One-step synthesis of pyruvic acid from glycerol oxidation over Pb promoted Pt/activated carbon catalysts

Article abstract of DOI:10.1016/S1872-2067(17)62835-3

One-step production of pyruvic acid through selective oxidation of glycerol was investigated using lead promoted platinum/activated carbon (Pb-Pt/AC) catalysts under mild conditions. The results of N₂ physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy revealed that the alloy phases of PtPb and Pt_xPb were favorable for pyruvic acid production from glycerol oxidation, whereas the Pb₃(CO₃)₂(OH)₂ and surface Pb⁰ species inhibited the glycerol conversion. The loading of Pb and the catalyst preparation method (including impregnation and deposition precipitation) affected the formation of different metal species. Pyruvic acid was obtained at a yield of 18.4% on a 5.0 wt% Pb-5.0 wt% Pt/AC catalyst prepared by co-deposition precipitation method and 500 °C argon treatment.

Full text of DOI:10.1016/S1872-2067(17)62835-3

Chinese Journal of Catalysis 38 (2017) 928–938
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
One‐step synthesis of pyruvic acid from glycerol oxidation over Pb
promoted Pt/activated carbon catalysts
Chen Zhang a,c, Tao Wang a,#, Yunjie Ding a,b,
*
a Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
b State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Liaoning, China
c University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O
A B S T R A C T
Article history:
One‐step production of pyruvic acid through selective oxidation of glycerol was investigated using
lead promoted platinum/activated carbon (Pb‐Pt/AC) catalysts under mild conditions. The results
of N2 physisorption, X‐ray diffraction, X‐ray photoelectron spectroscopy, and high‐resolution trans‐
mission electron microscopy revealed that the alloy phases of PtPb and PtxPb were favorable for
pyruvic acid production from glycerol oxidation, whereas the Pb3(CO3)2(OH)2 and surface Pb0 spe‐
cies inhibited the glycerol conversion. The loading of Pb and the catalyst preparation method (in‐
cluding impregnation and deposition precipitation) affected the formation of different metal spe‐
cies. Pyruvic acid was obtained at a yield of 18.4% on a 5.0 wt% Pb‐5.0 wt% Pt/AC catalyst pre‐
pared by co‐deposition precipitation method and 500 °C argon treatment.
Received 9 March 2017
Accepted 10 April 2017
Published 5 May 2017
Keywords:
Glycerol oxidation
Pyruvic acid
Lead promoter
Platinum
Activated carbon
© 2017, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
Pyruvic acid (PA) has been widely used as food additives,
precursors for drugs and agrochemicals, as well as weight‐loss
The challenges of sustainable development, such as in‐
creasing energy consumption, expanding commodity demands,
and environmental concerns, are calling for the efficient utiliza‐
tion of renewable resources. As an easily available byproduct of
biodiesel production, glycerol has drawn increased attention
because of its abundant functional groups [1–3]. Various val‐
ue‐added derivatives from glycerol have been obtained through
different reactions, including selective oxidation [4,5], hydro‐
genolysis [6,7], and dehydration [8,9], increasing the feasibility
of using glycerol as a bio‐building block. Therefore, to explore
new pathways of glycerol conversions and enhance the com‐
petitiveness of the biodiesel industry is attractive.
supplements [10,11]. Because of the many promising applica‐
tions of PA, its commercial market is considerable. PA is pro‐
duced by fermentation of glucose or dehydrative decarboxyla‐
tion of tartaric acid [12]. However, the problems of these
methods remain challenging because the product separation
efficiencies in the biological methods are low, whereas the py‐
rolysis of tartaric acid consumes a large amount of KHSO4 and
energy [13]. Thus, developing renewable alternative pathways
to produce PA under mild conditions is highly appealing.
The one‐step transformation of glycerol to PA is a potential
option with high atom efficiency, which could be an addition to
the reported PA production methods, including oxidations of
* Corresponding author. Tel/ Fax: +86‐411‐84379143; E‐mail: dyj@dicp.ac.cn
# Corresponding author. Tel/ Fax: +86‐411‐84379143; E‐mail: wangtao@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21176236).
DOI: 10.1016/S1872‐2067(17)62835‐3 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 38, No. 5, May 2017

Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
929
propylene glycol or lactic acid (LA) [14–16]. This one‐step
h, it was denoted as 5Pb‐5Pt/AC‐Co‐DP‐500Ar.
pathway is viable in a fermentation method [17], but there are
limitations in scaling‐up. As for chemical methods, recent pro‐
gresses on PA production from LA (or lactate) [13,18,19] and
LA production from glycerol [20–23] have shed light on this
one‐step strategy. In liquid‐phase LA oxidation to PA, hetero‐
geneous bimetallic catalysts have been frequently adopted
[15,18,24]. These catalysts commonly consist of noble metals
such as Pt or Pd as active sites, heavy metals such as Pb, Te, and
Bi as additives, and carbon as a support [15,18,24]. For glycerol
oxidation to LA, we previously reported that a 1.0 wt% Pt/AC
catalyst performed well under mild conditions, with almost no
PA detected [25]. Hayashi et al. reported that Pb was a key ad‐
ditive for Pd/C catalyst in PA production from LA [15]. There‐
fore, the introduction of Pb promoter to a Pt/AC catalyst is ex‐
pected to enhance the product distribution and PA yield during
glycerol oxidation.
