A Combined Catalyst of Pt Nanoparticles and TiO2 with Water-Tolerant Lewis Acid Sites for One-Pot Conversion of Glycerol to Lactic Acid

Article abstract of DOI:10.1002/cctc.201501197

Catalytic conversion of glycerol to valuable chemicals has been recognized as an attractive and challenging reaction in biorefinery. In this paper, we demonstrated that a combined catalyst of Pt nanoparticles and TiO₂ worked as a highly active catalyst for the one-pot conversion of glycerol to lactic acid in water. The yield of lactic acid reached 63 % under oxygen atmosphere without the use of any additives such as strong bases, and the catalyst could be reused without significant loss of the catalytic performance. The mechanistic studies revealed that Pt nanoparticles on TiO₂ selectively oxidized glycerol to C3 aldehyde/ketone, and Lewis acid sites on TiO₂ smoothly promoted the dehydration and rehydration/rearrangement reactions of the intermediates to produce lactic acid efficiently.

Full text of DOI:10.1002/cctc.201501197

DOI: 10.1002/cctc.201501197
Full Papers
A Combined Catalyst of Pt Nanoparticles and TiO with
2
Water-Tolerant Lewis Acid Sites for One-Pot Conversion of
Glycerol to Lactic Acid
[
a]
[a]
[a, b]
[c]
Tasuku Komanoya, Ayaka Suzuki, Kiyotaka Nakajima,
Masaaki Kitano,
[a]
[a, d, e]
Keigo Kamata, and Michikazu Hara*
Catalytic conversion of glycerol to valuable chemicals has been
recognized as an attractive and challenging reaction in biorefi-
nery. In this paper, we demonstrated that a combined catalyst
catalyst could be reused without significant loss of the catalyt-
ic performance. The mechanistic studies revealed that Pt nano-
particles on TiO selectively oxidized glycerol to C3 aldehyde/
2
of Pt nanoparticles and TiO worked as a highly active catalyst
ketone, and Lewis acid sites on TiO smoothly promoted the
2
2
for the one-pot conversion of glycerol to lactic acid in water.
The yield of lactic acid reached 63% under oxygen atmosphere
without the use of any additives such as strong bases, and the
dehydration and rehydration/rearrangement reactions of the
intermediates to produce lactic acid efficiently.
Introduction
Glycerol (1,2,3-propanetriol) is an abundant and sustainable
biomass resource because it is obtained as a main coproduct
of biodiesel formation through the transesterification of seed
tives, biodegradable polymers, and as a platform chemical in
[
3]
biorefinery. LA is mainly produced by the fermentation of car-
bohydrates via the corresponding lactate, however, the pro-
duction efficiency is still low and large amounts of salts are
formed as byproduct wastes. In this context, there is a strong
demand for the development of novel chemical processes for
the one-pot synthesis of LA from glycerol including a better
method to directly separate LA.
