Catalytic hydrogenation of dihydrolevoglucosenone to levoglucosanol with a hydrotalcite/mixed oxide copper catalyst

Article abstract of DOI:10.1039/c9gc00564a

Levoglucosanol (LGOL) is a critical intermediate for the bio-based production of hexane-1,2,5,6-tetrol, 1,2,6-hexanetriol, and 1,6-hexanediol. Here we report on the aqueous-phase hydrogenation of cellulose-derived dihydrolevoglucosenone (Cyrene) to LGOL using a calcined and reduced heterogeneous copper/hydrotalcite/mixed oxide catalyst, denoted as Cu8/MgAlO_x-HP. The turnover frequency for LGOL conversion over this copper-containing catalyst is equal to 0.013 s^-1 at 353 K as measured in a flow reactor which is half the one obtained using 0.4 wt% Pd/Al₂O₃. Moreover, while Cu8/MgAlO_x-HP shows a stable activity, the activity of 0.4 wt% Pd/Al₂O₃ decreases with time-on-stream. Neither Cu-nor Al-leaching is observed (resp. <1 ppb and <1 ppm) but Mg leaching can be seen (5.5 ppm). The latter leaching relates to the acidity of the Cyrene/H₂O mixture (pH 3.5-4.5 range), which is due to the occurrence of the geminal diol moiety of Cyrene, an acidic species. In contrast, additional and consecutive oxidation and reduction of the catalyst leads to a gradual decrease in activity over time. Applying still further oxidation/reduction cycles to this catalyst tends to decrease its activity with some overall stabilization being observed from the fourth run onwards. Mg-leaching is shown to change the relative meso-to-macro pore content, but leaves the total pore volume unchanged between the fresh and the spent catalyst. In spite of the high copper loading (8 wt%), small Cu-nanoparticles (2-3 nm) are present over the hydrotalcite/mixed oxide surface of the Cu8/MgAlO_x-HP material, and these particles do not aggregate during the hydrogenation reaction.

Full text of DOI:10.1039/c9gc00564a

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Catalytic hydrogenation of dihydrolevoglucosenone
to levoglucosanol with a hydrotalcite/mixed oxide
Cite this: DOI: 10.1039/c9gc00564a
copper catalyst†
a,d
Mario De bruyn,
*
a,b Canan Sener, a Davi D. Petrolini, c Daniel J. McClelland,
c
Jiayue He, a Madelyn R. Ball, a Yifei Liu,a Leandro Martins,
James A. Dumesic, a George W. Huber a and Bert M. Weckhuysen
b
Levoglucosanol (LGOL) is a critical intermediate for the bio-based production of hexane-1,2,5,6-tetrol,
1,2,6-hexanetriol, and 1,6-hexanediol. Here we report on the aqueous-phase hydrogenation of cellulose-
derived dihydrolevoglucosenone (Cyrene™) to LGOL using a calcined and reduced heterogeneous
copper/hydrotalcite/mixed oxide catalyst, denoted as Cu8/MgAlOx-HP. The turnover frequency for LGOL
conversion over this copper-containing catalyst is equal to 0.013 s−1 at 353 K as measured in a flow
reactor which is half the one obtained using 0.4 wt% Pd/Al2O3. Moreover, while Cu8/MgAlOx-HP shows a
stable activity, the activity of 0.4 wt% Pd/Al2O3 decreases with time-on-stream. Neither Cu- nor Al-leach-
ing is observed (resp. <1 ppb and <1 ppm) but Mg leaching can be seen (5.5 ppm). The latter leaching
relates to the acidity of the Cyrene/H2O mixture (pH 3.5–4.5 range), which is due to the occurrence of
the geminal diol moiety of Cyrene, an acidic species. In contrast, additional and consecutive oxidation
and reduction of the catalyst leads to a gradual decrease in activity over time. Applying still further oxi-
dation/reduction cycles to this catalyst tends to decrease its activity with some overall stabilization being
observed from the fourth run onwards. Mg-leaching is shown to change the relative meso-to-macro
pore content, but leaves the total pore volume unchanged between the fresh and the spent catalyst. In
spite of the high copper loading (8 wt%), small Cu-nanoparticles (2–3 nm) are present over the hydro-
talcite/mixed oxide surface of the Cu8/MgAlOx-HP material, and these particles do not aggregate during
the hydrogenation reaction.