We report the one‐pot production of PA from selective oxi‐
dation of glycerol under mild conditions. The Pb loading is op‐
timized for PA selectivity. The Pb‐Pt/AC catalysts prepared via
different methods are investigated, including impregnation,
deposition precipitation, and further calcination under an Ar
atmosphere. N2 physical adsorption, X‐ray diffraction (XRD),
X‐ray photoelectron spectroscopy (XPS), and transmission
electron microscopy (TEM) analyses are adopted to uncover
the structure‐activity relationships of catalysts.
2.1.3. Co‐impregnation method (Co‐Im)
An amount of Pb(NO3)2 and H2PtCl6 were added into 4 mL of
deionized water and co‐impregnated onto 2.0 g of AC support.
The sample was dried at 120 °C for 12 h and treated under H2
or Ar atmosphere at 500 °C for 4 h. The metal loadings were the
same as the catalysts in Section 2.1.2. The obtained catalysts
were
denoted
as
5Pb‐5Pt/AC‐Co‐Im‐500H2
and
5Pb‐5Pt/AC‐Co‐Im‐500Ar.
2.2. Catalyst characterization
N2 physical adsorption of the samples was performed on a
Quantachrome Autosorb‐1 instrument. The samples were de‐
gassed at 250 °C for 12 h before testing. The crystalline phases
of the catalysts were tested by XRD with Cu Kα1 radiation on a
PANalytical X'Pert PRO diffractometer at 40 kV and 40 mA.
TEM and high‐resolution TEM (HR‐TEM) were performed on a
JEM‐2100 electron microscope operating at 200 kV. XPS was
performed on a Thermo ESCALAB 250Xi X‐ray spectroscopy
spectrometer. The monochromatic Al Kα source (1486.6 eV)
was operated at 15 kV. The C ls peak at 284.6 eV was adopted
for correction of the charging effects.
2.3. Glycerol oxidation reaction
2. Experimental
The glycerol oxidation reaction was performed in a 100‐mL
three‐neck flask in an oil bath, with 25.0 g of glycerol solution
(10.0 wt%), 1.90 g of LiOH·H2O (purity at 90%) and 0.25 g of
catalyst [25]. After the reaction, the solution was filtrated, neu‐
tralized by H2SO4, and diluted with deionized water. An Agilent
1100 high performance liquid chromatography system
equipped with a refractive index detector was applied for
product analysis. In addition, an Alltech OA‐1000 column was
used at a separation temperature of 80 °C. The mobile phase
was a H2SO4 aqueous solution (0.005 mol/L) operated at a
flowrate of 0.5 mL/min. All products were identified using the
retention time of pure materials and quantified by an external
standard method. The glycerol conversion and liquid product
selectivity calculations were conducted using the following
equations, with Con. representing the conversion of glycerol, Sa
representing the selectivity of product a, R0 and Rt representing
the concentration of glycerol at the reaction time of 0 and t, and
Pa representing the carbon molar concentration of product a at
the reaction time of t. From our experiment observations and
literature reports [15,18,24], the possible gas product was CO2,
which was in trace amount and would be converted to car‐
bonate in any basic solutions present.
2.1. Catalyst preparation
A series of Pb‐Pt/AC catalysts were prepared by the follow‐
ing methods. The Pt loading was fixed at 5.0 wt% in all
Pb‐Pt/AC catalysts.
2.1.1. Impregnation and deposition precipitation method
(Im‐DP)
An amount of Pb(NO3)2 was dissolved in 4 mL of deionized
water and impregnated onto 2.0 g of an activated carbon (AC)
support. The sample was dried at 120 °C for 12 h and reduced
with H2 at 400 °C for 4 h. Sequentially, Pt was deposited on the
as‐prepared Pb/AC sample by a deposition‐precipitation
method [26]. By changing the loading of lead, a series of
xPb‐5Pt/AC‐Im‐DP catalysts were obtained (x = 1, 3, 5, and 7
wt%, representing the Pb loading). If the 5Pb‐5Pt/AC‐Im‐DP
catalyst was further treated with Ar at 500 °C for 4 h, the ob‐
tained catalyst was denoted as 5Pb‐5Pt/AC‐Im‐DP‐500Ar. The
5Pt/AC‐DP catalyst was prepared by a deposition‐precipitation
method.
Con. = (R0 ‒ Rt) × 100%/R0
2.1.2. Co‐deposition precipitation method (Co‐DP)
Sa = Pa × 100%/∑Pa
AC support (2.0 g) was firstly dispersed in 200 mL of deion‐
ized water. Pb(NO3)2 and H2PtCl6 were introduced, reduced,
and deposited simultaneously on the AC support by a deposi‐
tion‐precipitation method. The catalyst was denoted as
5Pb‐5Pt/AC‐Co‐DP with the loadings of Pt and Pb both at 5.0
wt%. If the catalyst was further treated with Ar at 500 °C for 4
3. Results and discussion
3.1. Characterization of catalysts
3.1.1. N2 physical adsorption results

930
Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
Table 2
Table 1
Particle sizes of 5Pb‐5Pt/AC catalysts calculated from XRD data and the
Scherrer equation.
