fernando vallejos-burgos (nando) フェルナンド バ...
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Fernando Vallejos-Burgos (Nando)フェルナンド バイエホス-ブルゴスChemical Engineer, 2006Universidad de Concepción, Chile
6 months stay for PhD. Thesis @ Kaneko Laboratory, Chiba, JapanFebruary 2008
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Carbons & Catalyst Group www.udec.cl/~carbocat
Professors: Ximena García Alfredo Gordon Romel Jiménez Ljubisa R. Radovic
Research interests: Catalysts for environmental protection;
biomass use; combustion; and, more recently, coal & carbon structure and molecular modeling
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NOx emissions: in diesel engines especially
Important part of air pollution problem, they contribute to:
Global warming
Acid rain
Deteriorated water quality
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Approach - +
NO catalytic reduction with CO over TWC
Not effective under oxydizing conditions/ Sulfur poisoning
Simultaneous remotion of CO, NO and HC
SCR with NH3 NH3 handling and storage/ special systems for ‘ammonia slip’ avoiding
High NO remotion efficiency in O2
presence
SCR with HC Low selectivity / ‘HC slip’ High potential of NO remotion / efficient in presence of O2
Direct decomposition(perovskites, Cu-ZSM-5, Pt/Al2O3)
Low activity/ SO2 / O2 is dificult to desorb
Harmless, forms N2 + O2 / does not use reducing agents
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Environmental concern
NO reduction
NO decomposition
Coal- and/or biomass-derived catalysts
Active carbon
Metals supported on active carbon
Oxygen transfer
Role of metal species in improving the efficiency of oxygen-transfer-controlled reactions
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Structural support High surface area, optimal PSD
Reducing agent Cf + 2NO N2 + CO2
Cf + NO C-N + CO
Catalyst! 2Cf + 2NO N2 + O2 + 2Cf
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Iwamoto, M., S. Yokoo, K. Sakai and S. Kagawa (1981). "Catalytic decomposition of nitric oxide over copper(II)-exchanged, Y-type zeolites." J. Chem. Soc., Faraday Trans. 1(77): 1629 - 1638.
500 ºC
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Almusaiteer, K., R. Krishnamurthy and S. S. C. Chuang (2000). "In situ infrared study of catalytic decomposition of NO on carbon-supported Rh and Pd catalysts." Catalysis Today 55(3): 291-299.
400 ºC
Pd/C
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Practical
Cheap and abundant raw materials can be converted in highly efficient catalyst if the preparation conditions are carefully chosen
Fundamental
Catalyst efficiency in NO reduction or decomposition can be improved by optimizing oxygen transfer
The easier this transfer is, the lower the reaction T and the more probable that oxygen surface recombination results in Cf+O2
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(i) Dissociation of O2 (or CO2 or NO or H2O) on carbon “reactive sites”
2Cf + O2 → 2C(O)
Reactive sites : „unsaturated‟ carbon atoms, typically
located at the edges of crystallites…
Radovic, L. R. (2007). "Physical Chemistry (or Chemical Physics!?) of Carbon Surfaces: Applications and Fundamentals." The SGL Carbon Award Lecture, Carbon 2007 Seattle, WA, USA
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(ii) Surface migration of oxygen
2C(O) ↔ 2C–O
Surface
intermediates
Surface
‘spectators’
(complexes)
Radovic, L. R. (2007). "Physical Chemistry (or Chemical Physics!?) of Carbon Surfaces: Applications and Fundamentals." The SGL Carbon Award Lecture, Carbon 2007 Seattle, WA, USA
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(iii) Desorption of CO and/or CO2
2C(O) → 2CO (+mCf)
2C(O) → CO2 (+nCf)
m=2 (!?) n= 1 (?!)
Note: CO/CO2 = f(T, [C(O)], [C-O], carbon structure)
Radovic, L. R. (2007). "Physical Chemistry (or Chemical Physics!?) of Carbon Surfaces: Applications and Fundamentals." The SGL Carbon Award Lecture, Carbon 2007 Seattle, WA, USA
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2Cf + O2 → 2C(O)
2Cf + NO → C(N) + C(O)
2C(N) → N2 + 2Cf
C(O) ↔ C-O
2C(O) → CO2 + Cf
C(O) → CO (+ Cf)
Key step!
Key hypothesis
As oxygen surface coverage increases, CO CO2 ( O2?!)
(And as catalyst dispersion and catalyst/carbon contact improve, oxygen can accumulate on the carbon surface… This will be pursued and tested using TPD!)
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Oxygen transfer mechanism is also dominant in catalytic gasification reactions!
2Cf + O2 2C(O)
2Cf + NO C(N) + C(O)
2C(N) N2 + 2Cf
2Cat + O2 2Cat(O)
2Cat + 2NO 2Cat(O) + N2
Cat(O) C(O)
C(O) C-O
C-O C(O)
C(O) CO (+ Cf)
2C(O) CO2 + Cf
Oxygen spillover
Oxygen enhancement
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O
O O
O
O
O
O
O
- CO2
Analogous to benzene
oxide
to oxepin reaction!
