Efficient Generation of Lactic Acid from Glycerol over a Ru-Zn-CuI/Hydroxyapatite Catalyst

Article abstract of DOI:10.1002/asia.201700412

The biodiesel production process generates a significant amount of glycerol as a byproduct. A drive to add value has attracted worldwide attention, with the aim of improving the overall effectiveness and profitability of biodiesel production. Herein, we report hydroxyapatite (HAP)-supported Ru-Zn-Cu^I (Ru-Zn-Cu^I/HAP) as effective catalysts for the transformation of glycerol to lactic acid (LA).The catalysts were characterized by using different techniques. The effects of catalyst composition, reaction time, and temperature on the conversion and product distribution were investigated. It was revealed that Ru nanoparticles of less than 2 nm were dispersed uniformly on HAP. Cu^I could effectively inhibit the cleavage of C?C bonds, which led to improved yields of LA. Under optimized conditions, the yield of LA could reach 70.9 % over Ru-Zn-Cu^I/HAP. Furthermore, the catalyst could be reused at least four times without an obvious loss of activity or selectivity.

Full text of DOI:10.1002/asia.201700412

CHEMISTRY
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Accepted Article
Title: Efficient generation of lactic acid from glycerol over Ru-Zn-Cu(I)/
HAP catalyst
Authors: Zhiwei Jiang, Zhanrong Zhang, Tianbing Wu, Pei Zhang,
Jinliang Song, Chao Xie, and Buxing Han
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Efficient generation of lactic acid from glycerol over
Ru-Zn-Cu(I)/HAP catalyst
Zhiwei Jiang,[a] Zhanrong Zhang,[a] Tianbin Wu,[a] Pei Zhang,[a] Jinliang Song,[a] Chao Xie,[a] and Buxing
Han*[a,b]
Abstract: The biodiesel production process generates a significant
amount of glycerol as a by-product. Its valorization has attracted
worldwide attention in terms of improving the overall effectiveness
and profitability of bio-diesel production. Herein, we report
hydroxyapatite (HAP) supported Ru-Zn-Cu(I) (Ru-Zn-Cu(I)/HAP) as
effective catalysts for the transformation of glycerol to lactic acid
(LA).The catalysts were characterized by different techniques. The
effects of catalyst composition, reaction time and temperature on
conversion and the product distribution were investigated. It was
revealed that Ru nanoparticles of less than 2 nm were dispersed
uniformly on HAP. Cu(I) could effectively inhibit the cleavage of C-C
bonds, leading to improved yields of LA. Under optimized conditions,
the yield of LA could achieve 70.9% over Ru-Zn-Cu(I)/HAP.
Furthermore, the catalyst could be reused at least four times without
obvious loss of activity and selectivity.
variousvalue-added chemical products, such as propanediols4,
pyruvaldehyde,5 glyceric acid,6 acrylic acid,7 and acrolein8.
Among the various products that can be derived from glycerol,
lactic acid (LA) is an important bio-based platform chemical and
has been extensively employed in various industrial sectors such
as food, pharmaceutical and chemical industries.9 In addition,
this trend is also promoted by the growing interest in the
utilization of LA for the production of biodegradable and
biocompatible polylactic acid which is a sustainable bioplastic
material.10 Nowadays, LA is manufactured primarily via
anaerobic fermentation of edible carbohydrates (e.g. glucose or
sucrose).11 However, this technology suffers from poor
productivities and generally involves complicated processes. It is
thus desirable to develop alternative methods enabling an
effective large-scale production of LA.
