Catalytic conversion of glycerol to lactic acid over hydroxyapatite-supported metallic Ni0 nanoparticles

Article abstract of DOI:10.1166/jnn.2018.15327

Catalytic conversion of low-priced biomass glycerol to value-added lactic acid is an alternative route to the conventional fermentation process using sugar as the starting material. Nanosized hydroxyapatite-supported metallic Ni⁰ nanoparticles (Ni_x/HAP) prepared by the wetness chemical reduction method effectively catalyzed the conversion of high-concentrated glycerol (1.5-3 mol L^-1) to lactic acid in a NaOH aqueous solution. The Ni_x/HAP catalysts exhibited higher catalytic activity for glycerol conversion to lactic acid than the sole metallic Ni⁰ nanoparticles.When the reaction was carried out over the Ni_0.2/HAP catalyst with the initial glycerol and NaOH concentrations of 2.0 and 2.2 mol L^-1 at 200 °C for 2 h, the selectivity of lactic acid reached 94.7% at the glycerol conversion of 92.1%.

Full text of DOI:10.1166/jnn.2018.15327

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 4734–4745, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Catalytic Conversion of Glycerol to Lactic Acid Over
0
Hydroxyapatite-Supported Metallic Ni Nanoparticles
∗
∗
Lang Qiu, Haixu Yin, Hengbo Yin , and Aili Wang
Faculty of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China
Catalytic conversion of low-priced biomass glycerol to value-added lactic acid is an alternative
route to the conventional fermentation process using sugar as the starting material. Nanosized
0
hydroxyapatite-supported metallic Ni nanoparticles (Ni /HAP) prepared by the wetness chemical
x
−
1
reduction method effectively catalyzed the conversion of high-concentrated glycerol (1.5–3 mol L
ꢀ
to lactic acid in a NaOH aqueous solution. The Ni /HAP catalysts exhibited higher catalytic activity
x
0
for glycerol conversion to lactic acid than the sole metallic Ni nanoparticles. When the reaction was
carried out over the Ni0ꢁ2/HAP catalyst with the initial glycerol and NaOH concentrations of 2.0 and
− ꢀ
1
2
.2 mol L at 200 C for 2 h, the selectivity of lactic acid reached 94.7% at the glycerol conversion
of 92.1%.
Keywords: Glycerol, Lactic Acid, Hydroxyapatite, Nickel Nanoparticles.
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
Copyright: American Scientific Publishers
1
. INTRODUCTION
Delivered bywI int hg et nh tea use of NaOH as the homogeneous catalyst in
2
6
To avoid fossil fuel depletion and solve greenhouse gas
an aqueous solution. Alkali metal hydroxides exhib-
problem, researchers have made great efforts on the con-
version of biomass to biofuel and valuable chemicals.
ited higher catalytic activity than alkaline earth metal
hydroxides.
1
–13
18ꢀ23ꢀ26ꢀ27
Biodiesel, as a renewable and sustainable fuel, produced
by transesterification between methanol and vegetable oil
To decrease the reaction temperature, heterogeneously
catalytic conversion of glycerol to lactic acid has been
investigated over supported noble and non-noble metal cat-
alysts. The supported noble metal catalysts, such as Au,
Pt, and Pt/Au catalysts could effectively catalyze the aero-
bic conversion of glycerol to lactic acid in a NaOH aque-
4
–13
or animal fat has been widely used in the world.
Glyc-
erol, as a by-product, has been produced with ca. 10–20%
1
4ꢀ15
of the total volume of biodiesel.
In 2016, the biodiesel
market is estimated to be 37 billion liters. Above 4 bil-
lion liters of crude glycerol will be produced, causing an
ꢀ
ous solution at 90–180 C, giving the lactic acid yield of
1
6–18
28–31
overcapacity problem.
Therefore, effective conversion
above 80%.
of glycerol into high-valued chemicals has attracted great
attention of researchers in past decade.
In order to decrease the cost of noble metal for glyc-
erol conversion to lactic acid, copper-based catalysts were
investigated to catalyze glycerol conversion to lactic acid
1
9–22
Lactic acid can be synthesized using glycerol as a start-
ing material by hydrothermal method in an alkaline solu-
tion without or with the use of catalyst, being a potential
lactic acid production route to replace the conventional fer-
3
2–34
in an alkaline solution.
The copper-based catalysts
gave lactic acid yields in the range of 60%–77% after
ꢀ
32
reacting at 240 C for 6 h. The basic hydroxyapatite-
2
3–27
0
mentation process using sugar as the starting material.
and MgO-supported metallic Cu catalysts gave high lac-
tic acid yields of above 81% after reacting at 230 C
ꢀ
The recent research results dealing with the hydrothermal
conversion of glycerol to lactic acid are summarized as
follows.
3
3ꢀ34
0
for 2 h.
The non-noble metallic Cu catalysts exhib-
ited good catalytic activities for the catalytic conversion of
glycerol to lactic acid at a lower reaction temperature than
the hydrothermal method with the use of sole NaOH as the
catalyst. However, in the above-mentioned processes, the
Kishida et al. firstly reported that lactic acid with the
yield of above 90% was synthesized by the hydrother-
−1
ꢀ
mal conversion of glycerol (0.33 mol L ꢁ at 300 C
−1
glycerol concentration was generally ca. 1 mol L or
less. In the viewpoint of economy, catalytic conversion
∗
Authors to whom correspondence should be addressed.
4734
J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 7
1533-4880/2018/18/4734/012
doi:10.1166/jnn.2018.15327

0
Qiu et al.
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
of high-concentrated glycerol to lactic acid is worth of
investigation.
(PVP/Ni, m/m, 10:100), and 1 g of HAP powder were
added in 60 mL of anhydrous ethanol by ultrasonic treat-
ment for 30 min. The suspension was transferred into a
0
0
Metallic Ni and supported Ni catalysts exhibit good
catalytic activities for hydrogenation reactions in indus-
ꢀ
three-necked round bottom flask and preheated to 60 C
3
5–39
trial processes.
