AuPd-nNiO as an effective catalyst for the base-free oxidation of HMF under mild reaction conditions

Article abstract of DOI:10.1039/c9gc01283d

Au-Based catalysts supported on nanosized NiO (nNiO) were synthesized and were investigated in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free conditions using molecular oxygen as the oxidant, at 90 °C. By choosing the optimal composition of Au-Pd nanoparticles (6:4 Au/Pd atomic ratio), we report an efficient and stable nNiO-supported Au-Pd alloy catalyst. The presence of nNiO and Au-Pd nanoparticles on the surface was essential to achieve high conversion (95%) and high activity, high yield of FDCA (70%) and good level of stability. Significant synergistic effects were observed between Au and Pd in the alloy as well as on NiO. The present work provides mechanistic insights into the alloying effect and support-metal interaction in terms of understanding better the role of the alloy and support in affecting specific reaction pathways. Finally, the outcome of this knowledge can help develop efficient catalysts for the aerobic oxidation of biomass-derived molecules under base-free conditions in water and under mild reaction conditions.

Full text of DOI:10.1039/c9gc01283d

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DOI: 10.1039/C9GC01283D
ARTICLE
AuPd-nNiO as effective catalyst for the base -free oxidation of
HMF at mild reaction conditions
a
a
b
b
a
Danilo Bonincontro, Alice Lolli, Alberto Villa,* Laura Prati, Nikolaos Dimitratos, Gabriel M.
Received 00th January 20xx,
Accepted 00th January 20xx
c
d
d
a
a
Veith, Lidia E. Chinchilla, Gianlugi A. Botton, Fabrizio Cavani, Stefania Albonetti*
DOI: 10.1039/x0xx00000x
Au-based catalysts supported on nanosized NiO (nNiO) were synthesized and were investigated in the oxidation of 5-
hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in base-free conditions using molecular oxygen as the
oxidant, at 90 °C. By choosing the optimal composition of Au-Pd nanoparticles (6:4 Au/Pd atomic ratio), we report an efficient
and stable nNiO-supported Au-Pd alloy catalyst. The presence of nNiO and Au-Pd nanoparticles on the surface was essential
to achieve high conversion (95%) and high activity, high yield to FDCA (70%) and good level of stability. Significant synergistic
effects were observed between Au and Pd in the alloy as well as on NiO. The present work provides mechanistic insights to
the alloying effect and support-metal interaction in terms of understanding better the role of alloy and support in affecting
specific reaction pathways. Finally, the outcome of this knowledge can help developing efficient catalysts for the aerobic
oxidation of biomass-derived molecules under base-free conditions in water and mild reaction conditions.
for the synthesis of polyesters, such as polyethylene furanoate
5
, 6
Introduction
(PEF), a potential polymer to be used in soft drinks bottling,
as replacement of the oil-derived PET, with an annual estimated
production of 25 million tons in 2018. The HMF conversion into
FDCA has been investigated using a number of catalytic,
electrocatalytic and biocatalytic processes and typically occurs
via consecutive oxidation of the two moieties bonded to the
furan ring leading to a stepwise pathway, as reported in Scheme
. One of the most relevant industrial attempt to obtain FDCA
by HMF oxidation relies on the catalysts and technologies
developed in the AMOCO process for the oxidation of
paraxylene to terephthalic acid. In these operative conditions,
The need to decrease the dependence on fossil feedstocks to
produce fuels, chemicals and materials, has led scientists to look
for sustainable alternatives. In this context, non-edible
lignocellulosic biomass , have been pointed out as suitable
renewable resources in the replacement of non-renewable raw
materials for the synthesis of useful chemicals thanks to their
7
8
1
1
abundance and availability. To achieve this goal, different
approaches have been suggested. Among them, one of the
most investigated relies on the conversion of the renewable raw
material into the so called “platform molecules”, i.e. versatile
9
HMF is converted through the route “a” illustrated in Scheme
intermediates which can be converted, on their turn, into
1
0
1
.
However, the use of homogeneous catalyst (Co and Mn
acetate) and corrosive solvent (acetic acid) can be considered
as the main shortcomings of this process. Thus, efforts have
been devoted to the design of heterogeneous catalysts, and,
in this frame, the effectiveness of supported metal (mainly Au,
Pd, Pt) nanoparticles (NPs) in aqueous phase conditions has
been disclosed. As far as the use of supported Au NPs is
concerned, it has been found that high yield of FDCA can be
obtained in mild temperature (50-90°C) under strongly basic
conditions (pH=9-13), obtained by addition of inorganic soluble
2
different
high
added
value
chemicals.
5-
(hydroxymethyl)furfural (HMF), a platform chemical obtained
3
by fructose dehydration, could be considered as one of the
most representative examples, since it could be converted
through different chemical approaches into several chemicals.
The applications of synthesised chemicals are mainly related to
polymer industry,4 such as furandicarboxylic acid (FDCA).
Indeed, the latter has been proven to be a suitable monomer
1
1
1
2-16
bases (typically, NaOH and Na
2
CO
3
).
In such high pH
a. “Toso Monatanari” Department of Industrial Chemistry, University of Bologna,
Viale Risorgimento 4, 40136 Bologna, Italy. E-Mail: Stefania.albonetti@unibo.it
condition, it has been proven that the reaction pathway
involved differs from the previously described one, since HMF
conversion into FDCA passes through HMFCA as intermediate
(route b Scheme 1), being the formation of the latter strongly
favored respect to DFF (route Scheme 1) under basic
b.
Department of Chemistry, University of Milan, Via Golgi 19, 20133 Milan, Italy. E-
Mail: Alberto.villa@unimi.it
c.
Chemical Science Division, Oak Ridge Laboratory, Oak Ridge, TN 37831, USA
Canadian Centre of Electron Microscopy and Department of Material Science and
Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario
L8S 4M1, Canada
d.
1
7
conditions.
