Selectivity Control in the Tandem Aromatization of Bio-Based Furanics Catalyzed by Solid Acids and Palladium

Article abstract of DOI:10.1002/cssc.201600776

Bio-based furanics can be aromatized efficiently by sequential Diels–Alder (DA) addition and hydrogenation steps followed by tandem catalytic aromatization. With a combination of zeolite H-Y and Pd/C, the hydrogenated DA adduct of 2-methylfuran and maleic anhydride can thus be aromatized in the liquid phase and, to a certain extent, decarboxylated to give high yields of the aromatic products 3-methylphthalic anhydride and o- and m-toluic acid. Here, it is shown that a variation in the acidity and textural properties of the solid acid as well as bifunctionality offers a handle on selectivity toward aromatic products. The zeolite component was found to dominate selectivity. Indeed, a linear correlation is found between 3-methylphthalic anhydride yield and the product of (strong acid/total acidity) and mesopore volume of H-Y, highlighting the need for balanced catalyst acidity and porosity. The efficient coupling of the dehydration and dehydrogenation steps by varying the zeolite-to-Pd/C ratio allowed the competitive decarboxylation reaction to be effectively suppressed, which led to an improved 3-methylphthalic anhydride/total aromatics selectivity ratio of 80 % (89 % total aromatics yield). The incorporation of Pd nanoparticles in close proximity to the acid sites in bifunctional Pd/H-Y catalysts also afforded a flexible means to control aromatic products selectivity, as further demonstrated in the aromatization of hydrogenated DA adducts from other diene/dienophile combinations.

Full text of DOI:10.1002/cssc.201600776

DOI: 10.1002/cssc.201600776
Full Papers
Selectivity Control in the Tandem Aromatization of Bio-
Based Furanics Catalyzed by Solid Acids and Palladium
[
a]
[a, b]
[c]
[c]
Homer C. Genuino, Shanmugam Thiyagarajan,
Jan C. van der Waal, Ed de Jong,*
[
b]
[b]
[a]
[a]
Jacco van Haveren, Daan S. van Es,* Bert M. Weckhuysen, and Pieter C. A. Bruijnincx*
Bio-based furanics can be aromatized efficiently by sequential
Diels–Alder (DA) addition and hydrogenation steps followed
by tandem catalytic aromatization. With a combination of zeo-
lite H-Y and Pd/C, the hydrogenated DA adduct of 2-methylfur-
an and maleic anhydride can thus be aromatized in the liquid
phase and, to a certain extent, decarboxylated to give high
yields of the aromatic products 3-methylphthalic anhydride
and o- and m-toluic acid. Here, it is shown that a variation in
the acidity and textural properties of the solid acid as well as
bifunctionality offers a handle on selectivity toward aromatic
products. The zeolite component was found to dominate se-
lectivity. Indeed, a linear correlation is found between 3-meth-
ylphthalic anhydride yield and the product of (strong acid/
total acidity) and mesopore volume of H-Y, highlighting the
need for balanced catalyst acidity and porosity. The efficient
coupling of the dehydration and dehydrogenation steps by
varying the zeolite-to-Pd/C ratio allowed the competitive de-
carboxylation reaction to be effectively suppressed, which led
to an improved 3-methylphthalic anhydride/total aromatics se-
lectivity ratio of 80% (89% total aromatics yield). The incorpo-
ration of Pd nanoparticles in close proximity to the acid sites
in bifunctional Pd/H-Y catalysts also afforded a flexible means
to control aromatic products selectivity, as further demonstrat-
ed in the aromatization of hydrogenated DA adducts from
other diene/dienophile combinations.
Introduction
The high volatility of crude oil markets as well as the imple-
mentation of shale gas as a new hydrocarbon resource can
strongly impact the availability of some important commodity
offer an alternative sustainable resource for the production of
“drop-in” renewable aromatics that include terephthalic, (iso)-
phthalic, and trimellitic aromatic acids, which are essential pre-
[
1]
[2]
chemicals, including bulk aromatics. Sugar-derived furanics
cursors to various polymer products and fine chemicals.
Furanics-to-aromatics routes generally involve a two-step
catalytic conversion that consists of a symmetry-allowed [4+2]
Diels–Alder (DA) cycloaddition of a furanic diene with an ap-
propriate dienophile followed by a catalytic aromatization
step. An example of this route is the production of p-xylene
from ethylene and bio-based 2,5-dimethylfuran (DMF) by solid-
acid-catalyzed DA aromatization. For example, Williams et al.
used zeolite H-Y with a Si/Al ratio of 30 and zeolite H-Beta
with a Si/Al ratio of 12.5 for this reaction in heptane to achieve
[
a] Dr. H. C. Genuino, Dr. S. Thiyagarajan, Prof. Dr. B. M. Weckhuysen,
Dr. P. C. A. Bruijnincx
Inorganic Chemistry and Catalysis
Debye Institute for Nanomaterials Science
Utrecht University
Universiteitsweg 99, 3584 CG Utrecht (The Netherlands)
E-mail: p.c.a.bruijnincx@uu.nl
[b] Dr. S. Thiyagarajan, Dr. J. van Haveren, Dr. D. S. van Es
Food & Bio-based Research
[3]
Wageningen University and Research Centre
P.O. Box 17, 6700 AA Wageningen (The Netherlands)
E-mail: daan.vanes@wur.nl
75 and 90% p-xylene yields, respectively. Wang et al. later
demonstrated the synthesis of renewable benzene, toluene,
and p-xylene from (methylated) furans, also with ethylene,
[
c] Dr. J. C. van der Waal, Dr. E. de Jong
Avantium Chemicals
Zekeringstraat 29, 1014 BV Amsterdam (The Netherlands)
E-mail: ed.dejong@avantium.com
[4]
using various heterogeneous catalysts. Brønsted acid and
Lewis acid containing catalysts, such as WO -ZrO , niobic acid,
x
2
zeolite H-Y, and silica-alumina, were more active than catalysts
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under http://dx.doi.org/10.1002/
cssc.201600776.
that contained predominantly Lewis acid sites, such as g-Al O
2
3
and TiO (P25), which emphasizes the importance of strong
2
[4]
Brønsted acidity in the production of aromatics. In contrast,
Davis et al. showed that silica molecular sieves that contained
framework Lewis acid centers (e.g., Sn-, Zr-, and Zn-b zeolites),
catalyze the DA cycloaddition–dehydration reactions between
oxidized derivatives of 5-hydroxymethylfurfural (HMF) and eth-
ylene more efficiently than the corresponding Brønsted acidic
H-Al-b zeolite to give renewable-based terephthalic acid pre-
ꢀ
2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
This is an open access article under the terms of the Creative Commons
Attribution Non-Commercial NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited,
the use is non-commercial and no modifications or adaptations are
made.