The nickel-based catalysts should have
in a thermostatic bath under stirring. A saturated NaOH
anhydrous ethanol solution was added into the reaction
mixture to adjust the pH value of 12. A hydrazine hydrate
ethanol solution (8 mL in 100 mL anhydrous ethanol) was
good dehydrogenation performances according to cataly-
sis principle. Glycerol dehydrogenation is the first step
involved in the hydrothermal conversion of glycerol to lac-
tic acid.3
3ꢀ34
However, to the best of our knowledge, cat-
added dropwise to the reaction mixture and heated at 70 C
ꢀ
alytic hydrothermal conversion of glycerol to lactic acid
over nickel-based catalysts has not been reported.
In our present work, nanosized hydroxyapatite-
for 4 h under mild stirring. After reaction, the reaction
mixture was cooled down to room temperature. The as-
prepared Ni /HAP catalysts were filtrated and washed with
x
supported nickel (Ni /HAP) catalysts were investigated to
catalyze the hydrothermal conversion of high-concentrated
anhydrous ethanol for three times and kept in an anhy-
drous ethanol solution before characterization and cat-
alytic reaction. After filtration, the cake of the as-prepared
x
glycerol to lactic acid. The Ni /HAP catalysts were pre-
x
pared by the wetness chemical reduction method and
Ni /HAP catalysts were directly used for catalytic reac-
tion to prevent oxidation of metallic Ni component. The
x
0
characterized by XRD, TEM, HRTEM, BET, CO -TPD,
2
and atomic absorption spectrophotometer techniques. The
Ni /HAP catalysts were donated as Ni /HAP, Ni /HAP,
x
0ꢂ1
0ꢂ2
Ni /HAP catalysts effectively catalyzed the conversion of
Ni /HAP, and Ni /HAP. The properties of the Ni /HAP
x
0ꢂ3 0ꢂ4 x
high-concentrated glycerol to lactic acid at a relatively low
reaction temperature in a batch reactor.
catalysts are listed in Table I.
.4. Characterization of HAP and Ni /HAP Catalysts
2
x
The X-ray powder diffraction (XRD) patterns of the metal-
2
. EXPERIMENTAL DETAILS
0
lic Ni , HAP, and Ni /HAP catalysts were recorded on
x
2
.1. Materials
a diffractometer (D8 super speed Bruker-AEX Company)
Ammonia solution (25%), phosphoric acid (85%), cal-
cium nitrate tetrahydrate, anhydrous ethanol, sodium
hydroxide, nickel acetate tetrahydrate (C H O Ni·4H O),
using Cu Kꢃ radiation (ꢄ = 1.54056 Å) with Ni filter and
ꢀ
ꢀ
scanning (2ꢅꢁ from 10 to 80 . According to the Scher-
4
6
4
2
IP: 195.34.196.42 On: Wed r, e 1r ’3s Je uq nu a 2t i 0o 1n 8: D0 8=:5 2K : ꢄ0 /9( B cosꢅꢁ, the crystallite sizes of
polyvinylpyrrolidone (PVP k-30), hydrazine hydrate
0
Copyright: American Scientific Publishers
Ni nanoparticles (1 1 1) in the Ni /HAP catalysts were
x
(
N H · H O, 85%), glycerol, lactic acid, 1,2-pro pDa en el i dv ieo rl e, d by Ingenta
2
4
2
calculated. The value of K was taken as 1.0 and B was the
formic acid, acetic acid, oxalic acid, and isopropyl alcohol
were of reagent grade and were purchased from Sinopharm
chemical reagent Co., Ltd. All the chemicals were used as
received without further purification. Deionized water was
used through all the experiments.
full width of the diffraction line at half of the maximum
of XRD peak of metallic Ni (1 1 1). The results are listed
0
in Table I.
The microstructures and the average particle sizes of the
Ni /HAP catalysts were examined by transmission electron
x
microscopy (TEM) and High-resolution transmission elec-
tron microscopy (HRTEM) on a microscope (JEM-2100)
operated at an acceleration voltage of 200 kV. The sam-
ple was dispersed in anhydrous ethanol by ultrasonication
for 10 min, then a drop of the ethanol suspension was
placed onto a copper grid coated with a layer of amor-
phous carbon. The particle sizes of the Ni nanoparticles
were estimated from the TEM and HRTEM images.
2
.2. Preparation of Hydroxyapatite
Nanosized hydroxyapatite (HAP) with rod-like shape was
prepared according to the reported method.
equivalent volumes of calcium nitrate (1 mol L ꢁ and
phosphoric acid (0.6 mol L ꢁ aqueous solutions were
added into a three-necked round bottom flask. The aqueous
solution was heated to 40 C in a water bath. An ammonia
solution (25%) was added dropwise into the solution to
adjust its pH value of 10. After reacting at 40 C for 4 h,
the reaction solution was transferred into a Teflon-lined
autoclave and autoclaved at 100 C for 8 h. The resul-
tant HAP sample was washed with distilled water until the
conductivity of filtrate was less than 2 mS m . Finally,
the HAP sample was dried at 120 C overnight. The as-
prepared HAP nanorods were used as the catalyst support.
4
0ꢀ41
Typically,
−1
−1
ꢀ
The basicities of the HAP and Ni /HAP catalysts were
x
ꢀ
determined by the CO temperature-programmed desorp-
2
tion (CO -TPD) technique in a fixed-bed continuous flow
2
ꢀ
microreactor under atmospheric pressure. Firstly, the sam-
ꢀ
ples (0.1 g) were CO -saturated in a CO stream at 60 C
2
2
−
1
for 0.5 h. After purging with helium stream with a flow
ꢀ
−1
ꢀ
rate of 30 mL min at 60 C for 0.5 h to remove
the physically adsorbed CO , the samples were heated at
2
ꢀ
−1
ꢀ
1
5 C min to 750 C.
2
.3. Preparation of Ni /HAP Catalyst
A NOVA 2000e physical adsorption apparatus was
x
HAP-supported nickel catalysts (Ni /HAP; x, mole of Ni
to the 100 g HAP) were prepared by the wetness chemical
reduction method. A given amount of nickel acetate, PVP
used to determine the specific surface areas of HAP and
Ni /HAP catalysts by N adsorption/desorption technique.
