Supporting Material for
“Biomass Pyrolysis: Thermal Decomposition of Furfural and Benzaldehyde”
by AnGayle K. Vasiliou, Jong Hyun Kim, Thomas K. Ormond, Krzysztof M. Piech, Kimberly N.
Urness, Adam M. Scheer, David J. Robichaud, Calvin Mukarakate, Mark R. Nimlos, John W.
Daily, Qi Guan, Hans-Heinrich Carstensen, and G. Barney Ellison
While the main focus of this paper is on the experimental characterization of the pyrolysis of
furfural and benzaldehyde, electronic structure calculations and flow reactor simulations were
performed to support the kinetic interpretations given in the main text. Some results are presented
here as supporting information.
a. Benzaldehyde pyrolysis
Some key reactions responsible for the thermal decomposition of benzaldehyde are:
C6H5CHO  H + C6H5CO
C6H5CO  C6H5 + CO
C6H5 + H  C6H6
o-C6H4  HCCH + HCC-CCH
C6H5 + C6H5CHO  C6H6 + C6H5CO
C6H5CHO + H  reactions on the C7H7O PES
(1’)
(2’)
(3’)
(4’)
(5’)
Reactions 1’ and 2’ have been treated as a single reaction using the pre-exponential factor reported
by Grela and Colussi1 and a barrier height of 91.5 kcal mol-1 from CBS-QB3 calculations. We used
this higher barrier to be consistent with other CBS-QB3 based data even though the reported
experimental value is lower.2 Rate constants for reactions 3’ and 4’ have been taken from an
existing kinetic model3 and for reaction 5’ we used an estimate k5’ = 1012 exp(-1000K/T).
The relevant part of the C7H7O potential energy surface was re-investigated at the CBS-QB3
level of theory and is shown in Fig. S1. Even though the energy of H plus benzaldehyde is lower
than that for the product channel to formaldehyde plus benzene, this conversion can take place at
high temperatures. Furthermore, the lack of rotational and vibrational degrees of freedom limit the
entropy content of hydrogen atoms and enhance its conversion probability at high temperatures due
to Gibbs Free Energy reasons.
66.3
57.2
C6H5 + CH 2O
57.2
C6H5 + CH 2O
50.0
49.0
O
CH2
48.8

47.6
43.5
C6H5CHO + H
38.6
43.5
C6H5CHO + H
40.9
30.9
C6H6 + HCO
31.0
H2
C
O
29.3

O
CH2 
24.9
H
O
CH

Figure S1: Relevant aspects of C7H7O PES. Values are heats of formation at 298K in
kcal/mol calculated at the CBS-QB3 level of theory.
Based on this PES, we calculated the rate constants for all important channels using
QRRK/MSC theory. As input, high-pressure rate constants calculated with transition state theory
corrected for tunneling (Eckart method) were used. The collision parameters were taken to be the
same as for benzene.
Simulations of concentration versus time profiles were done for the conditions given in Table S1.
Table S1
Temperature
Pressure
Residence time
1600 K
150 Torr
250 s
Mole fraction He
Mole fraction C6H5CHO
99.7 %
0.3 %
constant along the reactor
constant along the reactor
This covers the estimated experimental
residence time of 100 - 200 s
The obtained profiles are shown in Fig. S2. In general, the predictions are in qualitative
agreement with the experimental observations, confirming the proposed reactions. Not shown, the
model also predicts the formation of HC≡CH and HC≡C-C≡CH in low concentrations.