[
1]
oils with alcohols. Along with the market growth in biodiesel
production, the selective conversion of glycerol into useful
chemicals (e.g., esters, ethers, acetals/ketals, diols, epoxides,
oxidation products) has also received significant attention in
[
2]
recent years. Among these, lactic acid (LA) is a promising
target chemical owing to its wide application to food addi-
As shown in Scheme 1, LA can be chemically obtained from
glycerol according to the following three sequential reactions:
(i) the oxidative dehydrogenation of glycerol to trioses (glycer-
aldehyde (GA) and 1,3-dihydroxyacetone (DHA)), (ii) dehydra-
tion of trioses to pyruvaldehyde (PA), and (iii) hydration/rear-
rangement of PA to LA. The DFT-calculated free energy dia-
gram for the one-pot conversion of glycerol to LA is shown in
Figure 1 (see also Table S1 in the Supporting Information). The
formation of C3 acids, such as glyceric acid and tartronic acid,
by the overoxidation of trioses was calculated to be more ther-
modynamically favorable than LA formation, which indicates
that fine control of the catalyst properties for oxidation and re-
arrangement is an important factor for the selective synthesis
of LA from glycerol. Brønsted bases or Lewis acids accelerate
+
[
a] Dr. T. Komanoya, A. Suzuki, Dr. K. Nakajima, Dr. K. Kamata, Prof. M. Hara
Materials and Structures Laboratory
Tokyo Institute of Technology
Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503 (Japan)
E-mail: mhara@msl.titech.ac.jp
+
[
b] Dr. K. Nakajima
Precursory Research for Embryonic Science and Technology (PRESTO)
Japan Science and Technology Agency (JST)
4-1-8 Honcho, Kawaguchi 332-0012 (Japan)
[
c] Dr. M. Kitano
Materials Research Center for Elemental Strategy
Tokyo Institute of Technology
Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503 (Japan)
[
d] Prof. M. Hara
Advanced Low Carbon Technology Research and Development Program
(
ALCA)
Japan Science and Technology Agency (JST)
-1-8 Honcho, Kawaguchi 332-0012 (Japan)
4
[
e] Prof. M. Hara
Frontier Research Center
Tokyo Institute of Technology
Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503 (Japan)
+
[
] Present address:
Institute for Catalysis
Hokkaido University
Kita 21 Nishi 10, Sapporo 001-0021 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201501197.
Scheme 1. One-pot conversion of glycerol to LA through (i) oxidation, (ii) de-
hydration, and (iii) hydration/rearrangement.
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lized on TiO is demonstrated to function as a recyclable solid
2
catalyst for the one-pot additive-free conversion of glycerol
into LA without significant loss of the catalytic activity.
Results and Discussion
The most suitable combination of noble-metal nanoparticles
(
as oxidation catalysts) and metal oxides (as Lewis acid cata-
lysts) for the one-pot conversion of glycerol to LA was ex-
plored under additive-free conditions (Table 1). Initially, the
[a]
Table 1. Effect of catalysts on one-pot conversion of glycerol into LA.
Entry
Catalyst
Conversion
of glycerol
[%]
Yield
of LA
[%]
Selectivity
to LA
[%]
Figure 1. Computational free energy diagrams of the transformation of glyc-
erol into LA (top) and tartronic acid (bottom). Energies are shown in
À1
kJmol
.
1
Pt–PVP+TiO
Pt–PVP+TiO
2
2
70
>99
19
20
11
3
49
63
14
6
2
1
70
63
72
30
15
40
31
–
[b]
2
3
4
5
6
7
8
9
1
Ir–PVP+TiO
2
Pd–PVP+TiO
Ru–PVP+TiO
Rh–PVP+TiO
2
2
2
the important step (iii) by benzilic acid rearrangement or an in-
[4]
tramolecular 1,2-hydride shift, respectively, so that various ef-
fective combined systems of Ir-, Cu-, Pt-, and Au-based oxida-
tion catalysts and homogeneous Brønsted bases (NaOH and
Ag–PEI+TiO2
Au–PEI+TiO
Cu–PVP+TiO2
4
7
1
2
<1
<1
39
36
28
15
7
3
<1
1
[
5]
<1
82
79
68
75
79
70
70
9
–
KOH) or Lewis acids (AlCl ) have been reported (Table S2).