Textural properties of activated carbon (AC), 5Pt/AC‐DP and Pb pro‐
moted 5Pt/AC catalysts.
Pt Pb3(CO3)2(OH)2 PtPb PtxPb
a
b
c
d
SBET
Vpore
Dmeso Dmicro
Entry
Catalyst
Entry
Catalyst
(nm)
8.8
(nm)
56.4
‒
(nm) (nm)
(m2/g)
1241
1165
1108
1032
889
(mL/g) (nm) (nm)
1
2
3
4
5
6
5Pb‐5Pt /AC‐Im‐DP
‒
‒
ACe
5Pt/AC‐DP
1
2
3
4
1.0
1.0
0.9
0.8
0.7
0.6
0.7
0.6
0.7
0.7
0.8
4.8
3.8
3.8
3.0
3.2
3.6
4.8
3.1
4.8
4.0
4.8
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
0.4
5Pb‐5Pt /AC‐Im‐DP‐500Ar 13.5
5Pb‐5Pt /AC‐Co‐DP 7.5
5Pb‐5Pt /AC‐Co‐DP‐500Ar 14.9
5Pb‐5Pt /AC‐Co‐Im‐500H2
5Pb‐5Pt /AC‐Co‐Im‐500Ar 13.3
47.1 26.0
60.7
‒
‒
‒
1Pb‐5Pt/AC‐Im‐DP
3Pb‐5Pt /AC‐Im‐DP
5Pb‐5Pt /AC‐Im‐DP
7Pb‐5Pt /AC‐Im‐DP
5Pb‐5Pt /AC‐Im‐DP‐500Ar
5Pb‐5Pt /AC‐Co‐DP
5Pb‐5Pt /AC‐Co‐DP‐500Ar
5Pb‐5Pt /AC‐Co‐Im‐500H2
52.5 14.2
‒
‒
‒
‒
‒
‒
5
6
7
8
9
10
‒
843
898
849
917
905
The XRD patterns of the xPb‐5Pt/AC‐Im‐DP catalysts are
shown in Fig. 2(a). Characteristic diffraction peaks at 39.8°,
46.2°, 67.5°, and 81.3° are assigned to the Pt(111), (200), (220),
and (311) reflections, respectively (JCPDS, 00‐004‐0802). Me‐
tallic Pt particles were present in all the samples. When Pb was
supported on the catalysts at a loading of 3.0 wt% or higher,
the characteristic reflection peaks of Pb3(CO3)2(OH)2 (JCPDS,
00‐013‐131) were observed. The major peaks at 34.2°, 27.1°,
24.6°, and 20.9° are indexed as (110), (015), (104), and (012)
planes, respectively.
11
5Pb‐5Pt /AC‐Co‐Im‐500Ar 1039
a Calculated by the Brunauer‐Emmett‐Teller (BET) method.
b Determined from the adsorbed nitrogen at a relative pressure (p/p0)
of 0.99.
c
Calculated on the adsorption curve by the Barrett‐Joyner‐Halenda
(BJH) method.
d Derived from the Horvath‐Kawazoe (HK) method [27].
e Reproduced data from previous work [26].
The XRD patterns of 5Pb‐5Pt/AC catalysts prepared by dif‐
ferent methods are shown in Fig. 2(b). They were denoted with
their preparation method because of their same metal loadings.
Characteristic Pt peaks were observed in all the 5Pb‐5Pt/AC
catalysts except Co‐Im‐500H2 (sample (5)). This indicates that
Pt particles were highly dispersed on the Co‐Im‐500H2 catalyst.
In contrast, the Co‐Im‐500Ar (sample (6)) catalyst shows more
intense metallic Pt peaks. This result may be related with the
availability of reducers during the reduction process, because
H2 (the reducer of Co‐Im‐500H2) is more accessible than AC
(the reducer of Co‐Im‐500Ar). From the XRD patterns, the par‐
ticle sizes of Pt were calculated using the Scherrer equation
(Table 2). The 500 °C Ar treatment of Im‐DP and Co‐DP cata‐
lysts also creates larger Pt particles (untreated at 8 nm vs
treated at 14 nm).
The N2 physical adsorption results of the AC support and
different catalysts are shown in Table 1 and Fig. 1. The specific
surface areas, pore volumes, and average mesopore sizes of
5Pt/AC‐DP and xPb‐5Pt/AC‐Im‐DP catalysts were considerably
smaller than those of the AC support, whereas the micropore
size remained unchanged. This result may be attributed to the
partial blockage of mesopores by the deposited metal species
[26]. When the Pb loading was increased to more than 3.0 wt%,
the catalyst surface areas and pore volumes decreased dramat‐
ically, indicating that the blockage was considerable. The
blockage was alleviated by treating the samples at 500 °C Ar
(or H2), as shown by the improved surface areas and pore
volumes. This result is also shown from the isotherms in Fig. 1,
where the introduction of Pb would result in the drop of iso‐
therms, and the 500 °C gas treatment lead to the elevation of
isotherms.
