Direct Catalytic Conversion of Biomass-Derived Furan and Ethanol to Ethylbenzene

Article abstract of DOI:10.1021/acscatal.7b03952

Herein, we report a synthetic strategy to convert biomass-derived unsubstituted furan to aromatics at high selectivity, especially to ethylbenzene via alkylation/Diels-Alder cycloaddition using ethanol, while greatly reducing the formation of the main side product, benzofuran, over zeolite catalysts. Using synchrotron X-ray powder diffraction and first-principles calculations, it is shown that the above methodology favors the formation of aromatic products due to ready alkylation of furan by the first ethanol molecule, followed by Diels-Alder cycloaddition with ethylene derived from the second ethanol molecule on a Br?nsted acid site in a one-pot synthesis. This gives a double-promoting effect: an alkyl substituent(s) on furan creates steric hindrance to inhibit self-coupling to benzofuran while an alkylated furan (diene) undergoes a Diels-Alder reaction more favorably due to higher HOMO energy.

Full text of DOI:10.1021/acscatal.7b03952

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Article
Direct Catalytic Conversion of Biomass-
Derived Furan and Ethanol to Ethylbenzene
Ivo Teixeira, Benedict T.W. Lo, Pavlo Kostetskyy, Lin Ye,
Chiu Tang, Giannis Mpourmpakis, and Shik Chi Edman Tsang
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b03952 • Publication Date (Web): 10 Jan 2018
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Direct Catalytic Conversion of BiomassꢀDerived
Furan and Ethanol to Ethylbenzene
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Ivo F. Teixeira,1 Benedict T.W. Lo,1 Pavlo Kostetskyy,2 Lin Ye,1 Chiu C. Tang,3 Giannis
Mpourmpakis,2* Shik Chi Edman Tsang1*
1Wolfson Catalysis Centre, Department of Chemistry, University of Oxford, OX1 3QR (UK); Eꢀ
mail: edman.tsang@chem.ox.ac.uk
2Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15261 (USA),
Eꢀmail: gmpourmp@pitt.edu
3Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire,
OX11 0DE (UK)
Abstract
Herein, we report a synthetic strategy to convert biomassꢀderived unsubstituted furan to
aromatics at high selectivity, especially to ethylbenzene via alkylation/DielsꢀAlder cycloaddition
using ethanol, while greatly reducing the formation of the main side product, benzofuran, over
zeolite catalysts. Using synchrotron Xꢀray powder diffraction and first principles calculations, it
is shown that the above methodology favors the formation of aromatic products due to readily
alkylation of furan by the first ethanol molecule, followed by DielsꢀAlder cycloaddition with
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derived ethylene from the second ethanol molecule on a Brønsted acid site in a one pot synthesis.
This gives a double promoting effect: alkyl substituent(s) on furan creates steric hindrance to
inhibit selfꢀcoupling to benzofuran while alkylated furan (diene) undergoes DielsꢀAlder reaction
more favorably due to higher HOMO energy.
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KEYWORDS: Biomass • Cycloaddition • Zeolite • synchrotron Xꢀray • Modelling
Introduction
The conversion of lignocellulosic biomass to renewable fuels and chemicals has attracted
significant attention as a key technology to enable the replacement of petroleum.1ꢀ2
Lignocellulosic biomass is the most promising renewable carbon energy source, as it is widely
available around the world at a relatively low cost.3 Although it is the most abundant plant
material resource, its conversion into chemical faces a range of technological and economic
challenges.4 In order to overcome these challenges, several different processes to obtain
chemicals and biofuels from biomass are currently under development.5ꢀ6 The most promising is
the multistep strategy using platform molecules as intermediates.7 Some platform molecules that
can be obtained from biomass at good yields are biomassꢀderived furans, such as furfural, 5ꢀ
hydroxymethylfurfural (HMF), 2ꢀmethylfuran (MF), unsubstituted furan and 2,5ꢀdimethylfuran
(DMF), etc.8
Furan and 2ꢀmethyfuran can be derived from the further conversion of furfural. Furan is obtained
from furfural decarbonylation (at 97% yield),9ꢀ10 whereas 2ꢀmethylfuran by the direct
hydrogenolysis of furfural (at 50% yield)10 or by its hydrogenation, followed by dehydration of
furfuryl alcohol (at 99% overall yield).3 Many recent studies have reported the DielsꢀAlder, DA
[4+2] cycloaddition reactions between these biomassꢀderived DMF and MF with ethylene,
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followed by dehydration producing aromatics, such as xylene and toluene, respectively.11ꢀ21 It is
however, ethylene that is currently produced through nonꢀrenewable petroleum routes. Although
impressive yields of xylene (90%) and toluene (50%) are achieved from the conversions of DMF
and MF, the conversion of unsubstituted furan into benzene or related aromatics gives
considerably much lower yield and selectivity. It is primarily due the favorable coupling reaction
between two furan molecules, which forms benzofuran (see Scheme 1). Chang et al. reported
only 5% of selectivity to benzene at 250 °C by ZrꢀBEA zeolite catalyst14 and 35% by BEA
zeolite under extremely high pressure of ethylene (62 bar) to enhance the DA rate.22 They also
showed that under 600 °C, the major products from furan conversion are benzofuran and coke
(60% carbon selectivity); the benzofuran intermediates can be further converted into aromatics at
higher temperatures.23 However, it is clear that benzofuran is still the inevitable main side
product due to the unprotected αꢀcarbon that subjects to side reactions. As a result, the route to
obtain ethylbenzene (a styrene precursor) from biomassꢀderived furan coupling with two
ethylene molecules at present is economically nonꢀviable since it is produced at a very low
yield.13
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CH3CH2OH
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Ethanol
Dehydration
-H2O
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H2C CH2
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+
H2O
Diels-Alder
Reaction
O
Benzene
O
Diels-Alder
Reaction
Furan
H2C CH2
Furan
Coupling
-H2O
-H2O
Alkylation
Ethylfuran
Ethylbenzene
O
Benzofuran
Scheme 1. Furan conversion into aromatics and the side product benzofuran.