The samples were degassed at 100 C for 2 h under
x
x
2
ꢀ
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018
4735

0
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
Qiu et al.
Table I. Physicochemical properties of the catalysts.
Crystallite sizes of
Ni (1 1 1) (nm)
Particle sizes of
Ni (nm)
Specific surface
areas (m /g)
Average pore
diameters (nm)
Basic strength at different
Total basicities
0
a
0
b
2
−1
c
−1
Catalysts
temperatures (ꢆmol CO g
ꢁ
(ꢆmol CO g
ꢁ
2
cat
2
cat
Ni
HAP
16.4
/
16
/
/
/
/
/
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
90.4
3.4
0.452 (117∼502 C)
0.456
0
.004 (585∼623 C)
Ni0ꢂ1/HAP
Ni0ꢂ2/HAP
Ni0ꢂ3/HAP
Ni0ꢂ4/HAP
14.6
16.3
17.5
18.2
14
16
17
17
70.9
65.4
62.8
60.4
3.3
3.3
3.2
3.1
0.405 (137∼558 C)
0.408
0.306
0.288
0.258
0
.003 (559∼613 C)
0.302 (140∼516 C)
0
.004 (555∼590 C)
0.276 (171∼489 C)
0
.004 (533∼568 C)
ꢀ
ꢀ
0.255 (179∼479 C)
0
.003 (522∼557 C)
Notes: aCrystallite sizes of Ni0 (nm) were calculated by Scherrer’s equation. bThe Particle sizes of Ni0 (nm) were determined by TEM. cThe total basicities of the Ni /HAP
x
catalysts were calculated from CO -TPD curves.
2
vacuum before the measurement. The N2 adsorption–
The organic acids present in the reaction mixture, such as
lactic acid, acetic acid, oxalic acid, and formic acid, were
analyzed on an Agilent HPLC system equipped with a tun-
able absorbance UV detector and a reverse-phase column
(Innoval ASB C18, 5 ꢆm, 100 Å, 4.6 mm × 250 mm) at
desorption isotherms of the samples were measured at
ꢀ
−
196 C. According to the BET method, the specific sur-
face areas were calculated.
The compositions of the Ni /HAP catalysts and the con-
x
2
+
ꢀ
centrations of Ni in reaction solutions were analyzed on
an atomic absorption spectrophotometer (TAS-986). The
results are listed in Table II.
30 C. The mobile phase was a methanol aqueous solution
−1
(10:90, V/V) with a flow rate of 0.8 mL min . The pH
value of the mobile phase was 2.3, which was adjusted
with phosphate buffer. The detection wavelength was
210 nm. A gas-phase chromatograph (SP-6800A) equipped
with a PEG-20 M packed capillary column (0.25 mm ×
2
.5. Catalytic Test
Catalytic conversion of glycerol to lactic acid over
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
3
0 m) and a FID was used to analyze the concentrations of
Ni /HAP catalyst was carried out in a 300 mL stainless
x
Copyright: American Scientific Publishers
the unreacted glycerol and produced 1,2-propanediol. The
steel reactor with a mechanical stirrer. A given amount
Delivered by Ingenta
isopropyl alcohol was used as the internal standard.
The product selectivity was calculated by carbon bal-
ance and the equation was listed as follows.
of Ni /HAP catalyst and 100 mL of aqueous solution of
x
glycerol and NaOH were added into the reactor. Then the
reactor was flushed with N to replace air inside for 10 min
2
before reaction. When the reaction temperature was raised
to prescribed value, agitation started at 300 rpm. The reac-
tion time was counted while the reaction temperature was
raised to the prescribed value. After reacting for a certain
time period, the reaction mixture was cooled down to room
temperature for analysis.
Product selectivity
= ꢇMole of productꢁ×ꢇCarbon number of product
moleculeꢁ/3ꢇMole of consumed glycerolꢁ
(1)
Hydrochloric acid (37%) was used to adjust the pH
of the reaction mixture to ca. 3 for HPLC analysis.
4
2
Ni
Table II. The compositions of freshly and spent Ni /HAP catalysts and
x
the concentration of Ni2 in reaction solution.
+
a
Ni0.4/HAP
+
−1
Catalysts
Mole of Ni to the 100 g HAP
Ni2 (g L
ꢁ
Ni0.3/HAP
Ni0.2/HAP
Ni0.1/HAP
Ni0ꢂ1/HAP
Ni0ꢂ1/HAP (spent)
Ni0ꢂ2/HAP
Ni0ꢂ2/HAP (spent)
Ni0ꢂ3/HAP
Ni0ꢂ3/HAP (spent)
Ni0ꢂ4/HAP
0.100:100
0.099:100
0.199:100
0.198:100
0.298:100
0.296:100
0.398:100
0.394:100
/
/
/
/
/
/
/
/
/
HAP
Ni0ꢂ4/HAP (spent)
Reaction solution
1
0
20
30
40
50
60
70
80
Not detected
2
θ(º)
Note: aThe experimental conditions: glycerol aqueous solution, 2 mol L , 100 mL;
−1
ꢀ
0
Ni /HAP, 0.736 g; NaOH/glycerol mole ratio, 1.1:1; reaction temperature, 200 C;
Figure 1. XRD patterns of the hydroxyapatite, metallic Ni , and fresh
x
0
reaction time, 2 h.
Ni /HAP catalysts. •, HAP; ꢀ, Ni .
x
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Qiu et al.
