Synergetic combination of an enzyme and gold catalysts for glucose oxidation in neutral aqueous solution

Article abstract of DOI:10.1016/j.apcata.2013.09.023

Glucose oxidation by enzyme takes place in neutral aqueous solution at room temperature, producing gluconic acid in equilibrium with gluconate, while gold catalysts exhibit much higher catalytic activity but in alkali solution to produce sodium gluconate. The combination of glucose oxidase with selected gold catalysts such as Au/ZrO₂ and Au/NanoDiamond led to improved catalytic performance in neutral solution at room temperature. Gold nanoparticles supported on ZrO₂ decomposed hydrogen peroxide (H ₂O₂) formed by the oxidation of glucose and depressed the damage of glucose oxidase by H₂O₂. In addition, Au/ZrO₂ utilized H₂O₂ produced by the enzyme to oxidize glucose to gluconic acid. In contrast, gold nanoparticles supported on NanoDiamond were active only for the decomposition of H₂O ₂, while the presence of NanoDiamond itself could encourage glucose oxidase for the selective oxidation.

Full text of DOI:10.1016/j.apcata.2013.09.023

Applied Catalysis A: General 468 (2013) 453–458
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Synergetic combination of an enzyme and gold catalysts for glucose
oxidation in neutral aqueous solutionଝ
Ayako Taketoshia,b, Sho Takenouchia,b, Takashi Takeia,b, Masatake Harutaa,b,∗
a Department of Applied Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo
192-0397, Japan
b Japan Science and Technology Agency, CREST, 4-1-8 Hon-cho, Kawaguchi, Saitama 332-0012, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 April 2013
Received in revised form
11 September 2013
Accepted 13 September 2013
Available online 21 September 2013
Glucose oxidation by enzyme takes place in neutral aqueous solution at room temperature, producing
gluconic acid in equilibrium with gluconate, while gold catalysts exhibit much higher catalytic activity
but in alkali solution to produce sodium gluconate. The combination of glucose oxidase with selected
gold catalysts such as Au/ZrO2 and Au/NanoDiamond led to improved catalytic performance in neutral
solution at room temperature. Gold nanoparticles supported on ZrO2 decomposed hydrogen peroxide
(H2O2) formed by the oxidation of glucose and depressed the damage of glucose oxidase by H2O2. In
addition, Au/ZrO2 utilized H2O2 produced by the enzyme to oxidize glucose to gluconic acid. In contrast,
gold nanoparticles supported on NanoDiamond were active only for the decomposition of H2O2, while
the presence of NanoDiamond itself could encourage glucose oxidase for the selective oxidation.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Gold nanoparticles
Glucose oxidase
Glucose
Aerobic oxidation
Gluconic acid
1. Introduction
useful catalytic performance leading to green sustainable chem-
istry [4–6]. For biomass derived resources, supported gold catalysts
Catalytic transformation of biomass derived natural resources
to valuable compounds is becoming of immense importance for
the sustainable development of chemical industry [1]. Ethanol (C2
compound) is produced from cones, sugar canes, and cellulose in
an amount of 81.40 million tons a year in 2011 in the world [2] and
occupies the majority of its commercial production. Glycerol (C3
compound) which is by-produced in the production of biodiesel
oil is produced in an amount of 0.75 million tons/year [3]. Glu-
cose (C6 compound) is also an important chemical resource which
is produced from starch in an amount of 20 million tons/year. In
the transformation of these biomass derived resources to valuable
compounds, chemical processes have a lot of advantages, for exam-
ple, higher purity and shorter reaction time, over the biological ones
using microorganisms [1].
show interesting catalytic performance. Ethanol can be selectively
transformed into acetic acid in aqueous solution on Au/MgAl2O4
catalyst [7] and into acetaldehyde by the gas phase oxidation on
Au/La2O3 and Au/MoO3 catalysts with molecular oxygen [8,9].
The hydrogenolysis of glycerol on Au/Al2O3 at 423 K selectively
produces 1,2-propane diol [10]. The aerobic oxidation of glucose in
strong aqueous alkali solution can produce sodium gluconate with
extremely high rate of reaction on Au/ZrO2. Turnover frequency per
surface exposed gold atoms (TOF) reached 45 s−1 [11].
