Production of renewable p-xylene from 2,5-dimethylfuran via Diels-Alder cycloaddition and dehydrative aromatization reactions over silica-alumina aerogel catalysts

Article abstract of DOI:10.1016/j.catcom.2015.07.008

We report the selective conversion of biomass-derived 2,5-dimethylfuran (DMF) to p-xylene (～ 70% selectivity) through Diels-Alder cycloaddition and subsequent dehydration with silica-alumina aerogel (SAA) catalysts. The high activity of SAA can be attributed to its high surface area, large mesoporous volume, and high acid site concentrations. The conversion of DMF and the yield of p-xylene were strongly dependent on the silica alumina ratio of SAA. A higher aluminum content in SAA led to a progressive increase in the concentration of Br?nsted acid sites and a corresponding increase in the p-xylene production rate. The effect of solvent on the production of p-xylene was examined, and it was found that the p-xylene production rate increases significantly in polar aprotic solvents (i.e. 1,4-dioxane).

Full text of DOI:10.1016/j.catcom.2015.07.008

Production of renewable p-xylene from 2,5-dimethylfuran via Diels-Alder
cycloaddition and dehydrative aromatization reactions over silica alumina
aerogel catalysts
Yanuar Philip Wijaya, Dong Jin Suh, Jungho Jae
PII:
DOI:
Reference:
S1566-7367(15)30017-0
doi: 10.1016/j.catcom.2015.07.008
CATCOM 4380
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
18 May 2015
9 July 2015
11 July 2015
Please cite this article as: Yanuar Philip Wijaya, Dong Jin Suh, Jungho Jae, Production
of renewable p-xylene from 2,5-dimethylfuran via Diels-Alder cycloaddition and dehy-
drative aromatization reactions over silica alumina aerogel catalysts, Catalysis Communi-
cations (2015), doi: 10.1016/j.catcom.2015.07.008
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ACCEPTED MANUSCRIPT
Production of renewable p-xylene from 2,5-dimethylfuran via Diels-Alder
cycloaddition and dehydrative aromatization reactions over silica alumina
aerogel catalysts
Yanuar Philip Wijaya1, Dong Jin Suh1,2, Jungho Jae1,2,*
1 Clean Energy Research Center, Korea Institute of Science and Technology, Hwarang-ro 14-
gil 5, Seongbuk-gu, Seoul 136-791, Republic of Korea;
2 Department of Clean Energy and Chemical Engineering, Korea University of Science and
Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-333, Republic of Korea.
*jjae@kist.re.kr
Abstract
We report the selective conversion of biomass-derived 2,5-dimethylfuran (DMF) to p-
xylene (~70% selectivity) through Diels-Alder cycloaddition and subsequent dehydration
with silica alumina aerogel (SAA) catalysts. The high activity of SAA can be attributed to its
high surface area, large mesoporous volume, and high acid site concentrations. The
conversion of DMF and the yield of p-xylene were strongly dependent on the silica alumina
ratio of SAA. A higher aluminum content in SAA led to a progressive increase in the
concentration of Brønsted acid sites and a corresponding increase in the p-xylene production
rate. The effect of solvent on the production of p-xylene was examined, and it was found that
the p-xylene production rate increases significantly in polar aprotic solvents (i.e. 1,4-dioxane).
Keywords: cycloaddition, Diels-Alder, 2,5-dimethylfuran, p-xylene, silica-alumina aerogels
(SAA)

