The selective oxidation of 1,2-propanediol to lactic acid using mild conditions and gold-based nanoparticulate catalysts

Article abstract of DOI:10.1016/j.cattod.2012.05.037

The use of bio-renewable resources for the generation of materials and chemicals continues to attract significant research attention. It is well established that glycerol is an excellent starting material for the production of 1,2-propanediol by dehydration/hydrogenation and that this can subsequently be oxidised to lactic acid, which has the potential to be used as a major chemical in the production of biodegradable polymers. Previous studies using gold catalysts for the oxidation of 1,2-propanediol have used elevated temperatures and pressures. We now show that the oxidation of 1,2-propanediol to form lactic acid can be carried out selectively under mild reaction conditions with gold-platinum catalysts prepared using a sol-immobilisation method, with activated carbon as the support. Carrying out the reaction at ambient temperature with air significantly improves the reaction in terms of its environmental impact and its industrial attractiveness, as lactic acid can be obtained with high selectivity.

Full text of DOI:10.1016/j.cattod.2012.05.037

Catalysis Today 203 (2013) 139–145
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The selective oxidation of 1,2-propanediol to lactic acid using mild conditions
and gold-based nanoparticulate catalysts
Yulia Ryabenkovaa, Qian Heb, Peter J. Miedziaka, Nicholas F. Dummera, Stuart H. Taylora,
Albert F. Carleya, David J. Morgana, Nikolaos Dimitratosa, David J. Willocka, Donald Bethella,
David W. Knighta, David Chadwickc, Christopher J. Kielyb, Graham J. Hutchingsa,∗
a Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
b Department of Materials Science and Engineering, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015, USA
c Chemical Engineering and Chemical Technology, South Kensington Campus, Imperial College London, SW7 2AZ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The use of bio-renewable resources for the generation of materials and chemicals continues to attract
significant research attention. It is well established that glycerol is an excellent starting material for the
production of 1,2-propanediol by dehydration/hydrogenation and that this can subsequently be oxidised
to lactic acid, which has the potential to be used as a major chemical in the production of biodegradable
polymers. Previous studies using gold catalysts for the oxidation of 1,2-propanediol have used elevated
temperatures and pressures. We now show that the oxidation of 1,2-propanediol to form lactic acid can
be carried out selectively under mild reaction conditions with gold–platinum catalysts prepared using a
sol-immobilisation method, with activated carbon as the support. Carrying out the reaction at ambient
temperature with air significantly improves the reaction in terms of its environmental impact and its
industrial attractiveness, as lactic acid can be obtained with high selectivity.
Received 27 October 2011
Received in revised form 21 May 2012
Accepted 21 May 2012
Available online 2 July 2012
Keywords:
Gold catalysis
Gold platinum alloy nanoparticles
Lactic acid
1,2-Propanediol oxidation
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Glycerol is currently a desirable starting material for the pro-
duction of value-added fine chemicals, being a bio-renewable
Lactic acid has the potential to be a major intermediate in the
production of biodegradable polymers. Currently, lactic acid is used
mainly as a fine chemical, with applications in the cosmetic, textile
and food industries. The realisation that polylactate is a biodegrad-
able plastic [1] has led to an enhanced interest in the transformation
of 1,2-propanediol into lactic acid, which could ultimately result in
the latter becoming a commodity rather than a fine chemical.
A synthetic process for producing lactic acid has been reported
by Prati and Rossi [2], which involves the reaction of acetaldehyde
and HCN along with a subsequent treatment with sulphuric acid.
However, this reaction is considered not to be very ‘green’ in charac-
ter due to the nature of the chemicals used and the waste products
generated. Lactic acid is mainly produced by a fermentation process
[1], which requires high dilutions and has a slow rate of reaction
as the enzyme action is inhibited by the reaction product. There-
fore, there is a definite need to produce lactic acid via a greener
route which this paper addresses by describing the oxidation of
1,2-propanediol to form lactic acid under mild, catalytic conditions.
feedstock that is a by-product of the manufacture of bio-diesel [3];
and with the current drive towards developing greener fuel sources,
the availability of glycerol as a raw material is likely to be sustained.