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
0
3
. RESULTS AND DISCUSSION
Scherrer’s equation, indicating that the metallic Ni par-
3
.1. XRD and AAS Analyses
ticles in Ni
(
x
/HAP catalysts were nanometer magnitude
Table I). The crystallite sizes of the metallic Ni in the
Ni /HAP catalysts increased with the increase in nickel
0
0
The XRD patterns of metallic Ni , HAP, and Ni /HAP
catalysts are shown in Figure 1. The XRD peaks of the
x
x
0
metallic Ni and Ni /HAP catalysts appearing at 2ꢅ = 44.5,
loadings.
x
ꢀ
5
1.9, and 76.4 were indexed as the (1 1 1), (2 0 0),
The XRD peaks of the HAP and Ni /HAP catalysts
x
and (2 2 0) planes of face centered-cubic (fcc) nickel
JCPDS 04-0850), respectively. No nickel oxides and
appearing at 2ꢅ = 25.9, 31.8, 32.2, 32.9, 34.1, 39.8, 46.7,
ꢀ
(
49.5, and 53.1 were ascribed to those of standard hydrox-
nickel hydroxides were detected, indicating that metallic
yapatite (JCPDS 09-0432). The supports in the catalysts
were still in hydroxyapatite phase.
0
Ni nanoparticles were prepared under the present exper-
0
imental conditions. The peak intensities of metallic Ni
The nickel contents in the fresh and spent Ni /HAP cat-
x
in the Ni /HAP catalysts increased with the increase in
alysts analyzed by AAS are shown in Table II. The nickel
contents in the fresh catalysts were close to those in the
spent ones, correspondingly. There was no nickel detected
x
0
nickel loadings. The crystallite sizes of Ni in the Ni /HAP
x
catalysts in a range of 14.6–18.2 nm were estimated by
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
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Figure 2. Continued.
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4737

0
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
Qiu et al.
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
Copyright: American Scientific Publishers
Delivered by Ingenta
0
Figure 2. TEM, SAED, HRTEM images of (a1, a2) metallic Ni , (b1, b2) Ni0ꢂ1/HAP, (c1, c2) Ni0ꢂ2/HAP, (d1, d2) Ni0ꢂ3/HAP, (e1, e2) Ni0ꢂ4/HAP, and
0
(
f1) HAP support. The typical supported Ni nanoparticles are marked by circling in the TEM images.
in the reaction solution. The results revealed that the metal-
lic Ni nanoparticles could attach at the HAP surfaces
tightly.
{2 0 0} (0.176 nm), {2 2 0} (0.125 nm), and {2 2 2}
(0.102 nm) lattice spacings of fcc nickel, respectively.
The metallic Ni nanoparticles had a poly-crystalline
0
0
structure.
3
.2. TEM and HRTEM Analyses
The TEM image shows that the HAP support was
nanorod with the average diameter and length of ca. 16 and
The TEM, SAED, and HRTEM images of the metal-
lic Ni , HAP support, and Ni /HAP catalysts are shown
in Figure 2. The TEM image shows that the metallic Ni
0
58 nm, respectively (Fig. 2(f1)). The TEM images of the
x
0
0
Ni /HAP catalysts show that the supported Ni nanoparti-
x
sample was composed of spherical nanoparticles with the
average particle size of 16 nm and the particle size dis-
tribution of 10–25 nm (Table I). According to the SAED
pattern (Fig. 2(a2)), the diffraction fringes of the metal-
cles had the average particle sizes in a range of 14–17 nm
(Figs. 2(b1–e1)). The lattice fringes of the Ni nanopar-
0
ticles in the Ni /HAP catalysts were around 0.203 and
x
0.176 nm, being close to the {1 1 1} and {2 0 0} lattice
spacings of fcc metallic nickel (Figs. 2(b2–e2)).
0
lic Ni sample were close to the {1 1 1} (0.204 nm),
4738
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018

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Qiu et al.
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
ꢀ
the regions of 100–250, 250–450, and 450–700 C are
assigned to CO desorption from weak-, medium-, and
2
4
3ꢀ44
strong-strength basic sites, respectively.
Therefore,
3
26
22
16
the HAP support and Ni /HAP catalysts possessed both
5
57
62
Ni0.4HAP
x
medium- and strong-strength basic sites. Their medium-
strength basicities were obviously higher than their strong-
strength basicities. However, the total basicities of the
Ni /HAP catalysts decreased with the increase in the Ni
contents, revealing that metallic Ni nanoparticles covered
3
5
Ni0.3HAP
Ni0.2HAP
3
5
71
x
3
12
0
6
01 Ni0.1HAP
2
92
the support surface, resulting in a decrease in the basicity.
6
09
HAP
3
.4. BET Analysis
The specific surface areas and average pore sizes of
0
100
200
300
400
500
600
700
the HAP support and Ni /HAP catalysts are listed in
x
Temperature (ºC)
Figure 3. CO -TPD patterns of HAP support and Ni /HAP catalysts.
Table I. The specific surface areas of the HAP support and
2
−1
Ni /HAP catalysts decreased from 90.4 to 60.4 m g
x
2
x
with increasing the Ni loadings. The average pore diame-
ters slightly decreased from 3.4 to 3.1 nm. The decrease
in the specific surface area and average pore diameter with
the increase in Ni loadings was probably due to that the
pores of HAP support were partially choked by supported
Table III. Catalytic conversion of glycerol with the use of sole NaOH
or Ni0ꢂ2/HAP catalyst.
Reaction
time (h)
Conversions of
glycerol (%)
Selectivities of
lactic acid (%)
Catalysts
0
metallic Ni nanoparticles.
a
NaOH
1
2
3
4
Trace
Trace
Trace
0.9
/
/
/
3
.5. Catalytic Conversion of Glycerol to Lactic Acid
3
.5.1. Catalytic Activities of Ni /HAP Catalysts
x
100
b
Before investigating the catalytic activities of Ni /HAP
Ni0ꢂ2/HAP
1
2
3
4
Trace
Trace
1.8
2.9
/
x
100
100
99.8
catalysts, the sole Ni0ꢂ2/HAP catalyst or NaOH was used
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
−1
in the catalytic conversion of glycerol (2.0 mol L ꢁ,
Copyright: American Scientific Publishers
ꢀ
after reacting at 200 C for 4 h, the glycerol conversions
Delivered by Ingenta
Notes: aGlycerol aqueous solution, 2.0 mol L , 100 mL; NaOH/glycerol mole
ratio, 1.1:1; reaction temperature, 200 C. Glycerol aqueous solution, 2.0 mol L
00 mL; Ni0ꢂ2/HAP, 0.736 g; reaction temperature, 200 C.