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1. Introduction
The development of processes that convert biomass into fuels and chemicals are essential
to reduce dependence on non-renewable resources such as fossil fuels [1, 2]. In this regard,
research into the production of the commodity chemicals such as benzene, toluene, and
xylenes from biomass has rapidly expanded in the past decade [3-5]. Especially, p-xylene is
one major chemical of interest due to the increasing global consumption of terephthalic acid
(TPA), used in the manufacture of plastic containers, synthetic fibers, and many other
products [5-10].
A promising approach has recently been demonstrated for the production of renewable p-
xylene. Williams et al. reported the one-pot conversion of biomass-derived 2,5-dimethylfuran
(DMF) to p-xylene with good selectivity (~75%) through a Diels-Alder cycloaddition
reaction over H-Y zeolite [11]. The conversion occurs in two-steps in which the first step is
the Diels-Alder cycloaddition of DMF and ethylene to form an oxanorbornene cycloadduct
intermediate and the second step is the dehydration of the resulting cycloadduct to p-xylene,
as shown in Fig. 1. Competing side reactions such as the hydrolysis of DMF to 2,5-
hexanedione (HDO) and the alkylation of p-xylene with ethylene can also occur and reduce
p-xylene selectivity. Chang et al. recently showed that the addition of an aliphatic solvent, n-
heptane, and the use of H-Beta zeolite further increase p-xylene selectivity to 90% by
suppressing side reactions such as the formation of HDO [12]. Gas-phase DFT calculation
showed that the Diels-Alder reaction of DMF and ethylene is thermally feasible (barrier of
24.7 kcal/mol), whereas the dehydration of the cycloadduct intermediate cannot proceed
uncatalyzed (barrier of 58.0 kcal/mol) [13, 14]. The introduction of Brønsted acidic H-Y
zeolite significantly lowered the dehydration barrier to 19 kcal/mol, indicating the necessity
of a Brønsted acid catalyst. However, Brønsted acids did not show any potential for decrease

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in the Diels-Alder reaction barrier, thereby making the uncatalyzed Diels-Alder reaction the
rate-determining step for p-xylene production [12].
In addition to microporous zeolites, other types of solid acid catalysts have demonstrated
high activity for the production of p-xylene. Wang et al. showed that good selectivity (~77%)
to p-xylene can be achieved with amorphous WOx-ZrO2 and niobic acid due to its strong
Brønsted acidity [15]. In a patented study, Brandvold reported that acid-washed activated
carbon can produce p-xylene with 30% yield [16].
In this work, we investigate the Diels-Alder cycloaddition and subsequent dehydration of
DMF and ethylene using silica alumina aerogel (SAA) catalysts. SAA demonstrates
comparable activity for p-xylene production to H-Beta zeolite, which has been reported as the
most active catalyst, under identical reaction conditions. A series of SAA catalysts with
different Si/Al ratios were prepared and tested to study the effect of acid site density on the p-
xylene production. We also examine the impact of solvent choice on the p-xylene yield using
several polar and non-polar solvents.
2. Experimental
2.1. Catalyst preparation and characterization
H-ZSM-5 (SiO2/Al2O3 = 30), H-Y (SiO2/Al2O3 = 30), H-BEA-38 (SiO2/Al2O3 = 38), and
H-BEA-25 (SiO2/Al2O3 = 25) were purchased from Zeolyst. SO4-ZrO2 (SZ) and WOx-ZrO2
were purchased from Alfa Aesar. SiO2–Al2O3 (SA, SiO2/Al2O3 = 11.2) was purchased from
Sigma-Aldrich. Zirconium phosphate (Zr-P) was prepared by a co-precipitation method at a
molar ratio of P/Zr = 2 as described elsewhere [17]. Acid-washed graphene oxide (GO) was
prepared by impregnation of the graphene oxide with 60% phosphoric acid and followed by
thermal activation at 1073 K. Silica-alumina aerogels (SAA) with different Si/Al ratios were
prepared using a sol-gel method followed by CO2 supercritical drying, based on the method

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described elsewhere [18-21]. All the catalysts were calcined in a muffle furnace at 773-873 K
for 4 h prior to reactions.
The compositions of the prepared aerogels were measured using inductively coupled
plasma atomic emission spectroscopy (ICP-AES, Polyscan-61E). Based on the ICP-AES
results, the silica-alumina aerogels containing Al/(Si+Al) = 0.12, 0.23, 0.33, 0.57, and 0.73
(mol/mol) were denoted as SAA-12, SAA-23, SAA-33, SAA-57, and SAA-73, respectively.
In addition, alumina aerogel was denoted as AA. All the aerogel catalysts were further
characterized by N2-physisorption (BELSORP-mini II), NH3-temperature programmed
desorption (NH3-TPD, BELCAT-B), and pyridine-Fourier transform infrared spectroscopy
(pyridine-FT-IR, Jasco FT/IR-4100 spectrometer). Detailed procedures for the synthesis and
characterization of the catalysts are given in the Supporting Information.
2.2. Catalytic experiments
Reactions were performed in a stainless steel 150 mL Parr reactor. DMF was reacted
with catalysts at a loading of 0.15±0.05 g catalyst and 3.9 mL DMF (10 wt% initial
concentration) in various solvents. Before reaction, the reactor was purged with N2 and then
pressurized to 20–30 bar with ethylene gas. The reactor was then heated up to 523 K and
stirred at 300±50 rpm with a gas entrainment impeller. After reaction, liquid products were
collected, filtered, and analyzed by using a gas chromatography equipped with flame
ionization detector (GC-FID, Agilent 7890A). The products were identified and quantified
based on the retention times and response factors of standard chemicals.
3. Results and Discussion
3.1. Effect of different acid catalysts