Glycerol has been shown to be an excellent starting material for
the production of 1,2-propanediol by dehydration/hydrogenation,
as has been reported by Miyazawa et al. [4]. Furthermore, 1,2-
propanediol has been shown to be an effective intermediate for
the production of lactic acid. Initial work by Tsujino et al. [5] using
Pd/C catalysts modified with Pb, Bi and/or Te, using aqueous con-
ditions at pH 8 and 90 ◦C, to oxidise at both the primary and
secondary alcohol groups, led not only to the formation of lactic
acid, but also to hydroxyacetone and pyruvic acid. Pinxt et al. [6]
showed that pyruvic acid was produced via two parallel pathways
from either lactic acid or hydroxyacetone using Pt modified by Pb,
Bi and Sn supported on carbon. These studies indicated that 1,2-
propanediol can effectively be converted to lactic acid, but the use
of Pd and Pt catalysts to do so leads to low selectivity for the desired
product.
Recently, interest has grown in using highly stable gold nanopar-
ticles for oxidation reactions [7]. Nano-particulate gold dispersed
on a range of oxide supports and carbon has been studied for a
wide range of catalytic redox reactions, such as CO oxidation [8,9]
and CO oxidation in the presence of H2, H2O and CO2 for fuel cell
∗
Corresponding author.
E-mail address: hutch@cf.ac.uk (G.J. Hutchings).
0920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2012.05.037

140
Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
applications [10,11]. Gold nanoparticles have also been shown to be
effective for the oxidation of alkenes [12] and alcohols [13], includ-
ing polyols such as glycerol [14,2,15]. Rossi and Prati were the first
to show that supported gold nanoparticles were effective for alco-
hol oxidation in the presence of base [16,17]. A number of more
recent studies have concentrated on the role of the gold particle
size [18], the catalyst pre-treatment [19] and catalyst preparation
method [20] on alcohol oxidation. Prati and Rossi were also the
first to demonstrate that gold supported on carbon could be used
to oxidise 1,2-propanediol to form lactic acid [21], with high con-
version and selectivity at O2 pressure of 3 bar and temperature of
90 ◦C.
We have demonstrated that alloying gold with palladium leads
to a significant enhancement of activity, with a simultaneous
retention of selectivity for alcohol oxidation to the corresponding
aldehyde [22]. Such catalysts also markedly improve the yield of
hydrogen peroxide in its direct synthesis from hydrogen and oxy-
gen [23–28]. In these earlier studies we used a wet impregnation
preparation method to generate the gold–palladium nanoparti-
cles. Recently, we have shown that a sol-immobilisation method
can give mono-metallic Au and Pd, and bi-metallic Au–Pd sup-
ported nanoparticles with enhanced activity for glycerol oxidation
[29]. We have also demonstrated that wet impregnation and sol-
immobilisation prepared Au–Pd catalysts, supported on TiO2, and
C are effective for the formation of lactic acid from 1,2-propanediol.
Sol-immobilisation catalysts proved to be the most effective, giv-
ing 96% selectivity at 94% conversion at 60 ◦C and 10 bar O2 [30]. In
this present paper, we extend our earlier studies of 1,2-propanediol
oxidation with Au–Pd materials to Au–Pt catalysts, and we now
show that by tailoring the catalyst composition together with the
reaction conditions, choice of support and reactor type, signifi-
cant activity for the oxidation of 1,2-propanediol can be achieved
under much milder conditions than those previously reported.
The decrease in reaction temperature and the use of air as an
oxidant means the catalytic oxidation is more environmentally
friendly and the simplified nature of the reaction makes it more
appealing as an industrial process. Furthermore, the drive towards
milder conditions could help prevent alternative oxidation path-
ways, reducing the formation of the undesired product, pyruvic
acid.
acid) under vigorous stirring. The amount of support material
required was calculated to give a total final metal loading of 1 wt%.
After 1 h the slurry was filtered, the catalyst washed thoroughly
with distilled water and dried at 110 ◦C overnight.