Received 13th February 2019,
Accepted 24th May 2019
DOI: 10.1039/c9gc00564a
rsc.li/greenchem
metal catalysts, most commonly Fe, Cu, Ni and Co. The use of
these elements is not always straightforward; for instance, both
Introduction
Heterogeneous catalysis has been a longstanding and pivotal Ni and Co are suspect carcinogenics.6,7 Also, when used as
technology for the conversion of petrochemical feedstocks into heterogeneous catalysts in polar media, such as water, these
fuels and chemicals, and more recently also for the conversion metals tend to leach.8 The specific case of cobalt is even more
of biomass.1–4 To date, Group VIII metals have been extensively problematic as (1) it is an essential component in Li-ion batteries
relied upon, most notably Pt, Pd and Rh. However, these metals making for a current demand in excess of 100 000 metric tons at
are costly and pose critical future supply issues.5 Thus, signifi- a compound annual growth rate (CAGR) of 11.6% and (2) no less
cant attention has been devoted to the development of base than 2/3 of the world’s cobalt supply is mined in the Democratic
Republic of Congo.9 In marked contrast, copper is only of
medium economic importance and has a reduced supply risk.5
Supported copper catalysts have been reported for the
reduction of both C–C double/triple bonds and a range of car-
aDepartment of chemical and biological engineering, University of
Wisconsin-Madison, 1415 Engineering Drive, 53706 Wisconsin, USA.
E-mail: debruyn@wisc.edu, mario.debruyn@gmail.com
bonyl groups, with CuCrO4 and Cu/ZnO being common.10,11
However, as Cu-based solid catalysts tend to suffer poor stabi-
lity, the addition of earth alkaline oxides or Al2O3 is often
needed to prevent metal sintering.12 This lack of stability is of
particular importance in gas-phase reactions where the
applied reaction temperature can exceed 410 K i.e. the temp-
erature at which surface Cu-atoms become mobile.11 Organic
bFaculty of Science, Debye Institute for Nanomaterials Science, Utrecht University,
Universiteitsweg 99, CGUtrecht 3584, The Netherlands
cInstituto de Química, Unesp - Universidade Estadual Paulista,
R. Prof. Francisco Degni 55, CEP 14800-900 Araraquara, SP, Brazil
dDOE Center for Advanced Bioenergy and Bioproducts Innovation, University of
Wisconsin-Madison, 1415 Engineering Drive, 53706 Wisconsin, USA
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9gc00564a
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liquid phase (transfer) hydrogenation reactions of carbonyl Cyrene with water. The reduced catalyst was found to yield a
groups using supported Cu catalysts have also been constant conversion (75%) over 25 h time-on-stream, while the
reported.13–15 Few successful aqueous hydrogenations using performance of the oxidized/reduced catalyst decreased gradu-
supported Cu-catalysts are documented; a rare example is the ally, though eventually stabilizing. Batch operation is found
reduction of furfural to furfuryl alcohol in water with a 5 wt% more suitable to higher Cyrene concentrations than flow oper-
Cu/Al2O3 (90 °C, 20 bar H2) catalyst, yielding 81% furfuryl ation. This work on the conversion of Cyrene to LGOL reflects
alcohol at 81% conversion.16
the growing interest in an alternative biorefinery concept
Here we report on an active Cu/hydrotalcite/mixed oxide where biomass-derived carbohydrates are directly converted to
catalyst that does not show measureable leaching of Cu during levoglucosenone (LGO) instead of mono/oligo carbohydrates
the low temperature H2-mediated hydrogenation of dihydro- and furan-containing molecules.17–19 Indeed, clear synthetic
levoglucosenone (Cyrene™) to exo and endo levoglucosanol routes from levoglucosanol (LGOL) (i.e., fully hydrogenated
(LGOL) in water (Scheme 1). Irrespective of the catalyst pre- LGO or Cyrene) to cis/trans tetrahydro-2,5-furan-dimethanol
treatment, neither copper (<ppb) nor aluminium (<1 ppm) (THFDM); 1,2,6-hexanetriol (HTO) and 1,6-hexanediol (1,6-
leaching could be observed. In contrast, 9.5 ppm Mg-leaching HDO) have been shown in publications by our group and a
was detected for calcined/reduced Cu8/MgAlOx-HP and range of DuPont patents.20–22 Furthermore, we have recently
5.5 ppm for only reduced Cu8/MgAlOx-HP. This leaching of Mg reported on the direct conversion of LGOL into (S,R)/(S,S)
could be linked to the dominant presence of the geminal diol hexane-1,2,5,6-tetrol (1256HT), a versatile new bio-derived
nature of Cyrene, an acidic species formed by the reaction of synthon, in high yield.23 These molecules can be used in a
range of industrial applications as outlined in Fig. 1.
