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MECHANISM OF SOOT FORMATION: OXIDATION. Michael Frenklach UC Berkeley & LBNL. MACCCR Fuel Summit September 17, 2012. extra: aromatic-edge size. +. +. Precursor Chemistry. fuel + O 2. Homogeneous Nucleation. Coagulation. Particle Dynamics. Agglomeration. C 2 H 2 , …. Growth. - PowerPoint PPT Presentation
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Michael FrenklachUC Berkeley & LBNL
MECHANISM OF SOOT FORMATION: OXIDATION
MACCCR Fuel SummitSeptember 17, 2012extra: aromatic-edge size
Coagulation +
Agglomeration +
Precursor Chemistry fuel + O2
Homogeneous Nucleation
ParticleDynamics
SurfaceReactions
C2H2, …Growth
SURFACE REACTIONS
H-abstraction
H-additionO2
oxidationoxidation
OH
C2H2•
Frenklach 1989; Frenklach & Wang 1991:
• assumed analogous to gaseous aromatics• assumed armchair sites
Graphene Edges
zigzag
armchair
+C2H2
-H
-H
+H
+C2H2
+C2H2
-H
-C2H2
+H
+H
-C2H2
-H
+H
+H
-H
-H
-C2H2
-H
-H
-H
-C2H2
+C2H2
-H
+C2H2
+C2H2
-H
-H
+C2H2
-H
-H
-H
DETAILED KINETIC MONTE-CARLO MODELWhitesides & Frenklach, JPC A 2010
rate coefficients: Schuetz, Whitesides, You, Frenklach, Kollias, Domin, Zubarev, Lester, … 2005-10
1500 K
2000 K
2500 K
DEVELOPED MORPHOLOGIES
Coagulation +
Agglomeration +
Precursor Chemistry fuel + O2
Homogeneous Nucleation
ParticleDynamics
SurfaceReactions
C2H2, …Growth
O2, OH, …Oxidation
Oxidation of Aromatics
O+ CO
(+ O2, OH, ...)
OO
Oxyradicals are likely key intermediates
(Lin and Lin, JPC 1986)(Carstensen and Dean, IJCK 2012)
O+ CO
(+ O2, OH, ...)
(Zhou, Kislov, Mebel, JPC A 2012)
Computational DetailsQuantum chemistry calculations DFT - B3LYP/6-311G(d,p)
Reaction kinetics 1500-2500 K, 0.01- atm using MultiWell 2011.3
Comparison to experiments
Computational results: You, Zubarev, Lester, Frenklach, JPC A 2011
101
102
103
104
105
106
107
0.6 0.7 0.8 0.9 1
1000/T(K)
2 atm
0.5 atm
k (s
-1)
T(K)1600 1300 1000
O
+ CO
P
Lin and Lin (1986) 0.4 – 0.9 atm
Frank et al. (1994) 1.3 – 2.5 atm
B3LYP, M05-2X and M06-2X
47.8(45.4)[43.2]
36.5(34.7)[33.0] 24.7
(22.9)[21.9]
+ CO
0(0)[0]
50.8
(50.5)[49.3]
55.3
(54.6)[52.3]
39.7
(38.6)[36.5]
70.2
(73.4)[69.2] 63.0
(67.6)[63.3]
73.8(77.3)[74.9]
B3LYP:
(M05-2X):
[M06-2X]:
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
B3LYP
M05-2X
M06-2X
+ COP
1 atm
Basis set: 6-311G(d,p)
0 0.0001 0.0002
10-3
10-2
10-1
100
Spe
cies
Fra
ctio
n
Time (sec)
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
Ave
rage
Vib
ratio
nal E
nerg
y (c
m-1
)
Multiwell
+ CO
O
Solves time-dependent 1-D energy transfer master equations
Solved stochastically using the Gillespie algorithm
-Argon was the bath gas collider
average vibrational energy of reactant
kT,P= slope
kT,P
Temperature dependent Edown expression from Hippler, Troe, Wendelken, JCP 1983.