Glucose oxidation can also be performed using a biocata-
lyst, namely glucose oxidase (GOx), which gives low initial rate
(1.7 × 10−6 mol L−1 s−1) but a high TOF of 145 s−1. Glucose oxidase
can work in neutral solution at room temperature and can produce
gluconic acid [12]. Gluconic acid is used as a complexing agent in
industrial cleaning of metal surfaces and as a food additive. Since
gluconic acid is a mild acid, it is in equilibrium with alkali gluconate
under reaction conditions. The amount of strong acid required to
obtain gluconic acid can be minimized if the reaction proceeds
in neutral or acidic solution. In contrast, supported gold catalysts
give much higher initial rate (1.4 × 10−4 mol L−1 s−1) but in alkali
solution at higher temperature [11,13–15].
Gold nanoparticles (hereafter denoted as NPs) supported on
base metal oxides, carbon, and polymers exhibit unique and
ଝ
A
publisher’s error resulted in this article appearing in the wrong issue.
The article is reprinted here for the reader’s convenience and for the continuity
of the special issue. For citation purposes, please use http://dx.doi.org/10.1016/
j.apcata.2013.09.025
Our attempt is to combine glucose oxidase as a biological cat-
alytic system with supported gold NPs as an artificial catalytic
system to seek for synergetic improvement in catalytic perfor-
mance. Vennestrøm et al. have recently reported the combination
∗
Corresponding author at: Department of Applied Chemistry, Graduate School of
Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa,
Hachioji, Tokyo 192-0397, Japan. Tel.: +81 42 677 2852; fax: +81 42 677 2852.
E-mail address: haruta-masatake@tmu.ac.jp (M. Haruta).
0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apcata.2013.09.023

454
A. Taketoshi et al. / Applied Catalysis A: General 468 (2013) 453–458
of glucose oxidase with titanium silicalite-1 to utilize the by-
product of one reaction (H2O2) for the second one (epoxidation
of allyl alcohol) [16]. Our idea, which can be expressed by “a hybrid
of an enzyme catalyst with artificial catalysts for the same reac-
tion”, has come out from the instructive and inspiring review article
presented by Professor Bernard Delmon [17]. He has proposed a
bridged system between man-made functional solids and enzyme.
We hope that this paper could present a preliminary example of
his concept.
(100 mL) of KMnO4 (37 mmol) at room temperature, and the mix-
ture was stirred at that temperature for 30 min. The precipitate
was repeatedly washed with distilled water until the pH reached a
steady value of around 4. The precipitate was collected by filtration,
dried at 120 ◦C overnight, and then calcined in air at 300 ◦C for 4 h.
Fe2O3, Co3O4, NiO, CuO and La2O3 were prepared by the neu-
tralization method. An aqueous solution of metal nitrate (0.1 M L−1
)
was rapidly added into an aqueous solution of Na2CO3 (1.2 equiv.,
0.1 M L−1) at 70 ◦C. After stirring for 1 h, the suspension was cen-
trifuged and the precipitate was repeatedly washed with distilled
water until the pH reached a steady value of around 6. The precip-
itate was filtrated, dried at 120 ◦C overnight, and then calcined in
air at 300 ◦C for 4 h.
2. Experimental
2.1. Materials
2.3. Deposition of gold NPs on carbons and metal oxides
The majority of metal oxide supports used were commercially
available metal oxide powders: Al2O3 (Sumitomo Chemical, AKP-
GO15, 148 m2 g−1), SiO2 (Fuji Silysia Chemical, CARiACT Q-10,
300 m2 g−1), TiO2 (Nippon Aerosil, P-25, 50 m2 g−1), ZnO (Hakusui
Tech, ZINCOX SUPER F-2, 14 m2 g−1), ZrO2 (Dai-ichi Kigenso
Kagaku Kogyo, RC-100, 80–120 m2 g−1), SnO2 (Sigma–Aldrich,
nanopowder, <100 nm), and CeO2 (Dai-ichi Kigenso Kagaku Kogyo,
166 m2 g−1). Two types of carbon supports were used, namely, Nan-
oDiamond (ND) (NanoCarbon Research Institute, NanoAmando,
4–5 nm) and KetjenBlack (KB) (Lion, CARBON ECP, 780 m2 g−1).