Hypothetical route to CO2 formation (with participation of basal-plane, epoxy-type oxygen)
DH= +3.9 kcal/mol DH= -48 kcal/mol
DH= 0 kcal/mol
DH= -19 kcal/mol
Radovic, L. R. (2007). "Physical Chemistry (or Chemical Physics!?) of Carbon Surfaces: Applications and Fundamentals." The SGL Carbon Award Lecture, Carbon 2007 Seattle, WA, USA
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Hypothetical route to O2 formation (with participation of basal-plane, epoxy-type oxygen)
O O + O2
?!
2C + 2NO = O2 + N2 + 2C?!
2 2 2 22 2catalizadorH O ac O g H O l
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Make cheap, efficient and easy-to-prepare catalysts for NO reduction or decomposition
Investigate the effect of preparation conditions on catalytic activity
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AR-C (As received coal, grinded and sieved) Dem-C (Acid demineralization) Dem-C-*** (Pyrolyzed, 550-700-850-1000ºC) Dem-AC-*** ** (CO2 activation, 825ºC)
Metal addition (Co, Cu and K) Incipient wetness impregnation (IWI) Nitrate
decomposition HTT
Ion exchange (IE) HNO3 oxidation
Phthalocyanines
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Not impregnated Incipient wetness impregn. Ion exchanged
AR-C Co-AC-IWI-1000 1h Co-AC-IE-1000 1h OX
Dem-C Co-AC-IWI-1000 6h Co-AC-IE-1000 6h OX
Dem-C-550 Co-AC-IWI-1000 12.5h Co-AC-IE-1000 12.5h OX
Dem-C-700 Co-AC-IWI-1000 24h Co-AC-IE-1000 24h OX
Dem-C-850 Cu-AC-IWI-1000 1h Cu-AC-IE-1000 1h OX
Dem-C-1000 Cu-AC-IWI-1000 6h Cu-AC-IE-1000 6h OX
Dem-AC-1000 1h (and OX) Cu-AC-IWI-1000 12.5h Cu-AC-IE-1000 12.5h OX
Dem-AC-1000 6h (and OX) Cu-AC-IWI-1000 24h Cu-AC-IE-1000 24h OX
Dem-AC-1000 12.5h (and OX) K-AC-IWI-1000 1h K-AC-IE-1000 1h OX
Dem-AC-1000 24h (and OX) K-AC-IWI-1000 6h K-AC-IE-1000 6h OX
K-AC-IWI-1000 12.5h K-AC-IE-1000 12.5h OX
K-AC-IWI-1000 24h K-AC-IE-1000 24h OX
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For supports: Water pore volume (needed for IWI)
PZC
N2 adsorption
CO and CO2 desorption
For catalysts: NO catalytic activity (NO, CO and CO2 analyzer)
O2 catalytic activity (MS analyzer)
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1400
1200
1000
800
600
400
200
0
BE
T a
rea
(m
2/g
)
2520151050
Activation time (h)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Po
re v
olu
me
(cc/g
)
50
40
30
20
10
0
Bu
rno
ff (%)
BET area
Pore volume
Burnoff
Dem-AC-1000 textural comparison
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1000
800
600
400
200
0
NO
co
nce
ntr
atio
n (
pp
m)
1000900800700600500400300200
Temperature (ºC)
'Dem-C-1000' 'Dem-AC-1000 6h' 'Dem-AC-1000 12.5h' 'Dem-AC-1000 24h' 'Dem-AC-1000 24+h'
NO reduction capacity
Demineralized carbons
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1000
800
600
400
200
0
NO
co
nce
ntr
atio
n (
pp
m)
1000900800700600500400300200100
Temperature (ºC)
NO reduction capacity
Incipient wetness impregnated
Co Cu K
1000
800
600
400
200
0
NO
co
nce
ntr
atio
n (
pp
m)
1000900800700600500400300200100
Temperature (ºC)
NO reduction capacity
Ion exchanged
Co K
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For textural properties:
Burnoff a activation time (OK)
Adsorption capacity a burnoff (OK)
Water penetration a burnoff (OK)
For demineralized carbons and NO reduction:
Activity is higher after activation
Activity is not increased when S.A. increases
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For IWI metal added (NO reduction activity):
Low conversion: Co>Cu>K
High conversion: Co>K>Cu
More surface area is better
For IE metal added (NO reduction activity):
Very low conversion: K>Co
The rest: Co>K
Only at low conversion, more surface is better
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Effect of CO2 activation on functional groups Types of sites created (quinone?)
Size of pores developed Effect of oxidation on activated carbons Amount of carboxylic groups created
Amount of metal exchanged sites Effect of metal addition Changes in PSD
Interactions C-Me (carbon matrix and metal)
Metal dispersion
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1. Minimize carbon consumption2. Maximize the extent of NO chemisorption
by selecting the catalyst with the highest affinity towards NO
3. Maximize the rate of oxygen transfer by maximizing the catalyst/carbon contact area
Illán-Gómez, M.J., A. Linares-Solano, L. R. Radovic and C. Salinas-Martínez de Lecea (1996). “NO reduction over activated carbons. 7. Some mechanistic aspects of uncatalyzed and catalyzed reaction" Energy & Fuels. (10): 158 - 168.
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Spectroscopy of surface chemistry
XPS, FTIR, DRIFTS
Metal content & dispersion
XPS, XRD, TEM
Carbon structure
XPS, XRD, SEM, N2 ads, Raman
Electronic properties
SQUID, ESR, c
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Thank you for your time!