bottom, 25?, 100?, 200?, 300?, 400?
The band at 1661cm-1 and 1224cm-1 were
associated to bicarbonate species, the band at
1395cm-1 was assigned to bidentate carbonate
species.
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CO2 adsorption on Mg/Al 1
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From top to bottom, 25?, 100?, 200?, 300?, 400?
The band at 1625cm-1 and 1303cm-1 were assigned
to bicarbonate species, the band at 1597cm-1
were associated to bidentate carbonate species.
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CO2-TPD profile with different Mg/Al ratios

• For Mg/Al ratio equal to 3, it has three main
  desorption peaks at 360K,474K,and 508K,
  indicating that there are three main kinds of
  adsorption sites with different strengths of
  basicity.
• With the content of Al increasing, weak basic
  sites and medium basic sites increased compared
  to MgO.
• When Mg/Al ratio equal to 1, the desorption
  temperature obviously decreased

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The absorption of the material
capacity for CO2
CO2 adsorption amount in the materials keep
unchanged
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Summary

• The results of CO2-TPD and FTIR suggested that
  the surface hydroxyl groups and the acid-base
  pairs can reacted with CO2 to form bicarbonate
  and bidentate carbonate species.
• With the content of Al increasing, weak basic
  sites and medium basic sites increased.
  Increasing of the weak basic sites and medium
  basic sites can decrease temperature of CO2
  desorption.

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Future work Improving the absorption
capacity of the material Further
decreasing the desorption temperature of CO2

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Acknowledgement
Prof. Y.H. Sun Prof. Wei Wei Prof. F.K. Xiao Dr.
N. Zhao Dr. Lianxiu Guan Dr. Xing Fu PetroChina
and CAS for financial support
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Thanks for your attention !