Here, we demonstrate the conversion of biomassꢀderived furan to aromatics, especially to the
highly desired product, ethylbenzene using bioꢀderived ethanol in totally green synthesis rather
than ethylene, while greatly attenuating the yield of the side product, benzofuran, over acidic
zeolite catalysts. The conversion is based on the DA [4+2] cycloaddition of readily formed
ethylfuran intermediate with in-situ produced ethylene from ethanol dehydration (ED) in a ‘oneꢀ
pot’ solventꢀfree reaction.
Results and Discussion
First, we compared the catalytic performance of furan with ethanol or ethylene over USY zeolite
(Si/Al = 250). Under our optimized reaction conditions, the conversion of furan with ethylene
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produces benzofuran as a major product of 63% selectivity (see Fig. 1), followed by benzene
35% and 2% of alkylated aromatics. When the same reaction is performed using ethanol at the
same molar ratio, the product selectivity is completely different. The selectivity to benzofuran
and alkylated benzofurans is greatly reduced to 23% and the overall selectivity to aromatics is
improved to 67%.
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Figure 1. Conversion and selectivity for furan to aromatics catalyzed by zeolite HUSY
(Si/Al=250) with ethylene or ethanol, under optimized reaction conditions. Temperature 300 °C,
reaction time 8 h, and (black) molar ratio of ethanol to furan of 10:1, (gray) 40 bar of ethylene.
All products were quantified, and the carbon balance was achieved at a minimum of 90%.
In Fig.2 the conversion and product distribution for the reaction performed with ethanol (10:1)
over HUSY (Si/Al=250) is shown. 70% of the furan was converted with 45% selectivity to
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ethylbenzene, 7.9% to diethylbenzene, 14% to other alkylated aromatics (mainly
triethylbenzene), 12.5% to ethylfuran and only traces of benzene were detected (around 1%).
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Figure 2. Conversion and selectivity for furan transformation into aromatics catalyzed by 0.4g of
zeolite HUSY (Si/Al=250). Reaction conditions: temperature 300 °C, 10:1 Ethanol/Furan molar
ratio and reaction time 8 h in 100mL reactor. All products were quantified, and the carbon
balance was achieved at a minimum of 90%.
The initial rate of reaction for furan conversion also increases from 0.12 to 0.23 mol gcatꢀ1 hꢀ1,
when ethanol is used instead of ethylene; but the conversion after prolonged period (e.g. 8 h)
converges (ca. 70% for both ethylene and ethanol). Despite the distribution of aromatic products,
ethylbenzene remains as the main product which is valuable for the petrochemical industry.
Ethylbenzene is generally used to produce styrene for polystyrene synthesis, whereas other
alkylated aromatics require a further transalkylation step in order to improve the quality of the
aromatic products for other polymers and chemicals processing.24ꢀ25
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It is also found that the catalytic performance is dependent on the framework type and the acidity
of the zeolite catalysts (see Table 1, Fig. 3). To decouple these effects, zeolites with similar
morphology (Fig. S12) and crystallinity (Fig. S11) were tested. The zeolites with larger pores,
i.e. USY and BEA, have more superior aromatic selectivity. Although all the zeolites show much
lower selectivity to benzofuran than that reported in literature when ethylene was used,15, 22
HZSMꢀ5 zeolite still produces benzofuran as the major product. This agrees with the literature
that HZSMꢀ5 is a poor catalyst in converting furans into aromatics by the DA reaction.11 As a
typical DA cycloaddition reaction requires a rigid geometric overlap of HOMOꢀLUMO orbitals,
HZSMꢀ5 with smaller pore may not be able to accommodate the spatial needs of the transition
state formed between diene and dienophile.