The conversion of glycerol to LA has been studied in both
homogeneous12 and heterogeneous phases.13 Lu et al.
investigated the conversion of glycerol to LA using homogenous
iridium-based catalytic systems under H2-acceptorless conditions
and high yield of LA could be obtained.12b In heterogeneous
catalytic systems, the conversion of glycerol to LA was
investigated under reductive conditions or in the presence of
hydrogen acceptor. Maris et al. used commercial
carbon-supported Ru and Pt catalysts to generate LA from
glycerol in basic solutions at 473 K and 40 bar H2.13e Shen et al.
found that the selectivity of LA could reach 86% at 30% glycerol
conversion with a TiO2 supported bimetallic Au-Pt catalyst, using
oxygen as hydrogen acceptor.13a The use of oxygen as hydrogen
acceptor leads to many undesired side reactions, rendering the
overall process less effective. To address this drawback,
ethylene was utilized as hydrogen acceptor with heterogeneous
monometallic Pt catalyst, the selectivity of LA could be up to
95%.13d
During the conversion of glycerol to LA, the dehydrogenation of
glycerol is the rate-determining step and Ru is well known to be
active for this transformation.12c, 13e Notably, copper could also
promote the dehydrogenation reaction and suppress the
undesired C-C bond rupture.14 Moreover, some studies proposed
that LA was generated from glyceraldehyde via 1, 2-hydride
shift.15 Zn2+ could potentially enhanced the 1, 2-hydride shift and
improve the yield of LA.16
Introduction
Efficient use of natural resources in
a sustainable and
environmentally benign manner is important for the transition
from the current petro-based economy to a future bio-based
economy.1 The production of biodiesel via transesterification of
triglycerides is a promising and attractive approach for the
generation of renewable energy.2 However, during this process,
glycerol (around 10 wt.%) is inevitably generated as
a
by-product.3 Valorization of the surplus glycerol to value-added
products such as high-value chemical compounds is therefore of
great importance, in terms of improving the overall effectiveness
and profitability of bio-diesel production plants. In this context,
many studies have demonstrated the potential of glycerol as a
bio-derived
building
block
for
the
synthesis
of
[a]
Dr. Z. Jiang, Dr. Z. Zhang, Dr. T. Wu, Dr. P. Zhang, Dr. J. Song, Mr.
C. Xie, and Dr. B. Han
Beijing National Laboratory for Molecular Sciences, CAS Key
Laboratory of Colloid and Interface and Chemical Thermodynamics,
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190 China
Hydroxyapatite (HPA) has high ion-exchange and adsorption
abilities, and therefore the active species can be immobilized
stably on its surface. HAP supported Ru,17 Cu,18 Zn,19 Ag,20 Pd,21
Au22 have shown excellent catalytic performances in a wide
range of chemical reactions such as oxidative cleavage of
alkenes, CO2 cycloaddition reactions, epoxidation of styrene, and
partial hydrogenation of benzene to cyclohexene.
E-mail: Hanbx@iccas.ac.cn
[b]
Dr. B. Han
University of Chinese Academy of Sciences
Beijing 100049 China.
Supporting information for this article is given via a link at the end of
the document.
To the best of our knowledge, HAP as a catalyst support for
glycerol conversion has not been reported. Herein, we prepared
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Ru/HAP, Ru-Zn/HAP Ru-Zn-Cu(I)/HAP by an ion-exchange
method. The effects of catalyst composition and reaction
conditions on the distribution of liquid and gaseous products
were investigated. It was found that the catalysts had satisfactory
performance for the reaction. Especially, Ru-Zn-Cu(I)/HAP was
very active and selective for the reaction.
indicating that the Ru NPs are crystalline. No metallic Zn
particles were observed in the TEM images of the Ru-Zn/HAP
and Ru-Zn-Cu(I)/HAP (Figure 2b and 2c). In addition, elemental
distribution images of Ru-Zn-Cu(I)/HAP further illustrate the
co-existence of Ru, Zn and Cu elements (Figure S1).
Results and Discussion
Catalyst characterization
The XRD patterns of the HAP and as-prepared Ru/HAP,
Ru-Zn/HAP and Ru-Zn-Cu(I)/HAP catalysts are shown in Figure
1. The XRD patterns of Ru/HAP catalyst was in good consistency
with the parent HAP. This indicates that there were no
transformations of the catalyst support framework during
preparation of the Ru/HAP. In addition, new diffraction peaks
were observed in the XRD patterns of Ru-Zn/HAP and
Ru-Zn-Cu(I)/HAP catalysts, suggesting the formation of new
crystals for Zn-HAP and Cu(I)-HAP. The characteristic diffraction
band of Ru (2 = 44°) cannot be observed due to the small size
and high dispersion of the Ru particles on the HAP.