Results and discussion
Batch reactions
The catalytic hydrogenation of Cyrene to LGOL was studied
from 5 wt% Cyrene in water solutions and using 8 wt% (ICP)
copper supported on a mesoporous/macroporous structured
MgAl hydrotalcite (Mg/Al = 1) – hereafter this catalyst is
denoted as Cu8/MgAlOx-HP. The catalyst was always oxidized
Scheme 1 Hydrogenation of dihydrolevoglucosenone (Cyrene™) into
endo/exo-levoglucosanol (LGOL).
Fig. 1 Overview of the synthetic possibilities starting from levoglucosanol (LGOL) as a platform molecule.
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and reduced and then further subjected to a re-reduction or
additional oxidation/reduction cycles, as indicated. The hydro-
talcite support was made following a recently published pro-
cedure by Petrolini et al. and constitutes the sol–gel transition
of Mg and Al precursors in the presence of structure directing
agents (SDA): pluronic surfactant and n-dodecane as an emul-
sion.24 Using this catalyst, batch reactor experiments were con-
ducted to explore the effect of hydrogen pressure on the hydro-
genation of Cyrene to LGOL at a fixed temperature of 333 K
and for a fixed reaction time of 18 h. The LGOL conversion
increased with increasing hydrogen pressure, suggesting a
positive reaction order in hydrogen (Fig. 2A). The LGOL endo/
exo ratios were found to be insensitive to both hydrogen
pressure and conversion. Cu8/MgAlOx-HP had a higher activity
than Cu8/MgAlOx-LP, a reference catalyst prepared in the
absence of SDA (Fig. 2A). This higher activity could be attribu-
ted to an enhanced copper dispersion on Cu8/MgAlOx-HP
than on its less porous equivalent Cu8/MgAlOx-LP – respect-
ively 7.2 vs. 5.3% (as determined by N2O titration – see ESI† for
details). In this respect, we note that MgAlOx-HP and MgAlOx-
Fig. 3 TEM images of Cu8/MgAlOx-HP (A & B); Cu8/MgAlOx-LP (C) and
Cu8/MgAlOx-HP after batch reaction (333 K for 18 h) (D); subfigure E
depicts their respective Cu-nanoparticle size distributions. Average (avg.)
particle sizes determined from ∼1000 particles.
LP have respective surface areas of 171 and 106 m2 g−1
.
Furthermore, given the high copper loading of 8 wt%, it is also
noteworthy that Cu deposition on the highly mesoporous
MgAlOx-HP gives a narrower particle size distribution (2–4 nm)
than obtained for Cu8/MgAlOx-LP (2–10 nm range) (Fig. 3).
Importantly, the Cu-particle size distribution was found to be
nearly identical before and after reaction (Fig. 3). In terms of
the turnover frequency (TOF), Cu8MgAlOx-HP and Cu8MgAlOx-
LP realize respective TOFs (333 K) of 0.0117 s−1 and 0.0093 s−1
,
representing a 20% increase in activity. Cu 2p XPS analysis of
oxidized/reduced Cu8/MgAlOx-HP (Fig. 4A – Scan A) and Cu8/
MgAlOx-LP (Fig. 4A – Scan B) revealed the absence of Cu(II)
species. Additional examination of the Auger LMM spectrum
points to the presence of Cu(I) and Cu(0) in both Cu8/MgAlOx-
LP & HP (Fig. 4B – Scans A&B). Fig. 2B shows the influence of
temperature (353 and 373 K) on the catalytic activity of Cu8/
MgAlOx-HP in Cyrene/LGOL hydrogenation. The TOF (∼45%
conversion) is 0.116 s−1 at 373 K. Table 1S† details the
Fig. 2 (A) Effect of the H2 pressure on the LGOL yield and its endo/exo
ratio for the Cu8/MgAlOx-HP and Cu8/MgAlOx-LP catalysed Cyrene to
LGOL conversion at 333 K for 18 h (B) influence of the temperature (353
& 373 K) on the Cyrene to LGOL reaction with the Cu8/MgAlOx-HP cata-
lyst. Batch reactor. All batch experiments were conducted with 2 mmol
Cyrene in 5 mL water (∼4.9 wt%), 25 mg catalyst and 60 bar H2.