−1
were less than 3% and lactic acid was the main product
ꢀ
b
−1
,
(Table III). When both Ni /HAP catalyst and NaOH were
x
ꢀ
1
used in the catalytic conversion of glycerol, the glycerol
conversions and the lactic acid selectivities were above
79.0% and 89.5%, respectively (Table IV). It was reason-
3
.3. CO -TPD Analysis
2
To investigate the surface basicities of the HAP support
and Ni /HAP catalysts, the CO -TPD was carried out
able to conclude that NaOH and supported Ni /HAP cat-
alysts synergistically catalyzed the conversion of glycerol
to lactic acid.
x
x
2
(
Fig. 3). Their basic strengths are listed in Table I.
The HAP support and Ni /HAP, Ni /HAP, Ni /HAP,
When the Ni /HAP catalysts were used for catalyzing
0
ꢂ1
0ꢂ2
0ꢂ3
x
−1
Ni /HAP catalysts exhibited two CO desorption peaks
the hydrothermal conversion of glycerol (2.0 mol L ꢁ
0
ꢂ4
2
ꢀ
−1
at 292, 609; 312, 601; 316, 571; 322, 562; 326, 557 C,
respectively. Generally, the CO2 desorption peaks in
in a NaOH (2.2 mol L ꢁ aqueous solution, after react-
ꢀ
ing at 200 C for 2 h, the glycerol conversions increased
Table IV. The effect of Ni content in the catalysts on catalytic conversion of glycerol to lactic acid.
Selectivities (%)
a
Conversions
(%)
Lactic Oxalic Formic Acetic
Activities for glycerol
Activities for lactic
acid formation (h
Carbon
balances (%)
b
−1
c
−1
d
Catalysts
acid
acid
acid
acid
1,2-Propanediol
conversion (h
ꢁ
ꢁ
Ni
HAP
Ni0ꢂ1/HAP
Ni0ꢂ2/HAP
Ni0ꢂ3/HAP
Ni0ꢂ4/HAP
73ꢂ9
1ꢂ7
79ꢂ2
92ꢂ1
94ꢂ0
96ꢂ0
89.5
65.3
93.7
94.7
92.3
89.8
0.3
5.6
0.4
0.4
0.6
0.8
4.9
6.6
1.2
1.8
2.0
2.2
2ꢂ0
21ꢂ9
0ꢂ4
0ꢂ5
0ꢂ6
1ꢂ0
0
1ꢂ0
1ꢂ0
1ꢂ2
1ꢂ5
47ꢂ2
0
113ꢂ9
69ꢂ9
50ꢂ1
40ꢂ3
42ꢂ2
0
106ꢂ7
66ꢂ2
46ꢂ2
36ꢂ2
97.7
99.4
96.7
98.4
96.7
95.1
0ꢂ8
Notes: aReaction conditions: glycerol aqueous solution, 100 mL, 2.0 mol L ; NaOH/glycerol molar ratio 1.1:1; metallic Ni catalyst, 0.92 g; Ni /HAP catalyst, 0.736 g;
−1
x
reaction temperature 200 C; reaction time, 2.0 h. bGlycerol conversion activities normalized per metal atom. cLactic acid formation activities normalized per metal atom.
Carbon balances were calculated according to both detected products and reacted glycerol.
ꢀ
d
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018
4739

0
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
Qiu et al.
from 79.2% to 96.0% with the increase in metallic Ni0
loadings (Table IV). The selectivities of lactic acid were in
a range of 89.8%–94.7%. The selectivities of by-products
The carbon balance values over the Ni /HAP catalysts
x
were above 95.0%. The results revealed that the Ni /HAP
x
catalysts effectively catalyzed the hydrothermal conversion
of glycerol to the detected chemicals.
(
oxalic acid, formic acid, acetic acid, and 1,2-propanediol)
were less than 2.2%, respectively. The Ni /HAP cata-
The catalytic activities of the Ni /HAP and Ni /HAP
x
0ꢂ1
0ꢂ2
lysts exhibited high catalytic activities for the catalytic
conversion of glycerol to lactic acid. The Ni /HAP
catalysts for glycerol conversion were 1.5 and 2.4 times
that of the sole metallic Ni nanoparticle catalyst, respec-
0
0
ꢂ2
catalyst gave the highest lactic acid yield of 87.2%,
indicating that the Ni content also affected the product
yield.
tively (Table IV). The catalytic activities of the Ni /HAP
0
ꢂ1
and Ni /HAP catalysts for lactic acid formation were 1.6
0
ꢂ2
0
and 2.5 times that of the sole metallic Ni nanoparticle
(
a) 100
(b) 100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
90
80
70
60
50
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
40
Ni0.2/HAP
30
20
10
0
Ni0.3/HAP
Ni0.4/HAP
1
1
1
2
3
4
1
2
3
4
Time (h)
Time (h)
(
c) 10
(d) 10
9
9
8
7
6
5
4
3
2
1
0
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Copyright: American Scient8ific Publishers
Delivered by Ingenta
7
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
6
5
4
3
2
1
0
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
2
3
4
2
3
4
Time (h)
Time (h)
(
f) 10
(
e) 10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
2
3
4
2
3
4
Time (h)
Time (h)
Figure 4. Catalytic conversion of glycerol catalyzed by the Ni /HAP catalysts. Reaction conditions: glycerol aqueous solution, 100 mL, 2 mol L−1;
x
ꢀ
NaOH/glycerol mole ratio, 1.1:1; catalyst, 0.736 g; and reaction temperature, 200 C.