2.2. Catalyst testing
Reactions were carried out using a 50 ml Radleys low pressure
reactor. NaOH (0.48 g or 0.96 g) was dissolved in 1,2-propanediol
(20 ml, 0.6 M aqueous solution). The catalyst was added to the solu-
tion (molar ratio substrate:metal = 1000–16,000) in a round bottom
flask. The flask was charged with oxygen to the desired pres-
sure (1–3 bar), and heated to the required temperature (30–60 ◦C),
whereupon stirring was started. The solution temperature was
maintained for the desired reaction time (30–240 min), then cooled
to room temperature and the reaction mixtures were analysed by
HPLC and NMR spectroscopy.
The reaction was also performed on a larger scale in a 500 ml
wide neck flask with a water cooled jacket and a three neck flat
flange lid. The flask contained four plastic inserts to aid the for-
mation of vortices within the reaction mixture. A thermometer
was inserted into the central neck of the flange lid to monitor the
reaction temperature. The second neck was connected to a con-
denser and the third neck had a rubber stopper through which
(i) air was bubbled into the reaction mixture at atmospheric pres-
sure and (ii) reaction samples were obtained. The 0.5%Au + 0.5%Pt/C
catalyst (substrate:metal mol ratio = 5000 molar ratio) was added
to the solution at 25 ◦C and samples were obtained at various
time intervals (30–120 min). The samples were passed through a
0.22 ␮m syringe filter to remove the catalyst, and then activated
charcoal, and finally the filtered reaction mixture was analysed by
HPLC.
HPLC analysis was carried out using a Varian 920-LC fitted with
a metacarb 87H column with ultraviolet and refractive index detec-
tors. Reactants and products were separated using a metacarb 67H
column. The eluent was a solution of H3PO4 (0.01 M) with a flow of
0.3 ml min−1. Samples of the reaction mixture (0.5 ml) were diluted
to 5 ml using the eluent. Products were identified by comparison
with known pure samples. For quantification of the starting mate-
rial and products an external calibration method was used and the
calibration factor for each was calculated.
2. Experimental
1H NMR spectroscopy was used for product identification: spec-
tra were acquired over a 16 scan period on a Bruker 400 MHz DPX
system using a 5 mm auto tune broadband probe. All samples were
prepared with D2O.
2.1. Catalyst preparation
A
series of Au, Pt, Pd, Au–Pd, Au–Pt and Pd–Pt cata-
lysts supported on activated carbon (KB-B, G60, KB, Aldrich;
Table 1 compares the textural properties of these three sup-
ports) were prepared using a sol-immobilisation method. Aqueous
solutions of PdCl2 (Johnson Matthey) or H2PtCl6 (Johnson
Matthey) and HAuCl4·3H2O (Johnson Matthey) of the desired
concentration were prepared. To this solution polyvinylalcohol
(PVA) (1 wt% solution, Aldrich, weight average molecular weight
MW = 9000–10,000 g mol−1, 80% hydrolysed) was added (PVA/Au
(wt/wt) = 1.2). Subsequently, a freshly prepared 0.1 M solution of
NaBH4 (>96%, Aldrich, NaBH4/metal (mol/mol) = 5) was added to
form a sol. After 30 min of sol generation, the colloid was immo-
bilised by adding activated carbon (acidified to pH 1 by sulphuric
2.3. Catalyst characterisation
X-ray photoelectron spectroscopy (XPS) was performed on a
Kratos Axis Ultra DLD spectrometer employing a monochromatic
AlK␣ X-ray source (120 W) and analyser pass energies of 160 eV (for
survey scans) or 40 eV (for detailed scans). Samples were mounted
using double-sided adhesive tape and binding energies referenced
to the C(1s) binding energy of adventitious carbon contamination
which was taken to be 284.7 eV.
Samples for examination by scanning transmission electron
microscopy (STEM) were prepared by dispersing the dry catalyst
powder onto a holey carbon film supported by a 300 mesh copper
TEM grid. STEM high angle annular dark field (HAADF) images of the
bimetallic particles were obtained using an aberration corrected
JEOL 2200FS (S)TEM operating at 200 kV. X-ray energy disper-
sive (XEDS) spectra were acquired from individual nanoparticles
larger than 1–2 nm in size while rastering the beam over the entire
particle.