Figure 2. TEM images of (a) Ru/HAP, (b) Ru-Zn/HAP, (c) Ru-Zn-Cu(I)/HAP, (d)
HRTEM and Ru particle size distribution of Ru-Zn-Cu(I)/HAP, the
corresponding PSD histogram of the Ru NPs is given in the insert.
X-ray photoelectronspectroscopy (XPS) was used to
characterize the surface composition of Ru-Zn-Cu(I)/HAP
catalyst (Figure 3). Characteristic band for Cl 2p, I 3d or N 2p

cannot be observed, indicating that the Cl, I and NO3 were
completely removed. The narrow scan spectra of Zn 2p, Ru 3d
and Cu 2p are shown in Figure 3b, 3c and 3d. In Figure 3b, the
peak centered at 1022.6 eV was assigned to Zn 2p3/2
,
corresponding with 1022.5 eV of Zn2+ reported elsewhere.24 The
Zn 2p spectra of Zn/HAP and Ru/Zn/HAP are given in Figure S2.
The binding energies (BEs) of Zn 2p3/2 in the Zn/HAP (1022.4 eV)
and Ru/Zn/HAP (1022.6 eV) were close to the value reported in
the literature, demonstrating that valence of Zn has not changed
during the substitution procedure.25
Figure 1. XRD patterns of HAP and the synthesized Ru/HAP, Ru-Zn/HAP and
Ru-Zn-Cu(I)/HAP.
Figure 3c shows the Ru 3d spectrum of the Ru-Zn-Cu(I)/HAP
catalyst. The binding energy of 281.1 eV is assigned to Ru(0)
3d5/2, indicating that the metallic Ru was formed during the
reduction process. No peak for Run+ ion was observed in the
spectrum. The peak of Ru(0) 3d3/2 overlapped with the C 1s peak.
For comparison, the Ru 3d spectrum of the Ru/HAP and
Ru-Zn/HAP are shown in Figure S3. The BEs of Ru (0) 3d5/2 in
Ru-Zn-Cu(I)/HAP (281.1 eV), Ru-Zn/HAP (281.1 eV) and
Ru/HAP (280.9) were higher than that of metallic Ru (280.0
eV).26 The higher energy value may be attributed to the electron
properties of the HAP framework. The interaction between Ru
and the oxygen in the HAP framework renders the Ru surface
electron deficient, resulting in the increase of the BE of Ru (0)
particles.27
Figure 2 illustrates the TEM images of the Ru-HAP, Ru-Zn/HAP
and Ru-Zn-Cu(I)/HAP catalysts. It can be seen from Figure 2a-c
that the Ru nanoparticles dispersed uniformly on the surface of
the HAP, suggesting that HAP had excellent ion-exchange ability
to adsorb the Ru precursors and prevented the aggregation of
metallic particles during the reduction process. Figure 2d shows
the high resolution TEM (HRTEM) image of the Ru-Zn-Cu(I)/HAP
and the histogram of Ru particle size distribution. The average
particle sizes are around 1.6 nm. The lattice fringes with
interplanar spacing about 2.05 Å visualized in the inserted figure
of Figure 2d are ascribable to the (101) planes of hcp Ru,
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Figure 3d shows the Cu 2p spectrum of the Ru-Zn-Cu(I)/HAP.
The BE of Cu 2p3/2 (933.9 eV) was higher than that of Cu(II)
species (933.4 eV) on the HAP support (Figure S4). Moreover,
the BE of Cu 2p3/2 in the Cu(I)/HAP reported in the literature was
934.2 eV,18 demonstrating that Cu(I) and Cu(II) coexisted in fresh
Ru-Zn-Cu(I)/HAP. The existence of Cu(II) may be attributed to
the oxidation of Cu(I) during the XPS sampling procedure.
state of the Ru and Zn on Ru-Zn/HAP. Furthermore, the acidity of
Ru/HAP, Ru-Zn/HAP and Ru-Zn-Cu(I)/HAP were characterized
by NH3-TPD of, as shown in Figure S5. The results indicate that
Ru-Zn/HAP and Ru-Zn-Cu(I)/HAP had higher acidity than
Ru/HAP, which was attributed to addition of Zn2+. The higher
acidity of Ru-Zn/HAP and Ru-Zn-Cu(I)/HAP could be favorable to
1,2-hydride shift, and thus enhanced the selectivity of LA.
