Designing effective solid catalysts for biomass conversion: Aerobic oxidation of ethyl lactate to ethyl pyruvate

Article abstract of DOI:10.1039/c8gc00032h

The direct oxidative dehydrogenation of lactates with molecular oxygen is a promising route for producing bio-based pyruvates. But practical implementation of this route means high yields and mild conditions, which in turn require expensive noble-metal ca

Full text of DOI:10.1039/c8gc00032h

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Designing effective solid catalysts for biomass conversion: Aerobic
oxidation of ethyl lactate to ethyl pyruvate
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a*
Wei Zhang, Bernd Ensing, Gadi Rothenberg and N. Raveendran Shiju
DOI: 10.1039/x0xx00000x
The direct oxidative dehydrogenation of lactates with molecular oxygen is a promising route for producing biobased
pyruvates. But practical implementation of this route means high yields and mild conditions, which in turn require
expensive noble–metal catalysts. Here we report a novel catalytic approach for efficient conversion of ethyl lactate to
ethyl pyruvate. We show that vanadia supported on activated carbon acts synergistically with homogeneous pyridine–type
additives, giving high conversion and selectivity. Control experiments and simulations show that the reaction follows a
two–step pathway: first, the pyridine–lactate complex forms, followed by transfer to the vanadium active site where the
oxidation occurs. Building on these results, we design a new solid catalyst where the vanadia sites are impregnated on a
pyridine–rich carbonaceous support made from poly(4–vinylpyridine). This catalyst, made from abundant elements,
combines the advantages of the homogeneous pyridine additive and the vanadia active site. The combination lowers local
mass–transfer barriers and improves stability. The catalyst gives over 90% selectivity at 80% conversion at 130 °C and 1
atm oxygen, and can be reused at least five times without losing activity.
www.rsc.org/
1
9-21
oxides and iron phosphates.
While these routes show high
2
2
activity, they are also energy intensive. The lactate product is
2
easily over-oxidised, lowering the selectivity. This over-
Introduction
3
The 21st century is an exciting time for organic chemists. In the
coming decade, we can expect major changes in the
production and consumption habits of our society where
1
4
oxidation can be suppressed in liquid–phase systems, but the
milder conditions typically require noble metal catalysts for
2
oxygen activation. Hayashi et al. reported Pd–metal catalysts
4
1
carbon sources are concerned. The most significant is the
on activated carbon for the oxidation of lactate to pyruvate in
2
advent of electric vehicles running on batteries, which will
5, 26
2
affect the petrochemicals market. But just as important is
, 3
the presence of NaOH.
Ding and co-workers used 3Pb–
4
-6
1Pt/carbon black catalyst for the synthesis of pyruvic acid in
2
good yields, using an excess of LiOH to adjust the pH value.
the move towards biomass-based bulk- and fine-chemicals.
7
Biomass can replace fossil carbon sources, primarily through a
7
set of simple building blocks, so-called platform molecules.
, 8 Previously, we showed that activated carbon can enhances the
product selectivity, inhibiting the pyruvate polymerization in
A good example of these are lactic acid and lactates, which are
9
2
8
, 10
the liquid phase. Despite these achievements, however, no
simple and cost-effective catalytic system for the oxidation of
lactates to pyruvates with oxygen under mild conditions has
been reported. Developing such catalysts is essential if we are
to really replace fossil-based carbon sources with biobased
ones.
readily obtained from biomass fermentation.
Their market
1
1
size is already substantial, over $1.7 billion in 2015. They can
be converted to important industrial chemicals, including
1
2
pyruvic acid, acrylic acid, and propanediol. Pyruvic acid and
its esters, for example, are used in the food, cosmetics, and
1
3, 14
agrochemical sectors.
The direct catalytic oxidation of
Here we report that combining vanadium oxide catalysts and
base additives creates a catalytic system that can oxidise ethyl
lactate to ethyl pyruvate with molecular oxygen in high yields.
Following on our recent work on mesoporous vanadia-titania
lactic acid is a promising route to pyruvic acid, bypassing the
1
5, 16
current energy–intensive pyrolysis of tartaric acid.
But this
oxidation is a challenging process, not least because competing
over-oxidation pathways lower product selectivity and yields.
2
9
1
7, 18
catalysts, we screened different metal oxides supported on
activated carbon, examining the role of basic additives in this
oxidation reaction. Combining experiments and simulations,
we find that in the presence of pyridine additives, the reaction
follows a two-step pathway: the lactate first complexes with
the additive and then travels to the vanadium active site.
Based on these findings, we design an effective catalyst for this
Several groups have studied this reaction.