This publication is part of a Special Issue celebrating “10 Years of Chem-
SusChem”. A link to the issue’s Table of Contents will appear here once
it is complete.
[5]
cursors.
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An important general limitation of the coupling of the key
DA reaction directly with the catalytic aromatization step is the
thermal instability of the intermediate DA adduct, which is the
The influence of the acidity of solid catalysts has been stud-
ied in some detail in the direct DA aromatization of DMF and
ethylene. Williams et al. showed that good selectivity to p-
xylene can be achieved at both low and high DMF conversion
[
6]
result of the reversible nature of the DA reaction. Therefore,
catalytic DA aromatization reactions need to be performed
typically either at a low temperature or a high ethylene pres-
sure to limit retro-DA activity. Addressing this competition be-
tween aromatization by acid-catalyzed dehydration and the
loss of the DA adduct to retro-DA, Mahmoud et al. reported
a two-step route to (substituted) phthalic anhydrides by sepa-
rating the DA addition step from dehydration and using meth-
[3a]
with an H-Y-2.6 zeolite as the catalyst. Interestingly, H-Y zeo-
lites with Si/Al ratios of 2.6, 30, and 40 showed almost identical
catalytic performances, and the p-xylene production rates were
independent of the number of available Brønsted acid sites
[3a]
(BAS), which suggests a noncatalytic rate-limiting step. In
a separate study in which WO -ZrO was used as the catalyst,
x
2
Wang et al. showed that the p-xylene production rate was line-
[6a]
[4]
anesulfonic acid with acetic anhydride for the latter step. In
an alternative approach, we recently developed a three-step,
furanics-to-aromatics route by introducing an intermediate,
mild hydrogenation step after the DA addition of, for example,
arly dependent on the amount of acid sites instead. Theoreti-
cal studies by Patet et al. later proposed this difference to be
result of a kinetic regime change in this tandem reaction and
[11]
to be typical for coupled uncatalyzed–catalyzed steps.
2
-methylfuran (MF) and maleic anhydride (MA). The thermally
In our previous study, involving a reaction that must be
mechanistically different from the above-mentioned studies,
we observed that H-VUSY (H-Y with a Si/Al ratio of 6) produces
a higher total aromatics yield (84%) than steam-calcined-only
stable oxanorbornane adduct (denoted as MFMA[H]) was then
[
7]
obtained in a high yield and purity. The subsequent one-pot,
tandem catalytic dehydration and dehydrogenation of the hy-
drogenated DA adduct in toluene then allowed efficient aro-
matization to yield the desired aromatic product, in this case
[7]
H-Y with a Si/Al ratio of 2.6 (75%) at full conversion, which
shows that performance in this case is not simply dictated by
the number of acid sites. It can thus be anticipated that the
type, amount, and strength of the acid sites and any meso-
porosity in H-Y zeolites will play important roles in the overall
3-methylphthalic anhydride, with some concomitant formation
[
7]
of o- and m-toluic acid as decarboxylated products. A g-lac-
tone, formed by the acid-catalyzed isomerization of MFMA[H],
was identified as the primary intermediate in the aromatization
reaction. The use of a physical mixture of Very Ultra Stable H-Y
zeolite (H-VUSY) with a Si/Al ratio of 6 as a solid Brønsted acid
and Pd/C as a dehydrogenation catalyst thus allowed the effi-
cient aromatization of MFMA[H] by this new liquid-phase route
[10e]
catalyst efficiency for this aromatization reaction.
Variation
of mesoporosity can, for example, limit side reactions and pre-
vent carbon loss. Therefore, the careful tuning of both acidity
and porosity of zeolite H-Y-based catalysts is expected to allow
control over selectivity to the desired aromatic product. As the
reaction to and the first step from the g-lactone intermediate
[
7]
to give high total aromatics yields.
[8]
We also showed recently that the hydrogenated DA adducts
can be converted conveniently to renewable aromatics in
a solid-phase reaction using only a solid acid, that is, zeolite H-
Y with a Si/Al ratio of 2.6, as the catalyst without any solvent
or dehydrogenation catalyst, to give the same aromatic prod-
are purely acid catalyzed, we here first explore the interplay
between the acidity and porosity of various zeolite H-Y materi-
als to control aromatic product selectivity in the liquid-phase
reaction in the absence of a separate dehydrogenation cata-
lyst. Given that the presence of a dehydrogenation catalyst im-
[
8]
[7]
ucts in high yield. Notably, for both the liquid- and solid-
phase aromatization processes, some variation in the solid acid
catalyst used already suggested that the selectivity to the de-
sired aromatics depends strongly on the structural characteris-
tics of the solid acid catalyst, in particular, its acidity and
micro/mesoporosity.
proves the total aromatics yield significantly, the ratio of Pd
(e.g., Pd/C) to H-Y in the physical mixture was also varied with
the goal to further increase the yield and selectivity to the de-
sired aromatic product. Finally, as the solid-acid- and Pd-cata-
[7]
lyzed steps in the tandem reaction are coupled, bifunctional
catalysts with Pd in close proximity to the acid functionalities
were expected to improve catalyst performance and have
been evaluated.
Among the different solid acids tested, the large-pore zeolite
H-Y with FAU topology performed the best in the aromatiza-
[
7,8]
tion reaction.
crystal as a result of slow mass transfer through the micro-
pores can potentially lead to catalyst deactivation by carbona- Results and Discussion
The retention of molecules within the zeolite
[
9]
ceous material deposition. To ensure optimal active site ac-
cessibility and to enhance the molecular transport of reactants
and products, mesopores in zeolite H-Y are commonly intro-
duced by postsynthetic modifications, such as sequential
steam–calcination and acid leaching, which result in an in-
Catalyst characterization
Four different H-Y zeolites with Si/Al molar ratios that ranged
from 2.6 to 40 were studied in the aromatization of the
MFMA[H] adduct. These materials are denoted as H-Y-x in
which x is the Si/Al ratio of the material. Zeolite H-Y-2.6 was
[
9,10]
creased external surface area and pore volume.
Hierarchical
FAU-type zeolites are thus formed with enhanced hydrother-
mal stability and altered compositions (i.e., Si/Al ratio) caused
by the removal of part of the framework Al from the lattice to
form extra-framework Al (EFAl) species, accompanied by
steamed by the manufacturer, NH -Y (Si/Al=2.55) being the
4
[10c,12]
parent zeolite.