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Fig. 4 (A) X-ray photoelectron spectroscopy (XPS) data of Cu8/
MgAlOx-HP (scan A) and Cu8/MgAlOx-LP (scan B); (B) Auger LMM
spectra of Cu8/MgAlOx-HP (scan A) and Cu8/MgAlOx-LP (scan B).
observed rates for a range of flow/batch reactions. The acti-
vation energy (Ea) was determined to be 59 kJ mol−1 over the
333–373 K temperature range.
Flow reactions
To evaluate further the performance of these Cu-based catalyst
materials, flow experiments were performed. In
a first
approach, the performance of oxidized/reduced Cu8/MgAlOx-
HP was evaluated (Fig. 5A). A mild decrease of catalytic activity
is observed for the first three runs, the first order deactivation
rate constant being −0.0027 h−1. The ICP analysis indicated
that neither Cu nor Al leaching (respectively <1 ppb and
<1 ppm) was occurring but rather, a consistent leaching of
∼9.5 ppm Mg took place. Increasing the initial Cyrene concen-
tration from 1 to 5 wt% was found to amplify the Mg-leaching
to ∼30 ppm with again no detectable loss of copper nor alu-
minium (Fig. 5B). It is noteworthy, however, that a five times
increase of the Cyrene concentration gives a ten times higher
decrease in the initial catalytic activity [to a value of 0.027 h−1].
Following these observations, the pH of a range of Cyrene/H2O
solutions was measured, revealing a decrease of the pH even at
Cyrene concentrations down to 1 wt% (Fig. 5C). This phenom-
Fig. 5 (A) Five consecutive Cyrene to LGOL flow reactions (353 K, 60
bar H2, 1 wt% Cyrene in H2O) using 25 mg Cu8/MgAlOx-HP as the cata-
lyst; after each run the catalyst is re-oxidized and re-reduced (B) Cu8/
MgAlOx-HP catalysed Cyrene to LGOL reaction using a 5 wt% Cyrene in
H2O solution (353 K, 60 bar H2) (C) pH of a range of Cyrene/H2O mix-
tures as a function of the initial Cyrene concentration in wt%. (D)
Scheme of the Cyrene hydration reaction. Flow conditions (A) and (B):
Cyrene/H2O solution: 0.03 mL min−1, H2 gas: 20 mL min−1
.
enon can be attributed to the formation of geminal diol func- glucose-fructose isomerization, where the lactic acid side
tionality of Cyrene,25 a chemical species displaying at least one product is shown to leach Mg, and not Al, from the hydro-
acidic hydroxyl group (Fig. 5D). This behaviour is reminiscent talcite catalyst without causing structural deformation of the
of the work by Delidovich et al. on hydrotalcite-catalyzed catalyst.26 The reasons for the mild decrease of catalytic
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Table 1 Textural properties of the catalysts as determined by N2 physi-
sorption and mercury intrusion porosimetry
Pore volume mL g−1
Micro pore
t-plot
BET area
m2 g−1
Meso
Macro
Total
Cu8/MgAlOx-LP
Cu8/MgAlOx-HP
Cu8/MgAlOx-HP
after reaction
0.2
0.3
0.4
0.3
1.0
0.9
0.5
1.3
1.3
0
0
0
106
171
60
activity during the flow experiments are presently unclear but
may relate to the below options:
(1) Active Mg-leaching may undermine the stability of the
hierarchical pore structure in the Cu8/MgAlOx-HP material.
This change in pore structure could make active copper sites
progressively unavailable for reaction hence the gradual
decrease of the catalytic activity over time.
(2) Active Mg-leaching may create additional (micro) pores,
potentially allowing non-copper-containing flow routes to the
Cyrene/water reaction mixture.