Similar to the Im‐DP catalyst, characteristic peaks of
Pb3(CO3)2(OH)2 were also observed in Co‐DP catalyst. After 500
°C Ar treatment, these signals disappeared because of the de‐
composition of Pb3(CO3)2(OH)2 [28]. Platinum lead alloys
3.1.2. XRD analysis
700
550
(b)
(a)
Im-DP-500Ar
Im-DP
5Pt
500
450
400
350
300
250
200
150
1Pb-5Pt
3Pb-5Pt
5Pb-5Pt
7Pb-5Pt
600
500
400
300
200
100
Co-DP-500Ar
Co-DP
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
p/p0
p/p0
Fig. 1. N2 physical adsorption‐desorption isotherms of xPb‐5Pt/AC‐Im‐DP catalysts (a) and 5Pb‐5Pt/AC catalysts prepared by different methods (b).

Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
931
Fig. 2. XRD patterns of different samples. (a): (1) 5Pt/AC‐DP, (2) 1Pb‐5Pt/AC‐Im‐DP, (3) 3Pb‐5Pt/AC‐Im‐DP, (4) 5Pb‐5Pt/AC‐Im‐DP, (5)
7Pb‐5Pt/AC‐Im‐DP catalysts; (b): (1) 5Pb‐5Pt/AC‐Im‐DP, (2) 5Pb‐5Pt/AC‐Im‐DP‐500Ar, (3) 5Pb‐5Pt/AC‐Co‐DP, (4) 5Pb‐5Pt/AC‐Co‐DP‐500Ar, (5)
5Pb‐5Pt/AC‐Co‐Im‐500H2, (6) 5Pb‐5Pt/AC‐Co‐Im‐500Ar catalysts. Standard stick patterns of Pt, Pb3(CO3)2(OH)2, PtPb, and PtxPb are shown as refer‐
ences.
emerged, i.e., PtPb and PtxPb (JCPDS, 00‐006‐0374 and
00‐006‐0574). For Co‐Im‐500H2 and Co‐Im‐500Ar catalysts,
neither Pb3(CO3)2(OH)2 nor platinum lead alloys were detected.
convoluted with an experimental Gaussian curve (G = 0.2) for
data analysis. The position gap between deconvoluted Pt 4f7/2
and Pt 4f5/2 peaks was fixed at 3.3 eV, whereas that for Pb 4f
peaks was fixed at 5.0 eV. The full width at half maximum of the
curve of each group of deconvoluted Pt 4f7/2 and Pt 4f5/2 peaks
was kept the same, with the peak area of Pt 4f5/2 being 0.75
times of the area of Pt 4f7/2. A similar method was applied for
the Pb 4f spectra.
3.1.3. XPS analysis
The XPS spectra of the xPb‐5Pt/AC‐Im‐DP catalysts were
conducted (Fig. 3) to study the oxidation states of the surface
metals on the catalysts. The spectra data was processed by a
software called XPS Peak 4.1. The backgrounds of curves were
subtracted by the Shirley method. A Lorentzian function was
The Pt 4f spectra of monometallic 5Pt/AC‐DP catalyst and
bimetallic xPb‐5Pt/AC‐Im‐DP catalysts are shown in Fig. 3(a),
Pb 4f5/2
Pb 4f7/2
(5)
(a)
Pt 4f5/2
Pt 4f7/2
(b)
142.1 eV
138.5 eV
74.7 eV
75.9 eV
(5)
140.6 eV
71.4 eV
137.1 eV
135.6 eV
72.6 eV
143.5 eV
(4)
(3)
(2)
(1)
74.6 eV
75.9 eV
(4)
138.5 eV
71.3 eV
72.6 eV
140.5 eV
137.0 eV
135.5 eV
142.0 eV
143.5 eV
74.6 eV
75.9 eV
71.3 eV
(3)
72.6 eV
138.5 eV
137.2 eV
135.6 eV
140.6 eV
142.2 eV
143.5 eV
74.6 eV
76.1 eV
71.3 eV
72.8 eV
(2)
142.4 eV
138.5 eV
143.5 eV
74.8 eV
71.5 eV
137.4 eV
145
140
135
82
80
78
76
74
72
70
68
66
Binding energy(eV)
Binding energy(eV)
Fig. 3. XPS spectra of Pt 4f (a) and Pb 4f (b). (1) 5Pt/AC‐DP, (2) 1Pb‐5Pt/AC‐Im‐DP, (3) 3Pb‐5Pt/AC‐Im‐DP, (4) 5Pb‐5Pt/AC‐Im‐DP, (5)
7Pb‐5Pt/AC‐Im‐DP catalysts.