Table 1
Structural properties of the carbon supports used in this study.
Activated carbon support
Surface area (m2/g)
Pore volume (ml/g)
G-60
KB
KB-B
600
1500
1500
0.95
2
2

Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
141
Table 2
surface area, and we consider this parameter might be important in
determining the dispersion of the Au–Pt supported nanoparticles.
Moreover, a higher pore volume will facilitate the accessibility of
the substrate to the Au–Pt active site and lead to higher activity.
However, the surface area and pore volume of the KB and KB-B sup-
ports are similar (Table 1), yet the KB-B-supported catalyst gives a
slightly enhanced conversion, which implies that additional factors
other than surface area and pore volume are also involved, proba-
bly more related to the surface structure/chemistry of the carbon.
The KB-B activated carbon was used in all subsequent experiments.
Effect of the activated carbon support identity when using Au–Pt supported
nanoparticles for the selective oxidation of 1,2-propanediol.a
Support
Conversion (%)
Selectivity (%)
Lactate
Formate
Acetate
G60
KB
KB-B
70
76
80
86
89
89
4
3
2
10
8
9
a
Reaction conditions: catalyst AuPt = 1:1; 1 wt% total metal; water (20 ml); 1,2-
propanediol (0.6 mol); NaOH/1,2-propanediol molar ratio = 1; reaction temperature,
40 ◦C; substrate:metal mol ratio = 2000; reaction time = 4 h; TOF calculated at 4 h on
the basis of total metal loading; stirrer speed = 1000 rpm.
3.2. The effect of the metal on catalyst performance
A series of monometallic Au, Pd, Pt and bimetallic Au–Pd, Au–Pt
and Pd–Pt colloids were prepared and immobilised on the KB-B
activated carbon. Comparison of the catalytic activity of Au, Pd
and Pt supported catalysts (Table 3) showed that the Au catalyst
was superior with respect to the monometallic Pd and Pt catalysts.
Combining Pd or Pt with Au resulted in a significant increase in
conversion for the bimetallic supported Au–Pd and Au–Pt nanopar-
ticles by a factor of 1.5–2.5, whereas a Pd–Pt catalyst showed a
decrease in conversion with respect to the monometallic Au cata-
lyst. Nevertheless, it is evident that the bimetallic Pd–Pt catalysts
showed enhanced conversion with respect to the monometallic
Pd and Pt catalysts. An enhancement in the selectivity to lactate
was also observed with the utilisation of Au–Pd or Au–Pt catalysts.
3. Results and discussion
3.1. Effect of the activated carbon support
Three Au–Pt catalysts were prepared using the same starting
colloidal sol and the three activated carbon supports. These were
then evaluated as catalysts for the oxidation of 1,2-propane diol and
the results (Table 2) show that the catalysts all gave relatively high
conversions for this reaction. The catalyst prepared using the KB-B
activated carbon gave a slightly enhanced conversion as compared
to the others under identical reaction conditions. Hence, the high-
est catalytic activity was obtained with a support possessing a high
Table 3
Effect of supported nanoparticles identity on the selective oxidation of 1,2 propane diol.a
Catalyst
NaOH/Sb
Conversion (%)
Selectivity (%)
Lactate
Formate
Acetate
Hydroxy acetone
Pyruvate
TOF (h−1
)
2
1
46
30
<1
<1
50
78
61
52
33
22
67
62
–
4
3
–
–
2
3
1
2
1
4
29
35
–
–
6
11
12
17
4
0
0
–
–
0
0
0
0
0
0
0
0
–
–
0
0
0
0
0
0
460
300
–
Au
Pd
Pt
2 or 1
2 or 1
–
–
2
1
2
1
2
1
92
86
87
81
94
96
500
780
610
520
330
220
Au–Pt
Au–Pd
Pd–Pt
0
a
Reaction conditions: water (20 ml); 0.6 M 1,2-propanediol; 1,2-propanediol/total metal ratio = 4000; O2 3 bar at 40 ◦C; reaction time 4 h; TOF calculated at 4 h on the basis
of total metal loading; stirrer speed = 1000 rpm; support used activated carbon KB-B.
b
NaOH:substrate molar ratio.