Fig. 6 (A) X-ray photoelectron spectroscopy (XPS) data of recovered
Cu8/MgAlOx-HP (with peak fitting) and (B) Auger LMM spectra of recov-
ered Cu8/MgAlOx-HP.
(3) Even though no net copper leaching can be observed, it
is possible that copper species leach locally yet rapidly form
water insoluble species like Cu(II) carbonate hydroxide. While
the latter explanation is unlikely given the acidic reaction
medium, one could envisage the gradual (partial) formation of
copper aluminates, such as copper aluminate spinel (CuAl2O4)
or cuprous aluminate delafossite (CuAlO2), during the reaction, a
process known to require the presence of dilute acid.27
To evaluate hypothesis 1 & 2 we have performed N2 physi-
sorption and Hg intrusion porosimetry on Cu8/MgAlOx-HP,
Cu8/MgAlOx-LP and “Cu8/MgAlOx-HP after reaction” (Table 1
and Fig. S1 and S2†). From Table 1 it can be inferred that
“Cu8/MgAlOx-HP after reaction” has a somewhat increased
mesopore content, which is however balanced by a slight
decrease in the macropore content, leaving the total pore
volume (meso + macro) equal between the fresh and the spent
catalyst. We tentatively relate these changes in the relative
meso- and macropore content to structural rearrangements of
the pores, which may relate to Mg-leaching from the catalyst.
No significant difference in pore size distribution (macro +
meso) could be found between the fresh and the spent catalyst
(Fig. 2S†). All determined isotherms are type IV and no (super-
imposed) type I isotherm can be inferred (Fig. 2S†); applying
the t-plot to the determined isotherms shows no indication of
the occurrence of micropores.
combined XPS/Auger spectra also hint at the presence of Cu(I)
(Fig. 6A/B). It was found that the stability of the catalyst
material could be improved when, instead of dual oxidation/
reduction, only a reduction step was applied (Fig. 7). This
result hints at a negative influence of re-oxidation of the cata-
lyst, its main function being the re-conversion of hydrotalcite
into mixed oxide. For this reduced catalyst, ICP-AES analysis
showed the absence of both Cu and Al-leaching, while Mg-
leaching was found to decrease to 5.5 ppm. This result implies
that the reduced Cu8/MgAlOx-HP may be more stable than oxi-
dized/reduced Cu8/MgAlOx-HP. In flow reactor studies,
reduced Cu8/MgAlOx-HP was found to maintain constant
activity with an increase of the Cyrene concentration in the
It is further noteworthy that the fourth and fifth runs
depicted in Fig. 5A show an effective stabilization of the cata-
lytic activity. TEM analysis of the catalyst before and after
batch reaction shows no apparent changes in the particle size
(distribution) of the Cu nanoparticles (Fig. 3B, D & E). This
observation is in agreement with the ICP-established absence
of Cu-leaching and also indicates that the Cu nanoparticles in
this catalyst are not prone to agglomeration. XPS of the spent
Fig. 7 Comparative activity of “oxidized and reduced” and “sole
reduced” Cu8/MgAlOx-HP in flow (353 K, 60 bar H2, 1 wt% Cyrene in
H2O). Flow conditions: Cyrene/H2O solution: 0.03 mL min−1, H2 gas:
catalyst reveals the presence of Cu(II) (Fig. 6A) although the 20 mL min−1
.
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is higher than the one attained in flow [at 353 K: 0.013 s−1 for
a 1 wt% Cyrene/H2O feed and 0.011 s−1 for a 5 wt% Cyrene/
H2O feed].
(2) At a concentration of 5 wt% Cyrene in water, the pH of
the reaction mixture is ∼3.75. In a flow reactor set-up, this
value is the pH that the catalyst bed will be exposed to continu-
ously – affecting the entire catalyst bed over time. In contrast,
in a batch reactor this pH will gradually increase as Cyrene
present in the reaction mixture converts into non-acidic levo-
glucosanol. With Cyrene being in equilibrium with its acidic
geminal diol, any conversion of Cyrene into levoglucosanol
also means a decrease of the concentration of Cyrene’s
geminal diol and hence a gradual increase of the pH in the
batch reaction mixture.