932
Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
with two doublet peaks originated from the spin‐orbital split‐
ting of the Pt 4f7/2 and Pt 4f5/2 states. The deconvoluted peaks
of monometallic 5Pt/AC‐DP catalyst at 71.5 and 74.8 eV were
ascribed to the metallic form of Pt, meaning that its surface Pt
species generally remained unoxidized [26]. However, for
Pb‐promoted catalysts, the deconvoluted peaks at 72.6–72.8
and 75.9–76.1 eV indicate the presence of oxidized Pt species,
similar to the results in our previous report [16].
For Pb 4f spectra in Fig. 3(b), the binding energy (BE) peaks
were deconvoluted into two or three groups. The BE peaks at
138.5, 137.0–137.4, and 135.5–135.6 eV were ascribed to the
Pb4+, Pb2+, and Pb0 species, respectively [29–31]. Unlike sam‐
ples (3), (4), and (5), almost no Pb0 species was detected on the
surface of the 1Pb‐5Pt/AC‐Im‐DP catalyst. Therefore, the over‐
all oxidation state of Pb species on 1Pb‐5Pt/AC‐Im‐DP is higher
than other xPb‐5Pt/AC‐Im‐DP catalysts, influencing the oxida‐
tion state of the surface Pt species, which showed a higher BE
peak at 72.8 eV than the other three catalysts at 72.6 eV (Fig.
3(a)).
To observe the influence of the 500 °C Ar treatment on the
metal oxidation state, two representative 5Pb‐5Pt/AC catalysts
(i.e., the Co‐DP and the Co‐DP‐500Ar catalysts) were adopted
for XPS analysis (Fig. 4). The Pt 4f peaks (slightly) and the Pb 4f
peaks (obviously) shifted to a lower BE position after Ar treat‐
ment at 500 °C. Considering that carbon is frequently used as a
reducing agent, the treatment of Co‐DP catalyst may favor the
reduction of metals by the AC support. In addition, the Pt 4f
peaks of 5Pb‐5Pt/AC‐Co‐DP (Fig. 4(a), sample (1)) and
5Pb‐5Pt/AC‐Im‐DP catalysts (Fig. 3(a), sample (4)) were of
similar shape and position, whereas their Pb 4f peaks were
obviously different (Fig. 4(b) vs Fig. 3(b)). In a previous discus‐
sion, these two catalysts were of similar XRD patterns (Fig.
2(b)), but the XPS analysis demonstrated that their surface Pb
species were different, which would result in different catalytic
performance.
3.1.3. TEM analysis
The TEM images of two groups of representative catalysts
(Im‐DP vs Im‐DP‐500Ar, Co‐DP vs Co‐DP‐500Ar) are presented
in Fig. 5. The Ar treatment at 500 °C resulted in the metal parti‐
cle aggregation (Fig. 5(b) vs Fig. 5(d)), which agrees with the
XRD results. The HR‐TEM images demonstrated the respective
characteristic lattice fringes of the metallic particles. In images
of Im‐DP and Co‐DP, only characteristic patterns of Pt (111)
planes (d = 2.28 Å) (JCPDS, 00‐004‐0802) were observed.
However, PtPb alloys (JCPDS, 00‐006‐0374) were also detected
in Im‐DP‐500Ar and Co‐DP‐500Ar images. In Im‐DP‐500Ar,
PtPb(101) planes (d = 3.04 Å) were observed, whereas in
Co‐DP‐500Ar, PtPb (100) and (102) planes with d = 3.68 and d
= 2.20 Å, respectively, were observed. This also agrees with the
XRD analysis that Ar thermal treatment favored the Pt‐Pb al‐
loys formation.
3.2. Selective oxidation of glycerol
3.2.1. Optimization of Pb loading for xPb‐5Pt/AC‐Im‐DP
catalysts
Table 3 shows the results of glycerol oxidation reactions
over 5Pt/AC‐DP and xPb‐5Pt/AC‐Im‐DP catalysts with Pb
loading ranging from 1.0 to 7.0 wt%. From our previous opti‐
mization studies of alkaline salts and their ratios, we adopted
LiOH in this work [25]. Although the monometallic Pb/AC cat‐
Pt 4f5/2
(a)
Pt 4f7/2
71.5 eV
(b)
Pb 4f7/2
139.4 eV
Pb 4f5/2
74.8 eV
76.0 eV
(1)
144.4eV
(1)
72.7 eV
142.6 eV
(2)
137.6 eV
(2)
74.7 eV
76.2 eV
71.4 eV
72.9 eV
138.3 eV
137.1 eV
143.3 eV
142.1 eV
84 82 80 78 76 74 72 70 68 66
Binding energy (eV)
150
145
140
135
130
Binding energy (eV)
Fig. 4. XPS spectra of Pt 4f (a) and Pb 4f (b). Samples: (1) 5Pb‐5Pt/AC‐Co‐DP, (2) 5Pb‐5Pt/AC‐Co‐DP‐500Ar.

Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
933
Fig. 5. TEM images of Im‐DP (a); Im‐DP‐500Ar (b); Co‐DP (c); and Co‐DP‐500Ar (d) catalysts. The insets are high resolution images showing their
characteristic lattice fringes.
alyst showed no activity in converting glycerol (data not
shown), the addition of 1.0 wt% Pb to 5Pt/AC catalyst im‐
proved catalyst turnover frequency (TOF) compared with the
monometallic 5Pt/AC‐DP catalyst. For other xPb‐5Pt/AC‐Im‐DP
catalysts, the increase of Pb loading resulted in a decrease in
catalyst TOF (as well as glycerol conversion), and the changing
trend is consistent with that of their N2 physical adsorption
data. This result indicates that the decrease in surface area and
pore size can cause the decrease in catalyst activity (Table 1).
As shown in the XRD analysis (Fig. 2(a)), the increase in Pb
loading (> 1.0 wt%) leads to Pb3(CO3)2(OH)2 formation. This
might be one of the reasons for the decreased surface area and
pore volume. For the 1Pb‐5Pt/AC‐Im‐DP catalyst, although its
surface area was smaller, its catalytic performance is higher
than that of 5Pt/AC‐DP, and no characteristic peaks for
Pb3(CO3)2(OH)2 were detected. Therefore, Pb3(CO3)2(OH)2
might be the main reason for the catalyst activity decrease at
high Pb loading (> 1.0 wt%).
In addition, the analysis of Pb 4f spectra (Fig. 3(b)) of
xPb‐5Pt/AC‐Im‐DP catalysts suggested that surface Pb0 species
are unfavorable for the glycerol conversion. Because the Pb0
species were observed in all xPb‐5Pt/AC‐Im‐DP catalysts ex‐
cept the 1Pb‐5Pt/AC‐Im‐DP catalyst. The role of Pt species in
the enhanced glycerol conversion of the 1Pb‐5Pt/AC‐Im‐DP
catalyst could not be determined, because Pt0 and Pt2+ species
were detected in all the bimetallic catalysts (Fig. 3(a)).
Table 3
Effects of Pb loading on glycerol conversion and product selectivity for xPb‐5Pt/AC‐Im‐DP catalystsa.
TOF
(h‒1)b
76.7
Time
(h)
2
Conversion
(%)
36.2
96.3
100
47.6
92.3
100
35.2
80.7
98.9
33.2
80.4
100
Selectivity (%)
Catalyst
PAc
0.9
0.6
2.8
1.7
1.6
8.7
1.2
1.5
8.6
0.8
1.4
14.2
0.8
1.3
9.7
LA
GLYA
15.5
11.9
1.5
15.3
14.9
7.7
21.1
20.1
12.9
19.0
17.7
9.8
21.3
19.1
12.6
TA
2.6
GA
OA
1.6
1.6
AA
1.9
2.8
4.6
2.2
7.5
13.0
2.4
4.0
9.3
2.0
4.3
10.2
2.2
3.7
9.9
FA
1.4
4.2
0.1
2.1
0.7
0.7
2.1
0.6
0.4
1.8
0.6
0.3
1.3
0.4
0.5
68.3
67.7
44.9
61.8
56.5
36.7
55.1
53.6
34.3
61.8
63.3
34.9
61.5
61.2
35.4
7.8
5.7
2.2
9.8
6.5
2.7
7.8
5.4
3.2
6.6
3.8
2.0
4.2
3.4
2.8
5Pt/AC‐DP
6
5.5
10
2
6
10
2
6
21.9
3.4
7.9
22.0
3.6
4.5
12.5
5.1
5.5
1Pb‐5Pt/AC‐Im‐DP
3Pb‐5Pt /AC‐Im‐DP
5Pb‐5Pt /AC‐Im‐DP
7Pb‐5Pt /AC‐Im‐DP
100.8
74.5
70.3
72.6
17.9
5.1
9.3
10
2
6
10
2
6
22.3
3.9
5.9
12.6
4.0
3.0
9.1
3.7
19.5
5.1
7.0
34.3
88.3
100
3.9
10
19.8
9.4
a Reaction conditions: t = 90 °C, p = 1 atm, FO2 = 100 mL/min, nLiOH/nglycerol = 1.5, stirring rate = 800 r/min. b TOF was calculated based on the loading of
Pt since Pb mainly served as a promoter, and the 2 h reaction data was used for the calculation. c PA = pyruvic acid, LA = lactic acid, GLYA = glyceric
acid, TA = tartronic acid, GA = glycolic acid, OA = oxalic acid, AA = acetic acid, FA = formic acid.

934
Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
In terms of the target product PA, the introduction of Pb
2), with Pb3(CO3)2(OH)2 observed in both of them. Their Pt 4f
spectra were also of similar shape and position. However, their
Pb 4f spectra (Fig. 3(b) sample (4) vs Fig. 4(b) sample (1)) were
different, with the Pb0 species present only in the Im‐DP cata‐
lyst. Thus, the lower TOF and glycerol conversion of the Im‐DP
catalyst might be related with the Pb0 species.