Table 4
Effect of Au–Pt bimetallic catalyst loading on the selective oxidation of 1,2-propanediol at 60 ◦C.a
Catalyst
NaOH/Sb
Selectivity (%)
Conversion (%)
Lactate
Formate
Acetate
TOF (h−1
)
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
6
3
96
97
95
93
96
93
96
93
94
92
89
85
78
75
67
62
0
0
0
1
0
2
0
1
0
0
1
1
1
2
5
6
4
3
5
6
4
5
4
6
4
30
15
1%Pt
69
70
88
85
95
90
76
84
86
83
78
88
54
36
345
350
440
425
475
450
380
420
430
415
390
440
270
180
0.95%Pt + 0.05%Au
0.9%Pt + 0.1%Au
0.75%Pt + 0.25%Au
0.5%Pt + 0.5%Au
0.25%Pt + 0.75%Au
0.1%Pt + 0.9%Au
8
10
14
21
23
28
32
1%Au
a
Reaction conditions: water (20 ml); 0.6 M 1,2-propanediol; 1,2-propanediol/total metal ratio = 2000; O2 3 bar; reaction temperature 60 ◦C; reaction time 4 h; TOF calculated
at 4 h on the basis of total metal loading; stirrer speed = 1000 rpm.
b
NaOH:substrate molar ratio.

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Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
Table 5
Effect of AuPt bimetallic catalyst loading on the selective oxidation of 1,2 propane diol at 30 ◦C.a
Catalyst
NaOH/Sb
Conversion (%)
Selectivity (%)
Lactate
Formate
Acetate
TOF (h−1
)
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
<1
<1
24
30
55
60
58
65
69
73
59
66
48
61
35
24
30
18
–
–
–
–
0
1
2
2
2
2
2
3
2
4
2
3
5
5
5
4
–
–
4
6
5
8
5
9
6
14
18
25
36
37
39
47
45
47
–
–
1%Pt
96
93
93
90
93
89
92
83
80
71
62
60
56
48
50
49
120
150
275
300
290
325
345
365
295
330
240
305
175
120
150
90
0.95%Pt + 0.05%Au
0.9%Pt + 0.1%Au
0.75%Pt + 0.25%Au
0.5%Pt + 0.5%Au
0.25%Pt + 0.75%Au
0.1%Pt + 0.9%Au
0.05%Pt + 0.95%Au
1%Au
a
Reaction conditions: water (20 ml); 0.6 M 1,2-propanediol; 1,2-propanediol/total metal ratio = 2000; O2 3 bar; reaction temperature 30 ◦C; reaction time 4 h; TOF calculated
at 4 h on the basis of total metal loading; stirrer speed = 1000 rpm.
b
NaOH:substrate molar ratio.
Table 6
Effect of base identity on the selective oxidation of 1,2-propanediol using a 1 wt.%Au–Pt/carbon catalyst.a
Base
Conversion (%)
Selectivity (%)
Lactate
TOF (h−1
)
Formate
Acetate
Pyruvate
Hydroxy-acetone
LiOH
NaOH
KOH
RbOH
CsOH
80
78
69
66
53
85
86
85
88
89
4
3
3
3
3
11
11
12
9
0
0
0
0
0
0
0
0
0
0
800
780
690
660
530
8
a
Reaction conditions: 1,2-propanediol (0.6 mol); 1,2-propanediol/total metal ratio = 4000; base/1,2-propanediol molar ratio = 1; reaction temperature 40 ◦C; O2 3 bar;
reaction time 4 h.