Reagent grades, NH4VO3, MnCl2·4H2O, KMnO4, Fe(NO3)2·6H2O,
Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·6H2O, La(NO3)3·6H2O,
Na2CO3, NaOH, glucose were used as received. As gold precursors,
dimethyl AuIII acetylacetonate (Me2Au(acac)) was purchased from
Tri Chemical Laboratories Inc. Glucose oxidase (from Aspergillus
niger, 240,000 units g−1) was purchased from Wako Pure Chemical
Industries.
All gold catalysts were prepared by the solid grinding (SG)
method [18]. Briefly, dimethyl gold acetylacetonate, Me2Au(acac),
(8.3 mg) and support (1.0 g) were ground in an agate mortar for
20 min. The mixture was calcined in air at 300 ◦C for 4 h or reduced
in 20 vol% H2/N2 stream at 120 ◦C for 2 h. The gold loading was
0.5 wt%.
2.4. Characterization
Transmission electron microscope (TEM) and high-angle annu-
lar dark-field scanning TEM (HAADF-STEM) observations were
carried out by using a JEOL JEM-3200FS operating at 300 kV. At least
140 particles of gold were observed to estimate the mean diameters
and the standard deviation.
2.5. Catalytic tests
2.2. Preparation of metal oxide supports
Glucose oxidation was carried out by using 2 wt% glucose aque-
ous solution (31 mL), 0.13 g L−1 of GOx and 8.0 mg of inorganic
catalyst by bubbling O2 (60 mL min−1) at atmospheric pressure. The
aqueous dispersion was stirred at 30 ◦C under controlled pH of 7
V2O5 was prepared by calcination of NH4VO3 in air at 300 ◦C for
4 h. For the preparation of MnO2, an aqueous solution (30 mL) of
MnCl2·4H2O (50 mmol) was added slowly to an aqueous solution
Table 1
Aerobic oxidation of glucose catalyzed by GOx combined with supported gold NPs.a
b
Entry
Catalyst
Initial rate (molglucose L−1 s−1
)
Conv. after 1 h (%)c
1
2
3
4
5
6
7
8
9
GOx
GOx
GOx
GOx
GOx
GOx
GOx
GOx
GOx
Au/ZrO2
(7.4 1.4) × 10−5
(5.6 1.6) × 10−5
5.2 × 10−5
98
98
98
96
95
94
93
91
91
2
2
Au/NanoDiamond
Au/La2O3
Au/Al2O3
Au/CeO2
Au/SnO2
Pt/ZrO2
(5.4 1.6) × 10−5
6.2 × 10−5
2
5
6.8 × 10−5
(4.9 0.5) × 10−5
6.5 × 10−5
Au/MnO2
Au/Co3O4
5.8 × 10−5
10
11
12
13
14
15
16
17
18
GOx
GOx
GOx
GOx
GOx
GOx
GOx
GOx
GOx
−
(4.8 1.5) × 10−5
90
88
87
86
84
83
73
42
76
3
2
Au/Fe2O3
Au/SiO2
Au/TiO2
Au/ZnO
Au/V2O5
Au/NiO
4.2 × 10−5
(4.5 0.5) × 10−5
5.8 × 10−5
4.5 × 10−5
2.9 × 10−5
4.5 × 10−5
Au/CuO
Au/KetjenBlack
3.9 × 10−5
2.5 × 10−5
19
20
21
22
23
24
GOx
GOx
GOx
GOx
−
NanoDiamond
ZrO2
Al2O3
KetjenBlack
Au/ZrO2
Au/Al2O3
4.2 × 10−5
3.6 × 10−5
3.6 × 10−5
2.3 × 10−5
6.5 × 10−6
9.7 × 10−6
93
79
85
62
4
−
3
a
Reaction conditions: 2 wt% aqueous glucose solution (31 mL), GOx (0.13 g L−1), 0.5 wt% Au loading catalyst (8.0 mg), glucose/Au = 15,000 (mol/mol), O2 (60 mL min−1),
30 ◦C, pH 7.
b
Calculated from a straight line fitted to the conversion–time curve.
The pH of the solution was kept at 7 by the titration with 1 M NaOH aqueous solution. Conversion after 1 h was calculated by the amount of NaOH added.
c

A. Taketoshi et al. / Applied Catalysis A: General 468 (2013) 453–458
455
(
0.5) by titrating with 1 M L−1 NaOH aqueous solution. The con-
version of glucose was calculated from the total amount of NaOH
added. The reaction mixture was filtrated to remove the catalyst
and the filtrate was evaporated. The residue was analyzed by 1H
NMR (JEOL 300 MHz, D2O) to compare with authentic sample of
sodium gluconate.