Electronic Supplementary Information (ESI) available: [Fig S1-S5: STEM-HAADF
images XPS spectra of the catalysts; Fig S6 reaction parameter optimisation; Fig. S7
solutions after reaction; Fig S8-9: spent catalyst characterisation; Table S1
Comparison with the literature; Table S2-S3 additional catalytic data; Table S4: XRF
characterisation. See DOI: 10.1039/x0xx00000x
Further studies demonstrated that, gold based catalyst’s
activity could be improved by preparing alloyed bimetallic
nanoparticles, such as reported for Au/Cu-TiO (with a Au:Cu
2
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ARTICLE
Journal Name
active and selective under base-free conditions.26 The authors
View Article Online
DOI: 10.1039/C9GC01283D
attributed the high activity observed based on the availability of
both Lewis and Brønsted acid sites on the surface of the
Ru/MnCo O catalyst, which was confirmed by NH -TPD
2 4 3
characterization studies and the presence of Ru metallic species
with small particle size. Moreover, another green alternative
2
7
Scheme 1 HMF to FDCA possible routes
catalytic system was reported by S. Zhang and co-workers,
1
8
combining non-noble metal catalysts containing Ce, Fe, Zr and
the usage of ionic liquids for promoting the base-free
conversion of HMF. Ce0.5Fe0.15Zr0.35O catalyst was reported to
2
have high conversion (99.9% conversion) and moderate yield
to FDCA (44.2%) at 160 °C after 24 h of reaction, due to the
existence of active iron and zirconium species and the
formation of CeO -based solid solution that could facilitate the
2
formation of oxygen vacancies and therefore to improve the
redox properties of the catalyst.
ratio equal to 3:1) and Au/Pd-TiO
6
2
(with a Au:Pd ratio equal to
1
9
:1). This feature has been ascribed to the modification of the
electronic properties of the original metal (i.e. gold) which
arises from the preparation of the alloyed systems, that, on its
turn, leads to a cooperative effect that enhances the catalytic
properties of the monometallic system. However, even if lower
amount of base were used with some bimetallic catalysts, the
presence of NaOH is still the main concern from the industrial
point of view.
In fact, the main drawback related to the use of the
abovementioned gold-based catalysts is linked to the necessity
of working at very high pH, lowering the overall mass efficiency
of the reaction, since large excess of inorganic bases (from 2 to
Recently, Villa and co-workers demonstrated the possibility to
oxidize benzyl alcohol and other well-known aromatic and
aliphatic alcohols under base free conditions using metal
2
8
nanoparticles supported on nickel oxide supports . They
demonstrated that the use of nanometric NiO (nNiO) greatly
improved catalyst activity, mainly because of a cooperative
effect between Au and NiO. Moreover, NiO can be used as a
basic support for promoting HMF reaction.
2
0 equivalents respect to the HMF) are required to reach good
FDCA yield. Thus, the latest trend in HMF oxidation has been
focusing the development of catalytic systems able to perform
HMF oxidation under base-free conditions (see table S1 for
comparison of main results). In this frame, it has been proven
that by choosing suitable supports for metallic nanoparticles it
is possible to bypass the addition of the base to the reaction
mixture. For instance, carbon based material were found to be
suitable supports: functionalised carbon nanotubes (CNT) were
Therefore, in the present study, Au, Pd and Au/Pd nanoparticles
(Au:Pd metal molar ratio equal to 6:4, as a model well-defined
bimetallic catalyst for the upgrade of a range of biomass and
2
9
polyol-derived molecules ) were deposited on nNiO and their
catalytic behaviour was evaluated in the liquid-phase oxidation
of HMF in base-free conditions, demonstrating the possibility to
obtain high yield FDCA without the addition of any inorganic
base. This study highlights the importance of catalyst synthesis
for the improvement of sustainable chemical processes.
2
0
used as support for both alloyed Au/Pd and monometallic Pt
2
1
NPs, leading to highly active systems (FDCA yield 94 and 98%,
respectively). In these reports no HMFCA was detected in the
reaction mixture indicating that, under base-free conditions,
the reaction pathway involves DFF as intermediate (route “a”,
Scheme 1). Alternatively, a different approach is based on the
Experimental
2
2
use of intrinsically basic supports, such as hydrotalcite (HT) or
2
3
solid layered hydroxide. In these cases the reaction pathway Catalyst preparation
seems to involve HMFCA production (route “b” Scheme 1) even
nNiO has been prepared following the procedure reported
though no homogeneous bases were added to the reaction
mixture. In addition, it must be noted that, in absence of
homogenous base, higher temperatures are usually required to
perform the oxidation than the ones required to carry out the
reaction under basic conditions. Palkovits and co-workers
reported Ruthenium catalysts supported on covalent triazine
frameworks (CTF) to be active and selective under base-free
conditions for HMF oxidation using air as the chosen oxidant
with high conversion (99.9%) and yield (36.6%), at 140 °C and
30
-4
elsewhere. Ni(NO
)
3 2
2
x 6H O (5 x 10 M) (Sigma-Aldrich, purity
>
1
99.9%) and urea (Sigma-Aldrich, purity > 99.5%) (urea/Ni 10 :
mol mol ) were added to 200 ml of water under magnetic
-1
stirring. The solution was kept stirring for 6 h at 80 °C. The
Ni(OH) was separated from the solution by filtration and
2
washed several times. The powder was dried at 60 °C for 12 h
and then calcined at 300 °C for 3 h in static air.
Au-nNiO: Solid NaAuCl
solution (Au/PVA =1/0.5 wt/wt) were added to 100 mL of H
After 5 min, a fresh solution of NaBH (0.1 M) (Au/NaBH 1/4
4
2
• 2H O (0.051 mmol) and PVA (1%wt)
2
O.
2
0 bar of synthetic air and good recyclability. The authors claim
4
4
the improved activity and stability of Ru/CTF based on the
formation of mesoporous CTFs materials and the high degree of
polarity.24 In another study, the usage of commercial Ru/C
catalyst was reported as an efficient catalytic system for the
base-free conversion of HMF to FDCA and low degree of
deactivation.25 The authors reported that the favoured
oxidation reaction pathway is following the DFF/FFCA route
rather than the HFCA pathway. Recently, a new class of
mol/mol) was added to the solution under stirring. Within a few
minutes of sol generation, the colloid was immobilized by
adding the support under vigorous stirring. The amount of
support was calculated as having a total final nominal metal
loading of 1 wt. %. After 2 h the slurry was filtered, the catalyst
washed thoroughly with distilled water and dried at 80 °C for 4
h.