The role of Pb3(CO3)2(OH)2 could be illustrated by the fol‐
lowing comparison. For the Im‐DP and Co‐DP catalysts, their
TOF and glycerol conversions were generally enhanced after
treatment under Ar at 500 °C. On the one hand, this suggests
that the removal of Pb3(CO3)2(OH)2 might be beneficial to glyc‐
erol conversion. On the other hand, such an improvement
might be related with the formation of PtPb and PtxPb alloys.
The BE peak shift of Pb to a lower state might be associated
with the catalyst performance. The decomposition of
showed enhanced PA selectivity, which may be because of the
presence of Pb and the generation of oxidized Pt species in all
the four xPb‐1Pt/AC‐Im‐DP catalysts, which was caused by the
Pb promoter as shown in the XPS analysis (Fig. 3(a)). From the
product distributions, the introduction of Pb favored PA pro‐
duction and contributed to glyceric acid selectivity. However,
the productions of LA and oxalic acid were decreased. This
result may be because the presence of Pb favored LA consecu‐
tive oxidation towards PA, but not glyceric acid consecutive
oxidation and C–C cleavage reaction to oxalic acid [32]. The
5Pb‐5Pt/AC‐Im‐DP catalyst showed the highest performance
with a PA selectivity over 14%.
3.2.2. Further investigation on the roles of Pt and Pb species
To further explore the previous speculation on the roles of
surface Pb0 species and Pb3(CO3)2(OH)2, we prepared a series
of 5Pb‐5Pt/AC catalysts by different methods. Fig. 6(a) shows
the catalyst TOF, and Fig. 6(b) shows the glycerol conversion
over these 5Pb‐5Pt/AC catalysts with time on stream. As dis‐
cussed in Section 3.2.1, the decreases in glycerol conversion
were related with the Pb0 species. The comparison of catalyst
TOF in Fig. 6(a) and glycerol conversion in Fig. 6(b) between
Im‐DP and Co‐DP could further investigate the role of Pb0 spe‐
cies. The XRD patterns of Im‐DP and Co‐DP were similar (Fig.
120
100.8
(a)
100
80
95.1
92.1
75.4
72.6
70.3
60
40
20
100
(b)
80
60
40
20
20
18
16
14
12
10
8
Im-DP
Im-DP-500Ar
Co-DP
Co-DP-500Ar
Co-Im-500H
Co-Im-500Ar
(c)
6
4
2
0
2
4
6
8
10
Reaction time (h)
Fig. 7. TEM images of spent Co‐DP (a); Co‐DP‐500Ar (b) and
Co‐Im‐500Ar (c) catalysts. The insets are high resolution images show‐
ing their characteristic lattice fringes. A d = 2.33 Å from the patterns is
characteristic of PtxPb (111) planes (JCPDS, 00‐006‐0574).
Fig. 6. Effects of preparation method of 5Pb‐5Pt/AC catalysts on: cata‐
lyst TOF (a); Glycerol conversion (b); and PA selectivity (c). Reaction
conditions: t = 90 °C, p = 1 atm, FO2 = 100 mL/min, nLiOH/nglycerol = 1.5,
stirring rate = 800 r/min.

Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
935
selectivities of Im‐DP and Co‐DP catalysts were improved after
their treatment at 500 °C in Ar (Fig. 6(c)). The PA selectivity of
Co‐DP‐500Ar was almost 4.6 times higher than that of the un‐
treated Co‐DP catalyst, the PA yield reached 18.4% under the
present reaction conditions. Thus, the PA selectivity might also
be related with the removal of Pb3(CO3)2(OH)2 and the for‐
mation of platinum lead alloys.
Co-DP-spent
Co-DP-500Ar-spent
Co-Im-500Ar-spent
The role of PtPb and PtxPb alloys could be partly demon‐
strated by the comparison between the Co‐DP‐500Ar and the
Co‐Im‐500Ar catalysts. In both cases, the Pt and Pb metals were
reduced simultaneously on AC, and their calculated Pt particle
sizes were similar (Table 2). The Co‐DP‐500Ar catalyst contains
two more species than the Co‐Im‐500Ar catalyst, which were
the PtPb and PtxPb alloys. The former catalyst showed slightly
better glycerol conversion and much improved PA selectivity
than those of the latter one (Fig. 6). Therefore, the platinum
lead alloys might favor the glycerol activation slightly and its
transformation towards PA greatly. For fresh catalysts with
PtPb and PtxPb alloys present (i.e., Im‐DP‐500Ar and
Co‐DP‐500Ar catalysts), their PA selectivity maintained the
highest among all the catalysts tested.
We characterized three representative spent catalysts (i.e.,
Co‐DP, Co‐DP‐500Ar and Co‐Im‐500Ar catalysts, with three
different phases), to find more information about the role of
platinum lead alloys. The alloys were observed only on fresh
Co‐DP‐500Ar catalyst, yet they were observed on all the three
spent catalysts, as confirmed by both HR‐TEM and XRD anal‐
yses (Figs. 7 and 8). In addition, the XPS analysis of spent Co‐DP
and Co‐DP‐500Ar showed that the Pb 4f peak of Co‐DP shifted
Pt
PtPb
PtxPb
20
40
60
80
2
Fig. 8. XRD patterns of spent Co‐DP, Co‐DP‐500Ar and Co‐Im‐500Ar
catalysts. Stick patterns of Pt, PtPb, and PtxPb are shown as references.