3
0
Pt–PVP+Nb
2
O
5
48
45
42
20
9
4
–
12
3
–
However, these systems share common drawbacks in the com-
plicated procedure for catalyst/product(s) separation, difficulty
of reuse for expensive catalysts, and the additional neutraliza-
tion of lactate to obtain LA. Recently, a bifunctional Pt/Sn–MFI
zeolite catalyst has been reported to efficiently catalyze the
1
1
Pt–PVP+ZrO
Pt–PVP+Al O
2 3
2
12
13
Pt–PVP+MgO
Pt–PVP+SnO
Pt–PVP+SiO
Pt–PVP+AC
TiO2
1
1
1
4
5
6
2
2
[
6]
base-free one-pot conversion of glycerol to LA in water. In
this case, Sn–MFI acts as a heterogeneous Lewis acid catalyst,
however, a gradual decrease in the catalytic activity is ob-
served for the recycled catalyst, which is likely the result of sig-
nificant leaching of the Sn species in water in the presence of
17
18
Pt–PVP
62
<1
78
2
<1
55
1
2
9
0
blank
Pt/TiO
[c]
2
70
[
a] Reaction conditions: glycerol (1 mmol), metal oxide or AC (50 mg),
noble metal nanoparticles (metal: 0.1 wt% with respect to meal oxide or
AC), water (5 mL), 423 K, 18 h, O (0.5 MPa). Conversion (%)=converted
[7]
LA. Therefore, the development of active and durable com-
bined catalytic systems of oxidation and heterogeneous Lewis
acid catalysts is still a challenging issue to achieve efficient
one-pot conversion of glycerol to LA in aqueous media.
2
glycerol (mol)/initial glycerol (mol)”100. Yield (%)=carbon in product
(mol)/carbon in initial glycerol (mol)”100. Selectivity (%)=LA (mol)/con-
verted glycerol (mol)”100. Yields of other products are summarized in
Table S3. [b] 48 h. [c] Pt nanoparticles loaded TiO
action of Pt–PVP and TiO in water at 423 K for 1 h under 0.5 MPa O .
2
was prepared by the re-
We have recently reported that early transition metal oxides
such as TiO and Nb O can act as highly active and durable
2
2
2
2
5
heterogeneous Lewis acid catalysts for various types of reac-
tions, such as the direct conversion of glucose to 5-(hydroxy-
methyl)furfural, allylation of benzaldehyde with tetraallyltin,
and the rearrangement reaction of PA to LA in aqueous
effect of noble-metal nanoparticles stabilized with polyvinyl-
pyrrolidone (PVP) or polyethylenimine (PEI) (metal: 0.1 wt%
[
8]
media. Coordinatively unsaturated metal species such as
NbO and TiO tetrahedra formed on the oxide surface can
with respect to TiO ; Pt–PVP, Ru–PVP, Pd–PVP, Au–PEI, Ir–PVP,
2
Rh–PVP, Ag–PEI, Cu–PVP) on the one-pot reaction in the pres-
ence of TiO (50 mg) with O (0.5 MPa) at 423 K for 18 h was in-
4
4
function as water-tolerant Lewis acid sites, which results in
high catalytic activity comparable to that of the active homo-
2
2
vestigated. Apart from LA, the dehydrogenated/dehydrated
chemicals (DHA, GA, and PA) and some further oxidized prod-
ucts such as acetic acid (AA) were also formed, and the details
are summarized in Table S3. Among the nanoparticles tested,
the combined catalyst of Pt–PVP and TiO2 (denoted as Pt–
[9]
geneous Sc(OTf) catalyst. From these results, we envisaged
3
that a combined catalyst consisting of noble-metal nanoparti-
cles and an early transition metal oxide with water-tolerant
Lewis acid sites would be feasible for the one-pot conversion
of glycerol into LA in water; the former efficiently catalyzes the
selective oxidation of alcohols to carbonyl compounds with
PVP+TiO ) gave the highest yield of LA at 49%, with 70% se-
2
lectivity (Table 1, entry 1). If prolonging the reaction time from
18 h to 48 h, the LA yield increased up to 63% (entry 2). Nota-
[10]
molecular oxygen as the sole oxidant, and the latter exhibits
high catalytic performance for conversion of the resulting GA
or DHA into LA. Herein, a catalyst of Pt nanoparticles immobi-
bly, the Pt–PVP+TiO combined catalyst gave smaller amounts
2
of energetically stable C3 acids (2% selectivity) such as glyceric
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acid and tartronic acid by the overoxidation of trioses than
[
5,6]
those reported for Pt or Au catalysts (10–19% selectivity).