2 4
MnCo O spinel supported Ru catalysts were reported to be
2
| J. Name., 2012, 00, 1-3
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Pd-nNiO: Solid Na
solution (Pd/PVA =1/0.5 wt/wt) were added to 100 mL of H
After 5 min, a fresh solution of NaBH (0.1 M) (Pd/NaBH 1/8
mol/mol) was added to the solution under stirring. Within a few
minutes of sol generation, the colloid was immobilized by
adding the support under vigorous stirring. The amount of
support was calculated as having a total final nominal metal
loading of 1 wt. %. After 2 h the slurry was filtered, the catalyst
washed thoroughly with distilled water and dried at 80 °C for 4
h.
ARTICLE
2
PdCl
4
• 2H
2
O (0.051 mmol) and PVA (1%wt) Catalytic tests
View Article Online
DOI: 10.1039/C9GC01283D
The catalytic tests were performed in a lab scale autoclave
reactor (100 mL capacity from Parr), equipped with a
mechanical stirrer (0–600 rpm) and sensors for measuring
temperature and pressure. The aqueous solution of HMF
25mL, 0.02M) and catalyst (HMF/total metal molar ratio = 100)
were loaded in the reactor. HMF (purity >99%) was purchased
from AVABiochem and used without any purification.
2
O.
4
4
(
To perform the reactivity tests, a previously optimised
18, 31, 32
experimental protocol has been employed:
reactor was purged 3 times with O
at 10 bar. The temperature was increased to the set point
90 °C) and the reaction mixture was stirred at 400 rpm for the
the autoclave
AuPd-nNiO: Solid NaAuCl
O (0.020 mmol) (Au/Pd 6:4 mol/mol) and PVA (1%wt)
solution (Pd/PVA =1/0.5 wt/wt) were added to 100 mL of H O.
After 5 min, a fresh solution of NaBH (0.1 M) (Pd/NaBH 1/8
4 2 2 4
• 2H O (0.031 mmol) and Na PdCl •
2
(2 bar) and then pressurized
2H
2
2
(
4
4
whole duration of the experiment. Initial time (time zero) for
the reaction was considered when the set point temperature
was reached (after 10 min). At the end of the reaction, the
reactor was cooled down to room temperature and the solution
was filtered. Then, 1mL of the reaction mixture was collected
and diluted 5 times and, the resulting solution was then
analysed with an Agilent Infinity 1260 liquid chromatograph
equipped with an Aminex HPX-87H 300 mm × 7.8 mm column
mol/mol) was added to the solution under stirring. Within a few
minutes of sol generation, the colloid was immobilized by
adding the support under vigorous stirring. The amount of
support was calculated as having a total final nominal metal
loading of 1 wt. %. After 2 h the slurry was filtered, the catalyst
washed thoroughly with distilled water and dried at 80 °C for 4
h.
Catalyst characterisation
(
2 4
0.005 M H SO solution as mobile phase) and a diode array
TEM: Samples for transmission electron microscopy (TEM) detector. The compound quantifications were calculated from
studies were prepared by depositing small amounts of dry the peak areas after calibration using commercially available
catalyst powder onto holey carbon copper grids. Micrographs samples.
combined with analytical studies by energy-dispersive X-ray Recycling tests have been performed by reusing the recovered
(XEDS) and electron energy loss spectroscopy were performed catalyst without any further cleaning procedure.
in High Annular Dark Field mode using a FEI Titan3 80-300
microscope operated at 80kV. Digital Micrograph, TIA, and INCA
software’s were used for the analysis of the TEM micrographs
and XEDS spectra. The PSD, Gaussian fit, average particle
diameter, and metal dispersion were calculated assuming a
truncated cubooctaedron particle shape using Gauss software.
EELS data including drift correction base on the zero-loss peak,
background subtraction, and principal component analysis
Results and discussion
Catalyst characterisation
The morphology of the prepared catalysts was analyzed by
transmission electron microscopy (TEM). The as-prepared Au
nanoparticles on nNiO had a mean particle diameter (d
nm (Table 1) with the presence of large aggregated
nanoparticles (Figure S1). Smaller nanoparticles with a d of 3.6
nm where obtained for Pd-nNiO as it is shown in Table 1, with a
narrow particle size distribution (Figure S2). Moreover, similar
to the previous case aggregates of Pd nanoparticles were
observed. TEM analysis of AuPd-nNiO sample showed the
presence of two different types of structures: small
m
) of 5.2
(PCA), were processed using Gatan’s Digital Micrograph and
m
Hyperspy software’s.
X-ray photoelectron spectroscopy (XPS) data were collected
using a PHI 3056 XPS with an Al anode source operated at 15kV
and an applied power of 350W. The energy scale calibration of
the instrument is checked using a sputter cleaned piece of Ag.
Samples were manually pressed between two pieces of indium
foil; the piece of In foil with the sample on it was then mounted
to the sample holder with a piece of carbon tape (Nisshin E.M.
Co. LTD). The lowest C1s BE species were shifted about 0.1 eV
to 284.8 eV for comparison to literature values. There were no
treatments (i.e. cleaning, heating, processing) to the samples
before the XPS measurements. High resolution scans were
acquired with a 23.5 eV pass energy and 0.05 eV steps a
minimum of 50 times; survey scans were measured with a 93.9
eV pass energy and 0.5 eV energy steps a minimum of 25 times.
Surface concentrations are calculated by integrating the peaks
area and using standard atomic sensitivity factors supplied by
the equipment manufacturer. The spectra were deconvoluted
m
nanoparticles with a d of 3.3 nm and accumulated particles
forming aggregates (Figure S3). The EELS map (Figure 1)
obtained from a typical nanoparticle confirms that both Au (red)
and Pd (green) metallic components are intimately mixed within
the nanostructure and clearly shows that the Pd virtually forms
a thin layer around Au-Pd core particle. Furthermore, the
(S)TEM-EDS analysis confirms that all metal nanoparticles
analyzed are alloy structures (Figure 2). The obtained gold and
palladium concentration reveals an atomic ratio close to
1
.5Au:1Pd which is similar to the nominal value. However, the
larger agglomerated structures were found slightly gold rich,
being the atomic ratio close to 2Au:1Pd alloy structures.