4740
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018

0
Qiu et al.
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
catalyst. The catalytic activities of the Ni /HAP and
increased to 91.5%, 98.3%, 100%, and 100%, respectively
(Fig. 4(a)). After reacting for 1 h, the maximum lac-
tic acid selectivities of 95.0%, 96.4%, 94.1%, and 90.0%
were obtained, respectively. With prolonging the reaction
time to 4.0 h, the selectivities of lactic acid decreased
to 81.0%, 83.2%, 79.4%, and 79.0%. The selectivities
of the by-products were less than 2.9%, respectively
(Figs. 4(c–f)).
0
ꢂ3
Ni /HAP catalysts for glycerol conversion and lactic acid
0
ꢂ4
formation were comparable to those of the sole metallic
0
0
Ni nanoparticle catalyst. The content of the Ni nanopar-
ticles in the Ni /HAP catalysts obviously affected the con-
x
version of glycerol to lactic acid.
3
.5.2. Effect of Reaction Time
−1
When the catalytic conversion of glycerol (2.0 mol L ꢁ
Over the Ni /HAP catalysts, the maximum yields of lac-
x
was catalyzed by the Ni /HAP, Ni /HAP, Ni /HAP,
tic acid were obtained at 2 h. The reaction time period of
2 h was fixed to investigate the effect of other reaction
parameters on the catalytic conversion of glycerol.
0
ꢂ1
0ꢂ2
0ꢂ3
ꢀ
and Ni /HAP catalysts at 200 C, with prolonging
0
ꢂ4
the reaction time to 4.0 h, the conversions of glycerol
(
a) 100
(b) 100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
90
80
70
60
50
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
40
30
20
10
0
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
80
200
220
240
180
200
220
240
Temperature (ºC)
Temperature (ºC)
IP: 195.34.196.42 On: Wed, 13 Jun 2018 08:52:09
(
c) 10
(d) 10
Copyright: American Scientific Publishers
9
8
7
6
5
4
3
2
1
0
9
Delivered by Ingenta
8
7
Ni0.1/HAP
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
6
Ni0.2/HAP
5
4
3
2
1
0
Ni0.3/HAP
Ni0.4/HAP
1
80
200
220
240
180
200
220
240
Temperature (ºC)
Temperature (ºC)
(
e) 10
(f) 10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
80
200
220
240
180
200
220
240
Temperature (ºC)
Temperature (ºC)
Figure 5. Catalytic conversion of glycerol catalyzed by the Ni /HAP catalysts. Reaction conditions: glycerol aqueous solution, 100 mL, 2 mol L−1;
x
NaOH/glycerol mole ratio, 1.1:1; catalyst, 0.736 g; and reaction time, 2 h.
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018
4741

0
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
Qiu et al.
3
.5.3. Effect of Reaction Temperature
concentration probably caused the formation of undetected
products.
The glycerol conversions and product selectivities in
the catalytic conversion of glycerol over the Ni /HAP,
Ni /HAP, Ni /HAP, and Ni /HAP catalysts at different
The catalytic activities for glycerol conversion and lac-
0
ꢂ1
0
tic acid formation based on metallic Ni increased upon
0
ꢂ2
0ꢂ3
0ꢂ4
increasing glycerol concentration, indicating that metallic
reaction temperatures are shown in Figure 5. With increas-
0
ꢀ
ꢀ
Ni sites could effectively catalyze the glycerol conversion
ing the reaction temperature from 180 C to 240 C, the
glycerol conversions increased to 90.5%, 97.0%, 98.1%,
and 100%, respectively. The selectivities of lactic acid
decreased from 94.0% to 75.2%, 95.1% to 81.0%, 93.1%
to 75.1%, and 90.5% to 72.7%, respectively. When the
reaction temperature was 200 C, the maximum lactic acid
yields of 74.2%, 87.2%, 86.7%, and 86.2% were obtained,
respectively. The selectivities of the by-products were all
to lactic acid.
3
.5.5. Effect of NaOH/Glycerol Mole Ratio
With increasing the NaOH/glycerol mole ratios from 1.0:1
ꢀ
to 1.3:1, the conversions of glycerol over the Ni /HAP,
0ꢂ1
Ni /HAP, Ni /HAP, and Ni /HAP catalysts increased
0ꢂ2
0ꢂ3
0ꢂ4
to 84.4%, 95.9%, 97.5%, and 98.0%, respectively (Fig. 6).
The selectivities of lactic acid decreased from 94.8% to
86.8%, 95.6% to 89.1%, 93.6% to 82.8%, and 91.3%
to 80.8%. The selectivities of the by-products were less
than 2.9%. High NaOH/glycerol mole ratio favored the
catalytic conversion of glycerol. But excessive NaOH con-
tent decreased the selectivity of lactic acid.
less than 2.6%. The optimal reaction temperature was
2
ꢀ
00 C from the perspective of lactic acid yield.
3
.5.4. Effect of Glycerol Concentration
The glycerol conversion and lactic acid selectivity over the
Ni /HAP catalysts decreased upon increasing glycerol con-
x
centration (Table V). The Ni /HAP and Ni /HAP cata-
0
ꢂ2
0ꢂ3
3
.5.6. Effect of Catalyst Loading
With increasing the catalyst loadings from 0.368 to
.920 g, the conversions of glycerol over the Ni /HAP,
lysts exhibited high catalytic activities for the conversion
−1
of high-concentrated glycerol (1.5–3.0 mol L ꢁ to lactic
acid with the lactic acid selectivities of 82.6%–95.6% at
the glycerol conversions of 92.1%–97.7%. When the glyc-
0
0
ꢂ1
Ni /HAP, Ni /HAP, and Ni /HAP catalysts increased to
8
The selectivities of lactic acid decreased from ca. 95%
to 81%. The selectivities of the by-products were less than
2
0
ꢂ2
0ꢂ3
0ꢂ4
6.2%, 96.3%, 98.8%, and 99.5%, respectively (Table VI).