Ultrastable Y zeolites are typically prepared
by steaming of NH -Y-2.55 at ~5008C, a second steaming step
4
at ~7008C, and finally acid-leaching to obtain the desired Si/Al
[
10]
[10c,12]
changes in intrinsic acidity.
ratio.
For example, H-Y-6 was steamed and acid-leached
&
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[
a]
Table 1. Textural and acidic properties of fresh and reused solid acid catalysts, including the Pd-loaded catalyst materials.
Solid acid BET surface t-plot
t-plot
micropore
area [m g
t-plot
Mesopore
Total pore
volume [cm g
BJH average
pore diameter strength of acid sites
[nm]
Amount, type, and
2
À1
3
À1
3
À1
catalyst
area [m g
]
external
surface
micropore volume volume [cm g
]
]
2
À1
3
À1
À1
]
[cm g
]
[(mmolNH3
weak
g
STP) (Tmax [8C])
2
À1
area [m g
]
strong
[
b]
H-Y-2.55
H-Y-2.6
H-Y-6
529
556
709
814
658
830
19
83
184
259
243
260
511
473
526
556
416
570
0.20
0.23
0.26
0.27
0.20
0.28
0
0.20
0.39
0.48
0.56
0.49
0.56
1.21
4.1
3.3
2.9
3.1
2.9
1.09 (225)
0.33 (180)
0.32 (178)
0.09 (169)
0.06 (154)
0.10 (159)
0.16
0.22
0.29
0.29
0.28
0.20 (350)
0.39 (318)
0.25 (329)
0.15 (309)
0.24 (334)
H-Y-30
H-Y-40
reused
[
c]
H-Y-30
Pd/H-Y-30 781
Pd/H-Y-40 620
249
199
533
421
0.26
0.21
0.29
0.25
0.55
0.46
3.0
3.3
0.12 (162)
0.08 (159)
0.23 (320)
0.24 (293)
[
d]
[d]
[a] Adsorption–desorption isotherms, PSD curves, and TPD-NH
3 4
profiles are presented in the Supporting Information. [b] Parent zeolite (calcined NH -Y, Si/
Al ratio of 2.55, CBV300). [c] After third reuse and (re)calcination. [d] Estimated values from poorly resolved desorption peaks (Figure S12).
NH -Y-2.55, whereas H-Y-30 and H-Y-40 are obtained after an
n˜ ꢀ3748 (SiÀOH silanol groups), 3640 (OH groups in supercag-
4
À1
extra steaming step and acid-leaching step from NH -Y-
es), and 3555 cm (OH groups in small cavities) observed for
4
[
10c,12]
2.55.
The textural properties of the different H-Y-x zeolite
H-Y-6, H-Y-30, and H-Y-40 (Figure S4), which correspond to
[13]
materials under study are summarized in Table 1. As expected,
strong framework OH groups (BAS). Three additional peaks
[
13b]
[13c]
N physisorption measurements showed that the ultrastabiliza-
2
at n˜ ꢀ3660 (AlÀOH groups),
3600 (strong),
and
À1
tion of zeolite H-Y resulted in an increase in the BET surface
area (providing a value proportional to the volume adsorbed
for these microporous systems), t-plot external surface area,
and total pore volume. The presence of mesopores in zeolite
H-Y-2.6 is likely the result of the partial dealumination of the
zeolite framework. The further increase in mesopore volume
upon increasing the Si/Al ratio is in line with previous re-
3518 cm (shoulder) were seen only in steamed and partially
acid-leached H-Y-6, which can explain the high amount of acid
sites of this sample. The stepwise adsorption of CO on the five
H-Y zeolites at low temperature provided additional insights
into the type, strength, and distribution of their acid sites (Fig-
À1
ure S5–S9). The distinct v(OH) band at n˜ ꢀ3640 cm is per-
turbed first at low equilibrium CO pressures and gives rise to
[
9,10]
À1
ports.
ratio of 59%, followed by H-Y-30 (52%, the same Vmesopore), H-Y-
(46%), and H-Y-2.6 (41%). Hysteresis loops were observed in
the adsorption and desorption isotherms for the various H-Y
As expected, H-Y-40 gave the highest Vmesopore/Vtotal
the development of a v(OH) band at n˜ ꢀ3275 cm accompa-
À1
nied by two broad bands near n˜ ꢀ3410 and 3465 cm , in
[13]
6
agreement with previous reports. Simultaneously, the v(CO)
À1
stretching band at n˜ ꢀ2180 cm grows (LAS). The low-fre-
[9]
À1
zeolites (Figure S1), typical of such mesoporous materials.
quency OH stretching band at n˜ ꢀ3555 cm was not per-
The pore size distribution (PSD) curves from the desorption
branch exhibit a sharp peak at ~4 nm and a peak that broad-
ens as the extent of dealumination increases (e.g., ~4–20 and
turbed by CO because CO cannot access the small sodalite
[13]
cages.
As shown previously, EFAl species contribute significantly to
[13]
~
4–45 nm for H-Y-2.6 and H-Y-30, respectively; Figure S2),
the generation of both the LAS and BAS of H-Y zeolites. The
which supports the increase in the degree of mesoporosity.
Furthermore, the peak maxima show a gradual shift to larger
pore diameters with the increase of the Si/Al ratio, which is
a consequence of the increasing amount of EFAl species re-
acidity of their OH groups is evident in the pronounced v(CO)
À1
band in H-Y-2.6 and H-Y-6 centered at n˜ ꢀ2165 cm at rela-
tively low equilibrium CO pressures, for example, ~0.6 mbar
(Figure 1a). Notably, the appearance of the well-known band
[
9]
À1
moved by the acid treatment.
at n˜ =2158 cm , recorded for H-Y-30 and H-Y-40 only, is attrib-
[
13e]
The total amount of acid sites in H-Y zeolites, as measured
by temperature-programmed desorption of ammonia (TPD-
uted to the interaction of SiOH with CO.
The appearance of
À1
a (weak) shoulder at n˜ ꢀ3465 cm (in H-Y-6) accompanied by
À1
NH ), decreased in the order H-Y-6>H-Y-2.6>H-Y-30>H-Y-40
another one at n˜ ꢀ3530 cm (in H-Y-2.6 and H-Y-6) after CO
3
(Table 1). Both H-Y-6 and H-Y-2.6 contain large amounts of
adsorption at, for example, ~1 mbar (Figure 1b), further dem-
weak acid sites (i.e., Lewis acid sites, LAS), whereas H-Y-30 and
H-Y-40 do not (Figure S3). For both types of acid sites, a shift
of the desorption maximum (Tmax) towards a lower tempera-
ture is observed as the extent of dealumination increases,
except for H-Y-30. In terms of the amount and strength of acid
sites, H-Y-40 is the least acidic and is expected to contain the
lowest quantity of EFAl species.
onstrates the presence of such acidic EFAl species, as observed
[13a]
previously.