Time [s]
Figure S2: Simulated concentration versus time profiles of some main species
detected in the PIMS and IR experiments of benzaldehyde pyrolysis
A rate analysis showed that indeed, a significant fraction of the benzaldehyde decomposes via
the (H addition, HCO elimination) step discussed in the main text. It also shows that unimolecular
bond scission plays an important role in the benzaldehyde consumption. From Fig. S2 we can see
that phenyl radicals are produced in rather high concentrations, meaning they do not very rapidly
decompose to o-benzyne, but instead can also participate in bimolecular H abstraction chemistry,
which yields benzene and reproduces the C6H5CO radical. The rate analysis reveals that this
channel clearly contributes to benzene formation under the conditions investigated. All data support
the conclusion, that bimolecular radical chemistry is important.
b. Furfural pyrolysis
Similar to the benzaldehyde case, a preliminary kinetic model was assembled for furfural
pyrolysis with the goal to test if the mechanistic interpretation presented in the main text are
reasonable. This mechanism contained the reactions that that place on the simplified PES shown in
Fig. S3. This figure shows that the carbene mechanisms (red, orange) require higher barriers than
ring-opening through 1,2-H (green lines), followed by either ring closure to yield -pyrone or furan
formation. Although all pathways are included in the mechanism, the green path is clearly
dominant. To this mechanism, furan decomposition and several other reactions are added.
42.1
36.7
30.8
46.3
40.1
37.3
28.2
27.7
31.9
32.0
27.3
27.4
21.8
CH2=C=CH2
+2 C=O
20.3
HC≡CCHO
+CH2=C=O
m/z=54+42
O
CHO
:C
H2C
H
-3.5
-7.4
m/z=40
-9.5
HC
-5.6
-13.6
O
+ CO
H
O
C
H
-18.6
C=CC=C=O
+CO
-24.0
O=C=CHCH=CHCHO
-35.1
-38.3
O
H
H
O
H
CHO
-48.5
O
H
H
furan
+ CO
O
H
O
H
furfural
 -pyrone
Figure S3: The lowest energy pathways on the C5H4O2 PES at the CBS-QB3 level.
Values are uncorrected heats of formation at 298K in kcal/mol.
Red and orange: carbene mechanisms; green: -pyrone pathway; blue: H-shift
Table S2
Temperature
Pressure
Residence time
1600 K
150 Torr
250 s
Mole fraction He
Mole fraction Furfural
99.7 %
0.3 %
constant along the reactor
constant along the reactor
This covers the estimated experimental
residence time of 100 - 200 s
The predictions for the conditions given in Table S2 are presented in Fig. S4.
Inspection of Fig. S4 reveals that all species predicted by the proposed mechanism are
formed on the approximate time scale of the experiment. Furthermore, the calculated vinyl ketene
concentration is low as is the -pyrone mole fraction at longer residence times. The high CO yield
demonstrates that furan is further reacting, producing a second CO molecule together with propyne.
This explains the high m/z 40 peaks observed in the PIMS experiments. The higher energy channels
of furan decomposition (CH2=C=O plus
) are also predicted and experimentally observed
(acetylene profiles are omitted in the plot).
Time [s]
Figure S4: Simulated concentration versus time profiles of some main species
detected in the PIMS and IR experiments of furfural pyrolysis.
Geometries of key transition states of the furfural PES
Many more pathways have been tested. The transition state for the direct 1,2-H shift of the formyl
hydrogen to the furan ring with simultaneous CO elimination could not be found at the CBS-QB3
level of theory despite numerous attempts.