Evaluation of Au4f data for Au-nNiO, revealed the presence of
one specie with BE 83.9 eV, which can be attributed to the
using Gaussian-Lorentzian functions and
background.
a Shirley-type
3
3, 34
presence of metallic Au (Table 1).
Evaluation of the Pd 3d
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ARTICLE
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3
6
data for Pd-NiO showed the presence of two Pd 3d5/2 species oxidation from the reaction with atmospheric
2
O .
View Article Online
o
DOI: 10.1039/C9GC01283D
Furthermore, this appears consistent with other reports of Pd
and 23% oxidized Pd respectively. The oxidized Pd makes up catalysts supported on C and C-N type supports indicating no
with binding energies of 335.6 and 337.4 eV attributed to Pd
δ+
35
3
7
a minority of Pd in the samples and is likely due to surface clear transfer of electron density to the nNiO. The Pd3d3/2
Table 1 Statistical median, standard deviation of the particle size and XPS for the Au-nNio, Pd-nNiO, and AuPd-nNiO catalysts.
Pd 3d5/2
Au 4f7/2
Catalyst
Mean particle diameter[nm]
5.2 ± 2.2
Pd0
-
Pd2+
-
Au0
83.9 eV
Au+
-
Au-nNiO
1
00%
Au-nNiO used
-
-
-
-
84.1 eV
100%
84.2 eV
100%
84.0 eV
100%
-
-
-
-
-
6
5
6
.3 ± 2.5
.9 ± 2.0
.1 ± 2.2
1
5 min
Au-nNiO used
0 min
-
3
Au-nNiO used 6
h
-
3
35.6 eV
7%
337.4 eV
23%
Pd-nNiO fresh
3.6 ± 0.8
7
AuPd-nNiO
fresh
AuPd-nNiO after
335.6 eV
76%
335.2 eV
n.d.
337.5 eV
24%
338.2 eV
n.d.
83.6 eV
90%
84.1 eV
n.d.
84.9 eV
10%
n.d.
3
3
.3 ± 1.1
.6 ± 1.4
4
uses
n.d.
n.d.=not determined
peaks were present at 341.0 and 343.4 eV due to Pd and Pdδ+ In all the catalyst, the Ni 2p data shows the presence of two low
0
respectively. After the addition of gold to the catalyst energy peaks (854.0 and 856.0 eV) which are attributed to the
formulation the resulting Au4f7/2 spectra has evidence for the presence of nNiO and Ni(OH)
presence of two Au species with binding energies of 83.6 eV and support (Figure S5). This assignment is supported by the O1s
4.9 eV as it is shown in Figure S4c. This is consistent with the data which shows three peaks at 529.3, 531.0, and 532.9 eV due
2
species on the surface of the
8
0
+ 34
δ+
formation of Au and Au . The presence of Au (10%) can be to Ni-O, Ni-OH and –OH species. There is very little residual
due to the incomplete reduction of gold. The slight negative carbon on the surface of the catalysts from adventitious carbon
shift in Au binding energy from gold foil (84.0) is likely due to or residual PVA (< 0.3 at%) so the O1s spectra is not due to
0
residual surfactant.
Preliminary tests
Preliminary tests were performed on the Au-nNiO catalyst
(
Figure S6), to understand if the operative conditions previously
1
8,
2
optimized by our group for this reaction (70°C, 4h, 10 bar O ),
3
1, 32, 43
can be employed with the catalysts studied in this work.
The tests performed under such operative conditions revealed
that a small amount of the fed HMF was converted (17%) with
an overall carbon balance >98%. Further tests aimed to increase
HMF conversion and FDCA yield. At first, reaction temperature
was increased from 70°C to 90°C: in this way conversion
increased (from 17 to 57%), as well as FDCA yield (from 1% to
Figure 1 Elemental mapping of AuPd-nNiO using electron energy loss spectroscopy (EELS)
1
3%). Then, under the re-optimised reaction temperature, it
the interaction of Au-Pd due to the formation and presence of
AuPd alloy nanoparticles and smaller particle size with respect
has been performed a test at longer reaction time (6h). As a
result of this further optimization it was possible to obtain a
FDCA yield of 25% at 71% HMF conversion.
3
8-40
to the monometallic Au sample.
This behavior has been
4
1, 42
already observed in the case of AuPt alloy.
With the
addition of gold there appears to be no change in the Pd3d3/2
XPS data, Figure S4, lower left, indicating that the Pd remains
mostly reduced with only about 24% of the Pd oxidized.
Catalyst screening
The activity toward HMF oxidation under base free condition of
the prepared materials was evaluated in the optimized
conditions (Figure 3).
4
| J. Name., 2012, 00, 1-3
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Figure 2 XEDS mapping of two representing AuPd particles.

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ARTICLE
The results of this screening demonstrated the inability of the suggests that under base-free conditions the rVaietwioAsrticolefOntlhinee
bare support to catalyse the reaction under base free conditions reaction rates of the single steps involvedDOinI: t1h0.e10H3M9/CF9oGxCid01a2t8io3Dn
with conversion levels below 5%. Similarly, Pd-nNiO sample did pathway is different respect to those reported for the same
not show any relevant catalytic activity but the presence of reaction conducted under basic conditions. In fact, at high pH,
small amount of DFF beside HMFCA at the end of the reaction, Au/Pd NPs containing catalysts, formed HMFCA as main
demonstrated the possibility to follow, in the reported intermediate while FFCA is quickly converted to FDCA, being the
conditions, both a and b reaction pathways reported in Scheme conversion of the alcoholic moiety the rate limiting step of the
4
5
1
. The use of an increased reaction time (15h – Table S2) led to reaction. On the contrary, in the studied base-free HMF
very similar catalytic results; moreover, the introduction of oxidation using nNiO supported systems, a significant change in
NaOH (HMF/NaOH molar ratio 2) confirmed the inability of Pd- the reaction rates seems to be present, with a strong drop in
nNiO to convert HMF also at high pH. Indeed, these conditions the transformation rate of FFCA to FDCA. Therefore, we focus
just promoted the formation of by-products due to HMF our studies on the understanding of the catalytic and structural
decomposition (Figure S7), since 77% HMF conversion was properties of the two gold-based (monometallic and bimetallic)
reached but 59% of carbon loss was observed (Table S2).
systems.