Pb3(CO3)2(OH)2 and the formation of PtxPb alloys can cause a
BE peak shift. Thus, further analysis is still necessary to clarify
the mechanism. For simplicity, the following discussion focuses
on the Pb3(CO3)2(OH)2 and PtxPb alloy species. For
Co‐Im‐500H2 and Co‐Im‐500Ar catalysts, Ar or H2 treatment at
500 °C prevented Pb3(CO3)2(OH)2 formation; moreover, neither
PtPb nor PtxPb alloys were observed. They still showed higher
TOF and glycerol conversion than the Im‐DP and Co‐DP cata‐
lysts. Therefore, the removal of Pb3(CO3)2(OH)2 is essential for
enhancing catalyst activity.
Similar to the enhancement effect on catalyst activity, the PA
(a)
(b)
Pt 4f7/2
Pt 4f5/2
Pb 4f7/2
Pb 4f5/2
143.6 eV
(1)
74.7 eV
75.9 eV
(1)
71.4 eV
72.6 eV
138.6 eV
142.7 eV
137.7 eV
(2)
(2)
138.6 eV
71.5 eV
143.6 eV
142.3 eV
74.8 eV
76.2 eV
72.9 eV
137.3 eV
84 82 80 78 76 74 72 70 68 66
Binding energy (eV)
150 148 146 144 142 140 138 136 134 132 130
Binding energy (eV)
Fig. 9. Pt 4f (a) and (b) Pb 4f XPS spectra of spent 5Pb‐5Pt/AC‐Co‐DP (1) and spent 5Pb‐5Pt/AC‐Co‐DP‐500Ar (2).

936
Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
Table 4
Glycerol conversion and product selectivity over spent 5Pb‐5Pt/AC catalystsa.
Selectivity (%)
Catalyst
Conversion (%)
PAb
6.1
LA
GLYA
15.2
15.7
TA
GA
2.2
OA
6.5
5.6
AA
7.3
9.4
FA
1.5
0.0
100
47.4
13.8
5Pb‐5Pt /AC‐Co‐DP‐Spent
97.0
12.2
37.5
17.1
15.7
5Pb‐5Pt/AC‐Co‐Im‐500Ar‐Spent
a Reaction conditions: t = 90 °C, p = 1 atm, 10 h, FO2 = 100 mL/min, nLiOH/nglycerol = 1.5, stirring rate = 800 r/min.
b See Table 3.
from 139.4 to 138.6 eV (Fig. 4(b) vs Fig. 9(b)) after the reaction.
The surface Pb species on Co‐DP‐500Ar catalyst remain the
same before and after the reaction, whereas the Pb species on
spent Co‐DP catalysts resemble that of the spent Co‐DP‐500Ar
catalyst, which agrees with the HR‐TEM and XRD results. The
spent Co‐DP and Co‐DP‐500Ar catalysts were evaluated under
the same reaction conditions, and they exhibited slightly better
PA selectivity than the fresh ones (Table 4). This suggested that
the PtPb and PtxPb alloys might be the active sites for PA pro‐
duction. However, their formation and catalytic mechanisms
still require further investigation.
methods greatly affect the catalyst performance, because of the
alteration of Pt and Pb species. The Pt‐Pb alloys are favorable
for glycerol transformation to PA, whereas the Pb3(CO3)2(OH)2
and the surface Pb0 species adversely affect glycerol conver‐
sion.
By
treating
the
5Pb‐5Pt/AC‐Im‐DP
(or
5Pb‐5Pt/AC‐Co‐DP) catalyst under a 500 °C Ar atmosphere,
Pb3(CO3)2(OH)2 can be prevented, and platinum lead alloys can
form. The highest PA yield was 18.4% under the present reac‐
tion conditions. Further optimization and better understanding
of the reaction are required.
We propose a possible reaction pathway for glycerol oxida‐
tion to PA and other products (Scheme 1). Glycerol is first de‐
hydrogenated to form intermediates, followed by their dehy‐
dration and intramolecular Cannizzaro rearrangement to LA
[33,21]. The introduction of Pb was beneficial for glycerol con‐
version when Pb3(CO3)2(OH)2 and surface Pb0 species were
absent, and the presence of platinum lead alloys favored the
transformation of LA to PA.
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Chen Zhang et al. / Chinese Journal of Catalysis 38 (2017) 928–938
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Graphical Abstract
Chin. J. Catal., 2017, 38: 928–938 doi: 10.1016/S1872‐2067(17)62835‐3
One‐step synthesis of pyruvic acid from glycerol oxidation
over Pb promoted Pt/activated carbon catalysts
Chen Zhang, Tao Wang *, Yunjie Ding*
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences
Over 18% yield of pyruvic acid was obtained over Pb‐Pt/AC cata‐
lyst through one‐step glycerol oxidation reaction under mild con‐
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Page numbers refer to the contents in the print version, which include
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