In the vapour
phase, various solid catalysts were reported, including metal
reaction, comprised of
a
pyridine-rich carbon support
impregnated with vanadia sites.
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Results and discussion
We started by testing various carbon–supported catalysts for
the oxidative dehydrogenation of ethyl lactate to ethyl
pyruvate under 1 atm oxygen pressure (eq 1). Initially, we
tested metal oxides known as good oxidation catalysts for
2
4, 30
alcohols:
iron oxide, cobalt oxide, copper oxide and
/C). These were compared to
vanadium oxide, (denoted as MO
x
commercial Pt/C and Ru/C catalysts. Table 1 summarises the
conversion, selectivity, yield and turnover number (TON)
values. Fe, Co, Cu and Pt did not catalyse this reaction. Ru/C
gave the highest selectivity at 99%, but with a low conversion
x
of 9%. Since VO /C showed the highest activity (34%
conversion and TON = 223), we decided to focus on vanadium–
based catalyst and try and improve the selectivity through
catalyst optimization.
Previous studies by our group and others showed that doping
carbon materials with nitrogen atoms can facilitate catalytic VO
Fig. 1 The influence of nitrogen additives on oxidation of ethyl lactate in the present of
x
/C catalysts. Reaction conditions: ethyl lactate 5 mmol, additives 5 mol%, VO
mg (0.15 mol% V relative to substrate), 1 atm O , diethyl succinate (solvent, 1 ml), 130
C, 4 h. The inset shows the selectivity profiles to ethyl pyruvate.
x
/C 25
3
0-32
oxidation reactions.
A key role in this surface activation is
2
°
probably attributed to pyridinic and pyrrolic nitrogen
33-36
groups.
We therefore decided to study the effects of
In a typical reaction, ethyl lactate (5 mmol) and oxygen were
reacted in the presence of using 25 mg of VO /C catalyst (0.15
various nitrogen–containing additives in our reaction system,
aiming to understand the effect of such additives on the
aerobic oxidation of lactates.
x
mol% V relative to substrate) in combination with different
nitrogen additives. Control experiments showed that diethyl
succinate is a good solvent under these conditions (see Fig. S1
in the supporting information). In all cases, the additive
amount was kept constant at 5 mol%. Fig. 1 shows the ethyl
lactate conversion profiles for three additives: pyridine,
pyrrole and N–methyl pyrrole. Adding pyridine facilitated the
reaction, while pyrrole and N–methyl pyrrole retarded it.
Importantly, adding pyridine also increased the selectivity
towards ethyl pyruvate, while with pyrrole and N–
methylpyrrole the selectivity was unchanged (see Fig. 1, inset).
These effects may be related to the additives’ basicity: Pyridine
is more basic than pyrrole, as its lone pair of electrons is not
delocalized on the aromatic ring. The Lewis basicity strength
pyridine > N–methylpyrrole > pyrrole correlates with the
Table 1 Catalytic oxidation of ethyl lactate with molecular oxygen over various
a
catalysts.
Conversion
b
Selectivity
b
(%)
Yield
(%)
–
c
Entry
1
Catalysts
C
TON
–
(
%)
trace
–
2
3
4
5
6
7
CoO
x
x
/C
/C
1
64
20
47
99
97
84
0.7
0.4
1.2
8.9
3.6
29
5
3
3
7
conversion.
CuO
2.2
2.4
9
To examine this hypothesis further, we studied various
pyridine additives bearing electron–withdrawing and electron–
donating groups (Table 2). The latter were more reactive. The
observed reaction rate constants (kobs) in the presence of
FeO
x
/C
8
d
Ru/C
Pt/C
36
140
223
e
meta–substituted pyridines were ranked –CH > –H > –Cl > –Br
3
4
>
–NO (cf. entries 2–5, Table 2). Ortho–substituents showed
2
VO
x
/C
34
similar trends (Table 2, entries 9–10 vs. entry 11).
The Hammett plot shown in Fig. 2 quantifies the meta–
38, 39
a
Reaction conditions: ethyl lactate 5 mmol, 25 mg MO
x
/C catalyst (metal loading substituent effect, with ρ = –2.68.
.3 mmol/g), 1 atm O diethyl succinate (solvent, 1
Good correlations are
2
0
b
2
,
ml), 130 °C, 4 h. obtained (R =0.86). This indicates that this reaction is
Determined by GC using biphenyl as an internal standard.
Calculated as moles of ethyl pyruvate per moles of metal loading.
substituent–sensitive and kinetically favored in the presence of
40, 41
c
d
e
electron–donating groups.
There are two exceptions,
Commercial 5 wt.