On the contrary, the results obtained using Au-nNiO sample Au-nNiO
clearly demonstrate that, even without the addition of base,
HMF conversion and selectivity as a function of time for Au-
nNiO catalyst is shown in Figure 4. The reported data show that
Au-nNiO sample is able to convert HMF in base-free conditions
even during the induction time, obtaining 7% of HMF
conversion when the set point temperature (90 °C) is reached
7
1% of HMF was converted after 6h of reaction. Both HMFCA
and FFCA were formed at the end of the process and FDCA was
produced with 25% of final yield.
The preparation of a bimetallic Au/Pd system (Au:Pd molar ratio
6
:4) led to a significant increase in terms of activity and
(t=0). In the early stages of the reaction, HMFCA and DFF were
especially of FDCA yield (95% of HMF conversion and 69% FDCA
yield), confirming once again that the alloyed bimetallic
structure enhances the catalytic performance of the parent
the main products detected, meaning that both reaction
pathways showed in Scheme 1 can occur. However, the
selectivities of these two intermediates evolved differently: DFF
selectivity steadily dropped within the first 30 minutes, while
HMFCA one was nearly steady within the same period, with a
constant decrease starting from 30 minutes on. FFCA formation
started at t=0 and its selectivity increased within the first 2h.
Since at t=0 FFCA was already present in the reaction medium;
it could be hypothesised that this intermediate derived from
DFF conversion since HMFCA was not converted in the first 30
1
9
metal, as already reported with titania and active carbon
4
4
supported materials (AC) with similar Au:Pd molar ratio.
However, it is noteworthy to emphasise that using nNiO as
support the reactions are carried out under base-free
conditions, indicating the important role of the support itself.
Indeed, it is possible to hypothesize that the nNiO support
changes the electronic and geometrical properties of the metal
affecting the substrate binding on the metal/support interface
Figure 4 HMF conversion and product yields for the prepared Au, AuPd and Pd catalysts
Figure 3 HMF Conversion and product selectivity as a function of time using Au-nNiO.
supported on nNiO. Reaction conditions: 90 °C, 6h, 10 bar O
2
, HMF/total metal molar
Reaction conditions: 90 °C, 10 bar O
2
, HMF/total metal molar ratio = 100. Legend: ■
ratio = 100. Legend: ■ HMF conversion, ■ HMFCA yield, ■ FFCA yield, ■ FDCA yield, ■
DFF yield.
HMF conversion,
selectivity.

HMFCA selectivity, ◄ DFF selectivity, ▲ FFCA selectivity, ► FDCA
and therefore HMF conversion is completed even without the minutes of reaction. Moreover, the presence of a lower amount
presence of a base. The catalytic results obtained using Au-nNiO of DFF at t=0 compared to HMFCA, could be ascribed to a faster
and AuPd-nNiO samples indicated the presence of high amount conversion of the former. FDCA formation started after 30
of FFCA intermediate after 6 h of reaction (25%). This result minutes, i.e. exactly when HMFCA was converted to FFCA,
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suggesting that FDCA production was probably achieved First, a preliminary experiment was carried out by rVeieawcAtritnicgleFOFnClinAe
through reaction pathway which does not involve DFF with the chosen catalyst, to verify its DabOiIl:i1t0y.1t0o39c/Co9nGvCe0rt12t8h3iDs
formation.
reaction intermediate. After 2 h of reaction, 30% conversion of
Therefore, the reported data indicate that, using Au-nNiO was shown (Table 2, entry 1) with complete transformation of
sample, significant changes in product selectivities were the reagent into FDCA, confirming the activity of the catalyst
observed after 30 minutes of reaction. Indeed, in the earliest towards FFCA conversion with low conversion but high
reaction stage, HMFCA and DFF were produced in parallel selectivity (100%).The use of DFF as reactant (Table 2, entry 2)
pathways, with different reaction rates and can be both led to 28% conversion with formation of FFCA, but in this case,
considered as primary intermediates of HMF oxidation. On the the formation of an unknown compound, named as X, was
other hand, FFCA formation increased up to 40% in the early observed. HPLC-MS analysis performed to separate and identify
period of the reaction and then its selectivity remained constant this product indicate the formation of oligomeric products,
with time, probably due to a similar rate of formation and probably obtained through a preliminary ring-opening reaction
conversion to FDCA. It must be said that this molecule, which is (Figure S8), nevertheless, some specific studies are still needed
normally found in very low amount in the presence of base, due to clearly identify this molecule.
to its fast transformation to FDCA, was present with high When DFF was loaded using a catalyst already tested for 30
quantity with respect to HMFCA.
minutes in HMF oxidation (Table 2, entry 3) a significant
Finally, the diacid product started to be formed at 30 minutes decrease in its conversion was observed (17% vs 28%),
and its selectivity continued to increase throughout the suggesting the partial deactivation of the catalyst versus DFF
reaction, until it reached a plateau (from 6h on), probably due transformation. This phenomenon could be ascribed to
to catalyst deactivation, which can be caused on its turn, to different causes: i) the partial covering of Au nanoparticles by
intermediate adsorption on catalyst surface.
NiO during the reaction or ii) the catalyst activity inhibition by
In order to verify the possibility to increase the catalytic activity some of the molecules present (or formed) in the reaction.
by addition of a base, HMF oxidation was evaluated by adding 2 In order to verify the first hypothesis, a test using bare nNiO to
equivalents of the NaOH in the reaction medium (Table S2). As oxidise DFF has been carried out (Table 2, entry 4). In these
already observed for Pd-nNiO, also in the case of Au-nNiO, the experimental conditions, high DFF conversion was obtained
higher pH did not increase the rate of FDCA formation. Indeed, (34%) but low FFCA selectivity was observed. Thus, NiO, which
HMF conversion was promoted (68% vs 15% after 30 min of was demonstrated to be inactive in HMF oxidation, was able to
reaction) and the yield in HMFCA was higher (36% vs 5%) but promote the conversion of DFF. However, its conversion manly
HMF degradation was predominant and carbon loss was found leads to the formation of an new undefined product (named as
to be very high.