Catalytic activity
The conversion of glycerol to LA with the production of hydrogen
was carried out at 140 °C under vacuum condition in the
presence of a base (NaOH to glycerol molar ratio of 1.5). The
results of the catalytic reactions are compiled in Table 1. Blank
reactions carried out demonstrated that glycerol was not
converted under our reaction conditions in the absence of
catalyst or base. This is consistent with the results reported by
Liu et al.13a Ru/HAP showed high activity with 100% conversion,
while a relatively low LA selectivity of 63.7%, due to the formation
of formic acid (FA) and 1,2-PROP (Table 1, entry 1). Moreover,
the gas product contained a large amount of methane (13.7
mol%) besides hydrogen. Maris et al also reported the similar
results.13e We can infer from this experimental result that the
dehydrogenation of glycerol to glyceraldehydes is base-assisted
in the present of Ru NP-based catalyst. 1,2-PROP was formed
from hydrogenation of pyruvaldehyde or its tautomer with
hydrogen.13d The degradation product was primarily formic acid
with CO2 and methane gas products because Ru is effective for
the cleavage of C-C hydrocarbon bonds.13e
Figure 3. XPS spectra of the Ru-Zn-Cu(I)/HAP catalyst (a) full spectrum; (b) Zn
2p spectrum; (c) Ru 3d spectrum; (d) Cu 2p spectrum.
To investigate the influence of the different ions on the glycerol
conversion in the present of Ru/HAP, several salts were studied
(Table 1, entries 2 to 5). Upon adding ZnSO4 in the reaction
As shown in the TEM images and the XPS spectra of
Ru-Zn-Cu(I)/HAP, Zn2+ exchanged onto HAP could not be
reduced by hydrogen at 200 °C. Ru3+ ions were reduced to Ru
nanoparticles supported on HAP by H2. The electronegativity of
Ru in Ru-Zn-Cu(I)/HAP was higher that of the metallic Ru due to
a tendency to attract the electrons from the oxygen in the HAP
framework. Cu(I) was successful exchanged onto Ru-Zn/HAP
through hydrothermal method, and didn’t affect the chemical
system,
a higher selectivity (78.4%) of LA was obtained
compared to that of Ru/HAP without ZnSO4, with a lower glycerol
conversion (74.5%) and relative high yields of FA and methane.
This reveals that Zn2+ could improve effectively the formation of
LA through benzilic acid rearrangement and could not suppress
the effect of Ru. Cu based catalysts has been demonstrated
conversion of glycerol to LA with high yield.13c CuSO4 and Cu2O
Table 1. Reaction results over different catalysts for the conversion of glycerol to LA[a]
sel.liquid prod. (%
）
Conv.
GLY(%)
liquid prod.
(%)
methane sel.
(%)
entry
catalyst
Ru/HAP
additive
----
LA
FA
28.5
8.2
PROP
6.0
EG
1.3
0.3
1.2
4.2
0.5
5.1
0.8
0.6
0.7
GLYA
TA
0.2
24.7
0.5
0.4
4.5
0.2
1.6
1.7
2.2
1
2
100.0
100.0
94.3
68.7
64.0
67.1
65.2
85.4
70.9
98.9
87.5
88.7
63.7
57.3
45.4
78.4
69.5
75.7
83.5
83.9
82.7
0.3
6.6
1.1
0.8
12.0
0.7
5.5
2.0
2.5
13.7
0.3
12.5
2.4
0.7
1.3
0.2
0.3
0.2
Ru/HPA
CuSO4
Cu
0.9
3
Ru/HAP
22.4
13.0
5.3
29.4
3.5
4
Ru/HAP
ZnSO4
Cu2O
----
74.5
5
Ru/HAP
100.0
72.3
8.7
6
Ru-Zn/HAP
Ru-Zn/HAP
Ru-Zn/HAP
Ru-Zn-Cu(I)/HAP
13.6
6.5
4.9
7
Cu2O
Cu2O
-----
73.9
2.1
8b
9c
100.0
100.0
10.0
8.1
1.8
2.1
[a] Reaction conditions: 20 mg catalyst, 2 mg additive, 0.1 g glycerol (GLY), 0.065 g NaOH (NaOH to glycerol molar ratio of 1.5), 2 mL water,
140 °C, 12 h. [b] 21 h. [c] 21 h.