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Figure 3. Conversion and selectivity for furan transformation into aromatics catalyzed by
different zeolites. Reaction conditions: temperature 300 °C, 0.4 g of catalyst, molar ratio
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Ethanol/Furan of 10:1 and reaction time 8 h. All products were quantified, and the carbon
balance was achieved at a minimum of 90%.
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Table 1. Properties of zeolites and rates of furan conversions
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Total acid sites[b] Surface Area[c] HꢀTOF[d]
Brønsted acid
Catalyst
Si/Al ratio[a]
sites[b] (mmol gꢀ1)
(mmol gꢀ1)
(m2 gꢀ1)
349
(102 hꢀ1)
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HZSMꢀ5
HZSMꢀ5
HUSY
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620
HBEA
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575
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[b]
from ICPꢀAES.
from ammoniaꢀTPD (there is an onꢀgoing debate whether the NH3ꢀTPD
technique can differentiate Brønsted acid sites from Lewis acid sites despite the fact that it is still
the most commonly used technique to estimate the amount and strength of the acid sites.) [c] from
BET over 0.05 < P/P0 < 0.3. [d] rate of mol. furan to mol. products per Brønsted acid site per hour.
We have also investigated the effect of acid site concentration in these zeolite catalysts. More
acidic zeolites favor higher furan conversion, with 100% conversion catalyzed over HBEA
(Si/Al=25) and 97% conversion over HUSY (Si/Al=6). This agrees with our expectation that the
furan reactions are likely catalyzed by the BAS of zeolites. The product distribution is also
affected by the Brønsted acid concentration, however, it seems to affect in a different degree
zeolites with different shapes. For the HZSMꢀ5 zeolites, less acidic samples show higher
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selectivity to aromatics, because the more acidic ones tend to produce other side products, such
as ketones. Zeolites with USY shape show better selectivity to aromatics when samples with
lower acid density are used. The conversion of furan into aromatics over HUSY (Si/Al=250) was
optimized in terms of increasing Ethanol/Furan ratio (see Fig. 4).
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Figure 4. Conversion and selectivity for furan transformation into aromatics catalyzed by 0.4g of
zeolite HUSY (Si/Al=250) with different molar ratios Ethanol/Furan. Reaction conditions:
temperature 300 °C and reaction time 8 h in 100mL reactor. All products were quantified, and
the carbon balance was achieved at a minimum of 90%.
Briefly, a higher Ethanol/Furan ratio gives higher conversion and selectivity toward aromatics.
However, the aromatic product distribution is significantly changed; a larger amount of di/triꢀ
ethylbenzene is produced (see Fig. 4). Interestingly, higher molar ratios of Ethanol/Furan further
disfavor the formation of benzofuran (undesirable product), reducing its selectivity from 36% to
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only 14% when the Ethanol/Furan ratio is increased from 3:1 to 30:1 (see Fig. 4). This may
suggest that the reduced coverage of furan on the BAS in favor of ethanol is spatially significant
to increase its DA crossꢀcoupling to aromatics at the expense of selfꢀcoupling product of
benzofuran. However, the competitive replacement of furan by ethanol as a simple site
competition model could not account for the significant increase in the overall furan conversions
at the increase in the Ethanol/Furan ratios (furan conversion increases from 42% to 92%) and no
comparable effect can also be seen by using higher Ethylene/Furan ratios. 15, 22
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Further, we studied the initial production rates for ethylfuran and aromatic products at different
Ethanol/Furan ratios (see Fig. 5) in order to gain a better understanding on their relationships.
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Figure 5. Initial production rate of ethylfuran and aromatics catalyzed by 0.4 g of zeolite HUSY
(Si/Al=250) with different molar ratios Ethanol/Furan at 300 °C in a 100 mL reactor.
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The initial production rate of ethylfuran rises sharply when the Ethanol/Furan ratio increases
from 3:1 to 10:1. However, it declines greatly and stays steadily at low values at the mole ratio of
15:1 to 30:1 probably due to a more favorable conversion of this intermediate to the final
aromatics products (see Fig. 5 and Fig. S2). As a result, the production rate of aromatics appears
to surpass that of the ethylfuran rate at increasing molar ratios of Ethanol/Furan. A similar trend
was observed for the HUSY zeolite (Si/Al=6), the initial rates, however, were an order of
magnitude higher. This is likely due to the significant difference in the concentration of Brønsted
acid sites (see Fig. S2), cf. 0.55 mmol gꢀ1 for the HUSY (Si/Al=6) and 0.052 mmol gꢀ1 for the
HUSY (Si/Al=250).
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Figure 6. Arrhenius plot for the conversion of furan into aromatics over 0.4 g of HUSY
(Si/Al=6) and the estimated activation energies.