The effect of base employed was studied and it was found that in
the case of Au and Au–Pd catalysts an increase in base concen-
tration was accompanied by an increase in conversion, which is
in good agreement with previous reports [16,17,21]. However, in
the case of Au–Pt catalysts, an increase in base concentration was
accompanied by a significant decrease in conversion. One possi-
ble explanation for this effect may be the coverage of Au–Pt active
sites by sodium ions, leading to the observed decrease in conver-
sion. However, in addition, it should be noted that differences in
surface concentrations of Pd and Pt and their relative stabilities
under 3 bar of oxygen and the basic reaction conditions could also
play a significant role. The electrode potentials for Au, Pd and Pt at
different pH values [31] indicate that Au is stable under the basic
reaction conditions used (i.e. pH ∼ 10), whereas Pd and Pt can be
partially converted to their corresponding oxides and hydroxides,
which might also correlate with the observed decrease in activity
for catalysts based on these metals.
Taking into account the fact that the Au–Pt catalyst showed
higher catalytic activity than the Au–Pd catalyst, a systematic study
of the Au–Pt weight ratio was carried out at a reaction temper-
ature of 60 ◦C, as shown in Table 4. Addition of a small amount
of Au (0.05 wt%) to Pt increased the activity significantly (based
on turnover frequency (TOF)), and by further increasing the Au
content a progressive increase in conversion was observed, with
a maximum being attained for 0.25 wt%Au. However, choosing a
Au content in the 0.5–0.75 wt% range led to a slight decrease in
catalytic activity, although at the highest Au loading of 0.9 wt%
the activity was restored. These results demonstrate the beneficial
effect of mixing gold with platinum and by selecting the appro-
priate Au/Pt ratio the catalytic activity could be tuned. Moreover,
the significant activity observed at low Au or Pt loadings sug-
gest that a dilute amount of either Au-in-Pt or Pt-in-Au is highly
desirable for achieving high activity, as has been observed previ-
ously in the case of the Au–Pd bimetallic catalyst system [32]. Our
Fig. 1. Oxidation of 1,2-propanediol with air using the 0.5%Au + 0.5%Pt/KB-B
catalyst. Reaction conditions: water (100 ml); 1,2-propanediol (0.6 M); NaOH/1,2-
propanediol molar ratio = 1; 1,2-propanediol/total metal ratio = 5000; reaction
time = 30–120 min; stirrer speed = 1000 rpm. Key: (ꢀ) 1,2-propanediol conversion;
(ꢁ) lactate selectivity.

Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
143
Fig. 2. XPS spectra of the monometallic Au, Pd and Pt catalysts supported on KB-B
carbon (all spectra normalised to the same intensity).
catalytic results also show that there is a distinct enhancement in
the selectivity to lactic acid with increasing Pt content. The effect
of the NaOH/1,2-propanediol ratio was also studied, and it is clear
that a lower selectivity to lactate was observed at lower NaOH/1,2-
propanediol molar ratios with these Au–Pt catalysts. It is interesting
that the effect of the NaOH/1,2-propanediol ratio was different for
the two AuPt catalysts (Table 3) and the catalyst becomes more
active at lower concentrations of base. Indeed, we have shown
recently [36] that supported AuPt catalysts can be highly effective
for the oxidation of glycerol under base-free conditions.
Fig. 3. XPS spectra of the bimetallic AuPt, PdPt and AuPd catalysts supported on
KB-B carbon.
formate decreased significantly. Moreover, in terms of activity, the
beneficial effect of alloying Au and Pt is evident.
3.3. Effect of base identity on catalyst performance
To investigate the effect of the counter cation for the hydroxide
base, experiments were carried out on the oxidation of 1,2-
propanediol with the 1 wt%Au–Pt/KB-B catalyst (Au:Pt = 1:1). The
bases investigated were LiOH, NaOH, KOH, RbOH and CsOH and the
results are presented in Table 6. The conversion of 1,2-propanediol
decreased as the size of the alkali metal ion increased, indicating
The effect of reaction temperature was also investigated in
this study and the same series of catalysts were tested at 30 ◦C
(Table 5). A lower reaction temperature was found to be benefi-
cial for the formation of lactate, as the generation of acetate and
Table 7
XPS characterisation of Au, Pd, Pt, Au–Pd and Au–Pt nanoparticles supported on C.