−1
erol concentration was 1.5 mol L , the maximum lactic
acid yields over the Ni /HAP and Ni /HAP catalysts
0
ꢂ2
0ꢂ3
were 92.8% and 91.5%, respect iI vP e:l y1 .9 T5 h. 3e 4 s. e1 l 9e c6 t. i4v 2i ti Oe sn o: fW ed, 13 Jun 2018 08:52:09
.3%, respectively. The results revealed that high catalyst
Copyright: American Scientific Publishers
the by-products were less than 2.3%, respectively. The car-
loading gave a high glycerol conversion while the exces-
Delivered by Ingenta
bon balances over the Ni /HAP catalysts decreased from
x
sive catalyst loading caused the decrease in lactic acid
selectivity. To obtain high lactic acid yield, the optimal
catalyst loading was around 0.7 g.
ca. 99% to 85% upon increasing the glycerol concentra-
−1
tions from 1.5 to 3.0 mol L , meaning that high glycerol
a
Table V. Effect of glycerol concentration on catalytic conversion of glycerol to lactic acid.
Selectivities (%)
Glycerol
Glycerol
Activities for
glycerol
1,2-Propanediol conversion (h
Activities for
lactic acid
formation (h
concentrations conversions Lactic Oxalic Formic Acetic
Carbon
−1
b
−1
c
−1
d
Catalysts
(mol L
ꢁ
(%)
acid
acid
acid
acid
ꢁ
ꢁ
balances (%)
Ni0ꢂ1/HAP
1.5
83.8
79.2
74.7
68.4
94.7
93.7
86.4
83.6
0.2
0.4
0.5
0.5
1.6
1.0
0.8
0.7
0.3
0.4
0.8
0.9
1.5
1.0
0.6
0.5
90ꢂ4
113ꢂ9
134ꢂ3
147ꢂ5
85ꢂ7
106ꢂ7
116ꢂ1
123ꢂ3
98.3
96.5
89.1
86.2
2.0
2.5
3.0
Ni0ꢂ2/HAP
Ni0ꢂ3/HAP
Ni0ꢂ4/HAP
1.5
97.1
92.1
95.0
94.1
95.6
94.7
87.8
85.0
0.2
0.4
0.5
0.5
1.9
1.8
1.2
0.9
0.4
0.5
0.9
0.9
1.6
1.0
0.7
0.7
55ꢂ3
69ꢂ9
90ꢂ1
52ꢂ8
66ꢂ2
79ꢂ1
91ꢂ1
99.7
98.4
91.1
88.0
2.0
2.5
3.0
107ꢂ2
1.5
97.7
94.0
95.3
94.6
93.7
92.3
85.4
82.6
0.2
0.6
0.7
0.8
2.2
2.0
1.3
1.1
0.6
0.6
1.0
1.2
1.8
1.2
1.0
1.0
39ꢂ0
50ꢂ1
63ꢂ4
75ꢂ6
36ꢂ6
46ꢂ2
54ꢂ2
62ꢂ5
98.5
96.7
89.4
86.7
2.0
2.5
3.0
1.5
98.6
96.0
88.8
80.9
91.1
89.8
84.5
80.6
0.3
0.8
0.8
0.9
2.3
2.2
1.5
1.2
0.7
0.8
1.3
1.4
1.9
1.5
1.2
1.0
31ꢂ0
40ꢂ3
46ꢂ5
50ꢂ9
28ꢂ3
36ꢂ2
39ꢂ3
41ꢂ0
96.3
95.1
89.3
85.1
2.0
2.5
3.0
Notes: aReaction conditions: glycerol aqueous solution, 100 mL; NaOH/glycerol mole ratio, 1.1:1; catalyst loading, 0.736 g; reaction temperature, 200 C; reaction time,
2
ꢀ
b
c
d
.0 h. Glycerol conversion activities normalized per metal atom. Lactic acid formation activities normalized per metal atom. Carbon balances were calculated according
to both detected products and reacted glycerol.
4742
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Qiu et al.
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
(
a) 100
(b) 100
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
90
80
70
60
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
50
40
30
20
10
0
1
.0:1
1.1:1
1.2:1
1.3:1
1.0:1
1.1:1
1.2:1
1.3:1
NaOH/Glycerol molar ratio
NaOH/Glycerol molar ratio
(
c) 10
(d) 10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
.0:1
1.1:1
1.2:1
1.3:1
1.0:1
1.1:1
1.2:1
1.3:1
NaOH/Glycerol molar ratio
NaOH/Glycerol molar ratio
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Copyright: American Scientific Publishers
(
e) 10
(f) 10
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9
8
7
6
5
4
3
2
1
0
9
8
7
6
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
5
4
3
2
1
0
Ni0.1/HAP
Ni0.2/HAP
Ni0.3/HAP
Ni0.4/HAP
1
.0:1
1.1:1
1.2:1
1.3:1
1.0:1
1.1:1
1.2:1
1.3:1
NaOH/Glycerol molar ratio
NaOH/Glycerol molar ratio
−1
Figure 6. Catalytic conversion of glycerol catalyzed by the Ni /HAP catalysts. Reaction conditions: glycerol aqueous solution, 100 mL, 2 mol L
catalyst, 0.736 g; reaction temperature, 200 C; reaction time, 2 h.
;
x
ꢀ
3
.6. Possible Reaction Routes
a basic environment.33ꢀ45 Pyruvaldehyde was formed from
2-hydroxypropenal via the keto-enol tautomerization.
4
6
According to the findings in our present work and the
reported reaction pathways for the catalytic conversion of
glycerol to lactic acid in an aqueous solution,
The resultant pyruvaldehyde was converted to lactate via
2
3ꢀ26ꢀ45ꢀ46
23ꢀ29ꢀ30ꢀ33
the
the Cannizaro reaction.
possible reaction routes over the Ni /HAP catalysts in an
For the byproducts, 1,2-propanediol was formed by
x
alkaline solution are summarized as follows (Scheme 1).