% ruthenium on carbon (Ru loading 0.5 mmol/g).
namely for hydroxyl and amino substituents, the former may
reflect the known tendency of phenol groups for trapping
Commercial 1 wt. % platinum on carbon (Pt loading 0.05 mmol/g).
4
2
free–radicals, thus hampering the oxidation reaction (Table
, entries 7 and 13). For the latter, the amino substituent
2
probably can compete with the pyridine as an organic base,
2
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thereby suppressing the reaction (Table 2, entries 8, 12 and profiles over a period of 1 h and determining the selectivity
4). and yield in the presence of various inorganic and organic
bases (Table S1). Plain VO /C gave 11% conversion and 86%
selectivity to ethyl pyruvate. Inorganic Brønsted bases, with
varying pK of 0.2–7.9, retarded the reaction (Table S1, entries
1
x
Table 2 Oxidation of ethyl lactate to ethyl pyruvate in the presence of pyridine
a
additives.
b
Conversion
Selectivity
Yield
(%)
29
–5
–1
c
1–4). These bases also promoted the decomposition of ethyl
pyruvate to ethanol. The organic bases piperidine,
diethylamide and aniline (Table S1, entries 6–7, 9), only show
Entry
Additive
none
b
b
k
obs (10 ∙Mh )
(%)
(%)
1
2
34
83
10.0
12.4
53
58
50
41
91
48
54
43
36
little advantages. Interestingly, pyridine, with its moderate pK
of 8.8 (Table S1, entry 8), gave the highest conversion (31%).
Generally, the lower pK of nitrogen-derived organic bases
represents the higher density of lone pair electron. Piperidine
pK =2.7) and diethylamide (pK =2.9) interact more strongly
b
3
4
5
6
93
87
87
80
14.4
11.7
9.4
b
(
b
b
with ethyl lactate than pyridine (Table S1). The latter probably
acts as a ‘catalytic shuttle’. The pyridine nitrogen first forms a
moderate hydrogen-bonding with the lactate OH. Then the
36
21
16
49
29
21
14
45
8.3
complex transfers to a VO /C active site, releasing the
x
4
3
reactant. In contrast, the strong organic bases piperidine and
diethylamide form a tighter lactate/base complex through
strong hydrogen-bonded networks, that are less likely to
release the activated ethyl lactate. This also explains why
amino-substituted pyridine suppresses activity (see Table 2).
The reason that aniline had no impact on the conversion, even
though its pKb is comparable to pyridine, may be because
aniline can form a Schiff base complex with the lactate
7
8
9
97
90
92
5.0
3.6
11.1
1
1
1
0
1
2
46
34
12
95
84
93
44
28
11
10.6
7.8
4
4
carbonyl group.
To understand this base effect, we studied the interaction
between ethyl lactate and pyridine/pyrrole compounds using
2.5
4
5, 46
density functional theory (DFT) calculations.
Geometry
1
1
3
4
35
6
88
52
31
3
8.1
1.4
optimization shows that both pyridine and pyrrole can form
hydrogen–bond with the hydroxyl group of ethyl lactate (Fig.
S2). The hydrogen bond between pyridine and ethyl lactate
(
1.722 Å) is shorter than that of pyrrole (2.037 Å). The
interaction between ethyl lactate and pyridine is stronger than
that of ethyl lactate and pyrrole by 32 kcal/mol. Actually, the
hydroxyl H proton transfer is an essential step in this
a
Reaction conditions: ethyl lactate 5 mmol, additive 5 mol%, VO
x
/C 25 mg (0.15
mol% V relative to substrate), 1 atm O , diethyl succinate (solvent, 1 ml), 130 °C,
2
b
c
4
h. Determined by GC using biphenyl as an internal standard.
kobs is the
1
9
–1
observed zero–order rate constant (M∙h ).
reaction. To analyse whether pyridine or pyrrole act as
proton acceptors, we calculated the joint structures of ethyl
lactate–pyridine (denoted as EL–pyridine) and ethyl lactate–
pyrrole (EL–pyrrole) at different distances (Fig. S3). We found
that pyridine can easily accepted the hydroxyl H of ethyl
lactate, while pyrrole repelled it. This can also explain why
pyrrole compounds supress the reaction.
Fig. 2 Hammett plot for ethyl lactate oxidation over various meta–substituted pyridine,
meta–Hammett constant. Reaction conditions: ethyl lactate 5 mmol, additives 5 mol%,
VO /C 25 mg (0.15 mol% V), 1 atm O , diethyl succinate (solvent, 1 ml), 4 h.