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HUSY (Si/Al=6) was then chosen for kinetic studies using the Arrhenius plots (see Fig. 6) with
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ꢀ1
the highest initial rate (0.64 mol gcat hꢀ1) for the conversion of furan. The apparent activation
energy (Ea) is estimated to be 91±9 kJ molꢀ1 for the formation of aromatics, whereas the Ea for
benzofuran is 103±11 kJ molꢀ1. Thus, the formation of benzofuran is more favorable with higher
selectivity than that of aromatics as observed experimentally if ethylene is used as the
dienophile. Clearly, the use of ethanol can provide an alternative pathway of even lower overall
activation energy to couple with furan to aromatics (ethylbenzene) by DA cycloaddition on the
BAS as similar to the reported catalytic route to convert ethanol/DMF to xylene.26
We have recently developed a synchrotron Xꢀray powder diffraction (SXRD) combined with
Rietveld refinement method to elucidate adsorbate structures in zeolites. The alteration in
scattering parameters of modified framework atoms by the molecule(s) enables the probing of
adsorption geometries and interactions with the Brønsted acid site in terms of atomic distances
and angles, within experimental error.26ꢀ28
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Figure 7. SXRD and Rietveld refinement profiles of (a) furan and 5 bar of ethylene, (b)
equimolar of ethanol to furan, (c,d) their corresponding crystal structures showing a fraction of
an unit cell for illustration. All the symmetry related molecules are disregarded for clarity. The
atomic parameters from Rietveld refinement are summarized in Tables S1ꢀS2 in SI. Atoms are
represented in ball/sticks: white = Si/Al, red = O, black = C. No hydrogen atoms are plotted for
clarity.
Herein, we applied this SXRD and Rietveld refinement technique to study the fundamental
molecular interactions of furan/ethylene or furan/ethanol with BA in the zeolite. The HUSY
(Si/Al=6) sample is loaded with a mixture of (i) furan and 5 bar equivalent of ethylene, and (ii)
equimolar furan and ethanol. See Fig. 7 (a, b) for the corresponding SXRD and Rietveld
refinement profiles, and Fig. S3 for the Rietveld refinement profiles and derived crystal
structures of HUSY (Si/Al=6) preꢀadsorbed with ethanol and furan at ratios of 3:1 and 10:1 for
comparison. As seen in Fig. 7(c), upon the adsorption of ethylene and furan, only furan is
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detected. By measuring the closest interatomic distances between furan and the framework
oxygen atoms, two furan molecules are coꢀadsorbed onto the same framework O1 site associated
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with a T site (BAS) through its electronegative αꢀcarbon; O1ꢀCfuran1 = 3.20(3) Å and O1ꢀCfuran2
=
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3.65 (3) Å. This 2:1 furan to BAS stoichiometry matches with the similar observation that furan
adsorbs in HZSMꢀ5 at a furanꢀtoꢀaluminum molar ratio of 1.73.23 Ethylene is much weakly
bound on the BAS, which does not compete with furan for protonation; it therefore cannot be
detected by SXRD. This may reflect the ‘ethyl’ carboꢀcationic structure formed by protonation of
ethylene is intrinsically less stable. Excitingly, upon the adsorption of an equimolar of ethanol
and furan, a coꢀadsorption structure is detected, showing the competition for BAS by the ethanol
molecule. The closest interatomic distances between the adsorbates and the HUSY framework:
O1ꢀOethanol (= 3.30(4) Å) and O1ꢀCfuran (= 3.30(3) Å), see Fig. 7 (d). Both ethanol and furan
appear to interact with the same BAS. It is anticipated that when the Ethanol/Furan ratio
increases, more ethanol instead of furan will be protonated on the BAS. Indeed, when more
ethanol (with Ethanol/Furan = 3:1 or 10:1, see Fig. S4 and Tables S1ꢀS4) is adsorbed onto the
HUSY (Si/Al = 6) sample, a much higher site occupancy of ethanol is detected.
We further investigated the local concentration of ethanol and/or furan, and their corresponding
interactions with the BAS for HUSY (Si/Al=6) loaded with Ethanol/Furan ratios of 3:1 and 10:1
using FTIR spectroscopy. The IR spectrum for the sample loaded with 3:1 Ethanol/Furan (Fig.
S5) shows characteristic bands for adsorbed ethanol and furan; for ethanol: 2978 cmꢀ1 (CꢀH
stretching), 1448 cmꢀ1 (ꢀCH3 degenerate bending) and 1395 cmꢀ1 (ꢀCH3 symmetric bending);29
for furan: 1468 and 1478 cmꢀ1 (ring stretching (adsorbed)) and 1460 and 1490 cmꢀ1 (ring
stretching (free)).30 Apparently, the IR data corroborates with the SXRD observations, which
also show a coꢀexistence of adsorbed ethanol and furan species in the HUSY. In contrast, for the
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10:1 Ethanol/Furan sample, aside from the same characteristic bands for adsorbed ethanol, new
bands related with free ethanol molecules are also observed at 2980 cmꢀ1 (CꢀH stretching), 1455
cmꢀ1 (ꢀCH3 degenerate bending) and 1380 cmꢀ1 (ꢀCH3 symmetric bending).31 Whereas, most of
the furan bands at this molar ratio are too small to be identified, apart from the band 1490 cmꢀ1
related with free furan molecule. Thus, the FTIR confirms that under higher molar ratios of
Ethanol/Furan, ethanol is preferentially protonated, whereas under large excess of ethanol, free
ethanol is also present inside the zeolite pores, thus increases the ethanol local concentration.