Two bifunctional catalysts, 1 wt% Pd/H-Y-30 and 1 wt% Pd/
H-Y-40, were synthesized by incipient wetness impregnation.
The Vmesopore of Pd/H-Y-30 is the same as that of H-Y-30, but the
micropore area and volume decreased, which suggests that
some of the Pd nanoparticles (3.1Æ0.7 nm, determined by
transmission electron microscopy, TEM; Figure S10) are possi-
Fourier-transform infrared (FTIR) spectra of the four H-Y zeo-
[14]
lites and the parent sample under dehydrating conditions
bly located in the microporous domains. The CO-FTIR spec-
tra of Pd/H-Y-30 revealed the effect of Pd incorporation on the
À5
(
3008C, 10 mbar) show three distinct peak maxima located at
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ure S11). The reduction in the number of strong acid sites
(
BAS) was in agreement with the reduced amount and
strength of the high-temperature NH desorption peak of Pd/
3
H-Y-30 (Table 1, Figure S12). In Pd/H-Y-40, a decrease in the
mesopore volume and a clear shift of the peak maximum in
the PSD curve (Figure S14b) suggest that a significant portion
of the Pd nanoparticles (5.1Æ1.4 nm; Figure S13) are located
in the mesopore domains. Indeed, the v(OH) intensity of the
strong acid sites of H-Y-40 and Pd/H-Y-40 are very similar with
or without CO (Figure S15). For both bifunctional catalysts, the
observed increase in the amount of desorbed NH at low tem-
3
perature can be attributed to various amounts of Lewis acidic
[14b]
Pd centers.
Catalyst testing: Zeolites
The one-pot catalytic aromatization of the hydrogenated DA
adduct of 2-methylfuran and maleic anhydride (MFMA[H] 1) to
3-methylphthalic anhydride 4 using H-Y-2.6 in combination
with Pd/C is presented in Scheme 1. The g-lactone 2 (primary
intermediate) and the m-/o-toluic acids 5a/b are also included.
As aromatization and decarboxylation were also shown previ-
ously to occur to a limited extent in the presence of only H-Y-
[7]
2
.6, the catalytic aromatization of 1 was first investigated
with the acidic zeolites listed in Table 1 under reaction condi-
tions established previously (1.0 g of 1, 2008C, 24 h in tolu-
[7]
ene).
Among the four H-Y zeolites under study (10 wt% relative
to 1), H-Y-2.6 is the least active, but nevertheless shows high
selectivity to the desired product 4 (Table 2, entries 1–4). Nota-
bly, the use of only the H-Y zeolites allowed the observation
and identification of an additional intermediate, the 1,3-diene
anhydride isomer 3, which is suggested to be formed by zeo-
lite-catalyzed lactone ring opening followed by anhydride for-
mation. The identification of this intermediate was based on
Figure 1. Low-temperature FTIR spectra of the dehydrated H-Y-x zeolites
x=Si/Al ratio) in the a) v(CO) region at ~0.6 mbar CO and b) v(OH) region
at ~1 mbar CO. Stepwise, low-temperature CO-FTIR spectra of the five zeo-
(
lite H-Y materials under study are presented in Figures S5–S9.
1
the typical H NMR spectroscopic signature of the conjugated
acidity of the framework OH groups, as evidenced in the re-
duced intensity of the bands of both silanols and bridging
Si(OH)Al groups compared to the parent H-Y-30 sample (Fig-
1,3-cyclohexadiene ring (Figure S16). Moreover, the liquid-
phase zeolite-only-catalyzed aromatization reactions are ac-
companied by the formation of small amounts of the transfer
Scheme 1. Final step of the three-step (DA addition, hydrogenation, and catalytic aromatization) strategy to produce furan-derived aromatic compounds 4
and 5 using (tandem) zeolite H-Y and Pd/C and bifunctional Pd/H-Y catalysts.
&
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[
a]
Table 2. Reactivity of 1 with various zeolite H-Y catalysts.
[
b]
[c]
[c]
[e]
Entry Solid catalyst(s) Catalyst loading
Conversion
Yield [mol%] (selectivity [mol%])
Total aromatics yield Mole balance
[
d]
[mol%]
2
3
4
5a
5b
6
(selectivity) [%]
[%]
[
f]
1
2
3
4
5
6
7
8
9
H-Y-2.6
H-Y-6
H-Y-30
10
10
10
10
58
74
96
91
94
100
100
100
100
21 (36)
44 (59)
47 (49) 14 (15) 17 (18)
45 (49) 19 (21) 14 (15)
31 (33)
14
8 (14) 12 (21)
8 (11) 10 (14)
4 (7)
4 (5)
6 (6)
3 (3)
9 (10)
–
1 (2) 16 (28)
88
95
93
93
94
83
86
91
90
2 (3) 1 (2) 16 (22)
3 (3) 2 (2) 26 (27)
[f]
H-Y-40
–
3 (3) 17 (18)
[
g]
[f]
H-Y-40 + Pd/C
H-Y-2.6
H-Y-6
H-Y-30
H-Y-40
10 + Pd/C
–
2
45 (48)
25
2 (2) 1 (1) 56 (60)
33
33
33
33
21
14
14
8
7
6
7
9
60
71
68
69
[
[
[
f]
f]
f]
–
–
–
9
33
24
15
18
17
12
44
40
11
[a] Conditions: 1.0 g 1, 2008C, 24 h in toluene, Ar atmosphere (1 bar), catalyst(s) is indicated in the table. [b] wt% relative to 1. [c] Calculated by using q-
NMR spectroscopy using dimethyl 3,4-furan dicarboxylate as internal standard. [d] 4+5a+5b. [e] Mole balance determined from the total number of
moles calculated from the crude mixture after the reaction by NMR analysis. [f] Not observed. [g] 1 wt% Pd relative to H-Y-40.
hydrogenation product (4-methyl-4,5,6,7-tetrahydroisobenzo-
furan-1,3-dione 6), thought to result from (an isomer of) 3 by
double bond isomerization/hydrogenation as well as by the re-
(10 wt% relative to 2) under the same conditions (Table 3, en-
tries 1 and 2). These reactions resulted in the formation of the
same aromatic products, which emphasizes the role of 2 as
a primary intermediate, with H-Y-30 again slightly more active
and selective to 4 than H-Y-40. Notably, however, the yields of
aromatic products are significantly higher than those observed
if 1 was used as the substrate, indicating a change in acidity
requirement for further conversion of 2 compared to the con-
version of 1 to 2. The formation of decarboxylation products
was especially favored if we started from intermediate 2, as in-
dicated by an increase in the selectivity ratios of 5a/b to total
aromatics for zeolites H-Y-30 (from 33 to 48%) and H-Y-40
(from 17 to 51%), which suggests that the formation of aro-
matic products 4 and 5a/b have different orders in 2 and in-
volve different reaction pathways (i.e., 5a/b are not obtained
from 4 in the zeolite-only reactions).