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The Diels-Alder cycloaddition reaction of DMF and ethylene was studied with different
types of acid catalysts at 523 K for 4 h. Fig. 2 shows the conversion of DMF, the selectivity
to p-xylene, and the rate of p-xylene formation over several acid catalysts, and Table 1
summarizes the pore structure and acid sites of the catalysts as determined by N2-
physisorption and NH3-TPD measurements, respectively. Among the tested zeolite catalysts,
H-BEA-25 showed the highest conversion of DMF (55%) and the highest rate of p-xylene
formation (9.63 mmol/g cat.h). H-ZSM-5 and H-Y zeolite had relatively low conversions of
DMF (6.6 and 23.3%, respectively) and low rates of p-xylene formation (0.17 and 4.64
mmol/g cat.h). These results are consistent with prior work by Chang et al. [12], who
reported that the reaction with H-BEA is more active than that with H-ZSM-5 and H-Y
zeolite. Especially, the relatively low activity of H-ZSM-5 can be attributed to the slower
diffusion of the reactants and products, such as DMF/ethylene cycloadduct, within the
channels of H-ZSM-5 (5.5 - 5.6 Å) than within H-BEA-25 (6.6 - 6.7 Å) and H-Y (7.4 Å).
Compared to microporous zeolites, Zr-P, sulfated zirconia (SZ), WOx-ZrO2, and acid-
washed graphene oxide (GO) all showed significantly low activity for the production of p-
xylene. Although WOx-ZrO2 and acid-washed activated carbon showed high selectivity to p-
xylene in previous studies [15, 16], very low selectivity to p-xylene (<30%) was observed
with these catalysts here, possibly due to their low surface area or the absence of strong
Brønsted acid sites. Amorphous silica alumina (SA) with Si/Al = 5.6 also exhibited low
activity and low selectivity to p-xylene (<35%). Meanwhile, the silica alumina aerogel (SAA-
57) showed remarkable selectivity to p-xylene (55%) and a high rate of p-xylene formation
(9.81 mmol/g cat.h). The high activity of SAA-57 may be due to its high acid site density
(1.16 mmol/g) and high surface area (411 m2/g), which are comparable to those of H-BEA-25
as shown in Table 1. Importantly, SAA-57 has significantly larger pores which are 28 nm in

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diameter and a higher total mesoporous volume of 1.207 cm3/g compared to SA with pores
5.52 nm in diameter and a mesoporous volume of 0.473 cm3/g.
Overall, H-BEA-25 and SAA-57 are the most active and selective catalysts for this
reaction; they are able to convert DMF with more than 50% selectivity to p-xylene. At the
higher conversion (XDMF > 75%), SAA-57 was able to produce the higher yield of p-xylene
than H-BEA-25.
3.2. Effect of the Si/Al ratio of silica-alumina aerogels (SAA)
Because SAA-57 showed the highest rate of p-xylene production among the tested solid
acid catalysts, the aerogel catalysts were further investigated by varying the Si/Al ratio. Five
SAA samples with different Al/(Si+Al) compositions (0.73, 0.57, 0.33, 0.23, and 0.12) were
prepared for this purpose. N2 adsorption measurements confirmed that all of the aerogel
catalysts (except SAA-12) had high BET surface areas in the range of 351–473 m2/g, large
mesoporous volumes of 0.632–1.207 cm3/g, and monodisperse mesopores of approximately
18.51–28.07 nm (see Table 1).
NH3-TPD measurements revealed that the number of acid sites was proportional to the
Al content of the SAAs. The total number of acid sites increased with an increase in
Al/(Si+Al) in the following order: SAA-73 > SAA-57 > SAA-33 > SAA-23 ≈ SAA-12 (see
Table 1). The FT-IR spectra after pyridine adsorption at 423 K were recorded to quantify the
amount of Brønsted and Lewis acid sites as shown in Table 2. The amount of both Brønsted
and Lewis acid sites increased as the mole fraction of Al for the SAAs was increased up to
0.57 and then decreased with a further increase in the Al mole fraction. However, the ratio of
Brønsted to Lewis acid site density did not exhibit any correlation with the Al/(Si+Al)
compositions of SAAs.