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The above may support the site competition model at higher Ethanol/Furan ratios, such that
limited adsorbed furan couples with excess ethanol to give first order rate with respect to furan
concentration (see Fig. S6). However, the dramatic inhibition effect for benzofuran formation
and the subtle rate enhancement in furan conversion particularly to ethylbenzene at higher
Ethanol/Furan ratios are still unaccountable.
First principle calculations can provide insights into the species adsorption in the HUSY and the
detailed reaction energy profiles of the competing catalytic reactions. First, the adsorption
behavior of ethanol, ethylene, furan, and their mixtures in the pores of the zeolite were modelled
using the ONIOM method (see computational details in the SI). It is demonstrated that ethanol
binds on the BAS more strongly than furan or ethylene, with binding energies of ꢀ65.7, ꢀ26.0 and
ꢀ24.4 kJ molꢀ1, respectively. It is consistent the same trend of their calculated proton affinities in
gas phase (see Tables S5ꢀS6 and Fig. S8). Furan is weakly adsorbed, compared to strongly
adsorbed ethanol, which indicates the steric hindrance of furan adsorption into the pore of the
HUSY zeolite. Additionally, the strong coꢀadsorption of the ethanolꢀfuran dimer was also
observed within the HUSY model, with a calculated binding energy of ꢀ101.5 kJ molꢀ1, as shown
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in Fig. S8(d). This relative adsorption preference of ethanol over furan and particular the
formation of ethanolꢀfuran dimer agrees with our experimental SXRD data.
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Furthermore, electronic and Gibbs free energies were calculated using density functional theory
(DFT) to elucidate the energeticallyꢀpreferred mechanisms in the network of competing reaction
pathways as displayed in Scheme 1 and computational details in SI (Figs. S7, S9, S10). The
competing reactions produce desired aromatic products such as benzene and ethylbenzene, as
well as undesired furan derivatives (ethylfuran, benzofuran, etc.). The desired aromatic pathways
involve DA cycloaddition reactions between the furan or ethylfuran (diene) and ethylene
(dienophile). Typically, the intermediates in these reactions are bicyclic oxanorbornene. They
readily undergo dehydration to form aromatic products. Recent work on DA chemistry of furans
has shown that the rate limiting steps can be dependent on primarily DA cycloaddition step or
dehydration step of the cycloadduct intermediate.11, 26, 32 The undesired derivatives were shown
to form by side reactions of furan selfꢀcoupling (with additional furan) by DA route (the ring
opening route33 is shown to give higher activation energy, see Fig. 8) and furan alkylation (with
ethanol) to ethylfuran.
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Figure 8. Calculated electronic energies show the energetic profiles of the three DAꢀlimited
reactions – ethylated DA, ethanol DA and ethylene DA (magenta, green and black lines,
respectively) as well as two benzofuran formation reactions – furan coupling DA and ring
opening (purple and blue lines, respectively); RLS stands for rate limiting step.
Similar to our previous work,26 the interaction of ethanol with the acid site of the zeolite is the
key in initiating the formation of aromatic products. For the ethanolꢀfuran reactant pair, we
observed a cascade of reactions that was initiated by preferential protonation of ethanol on the
BAS. The protonated ethanol can directly react with the neighboring furan ring in dimer to form
ethylfuran, exhibiting very low calculated energy barriers (Ea = 41.3 kJ molꢀ1, Ga = 35.3 kJ molꢀ
1). This elementary step results in the formation of a protonated water molecule (hydronium ion,
H3O+) as a product, which can form hydrogen bonds with the ethylfuran (diene) and facilitate the
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coꢀadsorption of an additional ethylene molecule (dienophile). Alternatively, the protonated
ethanol can dehydrate via concerted elimination to form H3O+ and ethylene as the dienophile
source produced in-situ (Ea = 94.8 kJ molꢀ1, Ga = 67.1 kJ molꢀ1). Similar to the case of
ethylfuran, the hydronium ion stabilizes (through hydrogen bonding) the ethylene and furan
molecules, resulting in a favorable geometric configuration. The subsequent reaction step is the
[4+2] DA cycloaddition of the conjugated diene (furans) and dienophile (ethylene) and was
shown to be rateꢀlimiting in the BASꢀcatalyzed reactions, with the corresponding free energies,
enthalpies and entropies of rateꢀlimiting barriers involved in the competing mechanisms
presented in Fig. 8 and Table 2. The transition state structures of the rateꢀlimiting elementary
steps are shown in Fig. S7. Two BASꢀcatalyzed routes were considered in which H3O+ facilitates
furanꢀethylene (Ethanol DA) and ethylfuranꢀethylene (Alkylated DA) interactions. Also, a case
of direct DA reaction of protonated furan and ethylene in the absence of water was considered
(Ethylene DA). The coupling of two furan molecules to form benzofuran as a side reaction was
also evaluated. These calculations were repeated in the absence of the acid catalyst
(Uncatalyzed) with the exception of the Ethanol DA pathway, as the ethanol dehydration
reaction to produce the dienophile is acidꢀcatalyzed.