Y) detected from HPLC analysis (Figure S9). It is very important
The significant change in the activity of Au-nNiO sample after to underline that the product formed with bare nNiO was
few minutes of reaction in base-free conditions can be due to different from the one revealed with gold based catalyst,
possible modification occurring to the catalyst and/or the meaning that nNiO reactivity significantly differs from the one
inhibition effect on sample due to reactive intermediates showed by Au-nNiO material. In addition, it is worth to notice
produced during HMF oxidation. We can exclude the first that FDCA was never formed when DFF was used as starting
hypothesis as TEM and XPS performed on Au-nNiO after 15, 30 material, indicating that the only available route for its
min and 6 h of reaction did not show evident modifications in formation using NiO based catalysts proceeds through HMFCA
Au particle size and in Au oxidation state (Table 1).
reaction pathway.
For better understanding the specific role that the single Thus, it is possible to conclude that Au-nNiO catalyst is probably
reaction steps have on the overall reaction network, evaluation inhibited by the presence of DFF (or by the compounds formed
of the intermediates as starting reagents has been carried out from its conversion), which prevents FFCA transformation to
using Au-nNiO (Table 2).
FDCA. Therefore, a poisoning effect of DFF can be postulated,
being FFCA conversion into FDCA hampered when DFF is fed.
This hypothesis has been confirmed by two further tests, where
DFF and FFCA were used as starting material in different ratio
(Table S3). In these tests, irrespective of the DFF/FFCA molar
ratio, FDCA yield was always very low (around 2%), definitively
far from that obtained feeding the only FFCA, where 30% yield
to FDCA was observed. This data demonstrate once again the
negative effect played by the presence of DFF in the diacid
production.
Table 2 Catalytic tests using reaction intermediates (FFCA, DFF and HMFCA) as starting
material. Reaction conditions: 90°C, 2h, 10 bar O , HMF/total metal molar ratio = 100.
2
FFCA FDCA
Conv.
%)
Unkn Unkn.
Entry Reactant
sel
sel
(%)
100
-
-
-
(
X
Y
(%)
1
2
3
4
5
FFCA
30
28
17
34
36
-
No
Yes
Yes
Traces
Traces
No
No
No
Yes
No
DFF
32
27
4
DFFa
DFFb
On the contrary, the oxidation reaction using HMFCA as reagent
(Table 2, entry 5) produced both FFCA and FDCA, confirming the
HMFCA
69
31
possibility to form the diacid through HMFCA reaction pathway.
a
b
Catalyst: used Au-nNiO; Catalyst: nNiO
AuPd-nNiO
6
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17
2
DFF
93
83
View Article Online
DOI: 10.1039/C9GC01283D
To verify the possibility of metal leaching and the participation
of leached metal species in the reaction, a “hot filtration”
catalytic test was performed in order to evaluate the activity of
leached metal species from the catalyst. This test was carried
out by removing the catalyst after 2h of reaction and the
resulting solution has been loaded in the autoclave immediately
2
and charged with 10 bar of O and kept at 90 °C for 2h (Figure
6
). Since the conversion and the yields of the products remained
unchanged it was excluded the effect of homogeneous metal
species in the catalytic activity. To further exclude the leaching
of metals from catalyst, XRF test was carried out on the filtered
reaction solution after reactivity tests. Such tests revealed that
no homogeneous metals species were found, thus metal
leaching was excluded. To corroborate this hypothesis, XRF
tests were performed on the spent catalyst and, by comparing
those results with the ones measured for the fresh powder,
there were found no significant differences in both overall
metal loading and Pd/Au molar ratio (Table S4).
Since catalyst stability is one of the most important features
that has to be taken into account during the development of a
new material, reusability tests were carried out on the sample
that showed the highest performance, i.e. the bimetallic AuPd
system.
Figure 5 HMF Conversion and product selectivity as a function of time using AuPd-nNiO.
Reaction conditions: 90 °C, 10 bar O , HMF/total metal molar ratio = 100. Legend: ■
HMFCA selectivity, ◄ DFF selectivity, ▲ FFCA selectivity, ► FDCA
2
HMF conversion,
selectivity.

AuPd-nNiO catalysts with nominal Au:Pd molar ratio of 6/4
were evaluated for HMF free-oxidation in terms of activity and
long term stability. AuPd-nNiO catalyst displayed higher activity
and selectivity to the desired product and a distinct catalytic
behaviour compared to the monometallic Au-nNiO system as it
is presented in Figure 5. Indeed, appreciable quantity of FDCA
was already present at t=0, together with all the other reaction
intermediates, i.e. DFF, HMFCA and FFCA. The shape of the
curves representing FDCA and FFCA clearly shows the typical
trend of consecutive products, while the amounts of detectable
DFF and HMFCA were very low after the early period of the
reaction. These two intermediates were both formed from HMF
over AuPd-nNiO catalyst and their concentration decreased as
a function of reaction time with a similar trend, despite of what
observed for Au supported catalyst. By increasing reaction
timing (14h), it was possible to reach full conversion of HMF into
FDCA. Thus, it was hypothesized that the bimetallic system does
not suffer from deactivation as reported for the monometallic
system (Au-nNiO). In order to verify the ability of the bimetallic
catalyst to convert these two different intermediates, HMFCA
and DFF were separately used as reagent, (Table 3). After 2 h of
reaction, high conversion of both molecules was obtained,
demonstrating that FFCA can be produced efficient either from
DFF or HMFCA. Although, the use of gold promoted FFCA
formation from DFF, FDCA was not formed with this catalyst; on
the contrary, the use of a bimetallic system favoured also FDCA
formation from DFF.
Figure 6 Leaching tests for the prepared AuPd-nNiO. Reaction conditions: 90 °C, 10 bar
O
2
, HMF/total metal molar ratio = 100. Legend: ■ HMF conversion,

HMFCA
selectivity, ◄ DFF selectivity, ▲ FFCA selectivity, ► FDCA selectivity.
