Download presentation

Presentation is loading. Please wait.

1
**MECHANISM OF SOOT FORMATION: OXIDATION**

Michael Frenklach UC Berkeley & LBNL MACCCR Fuel Summit September 17, 2012 extra: aromatic-edge size

2
**Homogeneous Nucleation**

Precursor Chemistry fuel + O2 Homogeneous Nucleation Coagulation + Particle Dynamics Agglomeration + C2H2, … Growth Surface Reactions

3
**SURFACE REACTIONS Frenklach 1989; Frenklach & Wang 1991:**

assumed analogous to gaseous aromatics assumed armchair sites H-abstraction H-addition O2 oxidation OH C2H2 •

4
Graphene Edges zigzag armchair

5
**Detailed Kinetic Monte-Carlo Model**

Whitesides & Frenklach, JPC A 2010 rate coefficients: Schuetz, Whitesides, You, Frenklach, Kollias, Domin, Zubarev, Lester, …

6
**Developed Morphologies**

2500 K 1500 K 2000 K

7
**Homogeneous Nucleation**

Precursor Chemistry fuel + O2 Homogeneous Nucleation Coagulation + Particle Dynamics Agglomeration + C2H2, … Growth Surface Reactions O2, OH, … Oxidation

8
**Oxidation of Aromatics**

(Carstensen and Dean, IJCK 2012) (Lin and Lin, JPC 1986) (Zhou, Kislov, Mebel, JPC A 2012) Oxyradicals are likely key intermediates Generally we look at the oxidation of benzene. It forms an oxyradical which decomposes to form a 5-member ring and CO. How does that translate to a larger PAH? We have been examining the decomposition.

9
**Computational Details**

Quantum chemistry calculations DFT - B3LYP/6-311G(d,p) Reaction kinetics K, atm using MultiWell Comparison to experiments Frank et al. (1994) 1.3 – 2.5 atm Lin and Lin (1986) 0.4 – 0.9 atm Computational results: You, Zubarev, Lester, Frenklach, JPC A 2011

10
**B3LYP, M05-2X and M06-2X 1 atm + CO + CO Basis set: 6-311G(d,p) (0)**

47.8 (45.4) [43.2] 36.5 (34.7) [33.0] 24.7 (22.9) [21.9] + CO (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]: Basis set: 6-311G(d,p)

11
**Multiwell -Argon was the bath gas collider**

0.0001 0.0002 10 -3 -2 -1 Species Fraction Time (sec) 5000 10000 15000 20000 25000 30000 35000 40000 45000 Average Vibrational Energy (cm ) Solves time-dependent 1-D energy transfer master equations Solved stochastically using the Gillespie algorithm average vibrational energy of reactant kT,P= slope kT,P -technique explained well by David Golden -Argon was the bath gas collider

12
Edown Edown = 260 cm-1 Edown = cm-1 Lin and Lin (1986) Temperature dependent Edown expression from Hippler, Troe, Wendelken, JCP 1983.

13
Oxyradicals zigzag armchair

14
**Correlation with Aromaticity**

Harmonic Oscillator Measure of Aromaticity HOMA = HOMA limiting values HOMA = 0 (Kekulè form of benzene) HOMA = 1 (aromatic form of benzene)

15
**Thermodynamic Stability**

16
**Energy Correlation with Aromaticity**

kcal/mol Zubarev, Robertson, Domin, McClean, Wang, Lester, Whitesides, You, Frenklach, JPC C 2010

17
Larger Oxyradicals

18
**Combining All Oxyradical**

Zubarev, You, Domin, McClean, Lester, Frenklach, J Mater Chem 2011

19
**Decomposition of Zigzag Oxyradicals**

20
**Thermal Decomposition of Oxyradicals: Outer-ring Zigzag Edges**

kcal/mol

21
**Thermal Decomposition of Oxyradicals: Outer-ring Zigzag Edges**

22
**Thermal Decomposition of Oxyradicals: Inner-ring Zigzag Edges**

kcal/mol

23
**inner rings of zigzag edges do not oxidize fast**

-note that these results are done (You, Zubarev, Lester, Frenklach, JPC A 2011)

24
**Decomposition of Armchair Oxyradicals**

25
**Potential Energy Surfaces**

kcal/mol

26
**Decomposition Rate 10 atm 1 atm 0.1 atm 0.01 atm 10 atm 10 atm 1 atm**

-Make sure to emphasizes that the pressure dependence is new. Not seen in past. 1 atm 1 atm 0.1 atm 0.1 atm 0.01 atm 0.01 atm

27
**Armchair Decomposition**

“Free Edges” 2 Free Edge Free Edge Non-Free Edge 1 Free Edge 1 atm Ask question about blue line. 1 Free Edge kcal/mol

28
**Substrate Size 1 atm -Affect is larger then expected**

-More work needs to be done in understand the assumption from molecular to edge reaction.

29
**Zigzag vs Armchair 1 atm ZZ I ZZ II AC II AC I ZZ I ZZ II AC II AC I**

Armchair I ZZ I ZZ II AC II AC I 1 atm Armchair II ZZ I ZZ II AC II AC I Zigzag I -emphasize two things. Zigzag and armchair are the same. All at same time and same order of magnitude Zigzag II

30
**Oxyradical Decomposition**

31
**Kinetics Correlation with HOMA?**

HOMAoxyradical ring kT = 2000 K, P = ∞ (s-1) Barrier height (kcal/mol)

32
**> >> Conclusions Proliferation of zigzag-edges in flames**

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: 2 free edges free edge 1 free edge free edge no free edges > >> Proliferation of zigzag-edges in flames

33
**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

Similar presentations

Presentation is loading. Please wait....

OK

Select a time to count down from the clock above

Select a time to count down from the clock above

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google