The increase of the amount of different H-Y zeolites from 10
to 33 wt% (relative to 1) resulted in the full conversion of
1 for all catalysts, and intermediate 2 was not detected any-
more for H-Y-6, H-Y-30, and H-Y-40 (Table 2, entries 6–9). H-Y-30
again gave the highest amount of 4, which showed a more
than two-fold increase in yield. H-Y-6, which is the most acidic
zeolite (Table 1) but was treated much more moderately than
H-Y-30, gave the highest total aromatics yield at 71% at this
higher catalyst loading. However, H-Y-6 and H-Y-2.6 showed
considerably lower yields of 4 and noticeably higher yields of
5a+b. Indeed, the low-Si/Al-ratio H-Y zeolites show a higher
selectivity for decarboxylation (red and green bars, Figure 2),
lease of H (Table S1). Trace metal analysis of the H-Y samples
2
showed negligible concentrations of potential metal impurities
(Table S2) that could catalyze the required dehydrogenation
step; the acceptor-less H evolution step is, therefore, suspect-
2
ed to be noncatalytic under these reaction conditions. H-Y-30
is the most active catalyst, as 96% of 1 is converted and it
gives the highest total aromatics yield. Clearly, the conversion
order does not depend on the total acidity but more impor-
tantly on a combination of the nature of the acid sites and
mesoporosity and external surface area, as illustrated below.
The g-lactone 2 is the major product with all four zeolites, and
its accumulation at higher conversions suggests that it is in-
volved in the rate-determining step of the reaction. Both the
conversions and yields to 2 shown by H-Y-30 and H-Y-40 are
comparable (Table 2, entries 3 and 4), which demonstrates
a similar performance toward the acid-catalyzed isomerization
of 1. However, their total aromatics yields differ markedly,
which suggests that the number and type of acid sites matter
at the same mesoporosity (vide infra). The selectivity ratio of 4
to total aromatics (S4/S4+S5a+b) using H-Y-40 is significantly
higher at 83% than with H-Y-30 (67%), noting that the former
catalyst showed slightly lower activity and limited yields of 5a/
b.
The g-lactone 2 was then synthesized, isolated, and used as
a substrate for aromatization reactions with H-Y-30 and H-Y-40
[
a]
Table 3. Reactivity of 2 with H-Y-30 and H-Y-40 with or without a Pd/C catalyst.
[
d]
[f]
Entry
Solid acid
catalyst
Catalyst
loading
Pd/C
loading
Conversion
[mol%]
Yield [mol%] (Selectivity [mol%])
Total aromatics yield
(selectivity) [%]
Mole balance
[%]
[
b]
[c]
[e]
3
4
5a
5b
6
1
2
3
H-Y-30
H-Y-40
H-Y-40
10
10
10
0
0
1
93
90
94
11 (12)
14 (16)
–
30 (32)
27 (30)
50 (53)
21 (23)
20 (22)
28 (30)
6 (6)
8 (9)
4 (4)
6 (6)
7 (8)
5 (5)
57 (61)
55 (61)
82 (87)
81
86
93
[
g]
[a] Conditions: 1.0 g 2, 24 h in toluene, 2008C, Ar atmosphere (1 bar), catalyst(s) indicated in the table. [b] wt% relative to substrate 2. [c] wt% Pd relative
to H-Y-40. [d] Calculated by using q-NMR spectroscopy using dimethyl 3,4-furan dicarboxylate as internal standard. [e] 4+5a+5b. [f] Mole balance deter-
mined from the total number of moles calculated from the crude mixture after the reaction by NMR analysis. [g] Not observed.
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Figure 2. Selectivity ratios of aromatic products from 1 using solid acid catalysts (33 wt% relative to 1) with and without Pd. Results calculated from the data
presented in Tables 2, 4, and 5.
whereas H-Y-30 and H-Y-40 are in turn (much) more selective
for the production of 4 (black and blue bars). These results
may indicate that weak acid sites are involved in the decarbox-
ylation reaction. That H-Y-2.6 and H-Y-6 also contain strong
acid sites yet their selectivity to 4 is relatively low suggests
that their much higher concentration of weak acid sites than
in H-Y-30 and H-Y-40 pushes the reaction more towards decar-
boxylation. However, as shown above, the mesoporosity of
zeolites also changed on going from H-Y-2.6 to H-Y-6 and H-Y-
6
to H-Y-30. Thus, the high selectivity of H-Y-30 to 4 must also
reflect the positive effects of enhanced mesoporosity and ex-
ternal surface area because of the effective removal of agglom-
erated extra-framework materials that could hinder access to
the active sites. These effects seem to affect the selectivity to 4
more strongly than the amount of strong acid sites and
a higher strong-to-weak acid site ratio in H-Y-6. Importantly, on
going from H-Y-30 to H-Y-40, the Vmesopore remained constant,
which allowed the influence of the acid type ratio to be as-
sessed. With a strong acid sites and strong-to-weak acid site
ratio that is lower for H-Y-40, a decrease in the selectivity to 4
Figure 3. Correlation between the yield of 4 (full symbols) and selectivity
ratio of 4 to total aromatics (S4/S4+S5a+S5b; open symbols), and the acidi-
[
10d]
ty–mesoporosity coefficient (cstrong acid sites/ctotal acid sites·Vmesopore
)
of the four H-
Y catalysts at the full conversion of 1 (33 wt% H-Y relative to 1). Results cal-
culated from data presented in Tables 1 and 2.
(Table 2, entries 8 and 9) is then in line with the above. Taken
together, zeolite-only-catalyzed aromatization reactions clearly
show the need for a balanced concentration of acid sites and
accessibility to these sites to attain high selectivity to the de-
sired aromatic product. A strong correlation is thus found to
exist between the yield of 3-methylphthalic anhydride 4 at full
conversion and an acidity–mesoporosity coefficient, a com-
bined metric defined as the product of cstrong acid sites/ctotal acid sites
and Vmesopore of the H-Y zeolites (Figure 3). Recently, Keller et al.
introduced this performance descriptor for a zeolite-catalyzed
condensation reaction to emphasize the importance of the
[
10d]
combined influence of acidity and accessibility.