Fig. 8 Activity of reduced Cu8/MgAlOx-HP in flow (353 K, 60 bar H2,
5 wt% Cyrene in H2O). Flow conditions: Cyrene/H2O solution: 0.03
mL min−1, H2 gas: 20 mL min−1
.
(3) At a concentration of 1 wt% Cyrene in water, the pH of
the reaction mixture is ∼4.25. As shown in Fig. 7, under these
conditions the Cu8/AlMgOx-HP/LP catalysts are less affected,
both showing constant activity.
(4) We also note that hydrotalcite is a basic support and in
batch reactor studies it will have a larger additional effect on
the pH (catalyst exposure to 5 mL of 5 wt% Cyrene in water)
feed from 1 to 5 wt% for up to 25 h (Fig. 8). The maximal TOF
of 0.011 s−1 (353 K) is similar to the one obtained when using
a 1 wt% Cyrene feed (0.013 s−1 at 353 K). Longer reaction
times do however show a progressive deactivation (Fig. 8). As
stable activity was observed when using a 1 wt% Cyrene in
H2O feed (pH 4.25) (Fig. 7), this behaviour is attributed to the
constant exposure of the catalytic bed to a Cyrene/H2O feed
(5 wt%) with a lower pH of 3.75 (see also Fig. 5C). It is note-
worthy, however, that ultimately a stabilization of the catalytic
activity occurs with a constant 5.5% conversion (TOF 0.005 s−1
at 353 K) (Fig. 8). The number of turnovers for the reaction
shown in Fig. 8 was 2654 mol Cyrene per mol Cu. A small
amount of Cu and Mg leaching was found with 5–10 ppb Cu
and 30 ppm Mg in the reactor effluent.
Reduced Cu8/MgAlOx-LP was also found to be stable in flow
reactor studies (1 wt% Cyrene feed) yet at a lower activity than
Cu8/MgAlOx-HP, their respective turnover frequencies being
0.0105 s−1 (353 K) and 0.0130 s−1 (353 K). This result is in line
with the previously discussed batch experiments (see Fig. 2).
This result also indicates that meso/macroporosity positively
influences the activity level of the catalyst but is not crucial to
its stability. Also, the use of (expensive) pluronic in the syn-
thesis method of the layered double hydroxides is not a neces-
sity. With Cu8/MgAlOx-LP Mg leaching was determined at
5 ppm and no evidence of Cu leaching could be established.
The turnover frequency achieved with Cu8/MgAlOx-HP [0.013
s−1, 353 K] is half that obtained using 0.4 wt% Pd/Al2O3 [0.025
s−1, 353 K]. However, while the Cu8/MgAlOx-HP catalyst shows
a stable activity, the activity of 0.4 wt% Pd/Al2O3 decreases
with time-on-stream (Fig. 3S†). The latter decrease in activity
does not relate to Pd leaching.
Comparison flow vs. batch reactions
The difference between the flow and batch reactor studies
using 5 wt% Cyrene in water manifests itself at different levels:
(1) While Mg is progressively lost under flow operation, the
situation is different when the reaction is run in batch. In
batch, any leached Mg remains in the reactor and could poten-
tially influence the speciation of copper and/or the reaction. As
such, it is found that the TOF of Cu8/AlMgOx-HP when oper-
Fig. 9 (A) 1st run flow Cyrene/LGOL hydrogenation reaction using an
oxidized/reduced Cu8/MgAlOx-HP and an oxidized/reduced Cu8/SiO2
material (B) 2nd run flow Cyrene/LGOL hydrogenation reaction using
Cu8/MgAlOx-HP and Cu8/SiO2. Reaction conditions: 353 K, 60 bar H2,
1 wt% Cyrene in H2O. Flow conditions: Cyrene/H2O solution: 0.03
ated in batch [0.04 s−1 at 353 K for a 5 wt% Cyrene/H2O feed] mL min−1, H2 gas: 20 mL min−1
.
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than in a flow setting (catalyst exposure to 100–250 mL of
1–5 wt% Cyrene in water).