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Table 2. Elementary reaction barriers calculated for DA steps of relevant pathways in acidꢀ
catalyzed and uncatalyzed reactions. Reported values include electronic energies, free energies,
enthalpies and entropies at T = 573 K (experimental temperature).
ꢀEa
ꢀGa
ꢀHa
ꢀSa
Pathway
(kJ molꢁ1) (kJ molꢁ1) (kJ molꢁ1)
(J molꢁ1)
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Alkylated DA
Ethanol DA
97.7
100.3
108.7
79.5
127.7
127.7
146.3
105.5
136.2
140.7
178.5
95.5
97.3
ꢀ56.2
ꢀ53.0
ꢀ63.7
ꢀ53.0
ꢀ77.4
ꢀ83.6
ꢀ72.5
BAS
catalyzed
Ethylene DA
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75.2
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Furanꢀ Coupling DA
Alkylated DA
98.2
91.9
Uncatalyzed
Ethylene DA
98.7
92.8
Furanꢀ Coupling DA
144.2
136.9
The DA steps, involving ethylene as the dienophile source, were shown to be practically
uncatalyzed by the acidic proton (BAS catalyzed versus uncatalyzed – consistent with
previouslyꢀpublished work26) and vary minimally in terms of the calculated activation energies
(see Table 2). The Alkylated DA and Ethanol DA pathways were shown to be comparable in
terms of calculated barriers, with values in near perfect agreement. It suggests that furan
alkylation should not hinder cycloaddition reactions. The involvement of additional water
molecule in both pathways (produced in ethanol dehydration) decreases the entropic loss at the
DA transition state, favoring the Alkylated DA and Ethanol DA pathways (see Table 2 entropy
(S) and free energy (G) values). In addition, the enthalpic barrier for the DA step of the
Alkylated DA pathway relative to the Ethylene DA pathway was shown to decrease by 14.3
kJ/mol. The furan coupling pathway (Fig. S7(d)) was actually shown to be catalyzed by the BAS
of the zeolite and exhibit favorable DA cycloaddition barriers (Ea = 79.5 kJ molꢀ1, Ga = 105.8 kJ
molꢀ1), catalyzed by the acidic proton, bound on the αꢀcarbon of the (dienophile) furan ring. It
thus lowers the HOMO(diene)ꢀLUMO(dienophile) gap from 0.19 to 0.14 Hartree from
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uncatalyzed to protonated Furan Coupling DA (Fig. S9). The energy difference of the frontier
orbitals involved in the DA reactions was shown to corroborate with the reaction barriers in
literature.11, 26, 32 However, the rateꢀlimiting step in the furan coupling pathway was found to be
the water formation step during the dehydration of the cycloadduct intermediates, formed via DA
reactions, with the calculated electronic and free energy barriers of Ea = 98.8 kJ molꢀ1 and Ga =
96.6 kJ molꢀ1, respectively (Fig. 8, blue curve). In contrast, the oxanorbornene intermediates
formed in all other pathways are known to readily dehydrate to the aromatic products in the
presence of BAS 11, 26, 32 and evolve via sequential CꢀO and CꢀH cleavage reactions.
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-500
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(G) concerted - ethanol DA T = 573 K, P = 40 atm
(G) concerted - ethylene DA T = 573 K, P = 40 atm
(G) sequential - ring opening T = 573 K, P = 40 atm
-900
XIII
XIV
-1000
Figure 9: Calculated Gibbs free energies profiles of the three DAꢀlimited reactions – ethylated
DA, ethanol DA and ethylene DA (magenta, green and black lines, respectively) as well as two
benzofuran formation reactions – furan coupling DA and ring opening (purple and blue lines,
respectively); RLS stands for rate limiting step.
In addition to the rateꢀlimiting reaction energy barriers calculated for all pathways, the energetic
span model of Kozuch et al.34 was used to evaluate the kinetics of the reaction system for all the
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pathways. It was found that the Alkylated DA pathway was once again favored in terms of the
overall energetic span of the reaction, with calculated values of 114.8, 122.7, 146.0, and 146.7 kJ
molꢀ1 for the Alkylated DA, Ethanol DA, Furan Coupling and Ethylene DA, respectively. The
values of energetic span were calculated using Gibbs free energies of the relevant energetic states
(Fig. 9), calculated at the reaction temperature of 573 K, which are comparable to some of our
measured values with the same order (Fig. 6). Although the product selectivity trends have been
captured by our theoretical calculations, the deviations between the experimentally measured and
theoretically calculated barriers can be attributed to the absence of the zeolite pore environment
in our reaction pathway calculations.