Nomenclature: H atoms are frequently assumed; ‘#’ denoted a triple bond; cy(…) marks a cyclic
structure
a. Green pathway (-pyrone)
Furfural  O=C=CHCH=CHCHO
8 -0.690810 -1.348370 0.000048
6 -1.802216 -0.809609 0.000159
6 -1.890777 0.620967 0.000156
6 -0.672397 1.243649 0.000026
6
0.500536 0.490715 -0.000089
6 1.766316 0.187107 -0.000220
1 -0.595276 2.323589 0.000009
1 -2.825701 1.162041 0.000248
1 -2.715424 -1.423747 0.000260
8
2.810984 -0.384073 -0.000328
1
1.644987 1.454277 -0.000213
O=C=CHCH=CHCHO  -pyrone
6 -0.008972 -0.023910 0.000153
6
0.001311 0.016646 1.322051
6
1.168912 -0.002526 2.199593
6
2.439966 0.304353 1.910820
6
2.926537 0.804921 0.588118
8
3.339302 0.099660 -0.299072
8 -0.068933 -0.070475 -1.154628
1 -0.989145 0.008859 1.764783
1
0.940735 -0.314102 3.214102
1
3.199936 0.204959 2.680665
1
2.902447 1.911069 0.460861
O=C=CHCH=CHCHO  furan + CO
6
0.035902 -0.053676 0.062420
6
0.278793 -0.018817 1.424331
6
1.609199 0.298201 1.811269
8
2.225174 0.524716 0.111158
6
1.234041 0.200321 -0.616711
6
1.937163 -0.465894 3.318277
8
2.756326 -1.199207 3.663605
1 -0.446648 -0.353257 2.152154
1 -0.886548 -0.374017 -0.398263
1
1.389241 0.061190 -1.688112
1
2.015086 1.268613 2.069485
____________________________________________________________________________________
b. Yellow pathway (5-carbene)
Furfural  OHCcy(COC=CCH2C(:))
6 -1.848257 -0.006535 -0.898983
6 -1.855167 -0.022905 0.546239
6
0.272214 -0.012748 -0.064793
6 -0.495229 -0.056380 1.048010
8 -0.497598 0.074428 -1.195694
1 -2.147006 1.043854 -0.090749
1 -2.758294 -0.191439 1.118804
6
1.737332 -0.040182 -0.243749
1 -0.146853 -0.112124 2.066208
8 2.512557 -0.057492 0.681405
1
2.067120 -0.043284 -1.300294
OHCcy(COC=CCH2C(:))  HC#CCHO
6 -1.815890 0.119794 -1.073734
6 -1.854843 0.434616 0.278640
8 -1.193703 0.598039 1.213339
6 -0.021399 -0.103401 -1.436912
6
0.847640 -0.063235 -0.537246
6
1.831121 -0.017582 0.479862
1 -0.054038 -0.264032 -2.503572
1 -2.303661 -0.827876 -1.302162
1 -2.177532 0.928093 -1.709246
8
2.241847 -0.980488 1.110426
1
2.230304 1.002258 0.661199
____________________________________________________________________________________
c. Blue pathway (formyl-H migration to position 5)
Furfural  O=C=cy(COCC=C)
8 -0.513268 -1.053309 0.667771
6
0.214028 0.129584 0.872400
6 -0.628825 1.198175 0.350791
6 -1.539760 0.613859 -0.486629
6 -1.180804 -0.778363 -0.505882
6
1.293621 -0.050219 -0.159650
8 2.425251 0.071898 -0.400062
1
0.191689 -0.585883 -1.100358
1 -0.435658 2.251681 0.492772
1 -2.286380 1.082916 -1.110183
1 -1.790541 -1.581917 -0.904685
O=C=cy(COCC=C)  C=CC=C=O + CO
6 -0.020640 -0.034690 0.022062
6
0.174326 -0.049716 1.426415
8
2.219003 0.116302 1.260257
6
2.277492 0.192805 -0.035416
6
1.059682 0.245627 -0.779951
6
3.441329 -0.146779 -0.702089
8 4.504921 -0.154874 -1.158117
1
1.032438 0.264585 -1.861850
1
0.391290 0.844447 1.988053
1 -0.913831 -0.471503 -0.414914
1 -0.331325 -0.824542 2.005176
____________________________________________________________________________________
d. Red pathway (3-carbene pathway)