Acknowledgements
M. D. b. acknowledges the European Union’s Horizon 2020
research and innovation programme under grant agreement
No. 701028 (EU Marie Curie Global Fellowship). We thank
Mr Tony Duncan (CEO of Circa) for the generous provision of
dihydrolevoglucosenone (Cyrene™). The authors gratefully
acknowledge use of facilities and instrumentation at the
UW-Madison Wisconsin Centres for Nanoscale Technology
(wcnt.wisc.edu) partially supported by the NSF through
the University of Wisconsin Materials Research Science
and Engineering Centre (DMR-1720415). We thank the
UW-Madison Department of Chemistry for the use of a
Bruker Avance 500 MHz NMR Spectrometer; a generous gift
from Paul J. Bender enabled purchase of this spectrometer in
2012. D. J. M. was funded by the DOE Center for Advanced
Bioenergy and Bioproducts Innovation (U.S. Department
of Energy, Office of Science, Office of Biological and
Environmental Research under Award Number DE-SC0018420).
Reference reaction
The catalytic performance in the flow mode of oxidized/
reduced Cu8/MgAlOx-HP in the Cyrene/LGOL hydrogenation
reaction was compared to oxidized/reduced Cu8/SiO2 as a
reference catalyst. As can be seen from Fig. 9A, the first run
with Cu8/SiO2 showed initially a similar activity to Cu8/
MgAlOx-HP which then rapidly decreases. Re-oxidation and re-
reduction of the spent Cu8/SiO2 catalyst showed a further
decrease of the catalytic activity (Fig. 9A ↔ 9B). A Cu8/SiO2
catalyst that has only been subjected to reduction displays a
similar behaviour, as shown in Fig. 4S.† Irrespective the pre-
treatment, the deactivation of Cu8/SiO2 is not due to Cu
leaching.
Conclusion
We have demonstrated that Cu supported on hydrotalcite can
attain a high and stable catalytic activity for hydrogenation of
Cyrene, and this behaviour is independent of the exact pre-
treatment conditions, but with a preference to re-reduction
over additional oxidation/reduction cycles. Performance of the
catalyst in flow reactor studies is distinctly different from
batch operation, with higher TOF numbers for batch oper-
ation. The heterogeneous Cu-catalysts do not undergo leaching
of Cu, which is a rare feature in the absence of special nano-
particle coatings (e.g. ALD). Leaching of Mg was observed,
which could be linked to the presence of the geminal diol
functionality of Cyrene, an acidic species. TEM imaging
revealed further that the Cu particle size distribution remains
unchanged before and after reaction. Given the dilute aqueous
reaction media (1–5 wt% Cyrene in water), direct isolation of
levoglucosanol is preferentially achieved by extraction with
benign bio-based solvents, such as 2-methyltetrahydrofuran.28
However, as presently levoglucosanol has no known appli-
cations, its main potential lies in its further conversion to
added-value products, such as hexane-1,2,5,6-tetrol, THFDM;
1,2,6-hexanetriol and 1,6-hexanediol (Fig. 1). As the formation
of the latter compounds from levoglucosanol requires the pres-
ence of an aqueous medium, no immediate need exists to
isolate levoglucosanol. The presence of limited quantities of
Mg (ppm) is not expected to influence the isolation procedures
involved for production of levoglucosanol or any of its deriva-
tives. Future work will involve the evaluation of the Cu8/
MgAlOx-HP catalyst towards the hydrogenation of a range of
carbonyl-containing substrates and a full elucidation of the
catalytic cycle.
References
1 R. Schlogl, Angew. Chem., Int. Ed., 2015, 54, 3465–
3520.
2 J. W. Medlin and M. M. Montemore, Nat. Chem., 2015, 7,
378–380.
3 Y. C. Lin and G. W. Huber, Energy Environ. Sci., 2009, 2, 68–
80.
4 B. N. Kuznetsov, N. V. Chesnokov, O. V. Yatsenkova and
V. I. Sharypov, Russ. Chem. Bull., 2013, 62, 1493–1502.
5 Critical raw materials for the EU, https://ec.europa.eu/
growth/tools-databases/eip-raw-materials/en/system/files/
ged/79%20report-b_en.pdf, (accessed 10/09/2018).
6 L. Leyssens, B. Vinck, C. Van Der Straeten, F. Wuyts and
L. Maes, Toxicology, 2017, 387, 43–56.
7 K. K. Das, S. N. Das and S. A. Dhundasi, Indian J. Med. Res.,
2008, 128, 412–425.