σ
x
2
We then studied how base additive could influence this
Fig. 3 Potential energy profile of the activation process of ethyl lactate by pyridine. The
reaction. This was done by monitoring the initial reaction atomic configurations corresponding to the initial, transition and intermediate state.
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(
a)
H
H
H
H
H
H
H
H
H
H
H
N
O
Cl
N
H
O
O
Intermediate state
pyridine hydrochloride
Fig. 4 (a) The structures of simulated intermediate and pyridine hydrochloride. (b) The time–resolved conversion profile of ethyl lactate over different additives in the present of
VO /C catalyst. Reaction conditions: ethyl lactate 5 mmol, additives 5 mol%, VO /C 25 mg (0.15 mol% V), 1 atm O , diethyl succinate (solvent, 1 ml), 130 °C. (c) Kinetics plots for the
conversion of ethyl lactate over different additives in the present of VO /C, catalyst, where C represents the substrate concentration at time t and C is the initial concentration.
d) Selectivity to ethyl pyruvate plotted against ethyl lactate conversion, additive: red: pyridine hydrochloride (5mol %), black: {pyridine + HCl} (5 mol% each).
x
x
2
x
t
o
(
–
The DFT results suggest that pyridine could trigger ethyl lactate (Fig. 4d), ruling out an effect of a separate Cl counter ion.
dissociation via proton transfer. As shown in Fig. 3, this These control experiments confirm that, protonated pyridine
reaction proceeds through a concerted mechanism, starting plays a vital role in this reaction, in agreement with the DFT
from the initial reactant complex. First, the hydroxyl proton simulation results.
transfers to the pyridine nitrogen, forming a transition state We then hypothesised that the ethyl lactate molecules first
with a relative energy of –7 kcal/mol (with respect to interact with pyridine via hydrogen bonding and only then
separated reactants). Next, the carboxyl oxygen rotates travel to the vanadium oxide active site. To test this, we ran a
towards the protonated nitrogen via hydrogen bond (1.46 Å).
simultaneously, the hydroxyl oxygen moves towards the
neighbouring pyridine hydrogen, giving another hydrogen
bond with the length of 1.73 Å. Finally, an intermediate is
produced by forming an eight-membered ring between the
ethyl-propionate-2-oxide and pyridine species. In addition, the
β
–hydrogen of ethyl-propionate-2-oxide was also activated by
pyridine: the C–H bond stretches from 1.121 Å to 1.125 Å
during this process.
β
From the DFT simulation, we know that pyridinic nitrogen can
be protonated by ethyl lactate, facilitating the formation of a
key intermediate in this reaction. To validate the simulations,
we ran a series of control experiments using pyridine
hydrochloride (Fig. 4). This additive should react with ethyl
lactate to give
a structure similar to our simulated
intermediate (Fig. 4a). Indeed, adding pyridine hydrochloride
gave an ethyl lactate conversion of 10% in the first 10 min,
compared to 4% in the presence of pyridine and no conversion
at all in the absence of additive (Fig. 4b). The reaction rate also
increased in the order: pyridine hydrochloride > pyridine >> no
additive (Fig. 4c). In another control experiment, we added Fig. 5 (a) Plots of ethyl lactate conversion and ethyl pyruvate selectivity against reaction
both of pyridine and HCl as separate additives (first the time; Reaction conditions: ethyl lactate 5 mmol, additive 5 mol%, VO
x
/C 25 mg (0.15
ml). (b)
Proposed migratory behaviors of 4–methylpyridine–ethyl lactate and P4VP—ethyl
lactate towards VO /C catalyst.
mol% V),
1
atm
O
2
,
130 °C, diethyl succinate (solvent,
1
pyridine and then the acid to minimize the formation of
protonated pyridine). This {pyridine + HCl} combination gave
much lower conversion compared with pyridine hydrochloride
x
4
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series of experiments with a solid poly–4–vinylpyridine (P4VP),
which can be considered as a “stationary pyridine”. This was
compared to its simplest homogeneous analogue, 4–
methylpyridine. As shown in Fig. 5a, 4– methylpyridine gave
much higher conversion than P4VP. Even after 8 h, the
conversion in the presence of P4VP was < 20%. This supports
our hypothesis that the ethyl lactate first interacts with the
pyridine, forming a complex, which travels to the vanadium
oxide active site (Fig. 5b). This transfer step is hampered by the
bulk polymer additive P4VP. Indeed, in the absence of any
x
additive, VO /C itself can catalyze this reaction (cf. Fig. 1, no
additive). Adding pyridine improves the results, but adding
P4VP, which is a large polymer, retards the reaction.