Edown
Edown = 260 cm-1 Edown = 439-545 cm-1
Lin and Lin (1986)
O
+ CO
4321
4321
12
3 4
123
4
zigzag armchair
OXYRADICALS
2
CC CC-aromatic1
257.71
n
i
r rn
Correlation with Aromaticity
Harmonic Oscillator Measure of Aromaticity
HOMA = 1 (aromatic form of benzene)
HOMA = 0 (Kekulè form of benzene)
HOMA =
HOMA limiting values
Thermodynamic Stability
0
5
10
15
20
2.3 2.4 2.5 2.6 2.7 2.8
Rel
ativ
e E
ner
gy
Cumulative HOMA
kcal/mol
Energy Correlation with Aromaticity
Zubarev, Robertson, Domin, McClean, Wang, Lester, Whitesides, You, Frenklach, JPC C 2010
O
O
O
O
LARGER OXYRADICALS
COMBINING ALL OXYRADICAL
Zubarev, You, Domin, McClean, Lester, Frenklach, J Mater Chem 2011
Decomposition of Zigzag Oxyradicals
THERMAL DECOMPOSITION OF OXYRADICALS:
OUTER-RING ZIGZAG EDGES
kcal/mol
THERMAL DECOMPOSITION OF OXYRADICALS:
OUTER-RING ZIGZAG EDGES
THERMAL DECOMPOSITION OF OXYRADICALS:
INNER-RING ZIGZAG EDGES
kcal/mol
inner rings of zigzag edges do not oxidize fastO
+ CO
O
+ CO
+ CO
O
+ CO
O
(You, Zubarev, Lester, Frenklach, JPC A 2011)
Decomposition of Armchair
Oxyradicals
Potential Energy Surfaces
kcal/mol
Decomposition Rate
103
104
105
106
107
108
109
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
O
+ COP
103
104
105
106
107
108
109
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
O
+ COP
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)150020002500
O+ COP
10 atm
1 atm
0.1 atm
0.01 atm
10 atm
1 atm
0.1 atm
0.01 atm
10 atm
1 atm
0.1 atm
0.01 atm
+ CO
O
+ CO
O
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
O
+ CO
Armchair Decomposition
O
+ CO
kcal/mol
P
1 atm
Free EdgeNon-Free Edge
“Free Edges”2 Free Edge
1 Free Edge
1 Free Edge
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)2000 15002500
Substrate Size
+ CO
O
+ CO
O
O
+ CO
P
1 atm
104
105
106
107
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)20002500 1500
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
T(K)20002500 1500
Zigzag vs Armchair
O
+ CO
Armchair I
+ CO
OArmchair II
O+ CO
O
+ CO
Zigzag I
Zigzag II
P1 atm
ZZ I
ZZ II
AC II
AC I
ZZ I
ZZ IIAC II
AC I
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
20002500 1500T(K)
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
20002500 1500T(K)
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
20002500 1500T(K)
104
105
106
107
108
109
1010
0.4 0.45 0.5 0.55 0.6 0.65
k(s-1
)
1000/T(K)
20002500 1500T(K)
O
O
O
O
O
O
O
R O CO + ProductO
Oxyradical Decomposition
P
∆HOMAHOMA oxyradical ri
ng
46
48
50
52
54
56
58
60
62
-0.6 -0.4 -0.2 0 0.2
Bar
rier
heig
ht (
kcal
/mol
)
106
107
108
-0.6 -0.4 -0.2 0 0.2
kT
= 2
00
0 K
, P =
∞ (s-
1)
O
O
O
O
O
O
O
Kinetics Correlation with HOMA?
TS, reactant,HOMA HOMA HOMAn
i ii 2
Conclusions
The decomposition of oxyradicals: temperature, pressure, substrate-size, site dependent
armchair rates are close to those of a zigzag-edge
correlated with aromaticity
The following generalization can be made:
O2 free edges
free edge
free edge
O1 free edge
free edgeOno free edges
> >>
Proliferation of zigzag-edges in flames
ACKNOWLEDGEMENTS
DOE-BES
Prof. William A. Lester, Jr.Dr. Dmitry Zubarev (moving to Harvard U.)Dr. Russell Whitesides (now at LLNL)Prof. Xiaoqing You (now at Tsinghua U.)David Edwards