8 J. C. Lee, D. H. K. Jackson, T. Li, R. E. Winans,
J. A. Dumesic, T. F. Kuech and G. W. Huber, Energy Environ.
Sci., 2014, 7, 1657–1660.
9 F. Holmes, The World’s Cobalt Supply is in Jeopardy,
Forbes, 2018.
10 M. B. Gawande, A. Goswami, F. X. Felpin, T. Asefa,
X. X. Huang, R. Silva, X. X. Zou, R. Zboril and R. S. Varma,
Chem. Rev., 2016, 116, 3722–3811.
11 R. P. Ye, L. Lin, Q. H. Li, Z. F. Zhou, T. T. Wang,
C. K. Russell, H. Adidharma, Z. H. Xu, Y. G. Yao and
M. H. Fan, Catal. Sci. Technol., 2018, 8, 3428–3449.
12 N. Kaeffer, K. Larmier, A. Fedorov and C. Coperet, J. Catal.,
2018, 364, 437–445.
13 T. Subramanian and K. Pitchumani, Catal. Sci. Technol.,
2012, 2, 296–300.
14 R. Y. Fan, C. Chen, M. M. Han, W. B. Gong, H. M. Zhang,
Y. X. Zhang, H. J. Zhao and G. Z. Wang, Small, 2018, 14,
1801953.
Conflicts of interest
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This journal is © The Royal Society of Chemistry 2019
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Green Chemistry
15 F. Heroguel, B. P. Le Monnier, K. S. Brown, J. C. Siu and 22 A. M. Allgeier, W. I. N. De Silva, E. Korovessi,
J. S. Luterbacher, Appl. Catal., B, 2017, 218, 643–649.
16 R. Mariscal, P. Maireles-Torres, M. Ojeda, I. Sadaba and
M. L. Granados, Energy Environ. Sci., 2016, 9, 1144–1189.
17 M. De Bruyn, J. Fan, V. L. Budarin, D. J. Macquarrie,
L. D. Gomez, R. Simister, T. J. Farmer, W. D. Raverty,
C. A. Menning, J. C. Ritter, S. K. Sengupta and D. R. Corbin,
Process for preparing 1, 6-hexanediol, EP2797866(A1), 2014.
23 S. H. Krishna, M. De bruyn, Z. R. Schmidt,
B. M. Weckhuysen, J. A. Dumesic and G. W. Huber, Green
Chem., 2018, 20, 4557–4565.
S. J. McQueen-Mason and J. H. Clark, Energy Environ. Sci., 24 D. D. Petrolini, E. A. Urquieta-Gonzalez, S. H. Pulcinelli,
2016, 9, 2571–2574.
18 J. Y. He, M. J. Liu, K. F. Huang, T. W. Walker,
C. V. Santilli and L. Martins, Microporous Mesoporous
Mater., 2017, 240, 149–158.
C. T. Maravelias, J. A. Dumesic and G. W. Huber, Green 25 M. De bruyn, A. Misefari, S. Shimizu, H. Fish, M. Cockett,
Chem., 2017, 19, 3642–3653.
A. J. Hunt, H. Hofstetter, B. M. Weckhuysen, J. H. Clark
and D. J. Macquarrie, ACS Sustainable Chem. Eng., 2019,
7(8), 7878–7883.
19 G. R. Court, C. H. Lawrence, W. D. Raverty and A. J. Duncan,
Method for converting lignocellulosic materials into useful
chemicals, 2011/000030A1, 2011.
26 I. Delidovich and R. Palkovits, Catal. Sci. Technol., 2014, 4,
4322–4329.
20 J. Y. He, S. P. Burt, M. Ball, D. T. Zhao, I. Hermans,
J. A. Dumesic and G. W. Huber, ACS Catal., 2018, 8, 1427–1439. 27 C. Y. Hu, K. M. Shih and J. O. Leckie, J. Hazard. Mater.,
21 S. H. Krishna, D. J. McClelland, Q. A. Rashke, J. A. Dumesic
2010, 181, 399–404.
and G. W. Huber, Green Chem., 2017, 19, 1278–1285.
28 D. F. Aycock, Org. Process Res. Dev., 2007, 11, 156–159.
Green Chem.
This journal is © The Royal Society of Chemistry 2019