3. Results and discussion
3.1. Combination effect of enzyme and gold catalysts on glucose
oxidation
Table 1 shows the catalytic activity of glucose oxidase combined
with gold NPs supported on a variety of metal oxides and on car-
bons. The initial rate, which was calculated from the slope of the
straight part of conversion vs reaction time, shows the initial cat-
alytic activity, whereas the conversion of glucose after 1 h reaction
reflects the stability property of the catalytic systems. In the case
of several representative gold catalysts, they were prepared by 2–5
times by the same method under the same conditions and were
subjected to glucose oxidation (entries 1, 2, 4, 7, 10 and 12).
Supported gold NPs catalysts can be classified into two groups.
The first one showed increases in both initial rate of reaction
and conversion of glucose after 1 h reaction by the combination
with glucose oxidase. They are, in the order of decreasing catalytic
activity, Au/ZrO2, Au/ND, Au/La2O3, Au/Al2O3, Au/CeO2, Au/SnO2,
Au/MnO2, and Au/Co3O4 (entries 1–9). The second one showed
decreases in both initial rate of reaction and conversion after 1 h
and is composed of Au/Fe2O3, Au/SiO2, Au/TiO2, Au/ZnO, Au/V2O5,
Au/NiO, Au/CuO, and Au/KB (entries 11–18). There seems to be no
clear correlations between the kind of metal oxide supports and the
enhancing effect on the catalytic activity for glucose oxidation. It is
likely that synergy between supported gold catalysts and glucose
oxidase may depend on the biological compatibility rather than on
physicochemical properties of the support materials.
Fig. 2. Conversion–time curves for glucose oxidation in neutral aqueous solution at
30 ◦C with GOx and Au/ZrO2. Reaction conditions: 2 wt% aqueous glucose solution
(31 mL), GOx (0.13 g L−1), 0.5 wt% Au loading catalyst (8.0 mg), glucose/Au = 15,000
(mol/mol), O2 (60 mL min−1), 30 ◦C, pH 7. The pH of the solution was kept at 7 by
the titration with 1 M NaOH aqueous solution. Conversion was calculated by the
amount of NaOH added. (᭹) GOx + Au/ZrO2; (ꢀ) GOx; (ꢀ) GOx + ZrO2; (ꢁ) Au/ZrO2.
without gold deposition, ND, ZrO2, Al2O3, and KB, only NanoDi-
amond presented higher conversion of glucose after 1 h reaction
(entries 19–22).
Fig. 1 shows that glucose oxidase alone could not attain 100%
conversion because of the deactivation by H2O2 formed during
reaction. The combination with KB without gold deposition yielded
lower conversions than with Au/KB, suggesting that gold NPs could
facilitate the decomposition of H2O2. In fact, Table 2 shows that
deposition of gold NPs or Pt NPs on ZrO2, Al2O3, ND, and KB
increased the rate of H2O2 decomposition (entries 1–9). In con-
trast, the combination with ND without gold deposition yielded a
little higher conversion than glucose oxidase alone. Because H2O2
decomposition on ND was moderately fast similar to KB, it can be
assumed that the co-presence of ND enhances gluconic acid pro-
duction by glucose oxidase. Deposition of gold NPs on ND enabled
glucose oxidase to transform glucose with 100% conversion. This
It is interesting to note that two carbon materials show opposite
effect on the catalytic activity. Gold NPs deposited on KetjenBlack
having mesopores reduced the initial oxidation rate with glucose
oxidase by half, while gold NPs on NanoDiamond which were non-
porous enhanced the initial rate by 17%. Among supports alone
Fig. 1. Conversion–time curves for glucose oxidation in neutral aqueous solution
at 30 ◦C with GOx and Au/carbon supports. Reaction conditions: 2 wt% aqueous
glucose solution (31 mL), GOx (0.13 g L−1), 0.5 wt% Au loading catalyst (8.0 mg), glu-
cose/Au = 15,000 (mol/mol), O2 (60 mL min−1), 30 ◦C, pH 7. The pH of the solution
was kept at 7 by the titration with 1 M NaOH aqueous solution. Conversion was cal-
culated by the amount of NaOH added. (᭹) GOx + Au/ND; (ꢀ) GOx + ND; (ꢀ) GOx;
(ꢁ) GOx + Au/KB; (ꢁ) GOx + KB.