A similar
correlation is observed if the selectivity ratio of 4 to total aro-
matics is plotted against the same acidity–mesoporosity coeffi-
cient (Figure 3).
The reusability of H-Y-30, the best-performing solid acid cat-
alyst, was also assessed. H-Y-30 can be recycled efficiently after
regeneration by washing and calcination and gives the same
distribution of aromatic products after each reuse and regener-
Figure 4. Recyclability of H-Y-30 in the aromatization of 1 (1.0 g of 1,
33 wt% H-Y relative to 1, 2008C, 24 h in toluene, Ar atmosphere (1 bar); re-
generation by washing and calcination at 5008C, 6 h).
&
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ation (Figure 4). Indeed, TPD-NH experiments show that the
of intermediate 2 with 10 wt% of H-Y-40 with or without Pd/C
shows that the addition of the dehydrogenation catalyst gives
a higher selectivity to 4 with Pd/C present (Table 3, entries 2
and 3; Figure S19), which suggests that the dehydrogenation
catalyst pulls the reaction to 4 rather than to decarboxylation
(i.e., the yield of 4 increases much more than the yield of
3
total amount of acid sites remained the same after the third
reuse and (re)calcination (Table 1 and Figure S17). Furthermore,
the textural properties of the reused zeolite catalyst did not
change significantly, in line with its stable catalytic per-
formance.
5
a+5b). Indeed, as Pd is known for both dehydrogenation as
[15]
well as decarboxylation activity, these results suggest that
the former type of reactivity dominates under the applied con-
ditions. This effect is even more pronounced if the reaction of
1 and intermediate 2 with the combination of Pd/C and H-Y-40
are compared. The results thus show that even though Pd/C is
not involved directly in the conversion of 1 to 2, nor in the
first step that 2 subsequently undergoes, the Pd/C catalyst can
influence the equilibria involved in such a way that is benefi-
cial for both total aromatics yield and the selectivity to the de-
sired aromatic product 4. This could, for example, be the result
of the (rapid isomerization and) dehydrogenation of the diene
intermediate to give the aromatic anhydride product 4. The
latter was shown previously to be stable under reaction condi-
Catalyst testing: Zeolites combined with Pd/C
It was shown previously that an increase in temperature from
150 to 2008C using H-Y-2.6 (10 wt% relative to 1) was necessa-
ry to increase the conversion of 1 and the selectivity to the de-
[
7]
sired aromatic product 4. At 2008C, the addition of Pd/C as
a dehydrogenation catalyst (3 wt% relative to 1) to H-Y-2.6
(10 wt% relative to 1) was also shown to increase the yield of
4
from 22 to 56% and, consequently, the total aromatics yield
[
7]
from 26 to 75%. Here we show that for various H-Y zeolites
in the presence of Pd/C, the increase in temperature from 150
(Table S3) to 2008C (Table 2) indeed resulted in a significant in-
crease in yield and selectivity to aromatic products accompa-
nied by a concomitant decrease in the yields of 2 and 3. We
varied the ratio of the solid acid to the dehydrogenation cata-
lyst at 2008C and furthermore found that already the addition
of a very small amount of Pd/C even to the least acidic catalyst
[7]
tions, which suggests that the alternative decarboxylation
pathway should precede aromatization and involves the 1,3-
[16]
diene anhydride or its diacid precursor. Pd/C addition then
effectively suppresses this pathway if present in sufficient
amounts.
(i.e., H-Y-40) at low loading (10 wt% relative to 1) dramatically
increased the selectivity to 4 from 15 to 48%, primarily at the
expense of 2 and 3 (Table 2, entries 4 and 5; Figure S18). The
addition of Pd/C thus facilitates not only the dehydrogenation
of diene intermediate 3 as expected, but it also influences the
further conversion of the g-lactone intermediate 2. The latter is
remarkable as Pd is not directly involved in the first step after
An increase of the catalyst loading for the zeolite-only reac-
tions had a positive influence in terms of aromatic product
yield and selectivity (Table 2). The catalytic performance of the
four H-Y zeolite catalysts with 1 wt% Pd/C was, therefore,
tested at 33 wt% loading. The full conversion of 1 is now at-
tained, and 2 and 3 are not observed anymore for any combi-
nation of catalysts (Table 4). Similar total aromatics yields are
obtained for the four H-Y catalysts, but selectivities differ con-
siderably. Indeed, the high-Si/Al-ratio H-Y-30 and H-Y-40 again
show the highest selectivities to 4, whereas H-Y-2.6 and H-Y-6
produced more of the toluic acids, which is also seen with the
zeolite-only runs (Table 2). If H-Y-40 is used, for example, the
selectivity to 5a+b is only 21%, which is escalated to 32 and
34% if H-Y-2.6 and H-Y-6 are used, respectively (Table 4, en-
tries 1, 2, and 5). Comparing these results to the 33 wt% zeo-
lite-only results and to the 10 wt% H-Y with/without 1 wt%
2
, as evidenced by the reaction of g-lactone 2 and Pd/C, which
gives no conversion. Similarly, the conversion of 1 is not affect-
ed by the addition of the Pd/C catalyst as the first step is
purely acid catalyzed and the Pd/C adds very little to the over-
all acidity of the system. Furthermore, the selectivity ratio of 4
(80 vs. 83%) and 5a+b (17 vs. 20%) to total aromatics only
changed slightly in H-Y-40 with or without Pd (Figure 2), which
illustrates that the selectivity is dominated by zeolite-catalyzed
steps and can thus be controlled by the modification of this
catalyst only at this catalyst ratio. A comparison of the reaction
[
a]
[b]
Table 4. Reactivity of 1 with various H-Y zeolites with added Pd/C catalyst.