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The conversion, product selectivity, and yield of p-xylene as a function of the bulk Si/Al
ratio are shown in Fig. 3. The conversion of DMF and the yield of p-xylene increased with a
decrease in the Si/Al ratio from 9 to 1 and then decreased with a further decrease in the Si/Al
ratio. The highest conversion of DMF (90%) and the highest yield of p-xylene (60%) were
obtained at Si/Al = 1. The alumina aerogel (AA) showed significantly low activity toward p-
xylene production compared with the SAAs, indicating that Lewis acid sites are not effective
at catalyzing the dehydration of the cycloadduct.
The conversion of DMF and the yield of p-xylene showed a close correlation with the
concentrations of the Brønsted and Lewis acid sites over the SAAs. The yield of p-xylene
increased linearly with the density of acid sites. It has been shown that the initial Diels-Alder
reaction of DMF and ethylene proceeds uncatalyzed and the overall rate of p-xylene
formation is controlled by the catalyzed dehydration of the cycloadduct for H-Y zeolite and
WOx-ZrO2 [11, 13, 15, 22]. The rate of p-xylene formation increased with an increase in the
concentration of Brønsted acid sites [22] . Thus, the variation of the yield of p-xylene with
different Si/Al ratios of the SAAs can be explained by the dependence of the p-xylene
production rate on the concentration of the Brønsted acid sites.
In addition to the effect of acid site concentrations, the change of the p-xylene yield over
SAAs with different Si/Al ratios may be partially caused by the different deactivation
performances of the SAAs because the deactivation of the catalysts occurred during the
reaction by the formation of heavy oligomers on the catalyst surface (See Fig. S2). To check
this possibility, the initial rates of p-xylene formation were measured over SAAs (See Fig.
S4). The initial rate of p-xylene formation had linear dependence on the concentration of the
Brønsted acid sites over the SAAs, suggesting that the contribution from the catalyst
deactivation is insignificant.

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For all of the aerogel catalysts, the selectivity to p-xylene was between 50–70%. The
formation of several side products was also observed, as reported previously [11, 15]. These
side products include HDO formed by the hydrolysis of DMF, 3-methyl-2-cyclopentenone
(cyclopentenone) formed by the intramolecular aldol reaction of HDO, 1-methyl-4-
propylbenzene (alkylated) formed by the alkylation of p-xylene with ethylene, 3,6-dimethyl-
2-cyclohexen-1-one (cyclohexenone) formed by the isomerization of the DMF/ethylene
cycloadduct, and oligomers formed by the secondary addition of DMF or ethylene (see Fig.
1).
3.3. Effect of different solvents
The Diels-Alder reaction of DMF and ethylene was carried out in different types of
solvents, including heptane (non-polar), dioxane (polar aprotic), tetrahydrofuran (THF, polar
aprotic), and isopropanol (IPA, polar protic) to investigate solvent effects, which may reduce
the competing side reactions and increase the p-xylene selectivity. It has been shown that the
use of heptane as a solvent greatly reduces side reactions such as the hydrolysis of DMF and
the formation of oligomers from DMF [11, 23].
Fig. 4 shows the conversion of DMF, the product selectivity, and the yield of p-xylene in
various solvents with SAA-57 and H-BEA-25 catalysts. For both catalysts, the conversion of
DMF and the yield of p-xylene increased in the following order: IPA < heptane < THF <
dioxane, whereas the p-xylene selectivity increased in the following order: IPA < heptane ≈
dioxane < THF, demonstrating an enhanced rate of p-xylene formation in polar aprotic
solvents. Reactions in IPA, a polar protic solvent, exhibited the lowest p-xylene yields and
high selectivity to HDO. This is attributed to the instability of IPA under the applied reaction
conditions, where IPA is dehydrated to propene or 2-isopropoxypropane and releases water,
thereby increasing the hydrolysis of DMF to HDO.