Fig. 3. Conversion–time curves for glucose oxidation in neutral aqueous solution at
30 ◦C with GOx and Au/Al2O3. Reaction conditions: 2 wt% aqueous glucose solution
(31 mL), GOx (0.13 g L−1), 0.5 wt% Au loading catalyst (8.0 mg), glucose/Au = 15,000
(mol/mol), O2 (60 mL min−1), 30 ◦C, pH 7. The pH of the solution was kept at 7 by the
titration with 1 M NaOH aqueous solution. Conversion was calculated by the amount
of NaOH added. (᭹) GOx + Au/Al2O3; (ꢀ) GOx; (ꢀ) GOx + Al2O3; (ꢁ) Au/Al2O3.

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A. Taketoshi et al. / Applied Catalysis A: General 468 (2013) 453–458
Fig. 4. HAADF-STEM images of (a) Au/ND, (c) Au/ZrO2, (e) Au/Al2O3, (g) Au/KB, and distribution of the diameter of gold NPs in (b) Au/ND, (d) Au/ZrO2, (f) Au/Al2O3, and (h)
Au/KB.

A. Taketoshi et al. / Applied Catalysis A: General 468 (2013) 453–458
457
Table 2
The decomposition of H2O2 by gold and platinum catalysts.a
Table 3
The effect of H2O2 on aerobic glucose oxidation by gold and platinum catalysts.a
b
Entry
Catalyst
Rate of O2 generation (mL min−1
)
Entry
Catalyst
Conv. after 1 h (%)b
1
2
3
4
5
6
7
8
9
Au/ZrO2
Pt/ZrO2
Au/Al2O3
Au/NanoDiamond
Au/KetjenBlack
ZrO2
0.13
0.12
0.10
0.10
0.09
0.09
0.07
0.08
0.08
0.04
O2
O2 + H2O2
1
2
3
4
5
6c
Au/ZrO2
Au/Al2O3
Pt/ZrO2
Au/NanoDiamond
Au/KetjenBlack
GOx
4
3
0
0
0
12
5
0
0
4
Al2O3
86
67
NanoDiamond
KetjenBlack
blank
a
Reaction conditions: 2 wt% aqueous glucose solution (31 mL), 0.5 wt% Au
loading catalyst (8.0 mg), glucose/Au = 15,000 (mol/mol), O2 (60 mL min−1) or O2
(60 mL min−1) and 0.3 wt% H2O2 aqueous solution, 30 ◦C, pH 7.
The pH of the solution was kept at 7 by the titration with 1 M NaOH aqueous
solution. Conversion after 1 h was calculated by the amount of NaOH added.
10
a
Reaction conditions: 0.3 wt% H2O2 aqueous solution (10 mL), catalyst (2.7 mg),
b
30 ◦C, pH 7.
b
Measured by soap-film flow meter.
c
GOx (0.13 g L−1).
is probably because Au/ND decomposes H2O2 more rapidly and
avoids deactivation of glucose oxidase.
negative effect. In particular, Au/KB highly depressed glucose oxi-
dation by glucose oxidase even though the deposition of noble
metals increased the rate of H2O2 decomposition. The fact means
that the co-presence of KB itself caused the depression of the
enzyme activity (Fig. 1). Therefore the compatibility of support
materials with glucose oxidase is one of the key factors for synergy
effect as well as the ability for H2O2 decomposition.
Figs. 2 and 3 show that Au/ZrO2 and Au/Al2O3 which exhibited
the highest catalytic activity for the aerobic oxidation of glucose in
strong alkali solution were not active at all under neutral conditions
(Table 1, entries 23 and 24). However, the combination with glucose
oxidase appreciably increased the catalytic activity both in terms
of initial rate and conversion attained after 1 h reaction though the
combination of their supports alone with glucose oxidase showed
negative effect.