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Thus, the favored and readily preꢀalkylation of furan (to ethylfuran) by ethanol on the BAS not
only offers steric hindrance for selfꢀfuran coupling but notably increases the HOMO energy of
the substituted diene in a single pot synthesis.35 This decreases the HOMOꢀLUMO energy gap
(Fig. S9) that accounts for the faster reaction rate for the Alkylated DA route with the in-situ
generated ethylene (dienophile), forming corresponding oxabicyclic, which is then rapidly
dehydrated into the ethylbenzene product (Scheme 2).
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Scheme 2. Furan alkylation, followed by DA cycloaddition and dehydration, catalyzed by the
Brønsted acid sites in zeolite catalysts.
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Conclusions
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In summary, we have demonstrated a valuable biomass conversion strategy into useful products.
The zeolite catalysts provide unique and geometrically defined active BAS for a cascade ‘oneꢀ
pot’ reactions to form useful aromatics via the DA cycloaddition. The use of ethanol (can also be
produced from bioꢀsources) instead of traditionally used, nonꢀrenewable ethylene reduces
substantially the formation of the undesired side product – benzofuran. It makes possible for the
first time the conversion of the important platform molecule, the unsubstituted furan into
aromatics, especially the highly desired ethylbenzene, at high yield and selectivity at mild
conditions.
ASSOCIATED CONTENT
Supporting Information
Experimental and computational details on the DFT calculations can be found in the supporting
information, as well as Figures S1ꢀS10 and Table S1ꢀ S6 (PDF).
AUTHOR INFORMATION
Corresponding Authors
*edman.tsang@chem.ox.ac.uk, *gmpourmp@pitt.edu
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Author Contributions
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The manuscript was written through contributions of all authors. All authors have given approval
to the final version of the manuscript.
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Notes
The authors declare no competing financial interest. ASSOCIATED CONTENT
Supporting Information
Figures, Tables and relevant discussion with experimental and computational details is available
in the supporting information file. This material is available free of charge via the Internet at
http://pubs.acs.org.
ACKNOWLEDGMENT
Light Source Ltd (UK) for financial support and IFT is grateful to Brazil CsF/CNPq for a
scholarship & YL acknowledges the fellowship from Office of China Postdoctoral Council. PK
and GM would like to acknowledge the Donors of the American Chemical Society Petroleum
Research Fund (ACSꢀPRF) and the University of Pittsburgh Center for Research Computing for
computational resources. Supporting information for this article is given via a link at the end of
the document.
REFERENCES
1.
2.
RomanꢀLeshkov, Y.; Chheda, J. N.; Dumesic, J. A., Science 2006, 312, 1933ꢀ7.
Wright, M. M.; RomanꢀLeshkov, Y.; Green, W. H., Biofuels, Bioprod. Biorefin. 2012, 6,
503ꢀ520.
3.
4.
Technology 2010, 44, 5298ꢀ5305.
5.
Alonso, D. M.; Wettstein, S. G.; Dumesic, J. A., Chem. Soc. Rev. 2012, 41, 8075ꢀ8098.
Singh, N. R.; Delgass, W. N.; Ribeiro, F. H.; Agrawal, R., Environmental Science &
Huber, G. W.; Iborra, S.; Corma, A., Chemical reviews 2006, 106.
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Page 24 of 26
1
2
3
4
5
6
6.
7.
4838.
8.
Lin, Y.ꢀC.; Huber, G. W., Energy & Environmental Science 2009, 2, 68ꢀ80.
Luterbacher, J. S.; Martin Alonso, D.; Dumesic, J. A., Green Chemistry 2014, 16, 4816ꢀ
Zheng, A.; Zhao, Z.; Chang, S.; Huang, Z.; Zhao, K.; Wu, H.; Wang, X.; He, F.; Li, H.,
7
Green Chemistry 2014, 16, 2580ꢀ2580.
9. Pushkarev, V. V.; Musselwhite, N.; An, K.; Alayoglu, S.; Somorjai, G. A., Nano Letters
2012, 12, 5196ꢀ5201.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10.
Lange, J. P.; van der Heide, E.; van Buijtenen, J.; Price, R., ChemSusChem 2012, 5, 150ꢀ
166.
11.
Williams, C. L.; Chang, C.ꢀC.; Do, P.; Nikbin, N.; Caratzoulas, S.; Vlachos, D. G.; Lobo,
R. F.; Fan, W.; Dauenhauer, P. J., ACS Catalysis 2012, 2, 935ꢀ939.
12. Williams, C. L.; Vinter, K. P.; Chang, C.ꢀC.; Xiong, R.; Green, S. K.; Sandler, S. I.;
Vlachos, D. G.; Fan, W.; Dauenhauer, P. J., Catalysis Science & Technology 2016, 6, 178ꢀ187.