There is no significant difference in reaction between entry 17
for TiO without metal nanoparticles and entry 19 as a blank
2
test without any catalysts. Although the conversion of glycerol
reaches 62% using Pt–PVP without TiO (entry 18), the LA se-
2
lectivity is only 3%, which suggests that the high catalytic ac-
tivity and selectivity for the present reaction require both TiO2
and Pt–PVP. The one-pot reaction in the presence of Pt–PVP
and various metal oxides (TiO , Nb O , ZrO , Al O , SnO , SiO ,
2
2
5
2
2
3
2
2
and MgO) or activated carbon (AC) was also examined. Nb O5
2
and ZrO , early transition metal oxides with Lewis acid sites,
2
gave smaller LA yields and lower LA selectivity than TiO (en-
2
tries 10 and 11). The high density of water-tolerant Lewis acid
sites with poor basicity on TiO could be suitable for this reac-
Figure 3. HAADF–STEM images (top) and particle size distributions (bottom)
2
[
8,11]
of Pt–PVP and Pt/TiO after the reaction for 1 h, respectively.
2
tion.
Al O and MgO are inferior to Nb O and ZrO in cata-
2 3 2 5 2
lytic performance, and SnO , SiO and AC resulted in considera-
2
2
bly smaller LA yields, although glycerol conversion using these
materials exceeded 70%. This can be attributed to the absence
of Lewis acid sites which accelerate the selective conversion of
the trioses to LA (entries 12–16).
that of Pt–PVP, which suggests that Pt–PVP nanoparticles are
immobilized on TiO . Such immobilization can be expected to
2
occur during the early stages of the reaction. A Pt-nanoparti-
cles-loaded TiO sample (denoted as Pt/TiO ) was prepared by
To investigate the correlation of Pt–PVP with TiO , a time
2
2
2
course of the reaction was measured (Figure 2). The product
distribution is summarized in Figure S1 (Supporting Informa-
tion). The reaction was completely stopped by removal of
stirring Pt–PVP and TiO2 in water for 1 h at 423 K under
[
12]
0.5 MPa O2 followed by filtration. The resulting Pt/TiO ex-
2
hibited high catalytic performance comparable to that of the
Pt–PVP+TiO system (Table 1, entry 20).
2
The electronic state of Pt nanoparticles for Pt/TiO was eval-
2
uated by using X-ray photoelectron spectroscopy (XPS)
and the results are shown in Figure 4. Two peaks are observed
at 70.6 eV and 73.7 eV in Figure 4, assignable to Pt4f7/2 and
Figure 2. Time course of glycerol conversion for Pt–PVP+TiO
2
. (a) The reac-
at 423 K.
b) The reaction solution was filtrated after reaction for 3 h in the presence
tion was performed for 18 h in the presence of Pt–PVP+TiO
2
(
2
of Pt–PVP+TiO at 423 K, and then the filtrated liquid was heated at 423 K
(
total heating time; 18 h). Reaction conditions are the same as those report-
ed in Table 1. Yields of other products are presented in Figure S1.
2 2
Figure 4. Pt4f X-ray photoelectron spectra of (a) TiO and (b) Pt/TiO .
Pt–PVP+TiO . Pt–PVP itself can oxidize glycerol in the absence
2
of TiO and the glycerol conversion exceeds 60% at 18 h, as
2
0
[13]
shown in entry 18 in Table 1. It was confirmed by inductively
coupled plasma atomic emission spectroscopy (ICP–AES) analy-
sis that negligible amounts of Pt (<2%) and Ti (<0.01%) spe-
cies were present in the filtrate. Therefore, it is considered that
Pt4f5/2 of Pt , respectively. It was also confirmed by XRD, N2
adsorption–desorption isotherm, and FTIR measurements
using pyridine as a basic probe molecule that there is no sig-
nificant difference in the structure (Figure S2), surface area (Fig-
almost all Pt species are immobilized on TiO during reaction.