Despite the diffusion barrier created by P4VP, it does show
one important advantage: A high selectivity to ethyl pyruvate.
Fig. 7 Reaction profiles for ethyl lactate over two different catalyst systems (the inset
shows the corresponding selectivity to ethyl pyruvate). Reaction conditions: ethyl
We therefore reasoned that a carbonaceous support made lactate 5 mmol, 1 atm O , diethyl succinate (solvent, 1 ml); catalyst: VO /P4VP 25 mg,
2
x
from P4VP would combine the activity advantages of the VO
x
/C 25 mg (0.15 mol% V relative to substrate) and 4–methylpyridine 5 mol%; 130 °C.
Red: VO /P4VP catalyst, black: VO /C with 4–methylpyridine additive.
x
x
homogeneous additive with the selectivity advantages of the
heterogeneous one. This would give a stable solid oxidation
catalyst without any additives.
As shown Fig. 7, the new catalyst outperformed the control
combination of {4–methylpyridine + VO /C}. Ethyl lactate
To test this, we prepared a P4VP–supported vanadia catalyst
x
conversion over VO /P4VP reached 84% after 8 h, compared
x
(denoted as VO /P4VP). First, P4VP was calcined at 400 °C for 2
x
with 69% for {4–methylpyridine + VO /C}. The selectivity to
x
h under nitrogen. Then, the material was impregnated with
ethyl pyruvate was also higher (90% vs. 80%, respectively, see
inset in Fig. 7). Note that pyridine compounds themselves can
vanadyl acetylacetonate (VO(acac) ) ethanolic solutions, dried
2
and calcined to give VO /P4VP (Scheme 1, see experimental
x
4
7
be oxidized by vanadia. In the first 4 h, the {4–methylpyridine
VO /C} showed a higher conversion, but after 4 h, VO /P4VP
section for details). We ran X–ray photoelectron spectroscopy
+
(XPS) experiments to identify the chemical state of nitrogen
x
x
was better most likely because the pyridinic nitrogen in the
4
atoms of VO /P4VP. The N1s spectra of VO /P4VP showed a
x
x
8
VO /P4VP catalyst was protected by polymer matrix.
x
single peak, which was identical with pristine P4VP, belonging
to pyridinic nitrogen at 398.5 eV (Fig. 6). This suggests that the
Moreover, carbon formed on the surface of VO /P4VP during
x
the calcination process can acts as free–radical scavenger,
pyridinic nitrogen of VO /P4VP was preserved. These pyridinic
x
2
slowing the undesired side oxidation of ethyl lactate. As an
8
nitrogen in VO /P4VP are in close proximity to vanadia active
x
added bonus, the VO /P4VP catalyst is easily separated by
x
sites, reducing mass–transfer barriers.
simple filtration, and can be reused at least five times without
significant loss of activity (see Fig. S4). A comparison of the
catalytic performance of various catalysts reported previously
for the liquid-phase oxidation of lactate to pyruvate is shown
in Table S2. Among these, Li et al. reported a novel bi-
Scheme 1 The synthesis route of VO
x
/P4VP catalyst.
+
enzymatic parallel cascade system (Hemoglobin-NaD ) for the
bio-oxidation of lactate with H
selectivity of 94% with 81% yield at room temperate. The
reaction also can be done with H as an oxidant using Ti, Pt
or Pb-based catalysts (Table S2). Our designed VO /P4VP
2 2
O to pyruvate, giving a high
4
9
2 2
O
x
catalyst is among the best non-noble metal heterogeneous
catalysts. It gives high yield of ethyl pyruvate with just 0.15
2
mol% V at 1 atm O pressure.
Conclusions
Converting lactates to pyruvates can be done by oxidation with
molecular oxygen, but obtaining high yields is a challenge.
Vanadium oxides can catalyse this reaction, and the product
selectivity can be increased by adding pyridine. The reaction
has two key steps: complexation of the pyridine-type additive
Fig. 6 XPS studies showing high resolution N1s spectra of the pristine P4VP and to the substrate, followed by oxidation at the vanadium active
x
VO /P4VP catalyst.
site. In this two-step pathway, the diffusion to the active site
also plays a key role. The product yield can be maximised by
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designing a tailor-made catalyst that takes both steps into resulting black powder was ultrasonically dispersed into 50ml
account. This catalyst is made by first synthesising a support ethanol solution. Next, 0.3mmol vanadyl acetylacetonate
2
rich in “pyridine” groups, and then impregnating this support (VO(acac) ) was added to the mixture by stirring at 80°C
with vanadium sites, which are then oxidised to vanadia overnight in a 250 ml round bottomed flask. Then the solid
particles. The resulting catalyst is active and selective, giving was ground by mortar and pestle to fine powder, and
80% conversion with 90% selectivity to the desired product, Subsequent calcination at 400 °C for 2h under nitrogen, with a
ethyl pyruvate. It is also stable, and can be easily separated heating rate of 2 °C/min in a nitrogen flow.
and reused multiple time without losing activity.