However, in terms of product selectivity a significant difference
was observed, on the basis of the choice of reactant suggesting
the presence, in the case of DFF of some inhibition effects on
the transformation of FFCA to FDCA.
The reusability tests as shown in Figure 7 for the bimetallic
catalyst showed a high level of stability after three times
without any loss of activity; nevertheless, the fourth reaction
Table 3 Catalytic tests using reaction intermediates DFF and HMFCA as starting material. carried out on the same material was accompanied by a small
Reaction conditions: 90 °C, 2h, 10 bar O
ratio = 100.
2
, Catalyst AuPd-nNiO, HMF/total metal molar decrease in the catalytic performance. In fact, HMF conversion
was steady for the first three uses (95%), after that this value
dropped to 87%. Similarly, FDCA yield decreased from 70% of
the first three uses to 55%. Characterisation of the used catalyst
by means of TEM analysis was carried out and it was found that
Entry
1
Reactant Conv. (%) FFCA sel FDCA sel
(
41
%)
(%)
59
HMFCA
94
the d
m
AuPd particle size of the used AuPd-nNiO catalyst was
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similar to the fresh (3.3 and 3.6 nm, for fresh and used AuPd- reaction step in the presence of supported monVoiemw eArttiaclleliOcnAlinue
nNiO respectively, Table 1), even the formation of few catalysts under base-free conditions. FDinOaI:ll1y0,.1w03e9/Cp9reGsCe0n12t8a3Dn
aggregates was observed (Figure S10). However, XPS showed effective catalytic system that can promote the oxidation of
Au 4f and Pd 3d peaks with a reduced intensity (Figure S11), HMF to FDCA with high yield, activity and good level of stability
probably due to the adsorption of the products on the active without the use of base, making the process more green and
sites.
cost-effective.
Conflicts of interest
There are no conflicts to declare
Acknowledgements
This work was co-funded through a SINCHEM Grant and a PhD
Grant from the “Toso Montanari Foundation” (Bologna, Italy).
SINCHEM is a Joint Doctorate program selected under the
Erasmus Mundus Action 1 Programme (FPA 2013-0037) of the
European Union.
Lidia E. Chinchilla and Gianlugi A. Botton would like to thank to
the facilities and technical staff of the Canadian Centre for
Electron Microscopy (CCEM) at Macmaster University.
Notes and references
Figure 7 Reusability tests for the oxidation of HMF using AuPd-nNiO catalyst. Reaction
conditions: 90 °C, 6h, 10 bar O
2
, (HMF/total metal molar ratio = 100). Legend: ■ HMF
1.
R. A. Sheldon, Green Chemistry, 2014, 16, 950-963.
J. J. Bozell and G. R. Petersen, Green Chemistry, 2010, 12,
conversion, ■ HMFCA yield, ■ FFCA yield, ■ FDCA yield, ■ DFF yield.
2
.
5
39-554.
3
.
R.-J. van Putten, J. C. van der Waal, E. de Jong, C. B.
Rasrendra, H. J. Heeres and J. G. de Vries, Chemical
Reviews, 2013, 113, 1499-1597.
Conclusions
4
5
.
.
A. A. Rosatella, S. P. Simeonov, R. F. M. Frade and C. A. M.
Afonso, Green Chemistry, 2011, 13, 754-793.
A. Gandini, A. J. D. Silvestre, C. P. Neto, A. F. Sousa and M.
Gomes, Journal of Polymer Science Part A: Polymer
Chemistry, 2009, 47, 295-298.
H. Nakajima, P. Dijkstra and K. Loos, Polymers, 2017, 9, 523.
https://www.mordorintelligence.com/industry-
reports/global-polyethylene-teraphtalate-market-
industry, (accessed March 15th, 2018).
In summary, we have developed effective, stable NiO-based
supported Au-Pd catalysts that can efficiently promote the
base-free oxidation of HMF to FDCA in water using molecular
oxygen at mild reaction conditions. By using a specific Au:Pd
metal composition (6/4 atomic ratio) depositing preformed
Au/Pd nanoparticles on nNiO as the chosen support, we
succeeded to improve not only catalytic activity but also to
enhance the yield to FDCA, by minimising the synthesis of side
6
7
.
.
by-products and to improve overall the catalyst stability. NiO 8.
acts as an effective support providing basic sites that can 9.
Z. Zhang and K. Deng, ACS Catalysis, 2015, 5, 6529-6544.
US20150051412.
W. Partenheimer and Vladimir V. Grushin, Advanced
Synthesis & Catalysis, 2001, 343, 102-111.
1
1
1
1
0.
1.
2.
3.
promote the reaction and the proper choice of Au-Pd chemical
composition favours the formation of FDCA. Moreover, by
performing the aerobic oxidations of intermediates, like, DFF,
FFCA, HMFCA in the presence of bare NiO, Au-nNiO and AuPd-
nNiO, we found that the presence of nNiO promoted mainly the
conversion of DFF to FFCA (scheme 1, pathway a) and only with
the addition of Au the activation of HMF was favoured, showing
the synergistic effect between Au and nNiO. Moreover, in the
H. AitꢀRass, N. Essayem and M. Besson, ChemSusChem,
2
015, 8, 1206-1217.
O. Casanova, S. Iborra and A. Corma, ChemSusChem, 2009,
, 1138-1144.
2
Y. Y. Gorbanev, S. K. Klitgaard, J. M. Woodley, C. H.
Christensen and A. Riisager, ChemSusChem, 2009, 2, 672-
6
75.
presence of Au formation of the consecutive products HMFCA, 14.
FFCA and FDCA were observed. Addition of a second metal like
Pd with Au/Pd atomic ratio of 6/4 promoted significantly the
Z. Miao, Y. Zhang, X. Pan, T. Wu, B. Zhang, J. Li, T. Yi, Z.
Zhang and X. Yang, Catalysis Science & Technology, 2015,
5, 1314-1322.
J. Cai, H. Ma, J. Zhang, Q. Song, Z. Du, Y. Huang and J. Xu,
Chemistry – A European Journal, 2013, 19, 14215-14223.
K. R. Vuyyuru and P. Strasser, Catalysis Today, 2012, 195,
1
1
1
5.
6.