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Scheme 1. Proposed reaction pathway for glycerol conversion over Ru/HAP (a), Ru-Zn/HAP (b), and Ru-Zn-Cu(I)/HAP (c).
could effectively decline the production of FA and methane.
Moreover, Cu2O could raise notably the yield of the liquid
products, suggesting that Cu2O effectively restrained the the
cleavage of C-C hydrocarbon bonds. In addition, 1,2-PROP yield
would increase in the presence of Cu metal (Table entry 3),
which is consistent with the results of Cu/Al2O3 catalyst.28
Over Ru-Zn/HAP, high selectivity of LA (75.7%) and hydrogen
(99.8%) at a glycerol conversion of 73.9%, but the yield of liquid
product was relatively low (Table1 entry 6). By adding Cu2O in
the above reaction system, the selectivity of LA (83.5%) and the
yield of liquid products (98.9%) were both significantly enhanced
(Table entry 7). By increasing the reaction time from 12 to 21 h,
the glycerol conversion, catalyzed by Ru-Zn/HAP in the present
of Cu2O, reached 100%, maintaining the high LA selectivity of
83.9% (Table 1, entry 8). Finally, the Ru-Zn-Cu(I)/HAP was also
used to convert glycerol with a high yield of LA (70.9%) and a
high selectivity of hydrogen (99.8%). The gas chromatogram of
the gas products was shown in Figure S6. This suggested that
Cu(I) reduced effectively the degradation of the intermediates for
glycerol conversion, leading to a high selectivity of LA in liquid
products and a low selectivity of methane in gas products.
It has been well established that LA is generated from glycerol
Figure 4. Time course of glycerol conversion over Ru-Zn-Cu(I)/HAP catalyst.
Reaction conditions: 20 mg catalyst, 0.1 g glycerol, NaOH, 0.065g, and 2 mL
water, 140 °C.
via
dehydrogenation
of
glycerol
to
glyceraldehyde,
Table 2. Reaction results over Ru-Zn-Cu(I)/HAP catalyst for conversion of
glycerol to LA at different temperatures [a]
base-catalyzed dehydration and 1,2-hydride shift of the
intermediate. As shown in Scheme 1a, LA selectivity was was
relatively low on Ru/HAP, most probably due to the cleavage of
C-C bonds over this catalyst. The selectivity of LA increased
significantly over Ru-Zn/HAP because of the presence of Zn
active sites (Scheme 1b), as Zn2+ ions favored the 1,2-hydride
shift of pyruvaldehyde to LA. As Cu(I) was introduced into the
Ru-Zn/HAP catalyst, the cleavage of C-C bonds was restrained
notably, resulting in the improved catalytic performance for
glycerol conversion (Scheme 1c).
sel.liquid prod. (%）
Temperature
Entry
(°C)
100
120
140
160
Conv. (%)
26.7
LA
FA
9.5
PROP
0.5
EG
0.6
0.6
0.4
0.5
GLYA
6.2
TA
3.1
2.2
1.6
1.5
1
2
3
4
80.1
81.8
83.6
80.9
42.2
8.6
1.4
5.4
72.8
7.8
2.2
4.4
83.6
10.3
4.6
2.2
The effect of reaction time
[a] Reaction conditions: 20 mg catalyst, 0.1 g glycerol, NaOH, 0.065 g, and 2
mL water, reaction time of 12 h.