Procedure for catalyst testing
In a typical reaction, ethyl lactate (5 mmol), additive (5 mol%,
relative to substrate), catalyst (25 mg) and diethyl succinate (1
ml, solvent) were added in a 25 ml flask equipped with a
dioxygen balloon. The reaction mixture was heated to 130 °C
under magnetic stirring (800 rpm). After reaction, the flask was
cooled to room temperature. Next, the product was were
filtered using 0.45 µm PTFE syringe filters. Then, the filtrate
was directly analysed by GC by adding biphenyl (50mg) as
internal standard.
Experimental
Materials and instrumentation
Chemicals were obtained from commercial sources and used
®
as received. Activated carbon (Norit SX 1 G), ruthenium on
carbon (Ru/C, Alfa Aesar, 5wt. %), platinum on carbon (Pt/C,
®
Sigma-Aldrich, 1 wt. %), poly (4-methylpyridine) (P4VP,Reillex
4
02), cobalt nitrate hexahydrate (Co(NO
, vanadyl acetylacetonate (VO(acac) , Sigma-Aldrich, 98%),
∙9H O, Sigma-Aldrich,
∙3H O, Sigma-
99.5 %), (–)–Ethyl L–lactate (Sigma-Aldrich,
3 2 2
) ∙6H O, VWR, ≥96%
Density Functional Theory (DFT) Calculations
)
2
DFT calculations were performed using the CP2K software
package, uses the combined Gaussian and plane-wave (GPW)
iron nitrate nonahydrate (Fe(NO
3
)
3
2
≥
99.95%), copper nitrate trihydrate (Cu(NO
3
)
2
2
5
1
method for the calculation of forces and energies. The
valence orbitals were described by DZVP-GTH Gaussian basis
set, all calculations were carried out using the PBE density
functional augmented with the Grimme D3 dispersion
Aldrich,
≥
≥
98.0%), diethyl succinate (Sigma-Aldrich, 99%), all other
pyridine-derived chemicals were purchased from Sigma-
Aldrich. Gas chromatography (GC) analysis was collected by an
Agilent 7820A instrument equipped with a flame ionization
4
6
correction. The plane wave kinetic energy cutoff was set to
00 eV. We used the DIMER method to identified the
4
detector
dimethylpolysiloxane capillary column (VB-1, 30 m × 0.32 mm
3.00 μm). The metal loading was measured by inductively
(FID),
autosampler
(G4513A)
and
a
5
2
transition states. The adsorption energies were defined as ꢀE
= Etotal – Eethyl lactate – Epyridne/pyrrole, where Eethyl lactate, Epyridne/pyrrole,
×
and Etotal refer to the energies of the free ethyl lactate,
5
pyridine /pyrrole, and complex system, respectively.
coupled plasma (ICP) atom emission spectroscopy (AES) on a
Thermo IRIS Intrepid II XSP. XPS spectra were collected using a
Thermo Scientific K-ALPHA with Al-K radiation. S-shaped
background subtraction and fitting the experimental curve to a
combination of a Lorentzian (30%) and Gaussian (70%) lines.
3
Conflicts of interest
Binding energies (BE), referenced to the C 1s line at 284.6 eV, There are no conflicts to declare.
have an accuracy of ± 0.1 eV.
Procedure for carbon supported metal oxide (MO
preparation
x
/C)
Acknowledgements
The MO
x
/C catalysts were prepared following the procedure
W. Zhang thanks the China Scholarship Council for a PhD
fellowship. This work is part of the Research Priority Area
Sustainable Chemistry of the UvA, http://suschem.uva.nl.
5
reported by Srinivas et al. Example: VO
0
x
/C. 5.0 grams of
activated carbon was added into 50ml ethanol solution by
stirring for 30 min in a 250 ml round bottomed flask at room
temperature. Subsequently, 1.5 mmol vanadyl acetylacetonate
(
VO(acac)
2
) was added to the solution and stirred at 80°C Notes and references
overnight. After ethanol evaporation, the solid was continually
dried at 100 °C for 12 hours, then ground by mortar and pestle
to a fine powder. Followed by temperature-programmed heat-
treatment at 400 °C for 2 h, with a heating rate of 2 °C/min in a
1
2
M. He, Y. Sun and B. Han, Angew. Chem. Int. Ed., 2013, 52,
9620.