13.
14.
Cheng, Y.ꢀT.; Huber, G. W., Green Chemistry 2012, 14, 3114ꢀ3114.
Chang, C.ꢀC.; Je Cho, H.; Yu, J.; Gorte, R. J.; Gulbinski, J.; Dauenhauer, P.; Fan, W.,
Green Chemistry 2016, 18, 1368ꢀ1376.
15. Wang, D.; Osmundsen, C. M.; Taarning, E.; Dumesic, J. A., ChemCatChem 2013, 5,
2044ꢀ2050.
16.
Williams, C. L. Production of Sustainable Aromatics from Biorenewable Furans.
University of Massachusetts, Amherst, 2014.
17.
Pidko, E. A., ACS Catalysis 2017. DOI: 10.1021/acscatal.7b03343
18. Yin, J.; Shen, C.; Feng, X.; Ji, K.; Du, L., ACS Sustainable Chemistry & Engineering
2017. DOI: 10.1021/acssuschemeng.7b03297
19. Rohling, R. Y.; Hensen, E. J. M.; Pidko, E. A., ChemPhysChem 2017. DOI:
10.1002/cphc.201701058
Rohling, R.; Uslamin, E. A.; Zijlstra, B.; Tranca, I.; Filot, I. A. W.; Hensen, E. J. M.;
20.
Settle, A. E.; Berstis, L.; Rorrer, N. A.; RomanꢀLeshkov, Y.; Beckham, G. T.; Richards,
R. M.; Vardon, D. R., Green Chemistry 2017. DOI: 10.1039/C7GC00992E
21.
R., ACS Catalysis 2017, 148ꢀ187.
22. Chang, C.ꢀC.; Green, S. K.; Williams, C. L.; Dauenhauer, P. J.; Fan, W., Green
Chemistry 2014, 16, 585ꢀ588.
Li, H.; Riisager, A.; Saravanamurugan, S.; Pandey, A.; Sangwan, R. S.; Yang, S.; Luque,
23.
24.
Cheng, Y.ꢀT.; Huber, G. W., ACS Catalysis 2011, 1, 611ꢀ628.
Gallego, E. M.; Portilla, M. T.; Paris, C.; LeónꢀEscamilla, A.; Boronat, M.; Moliner, M.;
Corma, A., Science 2017, 355, 1051ꢀ1054.
25.
26.
Serra, J. M.; Guillon, E.; Corma, A., Journal of Catalysis 2004, 227, 459ꢀ469.
Teixeira, I. F.; Lo, B. T. W.; Kostetskyy, P.; Stamatakis, M.; Ye, L.; Tang, C. C.;
Mpourmpakis, G.; Tsang, S. C. E., 2016, 13061.
27. Ye, L.; Teixeira, I.; Lo, B. T. W.; Zhao, P.; Edman Tsang, S. C., Chemical
Communications 2017, 53, 9725ꢀ9728.
28. Ye, L.; Lo, B. T. W.; Qu, J.; Wilkinson, I.; Hughes, T.; Murray, C. A.; Tang, C. C.;
Tsang, S. C. E., Chemical Communications 2016, 52, 3422ꢀ3425.
29. Kondo, J. N.; Ito, K.; Yoda, E.; Wakabayashi, F.; Domen, K., The Journal of Physical
Chemistry B 2005, 109, 10969ꢀ10972.
30. Spoto, G.; Geobaldo, F.; Bordiga, S.; Lamberti, C.; Scarano, D.; Zecchina, A., Topics in
Catalysis 1999, 8, 279ꢀ292.
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4
5
6
7
8
31.
32.
Duan, H. Q.; Yan, R.; Koe, L. C. C.; Wang, X. L., Chemosphere 2007, 66, 1684ꢀ1691.
Nikbin, N.; Do, P. T.; Caratzoulas, S.; Lobo, R. F.; Dauenhauer, P. J.; Vlachos, D. G.,
2013, 297, 35ꢀ43.
33.
3, 2012ꢀ2019.
Vaitheeswaran, S.; Green, S. K.; Dauenhauer, P.; Auerbach, S. M., ACS Catalysis 2013,
9
34.
35.
Kozuch, S.; Shaik, S., Acc. Chem. Res. 2011, 44, 101ꢀ110.
John, I. G.; Radom, L., Journal of the American Chemical Society 1978, 100, 3981ꢀ3991.
10
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60
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SYNOPSIS TOC: A new synthetic strategy to convert biomass-derived unsubstituted furan to aromatics at high yield es-
pecially to ethylbenzene using bio-derived ethanol instead of non-renewable ethylene over zeolite catalysts, while greatly
reducing the formation of the side product benzofuran, over zeolite catalysts in a single pot green synthesis.
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