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The higher p-xylene yields in the polar aprotic solvents, including dioxane and THF,
compared to heptane may be due to either the enhanced Diels-Alder reaction rate or the
enhanced dehydration reaction rate. It is well established that the Diels-Alder reaction rate
increases when polar protic solvents such as water and ethylene glycol are used due to the
hydrophobic packing and hydrogen bonding interaction [24-27]. However, the cases of polar
aprotic solvents such as dioxane have rarely been reported. The direct measurement for the
rates of cycloadduct formation in different solvents was not possible because the formation of
the cycloadduct is not favorable thermodynamically at 523 K (ΔGrxn= 2.28 kcal/mol),
whereas the production of p-xylene is overwhelming favorable (ΔGrxn= −38.56 kcal/mol)
[11, 28]. Moreover, considering that the rate of p-xylene formation depends on the
concentration of Brønsted acid sites, the overall rate is likely limited by the dehydration of
the cycloadduct under the reaction conditions investigated. Therefore, compared to nonpolar
solvents, the higher p-xylene yields in the polar aprotic solvents can be attributed to the
enhanced dehydration rate.
To test this hypothesis, the rates of p-xylene formation at low conversion in different
solvents were measured with H-BEA-25 at different solid acid concentrations, as described in
Fig. 5. At a high solid acid concentration (7 mM), the rates of p-xylene formation in different
solvents were similar to each other, indicating that the solvent effect is negligible when a
sufficient number of Bronsted acid sites is available for the dehydration reaction and when
the overall rate of p-xylene production is limited by the Diels-Alder reaction. On the other
hand, at low solid acid concentrations (1.5 and 3 mM), the rates of p-xylene formation in
dioxane and THF were higher than those in heptane, demonstrating an enhanced dehydration
reaction rate in polar solvents. Also, this reactivity trend at low conversion suggests that the
solvent effect is not caused by the change of deactivation performance due to the stronger
extraction capability of oligomers from the catalyst surface. It is possible that the use of a

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polar solvent stabilizes charged intermediates in the dehydration of the cycloadduct, thereby
facilitating the dehydration reaction. Similar behavior was reported by Mellmer et al. and
Weingarten et al. in their investigations of solvent effects for the dehydration of biomass-
derived molecules [29, 30]. The use of polar aprotic solvents such as -valerolactone (GVL),
THF, and dioxane has been shown to lead to significant increases in reaction rates and
product selectivity for the dehydration of xylose and 1,2-propanediol, compared to water, due
to the stabilization of the acidic proton and the protonated transition states [29]. Overall, these
results demonstrate that the use of polar aprotic solvents accelerates the overall rate of p-
xylene production by increasing the dehydration reaction rate.
4. Conclusions
In summary, amorphous silica alumina aerogel (SAA) is a highly active catalyst for the
production of p-xylene from 2,5-dimethylene (DMF) and ethylene through a combination of
Diels-Alder cycloaddition and dehydration reactions. The high activity of SAA can be
attributed to its high surface area, large mesoporous volume, and high acid site
concentrations. Over the SAA catalysts with different Si/Al ratios, the conversion of DMF
and the yield of p-xylene are proportional to the concentration of the Brønsted acid sites,
indicating that the overall rate of p-xylene production is limited by the dehydration of the
cycloadduct of DMF and ethylene under the reaction conditions investigated. Among the
tested SAAs, the highest p-xylene yield of 60% was obtained with the SAA with Si/Al = 1
(SAA-57). The solvent plays a significant role in enhancing the rate of p-xylene production.
Polar solvents such as 1,4-dioxane lead to significant increases in the p-xylene production
rate compared to heptane. This enhanced activity is likely due to the stabilization of charged
intermediates in the dehydration of the cycloadduct, thereby facilitating the dehydration
reaction.

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Acknowledgements
This work was supported by the R&D Convergence Program of NST (National Research
Council of Science & Technology) of Republic of Korea /Korea Institute of Science and
Technology (KIST) (Project No. 2E25402). We acknowledge Dr. J. S. Yoon for providing
the aerogel samples.
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Ethylene and 2,5-Dimethylfuran Catalyzed by H-BEA, J. Phys. Chem. C, 118 (2014) 22090-
22095.
[29] M.A. Mellmer, C. Sener, J.M.R. Gallo, J.S. Luterbacher, D.M. Alonso, J.A. Dumesic,
Solvent Effects in Acid‐Catalyzed Biomass Conversion Reactions, Angew. Chem. Int. Ed.,
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Aprotic Solvents, ChemCatChem, 6 (2014) 2229-2234.