T. Wilberforce, Z. El-Hassan, F. N. Khatib, A. Al Makky, A.
Baroutaji, J. G. Carton and A. G. Olabi, Int. J. Hydrogen
Energy, 2017, 42, 25695.
nitrogen flow. The catalysts CoO
similarly prepared from the respective precursors
Co(NO ∙6H O, Cu(NO ∙3H O and Fe(NO ∙9H O.
Procedure for P4VP–supported vanadia preparation
VO /P4VP)
In a typical synthesis of VO
x x x
/C, CuO /C and FeO /C were
3
4
5
P. N. R. Vennestrøm, C. M. Osmundsen, C. H. Christensen
and E. Taarning, Angew. Chem. Int. Ed., 2011, 50, 10502.
3
)
2
2
3
)
2
2
3
)
3
2
A. Corma, S. Iborra and A. Velty, Chem. Rev., 2007, 107
411.
P. S. Shuttleworth, M. De bruyn, H. L. Parker, A. J. Hunt, V. L.
,
2
(
x
x
/P4VP catalyst. 10 grams P4VP was
Budarin, A. S. Matharu and J. H. Clark, Green Chem., 2014,
16, 573.
P. Demma Carà, M. Pagliaro, A. Elmekawy, D. R. Brown, P.
Verschuren, N. R. Shiju and G. Rothenberg, Catal.
Sci.Technol., 2013, 3, 2057.
transferd into a quartz boat with a quartz cover, and and then
wrapped using aluminum foil. The sealed P4VP was calcined at
6
400 °C for 2 h under nitrogen at a heating rate of 1 °C/min and
then cooled to room temperature. Then, 1 grams of the
6
| J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
7
8
9
P. Y. Dapsens, C. Mondelli and J. Pérez-Ramírez, ACS Catal., 41 A. H. St. Amant, C. P. Frazier, B. Newmeyer, K. R. Fruehauf
012, , 1487. and J. Read de Alaniz, Org. Biomol. Chem., 2016, 14, 5520.
E.-J. Ras, S. Maisuls, P. Haesakkers, G.-J. Gruter and G. 42 C. Viglianisi, V. Di Pilla, S. Menichetti, V. M. Rotello, G.
2
2
Rothenberg, Adv. Synth. Catal., 2009, 351, 3175.
R. Beerthuis, G. Rothenberg and N. R. Shiju, Green Chem.,
2015, 17, 1341.
0 Y. Fan, C. Zhou and X. Zhu, Catal. Rev., 2009, 51, 293.
Candiani, C. Malloggi and R. Amorati, Chem. Eur. J., 2014, 20
,
6857.
43 M. Lafrance and K. Fagnou, J. Am. Chem. Soc., 2006, 128
,
1
1
16496.
1 Global Market Insights, https://globenewswire.com/news- 44 F.-G. Xi, Y. Yang, H. Liu, H.-F. Yao and E.-Q. Gao, RSC Adv.,
release/2016/11/09/888221/0/en/Lactic-Acid-Market-size-
worth-over-6-billion-by-2024-Global-Market-Insights-
Inc.html, 2016.
2015,
45 J. Hutter, M. Iannuzzi, F. Schiffmann and J. VandeVondele,
Wiley Interdiscip. Rev. Comput. Mol. Sci., 2014, , 15.
5, 79216.
4
1
1
1
2 M. Dusselier, P. Van Wouwe, A. Dewaele, E. Makshina and B. 46 S. Grimme, J. Antony, S. Ehrlich and H. Krieg, J. Chem. Phys.,
F. Sels, Energy Environ. Sci., 2013,
3 P. Xu, J. Qiu, C. Gao and C. Ma, J. Biosci. Bioeng., 2008, 105
69.
4 S. Sugiyama, T. Kikumoto, H. Tanaka, K. Nakagawa, K.-I.
6
, 1415.
2010, 132, 154104.
,
47 W. F. Hoelderich, Appl. Catal. A, 2000, 194, 487.
48 W. Zhang, T. Liu, H. Wu, P. Wu and M. He, Chem. Commun.,
2015, 51, 682.
1
Sotowa, K. Maehara, Y. Himeno and W. Ninomiya, Catal. 49 H.-Y. Jia, M.-H. Zong, H.-L. Yu and N. Li, ChemSusChem, 2017,
10, 3524.
Lett., 2009, 131, 129.