[
d]
[f]
Entry
Solid acid
catalyst
Pd/C
loading
Yield/selectivity [mol%]
Total aromatics yield
(selectivity) [%]
Mole balance
[%]
[
c]
[e]
4
5a
5b
6
1
2
3
4
5
6
7
8
H-Y-2.6
H-Y-6
1
1
1
3
1
3
5
10
51
53
59
64
57
61
71
68
27
29
19
17
17
16
14
15
5
5
5
3
4
4
4
4
6
6
8
7
10
7
83
87
83
84
78
81
89
87
89
93
91
91
88
88
92
90
H-Y-30
H-Y-30
H-Y-40
H-Y-40
H-Y-40
H-Y-40
3
3
[a] Full conversion of substrate 1; intermediates 2 and 3 were not detected. [b] Conditions: 1.0 g of 1, 24 h in toluene, 2008C, Ar atmosphere (1 bar),
33 wt% H-Y relative to 1. [c] wt% Pd relative to H-Y. [d] Calculated by using q-NMR spectroscopy using dimethyl 3,4-furan dicarboxylate as internal stan-
dard; Yield=Selectivity. [e] 4+5a+5b; Yield=Selectivity. [f] Mole balance determined from the total number of moles calculated from the crude mixture
after the reaction by NMR spectroscopy.
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Pd/C results shows that at the higher zeolite loadings, the
amount of Pd added is not sufficient to drive the reaction to-
wards the desired product and achieve the same gain in selec-
tivity seen for the 10 wt% zeolite reactions with Pd. Indeed, as
the zeolite dominates the conversion, the aromatic product se-
lectivity in the reactions with Pd at higher zeolite loadings be-
comes more similar to that of the zeolite-only reactions.
the 2,5-dimethylfuran-derived hydrogenated DA adduct using
the bifunctional catalysts 1 wt% Pd/H-Y. At full conversion, the
selectivity ratio of 3,6-dimethylphthalic anhydride to total aro-
matics (3,6-dimethylphthalic anhydride+p-xylene+2,5-dime-
thylbenzoic) is 78%, compared to 74% for 1. These differences
in the reactivity of the three different hydrogenated DA ad-
ducts coincide with the ease of the acid-catalyzed ring open-
ing of the oxanorbornane ring, which depends on the furan
As expected, the selectivity to the desired aromatic product
[7]
4
can then be further improved by increasing the amount of
dehydrogenation catalyst, as shown for H-Y-30 and H-Y-40
Table 4 and Figure 2). For example, the selectivity of H-Y-30 to
substitution pattern. p-Xylene was detected with the 2,5-di-
methylfuran-derived hydrogenated DA adduct in yields up to
21%.
(
4
and 5a+b changed from 59 and 24 to 64 and 20% at 1 and
3
wt% Pd, respectively, (Table 4, entries 3 and 4; Figure S20).
The same enhancement was observed for H-Y-40, for which an
increase of the Pd loading to 5 wt% resulted in increased
yields of 4, a (slight) decrease in decarboxylation, and a de-
crease in the transfer hydrogenation product 6. A further in-
crease of Pd/C to 10 wt% at constant zeolite H-Y-40 loading,
however, did not result in any significant improvement in se-
lectivity and aromatic product distribution, which suggests
that the optimum amount of Pd is 5–10 wt% to give 71% as
the highest selectivity to 4. Pd/C alone at 10 wt% without H-Y
showed no conversion of 1.
Conclusions
We have demonstrated that hierarchically structured FAU-type
zeolites are highly efficient solid acid catalysts in the liquid-
phase conversion of furanics-derived hydrogenated Diels–Alder
adducts to renewable aromatic chemicals. Key to their catalytic
performance is the enhanced mesoporosity and external sur-
face area upon dealumination balanced with (accessible)
Brønsted acid concentration. The addition of a dehydrogena-
tion catalyst, that is, Pd/C, improves the selectivity to aromatic
products significantly at the expense of the g-lactone and the
newly identified 1,3-diene intermediates. Furthermore, the ad-
dition of Pd/C improves the selectivity of aromatic anhydride
formation strongly over toluic acid formation. The dependence
of selectivity on Pd concentration strongly suggests that effi-
cient coupling of the steps is essential to drive the reaction to-
wards the formation of the desired aromatic product 3-me-
thyphthalic anhydride. By optimizing the Pd-to-H-Y zeolite
ratio, the competitive decarboxylation reaction can thus be ef-
fectively suppressed. The aromatic product selectivity can also
now be tuned by controlling the vicinity of the dehydration
and dehydrogenation functionalities and, more importantly, by
careful choice of the zeolite H-Y catalyst used. The synthesized
bifunctional Pd/H-Y catalysts were also highly selective for the
aromatization of other hydrogenated Diels–Alder furan deriva-
tives. Overall, the zeolite component dominates the catalyst se-
lectivity, and the acidity–mesoporosity coefficient is again
Catalytic testing: Bifunctional Pd/H-Y catalysts
The results above show that the combination of Pd/C with H-
Y-30 or H-Y-40 is preferred in terms of selectivity to 4 and are
hence used as basis to prepare the bifunctional catalysts
1
wt% Pd/H-Y-30 and 1 wt% Pd/H-Y-40. At 33 wt% loading,
Pd/H-Y-30 and Pd/H-Y-40 catalysts give S4/S total products
ratios of 70 and 67%, respectively, at a full conversion of 1,
which is higher than the corresponding physical mixtures
(Figure 2). The bifunctional catalysts were also tested for other
substrate combinations (Table 5, entries 3–6). Using furan as
the diene in the aromatization reaction, lower activity and se-
lectivity for phthalic anhydride were obtained than for 1 as
substrate for both catalysts. In contrast, significantly higher
yields of total aromatics of up to 90% could be obtained with
[
a]
Table 5. Reactivity of different hydrogenated DA adducts using bifunctional Pd/H-Y catalysts.
[
c]
Entry
Yield [mol%] (Selectivity [mol%])
[
c]
[e]
Solid
catalyst
Conversion
[mol%]
Total aromatics yield Mole balance
[
b]
[d]
(selectivity) [%]
[%]
[
[
f]
f]
1
Pd/H-Y-30 X=CH
Pd/H-Y-40 X=CH
Pd/H-Y-30 X=Y=H
Pd/H-Y-40 X=Y=H
Pd/H-Y-30 X=Y=CH
Pd/H-Y-40 X=Y=CH
3
3
, Y=H 100
, Y=H 100
64
18
4
3
–
6
86
92
2
3
4
5
6
60
18
–
–
–
21
16
8
81
89
90
91
90
89
[
[
g]
g]
[f]
[f]
85
82
41 (48)
45 (55)
62
25 (29)
16 (20)
9 (11)
12 (15)
66 (77)
61 (75)
90
[
h]
[i]
3
3
100
100
7
4
–
–
[
h]
[i]
69
89
[a] Conditions: 1.0 g of substrate, 24 h in toluene, 2008C, Ar atmosphere (1 bar), 33 wt% Pd/H-Y relative to substrate. [b] Contained 1 wt% Pd relative to
H-Y. [c] Calculated by using q-NMR spectroscopy using dimethyl 3,4-furan dicarboxylate as internal standard. [d] 4+5a+5b; phthalic anhydride+benzoic
acid; 3,6-dimethylphthalic anhydride+p-xylene+2,5-dimethylbenzoic acid. [e] Mole balance determined from the total number of moles calculated from
the crude mixture after the reaction by NMR spectroscopy. [f] Not applicable. [g] Benzoic acid. [h] 2,5-Dimethylbenzoic acid. [i] Not observed.
