Ha et al.
Synthesis of Glycidol by Decarboxylation of Glycerol Carbonate Over Zn–La Catalysts with Different Molar Ratio
surface was free from impurities such as nitrates. X-ray
Photoelectron Spectroscopy (XPS, Sigma Probe XPS Sys-
tem, Thermo Fisher Scientific, UK) measurements were
performed in an ultrahigh vacuum to measure elemental
Figure 1. Decarboxylation of glycerol carbonate to glycidol.
concentration on the sample surface (spot size: 400 ꢆm).
The monochromatic Al Kꢂ (1486.6 eV) source was oper-
ated at 25 W and 15 kV. The background pressure in the
decarboxylation of glycerol carbonate. The surface prop-
erties of catalysts were investigated and its effects on the
reaction was studied in terms of acid/base site density.
−8
analyzing chamber was 6ꢄ7 × 10 Pa. The energy posi-
tion of a peak maximum was calibrated using the binding
energy of C1s at 284.6 eV. The O , Zn and La3d spectra
1s
2p
were recorded with the analyzer in a constant pass-energy
mode.
2
2
. EXPERIMENTAL DETAILS
.1. Catalyst Preparation
The catalysts were prepared by
method. First, Zn(NO ꢁ ·6H O (98%, Sigma-Aldrich) and
a
coprecipitation
2
.3. Catalytic Activity
3
2
2
A 500 mL four-necked flask equipped with a condenser
and a heating mantle was charged with a solvent and the
La(NO ꢁ ·6H O (99.9%, Sigma-Aldrich) individually dis-
3
3
2
solved in 250 mL distilled water. Next, a solution of
ꢀ
flask were gradually heated to 180 C under a pressure
NaNO (99%, DAEJUNG) and NaOH (97%, DAEJUNG)
3
of 0.05 MPa. 10 wt% of the prepared catalyst was used
as the weight ratio compared with the reactant. In order
to avoid occurrence of undesirable reactions such as reac-
tion between molecules of chemically unstable glycidol,
glycerol carbonate (Zeus oil and Chemicals Co., >95%) is
added dropwise to the flask. The obtaining glycidol is dis-
in distilled water as the precipitating agent was added to
the solution at a constant rate of 2 mL/min to prepare ZnO,
La O . The same procedure was used for the mixed oxide
catalysts with different Zn/La molar ratios by varying the
relative concentrations of the Zn and La salts. The pH of
the solution was maintained at 11 during synthesis by the
addition of precipitation agent to ensure complete precip-
itation of both Zn and La ions. The resulting mixture was
2
3
ꢀ
tilled out and collected in a receiver maintained −40 C.
The carbon dioxide gas, which was produced during the
reaction, was removed through a vacuum line connected to
a reaction system. After completion of the dropping, the
ꢀ
aged at 60 C for 18 h, then white precipitate was filtered
and washed several times with dist Di l lee ldi v ew r ae t de rb yu nI tni lg ep nH ta to: Universiteit Utrecht
IP: 5.101.221.62 On
ꢀ
resulting reaction mixture was proceeded further and aged
: Sat, 05 Nov 2016 14:55:16
of 6–7. Finally, the material was dried overnight at 105 C,
ꢀ
Copyright: American S fc oi er n2 ti hf i .c RP eu a bc lt i iso hn e pr sr oducts in the flask and receiver were
followed by calcination at 450 C for 6 h. The resulting
materials were denoted as ZnO, Zn5La5, Zn3La7, Zn1La9,
La O .
analyzed in a Gas Chromatography (GC, 7890A, Agilent,
USA) equipped with a HP-INNOWAX capillary column
2
3
(
30 m × 320 mm × 25 um) and a flame-ionization detec-
tor (FID).
2
.2. Catalyst Characterization
Powder X-ray diffraction (XRD, X’Pert-MPD, PHILIPS,
Netherland) patterns were obtained with a Cu Kꢂ radi-
ation (ꢃ = 1ꢄ5406 Å). Diffractograms were recorded
3. RESULTS AND DISCUSSION
3.1. Catalyst Characterization
The XRD patterns of Zn–La metal oxides are given
in Figure 2. The diffraction peak of ZnO corresponds
with hexagonal wurtzite structure. The diffraction pat-
tern observed for lanthanum oxide corresponds with
the powder diffraction data reported for La O (JCPDS
ꢀ
in the 2ꢅ range of 10–90 with a scanning rate of
ꢀ
0
.02 /min. The morphologies of catalysts were exam-
ined by Field Emission-Scanning Electron Microscopy
FE-SEM, SU-820, Hitachi, Japan). Samples were placed
(
over an aluminum drum and coated with a platinum
film using a Ion Sputter Coater (E-1045, Hitachi,
2
3
1
2
83-1344) and La(OH)3 (JCPDS 36-1481). Zn5La5,
Zn3La7, Zn1La9 exhibit a mixture of ZnO, La O and
Japan). N adsorption–desorption isotherm was obtained at
2
2
3
ꢀ
−
196 C using an gas adsorption analyzer (ASAP 2020,
La(OH) phases with higher intensity of the La O peaks
3
2
3
Micromeritics, USA) and specific surface area of catalysts
were calculated with the BET equation. Prior to measure-
with increase La molar ratio. Various polar crystal planes
of ZnO, such as ZnO (1 0 2), (1 0 3) and (1 1 2), could be
observed. That planes where concentration of zinc atoms is
ꢀ
ments, the sample was degassed in vacuum at 150 C
1
3
for 6 h to remove surface impurities and moisture. The
acidity and basicity of prepared catalysts were studied
by NH /CO Temperature Programmed Desorption (TPD,
higher, adsorption of carbonyl groups are favored. There-
fore, these polar surfaces can be attributed as the active
centers for ring-opening reactions of glycerol carbonate.
Figure 3 shows the corresponding scanning electron
micrographs for prepared catalysts. The single metal oxide,
ZnO and La O are in the form of flake with their
3
2
AutochemII2920, Micromeritics, USA). The samples used
for TPD were pretreated with 5% H /He at a flow rate of
2
ꢀ
2
0 mL/min and a temperature was then raised to 800 C
2
3
and maintained for 60 min under an argon flow rate of
0 mL/min. This pretreatment ensured that the metal oxide
size about 0.3 um. In the case of mixed oxide form
show composition of ZnO and La O forming chainlike
2
2
3
J. Nanosci. Nanotechnol. 16, 10898–10902, 2016
10899