5 E. Erlenmeyer, Ber. Dtsch. Chem. Ges., 1881, 14, 320.
6 F. Howard, Org. Syn. Coll., 1941, 1, 475.
7 P. Mäki-Arvela, I. L. Simakova, T. Salmi and D. Y. Murzin,
Chem. Rev., 2014, 114, 1909.
8 V. Escande, C. H. Lam, P. Coish and P. T. Anastas, Angew.
Chem. Int. Ed., 2017, 56, 9561.
9 K. T. Liu, X. M. Huang, E. A. Pidko and E. J. M. Hensen, Green 52 G. Henkelman and H. Jónsson, J. Chem. Phys., 1999, 111
Chem., 2017, 19, 3014. 7010.
0 X. Zhao, C. Zhang, C. Xu, H. Li, H. Huang, L. Song and X. Li, 53 K. De Wispelaere, B. Ensing, A. Ghysels, E. J. Meijer and V.
1
1
1
50 D. Srinivas, W. F. Hölderich, S. Kujath, M. H. Valkenberg, T.
Raja, L. Saikia, R. Hinze and V. Ramaswamy, J. Catal., 2008,
259, 165.
51 J. VandeVondele, M. Krack, F. Mohamed, M. Parrinello, T.
Chassaing and J. Hutter, Comput. Phys. Commun., 2005, 167,
103.
1
1
2
,
Chem. Eng. J., 2016, 296, 217.
1 M. Ai, Appl. Catal. A, 2002, 234, 235.
2 S. Lomate, T. Bonnotte, S. Paul, F. Dumeignil and B.
Katryniok, J. Mol. Catal. A: Chem., 2013, 377, 123.
3 S. C. A. Sousa and A. C. Fernandes, Coord. Chem. Rev., 2015,
Van Speybroeck, Chem. Eur. J., 2015, 21, 9385.
2
2
2
284, 67.
2
2
4 T. Mallat and A. Baiker, Chem. Rev., 2004, 104, 3037.
5 T. Tsujino, S. Ohigashi, S. Sugiyama, K. Kawashiro and H.
Hayashi, J. Mol. Catal., 1992, 71, 25.
2
6 H. Hayashi, S. Sugiyama, N. Shigemoto, K. Miyaura, S.
Tsujino, K. Kawashiro and S. Uemura, Catal. Lett., 1993, 19
69.
7 C. Zhang, T. Wang and Y. J. Ding, Appl. Catal. A, 2017, 533
9.
8 E. V. Ramos-Fernandez, N. J. Geels, N. R. Shiju and G.
Rothenberg, Green Chem., 2014, 16, 3358.
,
3
2
2
2
,
5
9 W. Zhang, G. Innocenti, P. Oulego, V. Gitis, H.-H. Wu, B.
Ensing, F. Cavani, G. Rothenberg and N. R. Shiju, ACS Catal.,
2
018, 10.1021/acscatal.7b03843.
3
3
3
3
3
3
3
3
3
0 T. K. Slot, D. Eisenberg, D. van Noordenne, P. Jungbacker and
G. Rothenberg, Chem. Eur. J., 2016, 22, 12307.
1 D. Eisenberg, W. Stroek, N. J. Geels, C. S. Sandu, A. Heller, N.
Yan and G. Rothenberg, Chem. Eur. J., 2016, 22, 501.
2 P. Zhang, Y. Gong, H. Li, Z. Chen and Y. Wang, Nat. Commun.,
2
013,
3 F. Wang, J. Xu, X. Shao, X. Su, Y. Huang and T. Zhang,
ChemSusChem, 2016, , 246.
4, 1593.
9
4 Q.-Y. Bi, J.-D. Lin, Y.-M. Liu, H.-Y. He, F.-Q. Huang and Y. Cao,
Angew. Chem. Int. Ed., 2016, 55, 11849.
5 D. Guo, R. Shibuya, C. Akiba, S. Saji, T. Kondo and J.
Nakamura, Science, 2016, 351, 361.
6 G. B. Shul’pin and E. R. Lachter, J. Mol. Catal. A: Chem., 2003,
1
97, 65.
7 S. E. Denmark and G. L. Beutner, Angew. Chem. Int. Ed.,
008, 47, 1560.
2
8 M. B. Khaled, R. K. El Mokadem and J. D. Weaver, 3rd, J. Am.
Chem. Soc., 2017, 139, 13092.
3
4
9 A. Grirrane, H. Garcia and A. Corma, J. Catal., 2013, 302, 49.
0 M. Wang, F. Wang, J. Ma, M. Li, Z. Zhang, Y. Wang, X. Zhang
and J. Xu, Chem. Commun., 2014, 50, 292.
This journal is © The Royal Society of Chemistry 20xx
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