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Table 1. Pore structures and acid sites of the catalysts (Si2Al, SiAl, 7Si3Al, 8Si2Al, and
9SiAl are silica-alumina aerogels, whereas SiO2-Al2O3 is a silica-alumina catalyst).
Acid
sites
a
b
c
d
e
f
SBET
Smicro
Sexternal
Vpore
Vmicro
Vmeso Dmeso
Si/Al
ratio
Catalyst
Code
(m2g-1)
(m2g-1)
(m2g-1)
(cm3g-1)
(cm3g-1) (cm3g-1)
(nm)
(mmol.g-1)
H-BEA-25
H-BEA-38
H-ZSM-5
H-Y
Zr(HPO4)2•H2O
WOx-ZrO2
SO4-ZrO2
SiO2-Al2O3
Si2Al
12.5
19
CP814E
CP814C
CBV3024E
CBV720
Zr-P
545
574
358
739
77
367
475
297
634
10
178
99
0.493
0.342
0.227
0.473
0.117
0.231
0.231
0.679
0.787
1.387
1.222
0.905
0.259
0.269
0.282
0.179
0.363
0.033
0.038
0.072
0.205
0.155
0.180
0.189
0.208
0.084
0.225
0.060
0.049
0.110
0.084
9.36
3.77
2.44
4.27
3.77
1.12[12]
1.21[12]
1.10[12]
0.58
15
61
15
105
67
N/A
N/A
N/A
5.6
0.5
1
0.78
WZ
88
6
82
0.193 10.70
0.74
SZ
162
489
351
411
432
473
189
46
116
419
275
343
380
386
150
0.159
0.473
8.19
5.52
1.23
SA
70
0.91
SAA-73
SAA-57
SAA-33
SAA-23
SAA-12
77
0.632 18.51
1.207 28.07
1.034 24.41
0.698 24.41
2.24
SiAl
68
1.16
7Si3Al
2.3
4
52
0.69
8Si2Al
87
0.60
9SiAl
9
39
0.175
3.77
0.63
a BET surface area
b Micropore area obtained by t-plot analysis
c External surface area obtained by t-plot analysis combined with BET surface area
d Single point adsorption total pore volume (P/P0=0.99)
e Single point adsorption micro pore volume (P/P0=0.20)
f Mean mesopore diameter obtained by BJH method
Table 2. Concentrations of the acid sites measured by pyridine-FT-IR.
Catalyst
Al/(Si+Al)
ρ
Brønsted (μmol/g)
ρ
Lewis (μmol/g)
BA/LA
SAA-73
SAA-57
SAA-33
SAA-23
SAA-12
0.73
0.57
0.33
0.23
0.12
0.074
0.097
0.087
0.081
0.065
0.012
0.023
0.014
0.011
0.010
6.1
4.2
6.4
7.5
6.8

ACCEPTED MANUSCRIPT
Fig. 1. Reaction pathway for the production of p-xylene via Diels-Alder cycloaddition
between DMF and ethylene, and subsequent dehydration of an oxanorbornene cycloadduct
[15].

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Fig. 2. Conversion, p-xylene selectivity, and rates of p-xylene formation in the Diels-Alder
cycloaddition reaction of DMF and ethylene (20 bar) in heptane as a solvent at 523 K for 4 h
with various catalysts.

ACCEPTED MANUSCRIPT
Fig. 3. Conversion and product selectivity for the reaction of DMF in dioxane with ethylene
(30 bar) at 523 K for 6 h with SAAs with different Si/Al ratios.

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Fig. 4. Conversion and product selectivity for the reaction of DMF with ethylene (30 bar) at
523 K for 6 h in various solvents with SAA-57 and H-BEA-25.

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Fig. 5. Rate of p-xylene production with H-BEA-25 at 523 K at 1.5, 3, and 7 mM H-BEA
acid site concentrations (R/C: reactant to catalyst mass ratio).

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Highlights
 Cycloaddition of dimethylfuran for renewable p-xylene with silica alumina aerogels
 The p-xylene yield is a function of the concentrations of the Brønsted acid sites.
 The rate of p-xylene production increases significantly in polar aprotic solvents.