&
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shown to be a key structure–performance indicator, in this
case for tandem catalytic aromatization. Ongoing computa-
tional studies are expected to provide further detailed insights
into the mechanistic pathways to the observed aromatics, in
particular the decarboxylation products.
Gemini field-emission scanning electron microscope with a Schottky
emitter operated at 2.0 kV. TEM measurements were conducted in
the bright-field imaging mode by using a Tecnai 20FEG transmis-
sion electron microscope operated at 200 kV. The mean particle
size of Pd in the bifunctional catalysts was calculated from at least
117 different particles observed by using TEM. Trace metals in H-Y
zeolites were quantified by using inductively coupled plasma
atomic emission spectroscopy (ICP-AES, Spectro Acros) after disso-
lution in aqua regia.
Experimental Section
Preparation of substrates and catalysts
The materials and methods used for the synthesis of (hydrogenat-
Catalytic testing and spent catalyst regeneration
ed) DA adducts and g-lactone intermediate 2 were reported previ-
[7]
ously. All zeolite Y catalysts used in this study were obtained
from Zeolyst International (CBV300, NH -Y, Si/Al=2.55; CBV600, H-
The catalytic reaction was performed in a continuously stirred
50 mL Parr batch reactor. Typically, the reactor was charged with
1.0 g of hydrogenated DA adduct, catalyst(s), and 30 mL of tolu-
ene. The reactor was then flushed with Ar, and the temperature
was increased to 150 or 2008C and held for 24 h. The reactor was
submerged in ice-cold water to quench the reaction rapidly. The
catalyst was separated from the mixture by centrifugation and fil-
tration and washed extensively with toluene. The solvent was
evaporated under reduced pressure by using a rotary evaporator
4
Y, Si/Al=2.6; CBV712, NH -VUSY, Si/Al=6; CBV760, H-SDUSY, Si/
4
Al=30; and CBV780, H-SDUSY, Si/Al=40) and pretreated by heat-
À1
ing them in stagnant air at 5508C (108C min ) for 6 h. Pd/C
(
10 wt% Pd on activated carbon) was obtained from Sigma–Aldrich
and used as received. Tetraamminepalladium(II) nitrate (10 wt% in
water, Sigma–Aldrich) was used as the precursor for the synthesis
of bifunctional Pd/H-Y catalysts. The bifunctional catalysts Pd/H-Y-
3
0 and Pd/H-Y-40 (1 wt% Pd relative to H-Y) were prepared by in-
to obtain the crude product. The identification of 2, 4, 5a, 5b, and
1
cipient wetness impregnation. After the overnight evaporation of
water at RT, the solids were further dried overnight at 608C and
then overnight at 1208C. The solids were ground, heated at 4008C
6
from the H NMR spectra of the crude products was based on
1
the reported H NMR spectra of the isolated and purified products
as described and adopted previously. The conversions and prod-
uct yields were calculated from the H NMR data using CDCl and
[7,8]
À1
À1
1
(
58Cmin ) for 6 h under N2 flow (100 mLmin ), and finally re-
3
À1
duced by heating from RT to 2008C (58Cmin ) for 6 h under flow-
ing pure H (60 mLmin ).
dimethyl 3,4-furandicarboxylate as solvent and internal standard,
respectively. The H-Y zeolites were regenerated and reused by
washing the spent catalysts with toluene and acetone, drying over-
À1
2
night at 608C, drying at 1208C for 6 h, and finally heating to 5008C
Catalyst characterization
À1
(108Cmin ) for 6 h under flowing air until samples that were com-
pletely white were obtained. H produced in the reaction was col-
The textural properties of the zeolite materials were determined by
2
lected in a gasbag and quantified by using micro-GC (Varian
CP490) equipped with a COX column and a TCD detector.
using a Micromeritics Tristar 3000 set-up. The N physisorption ex-
2
periments were conducted at 77 K after initial pretreatment of the
samples by degassing at 300 or 4008C for 12 h in a N2 flow. The
apparent surface area was determined using the BET method. The
total pore volume was determined from the single-point adsorp- Acknowledgements
tion isotherm, and the micropore volume was determined from
the t-plot analysis. The pore size and PSD were derived from the
This work is part of the research program Technology Areas for
desorption isotherm according to the Barrett–Joyner–Halenda
BJH) method. The overall acidity of the catalysts was determined
Sustainable Chemistry (TASC), which is partly financed by the
Netherlands Organization for Scientific Research (NWO).
(
by TPD-NH by using a Micromeritics ASAP 2920 instrument. Typi-
3
cally, the sample (100 mg) in a quartz reactor was dried in a He
À1
flow by heating (58Cmin ) from RT to 6008C. Subsequently, the
Keywords: acidity · biomass · hydrogenation · palladium ·
zeolites
sample was cooled to 1008C and NH pulses (10 vol% in Ar) were
applied at this temperature to eliminate physically adsorbed NH .
The sample was then heated to 6008C at 58Cmin to induce de-
sorption under flowing He. The desorbed NH was quantified by
using a thermal conductivity detector (TCD), obtained by integrat-
ing two clearly distinguishable peaks to determine the distribution
of weak (low temperature range) and strong (high temperature
range) acid sites. The total amount of NH desorbed was taken as
the total amount of acid sites. The FTIR spectra of the solid acids
3
3
À1
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Received: June 10, 2016
1
Revised: July 20, 2016
Published online on && &&, 0000
&
ChemSusChem 2016, 9, 1 – 11
www.chemsuschem.org
10
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPERS
Balancing act: A balance between the
acidity and porosity of H-Y zeolites and
efficient coupling with a Pd catalyst is
essential for the selective conversion of
bio-based furanics to renewable aromat-
ic chemicals.
H. C. Genuino, S. Thiyagarajan,
J. C. van der Waal, E. de Jong,*
J. van Haveren, D. S. van Es,*
B. M. Weckhuysen, P. C. A. Bruijnincx*
&& – &&
Selectivity Control in the Tandem
Aromatization of Bio-Based Furanics
Catalyzed by Solid Acids and
Palladium
ChemSusChem 2016, 9, 1 – 11
www.chemsuschem.org
11
ꢀ 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