Furfural  OHCcy(COC=CC(:))
6 -0.383391 0.146779 0.021773
6 -0.379506 0.164991 1.452137
6
1.722139 0.154251 0.527721
6
1.045866 0.243983 1.705066
8
0.897287 0.102009 -0.538304
6 -1.522246 -0.233625 -0.868219
1 -0.720605 1.204283 0.569750
1
2.775673 0.139606 0.287042
1
1.504340 0.312907 2.680669
8 -1.391357 -0.652414 -1.986121
1 -2.504017 -0.111831 -0.372932
OHCcy(COC=CC(:))  OHCC=C=CCHO
6
0.112394 -0.019195 0.155840
8
0.143941 -0.008584 1.422212
6
1.867291 0.012380 1.655982
6
2.397113 0.052938 0.353354
6
1.352522 0.011716 -0.542739
6
2.197041 -1.266189 2.431463
8
1.539855 -2.264724 2.414020
1
1.965046 0.912697 2.266412
1 -0.872787 -0.041346 -0.308064
1
1.413609 0.006514 -1.623410
1
3.144500 -1.184721 3.000674
OHCC=C=CCHO  C#CCCHO + CO
6 -0.019375 -0.033314 -0.023333
6
0.043189 -0.063442 1.364208
6
0.908600 -0.029597 2.267912
6
2.458115 0.046352 0.990467
8
3.576731 0.063840 1.238322
1
1.410610 0.034538 -0.000613
1
1.152194 -0.035490 3.311118
1 -0.277583 -0.947677 -0.556571
6 -0.481081 1.208136 -0.721687
8 -0.864112 1.225780 -1.864054
1 -0.410627 2.135212 -0.115051
C#CCCHO  C=C=C + CO
6
0.141288 -0.022338 -0.021393
1
0.168518 -0.064954 1.066490
6
2.067796 0.107457 -0.574188
1 -0.215422 -0.944189 -0.478594
6 -0.142221 1.180018 -0.635327
8
2.917408 -0.637280 -0.360459
1
1.698210 1.321651 -1.174004
6
0.470126 2.061110 -1.289523
1
0.398072 2.998421 -1.805526
C#CCCHO  furan
8 -0.914459 0.146509 -0.667916
6 -0.912904 0.024435 0.730794
6
0.315684 -0.229559 1.290268
6
1.175259 -0.132842 0.022057
6
0.323977 0.040725 -1.087264
1 -1.908304 0.076649 1.141338
1
1.108910 0.854028 0.665262
1
0.486273 0.098457 -2.152694
1
2.216699 -0.417765 -0.045714
____________________________________________________________________________________
e. 4-carbene pathway (not shown in the Fig. S3)
Furfural  OHCcy(C=CC(:)CO)
6 -1.860160 -0.019969 -0.552190
6 -1.853131 -0.026777 0.867722
6
0.259958 -0.019257 -0.067654
6 -0.414710 0.059154 1.112872
8 -0.585222 -0.060447 -1.132864
1 -2.657368 -0.248680 -1.247110
1 -2.164599 1.042510 -0.014068
6
1.707258 -0.036429 -0.378542
1
0.057431 0.120061 2.081907
8
2.557759 -0.011972 0.475932
1
1.948956 -0.074864 -1.458523
OHCcy(C=CC(:)CO)  C=C=CC(=O)CHO
8 -0.279063 -0.000003 -1.253137
6 -0.274850 -0.000011 0.033919
6
0.983531 0.000031 0.665493
6
1.998229 0.000074 -0.290717
6
1.350550 0.000058 -1.558191
6 -1.621486 -0.000063 0.708341
1
1.091282 0.000029 1.741477
1
1.462192 0.900973 -2.163410
1
1.462258 -0.900841 -2.163421
8 -1.739159 -0.000074 1.904892
1 -2.485803 -0.000090 0.018250
no low-energy pathways from C=C=CC(=O)CHO were found
References
1. Grela, M. A.; Colussi, A. J., J. Phys. Chem. 1986, 90, 434-437.
2. Solly, R. K.; Benson, S. W., J. Am. Chem. Soc. 1971, 93, 1592-1595. This experimental study reports
DH298(C6H5CO-H) = 86.9 ± 1.1 kcal mol-1. This value may be too low. CBS-QB3 ab initio electronic
structure calculations find this CH bond energy to be 92 kcal mol-1; the CBS-QB3 method is generally
accurate to ± 1 kcal mol-1.
3. Randolph, K. L.; Dean, A. M., 2007, 9, 4245-4258.