ure S3), and amount of Lewis acid sites between bare TiO and
2
2
In Figure 3, the high-angle annular dark-field scanning trans-
mission electron microscopy (HAADF–STEM) images of Pt–PVP
and the solid sample filtered out of the reaction solution after
Pt/TiO2 formed in the Pt–PVP+TiO system (Figure 5). These
2
0
results demonstrate that Pt nanoparticles are immobilized on
the TiO surface but do not prevent the Lewis acid catalytic ac-
2
1
h are presented. The images reveal that Pt nanoparticles are
tivity of TiO . Furthermore, the FTIR experiments revealed that
2
dispersed on the TiO surface and their particle size is close to
the bands attributed to CÀH and CÀN stretching of PVP
2
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over numbers for LA production based on bulk Pt metal and
Lewis acid sites on TiO were 7520 and 154, respectively. In ad-
2
dition, the XRD pattern, BET surface area, and STEM image of
the retrieved catalyst after three reuses did not much change
from those of the fresh Pt/TiO catalyst (Figure S2, S3, and S4).
2
As a result, Pt/TiO , which is smoothly formed from Pt–PVP+
2
TiO catalyst under the reaction conditions, functions as a recy-
2
clable and efficient catalyst for the one-pot synthesis of LA
from glycerol.
Reactions of GA, DHA, and PA as starting substrates instead
of glycerol were also examined under the same reaction condi-
tions as those in Table 1 to clarify the possible reaction path-
way and mechanism for the present system. The results are
Figure 5. Difference FTIR spectra of pyridine-adsorbed catalysts TiO
2
and Pt/
summarized in Table 2. In the case of Pt–PVP+TiO , the con-
2
TiO . L=coordinated pyridine on Lewis acid site, B=pyridinium ion formed
2
on Brønsted acid site.
[a]
2
Table 2. Conversion of intermediates into LA by Pt–PVP+TiO catalyst.
À1
À1
(
2970 cm and 1280 cm ) for Pt/TiO are much smaller than
2
Entry
Substrate
mmol]
Catalyst
Conversion
[%]
Yield of LA
[%]
those of a simple mixture of Pt–PVP and TiO (not shown), sug-
2
[
gesting the decrease in PVP covering Pt during reaction. It has
1
2
3
4
5
6
7
8
9
DHA (1)
DHA (1)
DHA (1)
DHA (0.5)
DHA (0.25)
GA (1)
GA (1)
GA (1)
GA (1)
PA (1)
without
22
97
95
98
>99
50
<1
39
40
50
58
2
40
42
29
<1
53
54
been generally accepted that Pt-nanoparticle-deposited TiO
2
TiO
Pt–PVP+TiO2
Pt–PVP+TiO
2
[
6]
are inactive for the one-pot reaction of glycerol to LA be-
cause the density of effective Lewis acid sites on TiO is typical-
2
2
[
14]
Pt–PVP+TiO2
without
ly not so high. However, the TiO used in this study has
2
a much higher density of effective water-tolerant Lewis acid
TiO
Pt–PVP+TiO2
Nb
without
TiO
Pt–PVP+TiO
2
99
[
8]
sites. In addition, the Lewis acid properties of TiO were not
>99
>99
34
95
97
2
much changed by the immobilization of Pt nanoparticles on
2 5
O
1
0
TiO , which resulted in high catalytic performance for the con-
2
1
1
PA (1)
PA (1)
2
version of glycerol to LA.