The supported metallic nickel nanoparticles catalyzed
the dehydrogenation of terminal hydroxyl group of glyc-
erol to glyceraldehyde. 2-Hydroxypropenal was formed
from the intramolecular dehydration of glyceraldehyde in
the hydrogenation of glycerol with resultant H over the
2
4
7ꢀ48
Ni /HAP catalysts.
The acetate and formate anions
x
were formed by the decomposition of lactate anions in an
3
3
alkaline solution, respectively. The oxalate anions were
3
3ꢀ34
probably formed by the cleavage of glyceraldehyde.
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018
4743

0
Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni Nanoparticles
Qiu et al.
a
Table VI. Effect of catalyst loading on catalytic conversion of glycerol to lactic acid.
Selectivities (%)
Catalyst
Glycerol
Activities for
glycerol
1,2-Propanediol conversion (h
Activities for
lactic acid
conversion (h
loadings conversions Lactic Oxalic Formic Acetic
Carbon
b
−1
c
−1
d
Catalysts
(g)
(%)
acid
acid
acid
acid
ꢁ
ꢁ
balances (%)
Ni0ꢂ1/HAP
0.368
63.4
72.7
79.2
86.2
94.9
94.6
93.7
82.7
0.1
0.3
0.4
0.5
0.5
0.6
1.0
1.4
1.1
0.9
0.4
0.4
1.7
1.2
1.0
0.6
182ꢂ3
139ꢂ5
113ꢂ9
99ꢂ2
173ꢂ0
132ꢂ0
106ꢂ7
82ꢂ1
98.3
97.6
96.5
85.6
0.552
0.736
0.920
Ni0ꢂ2/HAP
Ni0ꢂ3/HAP
Ni0ꢂ4/HAP
0.368
76.8
84.2
92.1
96.3
95.9
95.8
94.7
83.6
0.1
0.2
0.4
0.5
0.6
1.0
1.8
1.9
1.3
1.0
0.5
0.4
1.5
1.4
1.0
0.8
116ꢂ6
85ꢂ2
69ꢂ9
58ꢂ5
111ꢂ9
81ꢂ6
66ꢂ2
48ꢂ9
99.4
99.4
98.4
87.2
0.552
0.736
0.920
0.368
80.6
88.0
94.0
98.8
94.5
93.9
92.3
81.2
0.2
0.4
0.6
0.7
1.0
1.4
2.0
2.1
1.3
1.1
0.6
0.5
1.8
1.4
1.2
1.0
85ꢂ9
62ꢂ5
50ꢂ1
42ꢂ1
81ꢂ1
58ꢂ7
46ꢂ2
34ꢂ2
98.8
98.2
96.7
85.5
0.552
0.736
0.920
0.368
87.0
91.8
96.0
99.5
93.6
91.6
89.8
80.2
0.2
0.4
0.8
0.9
1.3
1.7
2.2
2.3
1.6
1.2
0.8
0.7
2.1
1.8
1.5
1.3
73ꢂ0
51ꢂ3
40ꢂ3
33ꢂ4
68ꢂ3
47ꢂ0
36ꢂ2
26ꢂ8
98.8
96.7
95.1
85.4
0.552
0.736
0.920
a
−1
ꢀ
b
Notes: Reaction conditions: glycerol aqueous solution, 2.0 mol L , 100 mL; NaOH/glycerol mole ratio, 1.1:1; reaction temperature, 200 C; reaction time, 2.0 h. Glycerol
c
d
conversion activities normalized per metal atom. Lactic acid formation activities normalized per metal atom. Carbon balances were calculated according to both detected
products and reacted glycerol.
+H2
HO
Ni Ni Ni
Ni
Ni
OH
1,2-Propanediol
HAP
Keto-euol
Cannizzaro
Reaction
O
HO
O
Tautomerism
HO
OH
–H2
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O
O
n: W
O
ed, 13 Jun 2018 08
O
:52:09
OH
2
O
Ni Ni Ni
Copyright: American Scientific Publishers
O
H
OH
O
OH
Glycerol
OH
Ni
Ni
Lactate
Glyceraldehyde
Delivered by Ingenta
2
-Hydroxypropenal
Pyruvaldehyde
HAP
O
OH
O
O
O
OH
O
+
O
O
O
Oxalate
Acetate
Formate
Scheme 1. Reaction routes for catalytic conversion of high-concentrated glycerol to lactic acid over the Ni /HAP catalysts in a NaOH aqueous
x
solution.
In our present work, some intermediates, such as pyru-
valdehyde, glyceraldehyde, and 2-hydroxypropenal were
not detected under our present experimental conditions,
indicating that these intermediates could be rapidly con-
verted to subsequent chemicals and finally to lactate and
by-products.
selectivities of 82.6%–95.6% at the glycerol conversions
of 92.1%–97.7%. The Ni /HAP effectively catalyzed the
x
conversion of high-concentrated glycerol to lactic acid at
a relatively lower reaction temperature as compared to the
hydrothermal conversion of glycerol to lactic acid in a
NaOH aqueous solution.
4
. CONCLUSIONS
Acknowledgments: The
work
was
financially
0
The HAP-supported metallic Ni nanoparticles were pre-
pared by the wet chemical reduction method. The average
particle sizes of metallic Ni nanoparticles on the sur-
supported by the funds from National Natural Science
Foundation of China (21506078 and 21506082) and China
Postdoctoral Science Foundation (2016M601739).
0
faces of HAP ranged from 14 to 17 nm. For the catalytic
0
reaction, metallic Ni nanoparticles and NaOH synergis-
tically catalyzed glycerol conversion to lactic acid. The
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Received: 7 August 2017. Accepted: 6 September 2017.
J. Nanosci. Nanotechnol. 18, 4734–4745, 2018
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