The effect of reaction time on glycerol dehydrogenation was
investigated on the Ru-Zn-Cu(I)/HAP catalyst. As displayed in
Figure 4, glycerol conversion increased from 49% to 100% when
the reaction time was increased from 6 to 24 h. In addition, the
selectivity for GLYA was found to gradually decline with the
increase in reaction time, while the selectivity for FA enhance
from 4.9 to 8.1, suggesting that the GLYA would further degrade
during the reaction process. It should be noted that the selectivity
for LA was very high (81.9~83.2) in the full time range, indicating
the high efficiency of the Ru-Zn-Cu(I)/HAP catalyst for glycerol
conversion.
The effect of reaction temperature
The effect of reaction temperature on the glycerol conversion and
product distribution is summarized in Table 2. Glycerol
conversion was enhanced with increasing temperature. The
selectivity of LA increased from 80.1% at 100 °C to 83.6% at
140 °C. However, the selectivity reduced to 80.9% at 160 °C.
Nevertheless, the selectivity of 1,2-PROP slightly increased from
0.5% to 4.6% with the increasing of reaction temperature.
Conversely, the selectivity for GLYA and TA marginally declined.
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In addition, the high reaction temperature also favored the
production of FA from glycerol. Hence, an appropriate reaction
temperature was necessary for the conversion of glycerol to LA.
In summary, Ru/HAP, Ru-Zn/HAP, and Ru-Zn-Cu(I)/HAP
catalysts have been prepared by an ion-exchange method. They
can be used for transformation of glycerol into LA effectively in
alkaline aqueous solutions. The Ru-Zn-Cu(I)/HAP is most
effective for the reaction and the yield of LA can reach 70.9% at
140 °C. Compared to the Ru/HAP catalyst, the introduction of
Zn2+ into the catalyst could significantly promote the selectivity of
LA and Cu(I) could effectively inhibit the cleavage of C-C bonds,
leading to high yields of LA. The catalyst is stable and can be
reused for at least four times without decreasing its catalytic
activity and selectivity.
Experimental Section
Materials
Glycerol (GLY, 98%), lactic acid (0.1 N), tartronic acid (TA, 98%) were
purchased from Alfa Aesar. Formic acid (FA, >98%) was obtained from
Fluka. Acetic acid (1 N) was provided by Aladdin. H2SO4 (98%), acetic
acid (AA, 99%), 1,2-propylene glycol (PROP), ethylene glycol (EG),
glyceric acid (GLYA) Zn(NO3)26H2O, Ruthenium (III) chloride trihydrate
(RuCl33H2O), sodium hydroxide (NaOH), Cu(NO3)23H2O, Cu2O, Cu
powder, CuI, acetonitrile, hydroxyapatite ([Ca5(PO4)3OH]) were all A. R.
grade and purchased from Sinopharm Chemical Reagent Co. Ltd.
Catalyst preparation
Figure 5. Reusability of the Ru-Zn-Cu(I)/HAP for glycerol conversion. Reaction
conditions: 20 mg catalyst, 0.1 g glycerol, NaOH, 0.065 g, and 2 mL water, 6 h.
The Ru, Ru-Zu catalysts supported on HAP with various contents were
prepared by ion-exchange method. In a typical procedure, HAP (1 g) was
dispersed in double deionized water (300 mL) under vigorous stirring for 2
h at room temperature. Then a certain amount of RuCl3 aqueous solution
(Ru: 10 wt.%) with various amounts of Zn(NO3)2 was added into the HPA
suspension. After being stirred for 2 h, the slurry was heated and refluxed
at 110 °C for 24 h. The obtained solid was collected by filtration and
washed with deionized water until the Cl and NO3 were not detectable.
The as-prepared catalyst was dried under vacuum at 60 °C overnight and
was then reduced in pure H2 at 200 °C for 2 h and subsequently cooled
slowly to room temperature in Ar. The catalysts without Zn are denoted as
Ru/HAP. When the nominal Ru/Zn wight ratio in the catalyst was 10:10
(i.e., Ru-Zn/HAP), the actual loadings of Ru and Zn determined by
inductively coupled plasma atomic emission spectroscopy (ICP-AES)
were 7.49 wt% and 9.78 wt%, respectively. For the preparation of
Ru-Zn-Cu(I)/HAP, CuI (0.19g, 1mmol) was dissolved in acetonitrile-water
(70 mL, 60:10). 0.5 g Ru-Zn/HAP was dispersed in the CuI solution under
vigorous stirring for 1h. The obtained mixture was sealed in a 100 mL
Teflon lined autoclave, heated to 140 °C in an oil bath and kept for 24 h.
