J.Q. Bond et al. / Journal of Catalysis 281 (2011) 290–299
299
consistent with thermodynamic expectations that the conversion
of GVL to PEA is an endothermic reaction. We consider this out-
come in the context of Eq. (12), where the barrier to ring formation
is expressed relative to that of ring opening, binding energies for
GVL and PEA, and the enthalpy change between gas-phase GVL
and PEA, suggested by prior studies to be endothermic and depen-
dent upon the isomer of PEA considered. It has been demonstrated
that the ring opening of GVL occurs with an enthalpy change of 17–
40 kJ molꢀ1 in computational [12] and experimental studies [25].
We expect that for comparable binding energies of GVL and PEA
(as suggested by the magnitude of adsorption coefficients), the for-
ward barrier would exceed that of the reverse barrier for this endo-
thermic reaction, and the model is thus consistent with the
expected thermodynamics of GVL ring opening.
production for a wide range of reaction conditions. The results
from this study can be used to aid in reactor design and process
optimization studies to assess the techno-economic feasibility of
producing liquid transportation fuels by the conversion of lignocel-
lulosic biomass to GVL combined with catalytic decarboxylation to
produce butene and alkene oligomers.
Acknowledgments
This work was supported by the Defense Advanced Research
Projects Agency (DARPA) and Army Research Lab (ARL) through
the Defense Science Office Cooperative Agreement W911NF-09-
2-0010/09-005334 B 01 (Surf-Cat: Catalysts for production of JP-
8 range molecules from lignocellulosic biomass). The views, opin-
ions, and/or findings contained in this article are those of the
authors and should not be interpreted as representing the official
views or policies, either expressed or implied, of the Defense Ad-
vanced Research Projects Agency or the Department of Defense.
In addition, this work was supported in part by the US Department
of Energy Office of Basic Energy Sciences.
EA ¼ EA
þ
D
HGVL
ꢀ
D
HPEA
ꢀ
D
Hrxn
ð12Þ
ꢀ1
1
ads
ads
Quantitatively, the difference in magnitude of forward and reverse
activation barriers observed here (27 kJ molꢀ1) is in the range sug-
gested by previously reported reaction enthalpies. This result sug-
gests that adsorptions of GVL and PEA occur with similar binding
energies and supports observations that both species interact with
the catalyst surface strongly and with comparable observed reac-
tion orders.
Excellent agreement is achieved with respect to trends in bu-
tene production using activation barriers for decarboxylation of
GVL and PEA of 175 and 142 kJ/mol, respectively, suggesting that
butene production from PEA is the lower-energy pathway; how-
ever, at typical temperatures of decarboxylation and within the
precision of the estimate, we cannot eliminate the possibility of di-
rect GVL decarboxylation, especially at short space times. Values of
ko are taken to be representative of the rate constant for each reac-
tion considered at the average temperature of the data set (595 K),
and these values are estimated to be 0.274, 0.0631, 0.0241, and
0.0173 minꢀ1 for GVL ring opening, PEA cyclization, GVL decarbox-
ylation, and PEA decarboxylation, respectively. Thus, while the
simple kinetic model outlined here is not intended as a definitive
description of reactions occurring during the decarboxylation of
GVL, this lumped model is effective in describing the rate of butene
production under reaction conditions that would be expected in
most biomass applications.
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In a previous publication, we reported the production of butene
from GVL followed by subsequent oligomerization to produce fuel-
grade liquid alkenes [10]. In the present work, we report results for
the reaction kinetics of the decarboxylation of GVL and PEA and
their interconversion over a SiO2/Al2O3 catalyst. In addition to
the catalytic decarboxylation of PEA, we consider that direct decar-
boxylation of GVL may also contribute to the total rate of butene
production (corresponding to about 10–20% of the overall rate at
typical reaction conditions). The increasing ratio 1-butene:2-bu-
tenes in the product mixture with decreasing space time supports
a mechanism where 1-butene is first formed via b-scission of inter-
mediate carbenium ions. The simple kinetic model developed in
this work provides a useful tool for predicting the rates of butene