Sample
BE Au 4f7/2
BE Pt 4f7/2
BE Pd 3d5/2
At%Au
At%Pt
At%Pd
0.5%Au + 0.5%Pt/KB-B
0.5%Pd + 0.5%Pt/KB-B
0.5%Au + 0.5%Pd/KB-B
1%Au/KB-B
1%Pd/KB-B
1%Pt/KB-B
84.1
0
84.0
84.2
0
0
84.1
84.1
71.5
71.7
0
0
0
71.4
71.8
71.5
0
335.7
335.7
0
335.6
0
1.03
0
1.07
2.29
0
0
0.82
0.73
1.31
1.50
0
0
0
0.31
1.38
0.73
0
0.77
1.34
0
1.39
0
0.5%Au + 0.5%/Pt/KB
0.5%Au + 0.5%Pt/G-60
0
0
0
0

144
Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
Fig. 4. (a) High angle angular dark field (HAADF) STEM image and (b) the corresponding particle size distribution of the 0.5%Au + 0.5%Pt/KB-B catalyst sample; (c) HAADF
image of an individual metal particle and (d) its corresponding XEDS spectrum confirming that it is a AuPt alloy.
that LiOH, NaOH and KOH are better choices of base for this partic-
ular reaction. This effect may possibly be due to the larger cations
being adsorbed on the catalyst surface leading to a loss of active
surface area.
3.5. Characterisation of the catalysts
The catalysts were characterised using XPS and transmission
electron microscopy and the studies presented here are additional
to those published previously [33,34]. Using these techniques it is
possible to determine the surface ratios of the metal and the sur-
face oxidation states along with the morphology of the supported
nanoparticles. Results of the XPS characterisation of the carbon sup-
ported nanoparticles are shown in Table 7 and Figs. 2 and 3. These
data indicate that all the Au species are present in the metallic state
as inferred by a Au(4f7/2) binding energy of ca. 84 eV, irrespective of
whether they are present in the mono- or bi-metallic systems. Sim-
ilarly, the reported Pt(4f7/2) energies (ca. 71.5 eV) are slightly higher
than expected for metallic Pt (71.1 eV), however, we consider this
is consistent with the nanoparticulate nature of the metal, since
3.4. Oxidation of 1,2-propanediol with air
To further decrease the environmental impact of this reaction,
studies were carried out using air as oxidant in place of pure oxygen.
With a substrate-to-metal ratio of 5000, a conversion of ca. 40%
was achieved after 2 h of reaction (Fig. 1). The selectivity towards
lactate (81% at 38% conversion) was decreased in comparison with
equivalent reactions in pure oxygen; however, the use of air in this
system represents a significant simplification of the overall reaction
process that makes it well worthy of further investigation.

Y. Ryabenkova et al. / Catalysis Today 203 (2013) 139–145
145
the effect of final state effects gives an apparent higher binding
energy in the small nanoparticles when compared with the bulk
material. For the monometallic catalyst the Pd(3d5/2) energies are
observed to be around 335.7 eV and this is intermediate to the ener-
gies of Pd(0) (334.8 eV) and Pd(II) (336.8 in PdO) [35]. This has been
ascribed in the past to both PdO or metallic Pd, a definite shoulder to
the monometallic Pd catalyst at ca. 337 eV is a clear indication that
PdO is present in these nanoparticles, along with metallic Pd as evi-
denced by the main intensity of the signal at 335.7 eV (Fig. 2), this
binding energy being consistent with the work of Rodriguez [36]
where a shift of ca. +0.7 eV is considered indicative of Pd alloying.
However, there is no evidence for PdO being present in the bimetal-
lic catalysts. Molar ratios for the Pt/Au and Pd/Au supported on the
KB-B carbon are found to be 1.25 (expected 1/1) and 1.25 (1.85
expected) respectively.
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Acknowledgements
This work formed part of the Glycerol Challenge and Sasol Tech-
nology (UK) Ltd. and the Technology Strategy Board are thanked
for their financial support. This project is co-funded by the Tech-
nology Strategy Board’s Collaborative Research and Development
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