1
2
2
Recycle experiments of Pt–PVP+TiO catalyst were conduct-
2
[
(
(
a] TiO
5 mL), 423 K, 1 h, O
mol)/initial substrate (mol)”100. Yield (%)=carbon in LA (mol)/carbon in
2
or Nb
2
O
5
(50 mg), Pt–PVP (0.1 wt% with respect to TiO
2
), water
ed to examine the durability of the catalyst. After the reaction
was carried out for 18 h, the catalyst was retrieved from the re-
action mixture by centrifugation. It was confirmed by ICP–AES
that the leaching of Pt species reached 7% after the catalytic
reaction for 18 h. Such leaching of Pt species was not observed
at the early stage of the reaction (1 and 3 h), suggesting that
small leaching of Pt species is caused by the increase in lactic
acid formation. As shown in Figure 6 and Table S4, the re-
trieved catalyst could be reused without significant loss of the
catalytic performance, even after three reuses. The total turn-
2
(0.5 MPa). Conversion (%)=converted substrate
initial substrate (mol)”100. Yields of other products are summarized in
Table S5.
version of each substrate and LA yields reached 95–99% and
40–58%, respectively, within 1 h (Table 2 entries 3–5, 8, and
12). These conversions and LA yields are comparable to those
for the reaction of glycerol with Pt–PVP+TiO after 18 h. In ad-
2
dition, bare TiO had almost the same catalytic performance as
2
that of Pt–PVP+TiO (entries 2 vs. 3, 7 vs. 8, and 11 vs. 12), al-
2
though the LA yield was negligibly small in the absence of the
catalysts (entries 1, 6, and 10). Lower LA yield for GA conver-
[
15]
sion over Nb O5 (entry 9) also represents the high efficiency
2
[
8]
of water-tolerant Lewis acid sites on TiO2 as well as glycerol
conversion (Table 1, entry 1 vs. 10). These results indicate that
the formation of LA from GA, DHA, and PA intermediates is
catalyzed by TiO and that oxidation of glycerol into GA/DHA
2
[
16]
could be the rate-determining step for the present reaction.
Notably, LA was not selectively obtained with only Pt–PVP,
even at a relatively high conversion of glycerol (Table 1,
entry 18). Therefore, glycerol oxidation into GA/DHA is cata-
lyzed by Pt nanoparticles loaded on TiO and the GA/DHA in-
2
termediates are thus easily converted into LA by TiO , and side
2
2
Figure 6. Recycle experiments of Pt–PVP+TiO for the one-pot reaction of
reactions such as the overoxidation and intermolecular con-
densation of GA/DHA are suppressed. The yield of LA in-
glycerol into lactic acid. The reaction was performed under the same condi-
tions as those of entry 1 in Table 1.
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creased with a decrease in the initial DHA concentrations,
which supports this pathway (Table 2, entries 3–5).
night under vacuum. XRD patterns were measured with Ultima IV
(
Rigaku) using CuKa radiation (40 kV, 40 mA). N adsorption–desorp-
2
tion isotherms were recorded at 77 K (0.050ꢀp/p ꢀ0.995) with
0
Nova-4200e (Quantachrome). The catalysts were pretreated under
vacuum at 423 K for 1 h to remove adsorbed water and gasses.
The isotherms were analyzed by the BET method to calculate the
Conclusions
The catalytic one-pot conversion of glycerol to LA was investi-
gated in water media under an oxygen atmosphere in the ab-
sence of any additives. Among the catalysts tested, the combi-
specific surface area in the range of 0.050 ꢀ p/p ꢀ 0.300.
0
FTIR spectroscopy measurement for acid site characteriza-
tion
nation of Pt nanoparticles and TiO exhibited high catalytic ac-
2
tivity and durability for the reaction. Pt nanoparticles oxidized
glycerol into GA/DHA, and Lewis acid sites on TiO readily ac-
The Lewis acid site density on TiO was estimated for pyridine-ad-
2
2
celerated the dehydration and 1,2-hydride shift reaction into
LA.
sorbed samples at 298 K. Pt/TiO sample for the IR measurement
2
was prepared in water solution for 1 h at 423 K under Ar. The
sample was pressed into a self-supporting disk (20 mm diameter,
ca. 20 mg) and placed in an IR cell attached to a closed glass-circu-
À3
lation system (0.38 dm ). The disk was dehydrated by heating at
Experimental Section
4
73 K for 1 h under vacuum to remove physisorbed water and was
Catalyst preparation
then exposed to pyridine vapor (>4 kPa) at RT. The intensities of
the IR bands measured at 1445 cm (pyridine coordinatively
À1
Anatase TiO2 was prepared by the hydrolysis of Ti(OiPr)4 (40 g,
Kanto Chemical) in distilled water (160 mL) at 313 K for 5 h with
stirring, followed by filtration and washing with distilled water.