3.4. Effect of H2O2 on glucose oxidation with O2
3.2. Characterization of the catalysts
Table 3 lists glucose conversion with O2 alone and with O2
and H2O2. On glucose oxidase, the conversion with O2 alone was
higher than with O2 and H2O2, indicating that the co-presence of
H2O2 depressed the oxidation reaction. On Au/ZrO2, the conversion
was appreciably increased from 4 to 12%. This may partly explain
why the combination of enzyme with Au/ZrO2 catalyst exhibits
enhanced catalytic activity. The gold catalyst utilizes H2O2 pro-
duced by glucose oxidation with the enzyme to gluconic acid and
at the same time it decomposes H2O2 to avoid the deactivation of
enzyme by H2O2.
Although gold NPs could not be observed by a high-resolution
TEM, the diameters of primary particles of ND could be estimated
to be 5–10 nm for Au/ND. Fig. 4a shows a HAADF-STEM image as
well as a distribution of the diameter of gold NPs in Au/ND. By
this technique even tiny gold NPs could be observed because the
contrast was intensified by the second power of the atomic weight
of the element, namely, [197(Au)/12(C)]2 = (16.4)2. Obviously, gold
NPs were highly and almost homogeneously dispersed. The mean
diameter and standard deviation of gold NPs were calculated to
be 2.4 nm 1.4 nm from about 30 images taken by a HAADF-STEM
(Fig. 4b).
4. Conclusions
The diameters of primary particles of ZrO2 were estimated to
be 5–10 nm by HR-TEM. A HAADF-STEM image for Au/ZrO2 which
exhibited the most efficient combination effect is shown in Fig. 4c.
The mean diameter of gold NPs on ZrO2 was calculated to be
4.2 nm 1.5 nm (Fig. 4d). In the case of Pt/ZrO2, platinum NPs could
not be observed even by a HAADF-STEM. It is probable that plat-
inum NPs were too small and below 2 nm in diameter. The Au/Al2O3
catalyst was composed of a mixture of 20–50 nm particles and nee-
dles of Al2O3. Gold NPs could be found but they were dispersed
with a small population density (Fig. 4e). The gold particles are
11.1 nm 6.6 nm in diameter (Fig. 4f). This feature is different from
that of a typical active gold catalyst. Accordingly, there is a large
room to improve the catalytic activity of Au/Al2O3. In Au/KB, the
diameters of primary particles of KB are 20–50 nm. The mean diam-
eter of gold NPs on KB was 6.5 nm 2.9 nm (Fig. 4h).
Aerobic oxidation of glucose has been conducted in neutral
aqueous solution at room temperature to produce acid-rich glu-
conate by using a hybrid system of a biological catalyst like an
enzyme and artificial catalysts like supported gold catalysts. Gold
catalysts were chosen because they exhibit higher catalytic activity
at around room temperature than other metal catalysts.
1) Gold NPs supported on
a variety of base metal oxides
and carbons showed positive synergy by the combination
with glucose oxidase, in particular, Au/ZrO2, Au/Al2O3, and
Au/NanoDiamond.
2) In the case of Au/ZrO2 and Au/Al2O3, the combination with their
supports alone showed negative effect whereas the gold cat-
alysts showed positive synergy caused by the following: they
decompose H2O2 produced by glucose oxidase and protect the
enzyme from oxidative damages by H2O2 and furthermore uti-
lize H2O2 for glucose oxidation to gluconic acid.
3) In the case of Au/ND which is active for H2O2 decomposition
but not active for the glucose oxidation with O2 and with O2
and H2O2, it can only prevent glucose oxidase from the oxida-
tive deactivation by H2O2. However, the presence of ND does
not cause the negative effect to glucose oxidase, in other words,
glucose oxidase is compatible with ND.
3.3. Decomposition of H2O2 by gold catalysts
Table 2 shows the decomposition of H2O2 on supported gold
catalysts and on support materials without gold deposition. All
materials show a certain degree of catalytic activity for H2O2
decomposition which avoids the deactivation of enzyme catalysts.
In the cases of Au/ZrO2, Au/ND, Au/Al2O3, Pt/ZrO2 and ND, the com-
bination with glucose oxidase showed positive effect as expected.
In contrast, in the cases of Au/KB, ZrO2, Al2O3 and KB, they showed

458
A. Taketoshi et al. / Applied Catalysis A: General 468 (2013) 453–458
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One of the authors (M. H.) is deeply grateful to Professor Bernard
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ment since he stayed in Louvain-la Neuve in 1981 and 1982. This
work has been conducted being inspired by his contact synergy
concept.
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