After cooled to room temperature, the obtained solid was washed with
acetonitrile until I was not detectable. The the solid materials were
washed with ethanol followed by drying in vacuo overnight at 60 °C,
yielding the Ru-Zn-Cu(I)/HAP catalyst with Cu content of 0.49 wt% as
measured by ICP-AES: 0.49 wt%).
Reuse of the catalyst
The reusability of the Ru-Zn-Cu(I)/HAP catalyst for the glycerol
conversion was investigated under the optimized reaction
conditions (Figure 5). The catalyst could be reused at least four
times without notable changes. From the TEM images of the
fresh catalyst and the catalyst reused after four cycles (Figure 6),
it is obvious that Ru nanoparticles were still highly dispersed on
HAP (Figure 6b) and the change of the morphology of the
catalyst was not obvious. The thermogravimetric (TG) and ICP
experiments of the fresh catalyst and the catalyst reused after
four cycles was examined. The TG study indicate that the
thermal stabilization of the Ru-Zn-Cu(I)/HAP catalyst after reused
was not changed compared to the fresh catalyst (Figure S7). ICP
analysis showed that the contents of Ru, Zn, and Cu in
Ru-Zn-Cu(I)/HAP before and after reaction was nearly the same.
This indicates that the Ru-Zn-Cu(I)/HAP was stable as catalyst
for converting glycerol to LA under the given reaction conditions.
b
a
Catalyst characterization
The contents of the Ru, Zn and Cu in the catalysts were determined by
ICP-AES (PROFILE. SPEC, Leeman). Powder X-ray diffraction (XRD)
patterns were recorded on a Rigaku D/max-2500 X-ray diffractometer
using Cu K radiation ( = 0.1406 nm). The structural properties were
characterized by transmission electron microscopy (TEM, JEOL
JEM-2100F). The X-ray photoelectron spectroscopy (XPS) data were
obtained with an ESCALab 220i-XL electron spectrometer from VG
Scientific using 300 W Al K radiation. The base pressure was about 3 
109 mbar. The binding energies were referenced to the C 1s line at 284.8
eV from adventitious carbon. Temperature-programmed desorption of
ammonia (NH3-TPD) was performed on Micromeritics’ AutoChem 2950
HP Chemisorption Analyzer. Thermogravimetric analysis (TGA) was
carried out on a Pyris TGA (Perkin-Elmer) at a heating rate of 10 °C/min
between 50 and 800 °C under nitrogen atmosphere.
Figure 6. TEM images of fresh Ru-Zn-Cu(I)/HAP (a) and the Ru-Zn-Cu(I)/HAP
after reused four times (b). The scar bar is 10 nm.
Conclusions
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Catalytic conversion of glycerol
Knight, D. W.; Taylor, S. H.; Hutchings, G. J., Angew. Chem. Int. Ed.
2011, 50 (43), 10136-10139.
The conversion of glycerol was performed in a 10 mL Teflon-lined
stainless steel autoclave equipped with a magnetic stirrer, which was
similar to that used previously.23 In a typical experiment, 0.1 g glycerol, 20
mg catalyst, 0.065 g NaOH, and 2 mL water were introduced into the
reactor. The air in the reactor was removed by vacuum. The reaction
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based on the following equation.
moles of carbon in the organic cheimcal
Yield =
 100%(1)
moles of carbon in feedstock
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Keywords: Glycerol conversion • Lactic acid • Heterogeneous
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10.1002/asia.201700412
Chemistry - An Asian Journal
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Zhiwei Jiang, Zhanrong Zhang, Tianbin
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Efficient generation of lactic acid from
glycerol over Ru-Zn-Cu(I)/HAP
catalyst
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