The resulting material was dried overnight at 353 K, and then was
bonded to Lewis acid sites, molecular absorption coefficient:
À1
[8b]
4.86 mmolcm ) were plotted against the amounts of pyridine ad-
sorbed on the Lewis acid sites of the samples.
calcined at 473 K for 5 h. ZrO was obtained by the calcination of
2
Zr(OH) (Aldrich) at 473 K for 5 h. Nb O (Companhia Brasileira de
4
2
5
Quantum chemical calculations
Metalurgia e Minerażo), Al O3 (Japan Reference Catalyst, JRC–
2
ALO–6), MgO (Ube Material Industries), SiO (Fuji Silysia Chemical,
The DFT calculations were conducted at the B3LYP level theory (6-
31+ +G* basis sets for H, C, and O) by using conductor-like polar-
izable continuum model (CPCM) with parameters of the Universal
2
CARiACT Q-10), and AC (Aldrich, Activated Charcoal Norit) were
purchased and pretreated at 473 K for 5 h under air except for AC.
Metal-nanoparticles-dispersed solutions (Aldrich) were utilized as
the oxidation catalyst without any pretreatment.
[17]
Force Field (UFF). The geometries of glycerol, lactic acid, and all
intermediates were optimized, and the vibrational analysis was per-
formed to confirm that they have no imaginary frequency. The
Gibbs free energies (at 1 atm and 298.15 K) were compared. All cal-
culations were performed with the Gaussian09 program pack-
Glycerol conversion
[18]
age.
The conversion of glycerol was operated in 18 mL Teflon high-pres-
sure reactor covered by SUS external cylinder with one gas injec-
tion port. The metal oxide or activated carbon (50 mg), metal
nanoparticle (0.1 wt% metals with respect to metal oxide or acti-
vated carbon), and aqueous glycerol solution (5 mL, 0.2m, glycerol:
Kanto Chemical) were loaded into the reactor, and then introduced
Acknowledgements
This work was supported in part by the Core Research for Evolu-
tional Science and Technology (CREST, JY230195) program and
the Novel Cheap and Abundant Materials for Catalytic Biomass
Conversion (NOVACAM, 7-NMP-2013-EU-Japan-60431) program
of the Japan Science and Technology (JST) Agency and the Euro-
pean Union.
at 0.5 MPa O . The reaction mixture was stirred at 423 K. After the
2
removal of the catalyst by filtration, the products in the liquid
phase were analyzed by HPLC (JASCO, LC-2000 plus) equipped
with Aminex HPX-87 H column (diameter: 300 mm”7.8 mm,
À1
eluent: 0.005m H SO 0.5 mLmin , temperature: 308 K), refractive
2
4
index (RI) and photodiode array (PDA). The spent catalyst was re-
covered by centrifugation. After washing with water (30 mL), the
recovered catalyst was dried at 353 K, and was utilized for reuse
experiment and/or characterizations. The reactions of DHA (Merck),
GA (Wako Pure Chemical Industries), PA (40 wt% solution, Aldrich),
Keywords: biomass · Lewis acids · oxidation · platinum ·
titanates
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Catalyst characterization
XPS analysis was performed with JEOL JPC-9010MC for Pt 4f using
MgKa radiation (1253.6 eV) at 10 kV and 25 mA. Samples were
pressed into pellet and fixed on a double-stick carbon tape. The
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8
3.8 eV). HAADF–STEM measurement were performed by using
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Received: November 2, 2015
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