7.
rate of HMF formation and the yield to FDCA (100% after 14h).
By studying the catalytic performance of HMFCA and DFF
intermediates it was evident that both reaction pathways were
observed with high activity and the addition of Pd further
enhanced the oxidation of FFCA to FDCA, a difficult elementary
1
44-154.
S. E. Davis, B. N. Zope and R. J. Davis, Green Chemistry,
012, 14, 143-147.
2
8
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 9 of 9
Please Gd roe en no tC ha ed mj u iss tt r my argins
Journal Name
ARTICLE
1
8.
S. Albonetti, T. Pasini, A. Lolli, M. Blosi, M. Piccinini, N. 43.
Dimitratos, J. A. Lopez-Sanchez, D. J. Morgan, A. F. Carley,
G. J. Hutchings and F. Cavani, Catalysis Today, 2012, 195,
A. Lolli, R. Amadori, C. Lucarelli, M. G. CutrufVeilelwo,AErt.icRleoOmnlbinie,
F. Cavani and S. Albonetti, MicropDoOrIo: u10s.1a0n3d9/MC9eGsCo0p1o2r8o3uDs
Materials, 2016, 226, 466-475.
1
20-126.
A. Lolli, S. Albonetti, L. Utili, R. Amadori, F. Ospitali, C.
Lucarelli and F. Cavani, Applied Catalysis A: General, 2015, 45.
04, 408-419.
44.
A. Villa, M. Schiavoni, S. Campisi, G. M. Veith and L. Prati,
ChemSusChem, 2013, 6, 609-612.
T. Pasini, M. Piccinini, M. Blosi, R. Bonelli, S. Albonetti, N.
Dimitratos, J. A. Lopez-Sanchez, M. Sankar, Q. He, C. J.
Kiely, G. J. Hutchings and F. Cavani, Green Chemistry, 2011,
13, 2091-2099.
1
9.
5
2
2
2
2
0.
1.
2.
3.
X. Wan, C. Zhou, J. Chen, W. Deng, Q. Zhang, Y. Yang and Y.
Wang, ACS Catalysis, 2014, 4, 2175-2185.
C. Zhou, W. Deng, X. Wan, Q. Zhang, Y. Yang and Y. Wang,
ChemCatChem, 2015, 7, 2853-2863.
N. K. Gupta, S. Nishimura, A. Takagaki and K. Ebitani, Green
Chemistry, 2011, 13, 824-827.
Z. Gao, R. Xie, G. Fan, L. Yang and F. Li, ACS Sustainable
Chemistry & Engineering, 2017, 5, 5852-5861.
2
2
4.
5.
J. Artz and R. Palkovits, ChemSusChem, 2015, 8, 3832-3838.
G. Yi, S. P. Teong and Y. Zhang, Green Chemistry, 2016, 18,
9
79-983.
2
2
2
2
3
6.
7.
8.
9.
0.
D. K. Mishra, H. J. Lee, J. Kim, H.-S. Lee, J. K. Cho, Y.-W. Suh,
Y. Yi and Y. J. Kim, Green Chemistry, 2017, 19, 1619-1623.
D. Yan, J. Xin, C. Shi, X. Lu, L. Ni, G. Wang and S. Zhang,
Chemical Engineering Journal, 2017, 323, 473-482.
A. Villa, C. E. Chan-Thaw, G. M. Veith, K. L. More, D. Ferri
and L. Prati, ChemCatChem, 2011, 3, 1612-1618.
L. Prati, A. Villa, F. Porta, D. Wang and D. Su, Catalysis
Today, 2007, 122, 386-390.
A. Villa, G. M. Veith, D. Ferri, A. Weidenkaff, K. A. Perry, S.
Campisi and L. Prati, Catalysis Science & Technology, 2013,
3
, 394-399.
3
3
1.
2.
S. Albonetti, A. Lolli, V. Morandi, A. Migliori, C. Lucarelli and
F. Cavani, Applied Catalysis B: Environmental, 2015, 163,
5
20-530.
A. Lolli, S. Albonetti, L. Utili, R. Amadori, F. Ospitali, C.
Lucarelli and F. Cavani, Applied Catalysis A: General, 2015,
5
04, 408-419.
3
3
3.
4.
G. M. Veith, A. R. Lupini and N. J. Dudney, The Journal of
Physical Chemistry C, 2009, 113, 269-280.
A. Villa, N. Dimitratos, C. E. Chan-Thaw, C. Hammond, G. M.
Veith, D. Wang, M. Manzoli, L. Prati and G. J. Hutchings,
Chemical Society Reviews, 2016, 45, 4953-4994.
C. E. Chan-Thaw, A. Villa, G. M. Veith and L. Prati,
ChemCatChem, 2015, 7, 1338-1346.
E. H. Voogt, A. J. M. Mens, O. L. J. Gijzeman and J. W. Geus,
Surface Science, 1997, 373, 210-220.
C. E. Chan-Thaw, A. Villa, D. Wang, V. D. Santo, A. Orbelliꢀ
Biroli, G. M. Veith, A. Thomas and L. Prati, ChemCatChem,
3
3
3
5.
6.
7.
2
015, 7, 2149-2154.
3
3
8.
9.
J. Radnik, C. Mohr and P. Claus, Physical Chemistry
Chemical Physics, 2003, 5, 172-177.
M. P. Casaletto, A. Longo, A. Martorana, A. Prestianni and
A. M. Venezia, Surface and Interface Analysis, 2006, 38,
2
15-218.
4
4
4
0.
1.
2.
A. Villa, A. Gaiassi, I. Rossetti, C. L. Bianchi, K. van Benthem,
G. M. Veith and L. Prati, Journal of Catalysis, 2010, 275,
1
08-116.
H.-Y. Park, T.-Y. Jeon, J. H. Jang, S. J. Yoo, K.-H. Choi, N. Jung,
Y.-H. Chung, M. Ahn, Y.-H. Cho, K.-S. Lee and Y.-E. Sung,
Applied Catalysis B: Environmental, 2013, 129, 375-381.
A. Villa, A. Jouve, F. J. Sanchez Trujillo, D. Motta, L. Prati
and N. Dimitratos, Catalysts, 2018, 8, 54.
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