Highly selective hydrogenation of α-pinene catalyzed by Ru
nanoparticles in aqueous micellar microreactors
Shengli Hou a, Xiaoyan Wang a, Changru Huang a, Congxia Xie a,*, Shitao Yu b
a
College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042,
Shandong, China
b
College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, Shandong, China
*Corresponding author. Tel/Fax: +86-532-84022719; E-mail: xiecongxia@126.com
S1. Experimental………………………………………………………………………2
S1.1 Materials……………………………………………………………………2
S1.2 Measurements………………………………………………………………2
S2. Results and discussion……………………………………………………………3
S2.1 Details of UV-Vis absorption spectra………………………………………3
S2.2 XPS spectra of Ru nanoparticles……………………………………………4
S2.3 XRD spectra of Ru nanoparticles…………………………………………4
S2.4 The influence of various reaction media……………………………………5
S2.5 The influence of various volumes water……………………………………5
S2.6 The influence of various metal precursors…………………………………6
S2.7 The influence of various surfactants………………………………………7
S2.8 Optimal conditions of α-pinene hydrogenation……………………………7
S2.9 Reproducibility of the reaction……………………………………………8
S2.10 Ru leaching in the process of recycling experiment………………………9
S2.11 The influence of n-heptane on α-pinene hydrogenation…………………9
S2.12 Images of vesicles during the hydrogenation of α-pinene………………10
S2.13 F127 micelles tested by DLS……………………………………………10
S2.14 Preliminary kinetics………………………………………………………11
S3. References………………………………………………………………………12
S1 Experimental
S1.1 Materials
α-Pinene (purity: 98%) was supplied by Jiangxi Hessence (China) Chemicals Co.
Ltd. RuCl3 (Ru content: 38%-42%) was supplied by Shanghai (China) Macklin
Biochemical Co. Ltd. PdCl2, RhCl3 and PtCl4 were supplied by CIVI-Chem (China)
Industrial Corporation. n-Heptane (purity: AR) was purchased from Sinopharm
(China) Chemical Reagent Co. Ltd. F127 was purchased from Shanghai (China)
Macklin Biochemical Co. Ltd. H2 (purity≥99.9%) was supplied by Qingdao (China)
Heli Co. Ltd. Sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium
chloride (CTAC) were purchased from Shanghai (China) Macklin Biochemical Co.
Ltd. Polyvinylpyrrolidone (PVP, Mw: 10000) and octoxinol were purchased from
Tokyo (Japan) Chemical Industry Co. Ltd. Water was double distilled and deionized
before use. Other reagents were of analytical grade purity.
S1.2 Measurements
The time of catalyst preparation was determined according to ultraviolet-visible
absorption spectra (UV-Vis, Varian Cary 500). 1 mL of the micellar solution was
diluted to 20 mL with distilled water before measurement.
The particle sizes and shapes of the Ru nanoparticles were measured by
transmission electron microscopy (TEM, Hitachi-7650). The specimens were
prepared by placing a drop of the catalyst on a copper grid and then evaporating the
solvent. The particle diameters were measured from the enlarged TEM photographs.
A particle size distribution histogram was obtained on the basis of the measurements
of about 400 particles.
The valence of Ru nanoparticles was tested by X-ray photoelectron spectroscopy
(XPS, Kratos Axis Ultra DLD). A mono Al Kα (hv=1486.6 eV) X-ray source was
used at a power of 150 W (15 kV). Binding energies were calibrated by using the C 1s
hydrocarbon peak at 284.60 eV. The samples were prepared by drying the Ru
nanoparticles in vacuum.
The amount of Ru leaching during the reaction was measured by inductively
coupled plasma-atomic emission spectrometry (ICP-AES, Prodigy XP, Leeman). A
certain amount of sample was dissolved in 5 mL aqua regia. The mixture was then
transferred to a 10 mL volumetric flask, diluted to 10 mL, and tested by ICP analysis.
The mean diameter of the P123 micelles containing Ru nanoparticles was
determined by dynamic light scattering (DLS, Nano ZS90, Malvern). The analysis of
the recorded correlation functions was conducted by using the cumulant method.
The vesicles photographs were captured by using a confocal laser scanning
microscope (CLSM, TCS-SP5-II, Leica).
The structure of the obtained Ru nanoparticls was determined by X-ray
diffraction (XRD, Enraf Noius CAD4).
The conversion and selectivity were measured in a gas chromatography (GC,
GC9790, Fuli) equipped with a flame ionization detector (FID) detector and an OV
1701 (50 m, 0.25 mm i.d.) column. The column temperature was 110 °C, and the
sample injector and detector temperature was 200 °C.
S2 Results and discussion
S2.1 Details of UV-Vis absorption spectra: In the procedure of Ru nanoparticles
preparation, in order to determine the reaction time which Ru3+ was reduced
completely to Ru0, the absorption spectra of Ru3+ was measured by UV-Vis. As
shown in Fig. S1, before heating, the absorption peaks at 300 nm and 510 nm
represented Ru3+ species [1]. With the reaction proceeding, the peaks decreased
slowly and gradually shifted to a short wavelength. After about 1 h, the absorption
peak at 300 nm and 510 nm completely disappeared, which indicated that Ru3+ was
completely reduced to Ru0. After about 2 h, the absorption spectra were almost
unchanged, which confirmed the formation of Ru nanoparticles [2].
1.00
0.75
Abs (a.u.)
F127
0 min
20 min
40 min
60 min
80 min
100 min
120 min
a
b
c
d
e
f
g
h
0.50
hg
0.25
f
e
d
c
b
a
0.00
200
600
500
400
300
Wavelength (nm)
Fig S1: Details of UV-Vis absorption spectra
Reaction conditions: RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate: 500 r/min; 40 °C; 0.2
MPa H2.
S2.2 XPS spectra of Ru nanoparticles: To confirm the formation of Ru nanoparticls,
XPS was employed to measure the valence state of the obtained Ru nanoparticls, and
the results were shown in Fig S2. The binding energies of Ru 3p1/2, Ru 3p3/2, and 3d5/2
in the micelles were found to be 484.6 eV, 461.8 eV and 280.2 eV, respectively, which
is concordant with the respective values for bulk Ru metals at 484.1 eV, 462.0 eV and
280.2 eV [3]. These results demonstrated that Ru3+ was reduced to zero-valence
metallic Ru.
Ru 3p
C 1s
Ru 3d5/2
Intensity (a.u.)
Intensity (a.u.)
C 1s
295
290
Ru 3p3/2
Ru 3p5/2
285
280
Binding Energy (eV)
275
500
490
480
470
460
450
Binding Energy (eV)
Fig S2. XPS spectra of Ru nanoparticles
S2.3 XRD spectra of Ru nanoparticles: XRD was employed to determine the
structure of the obtained Ru nanoparticls, and the results were shown in Fig S3. As
can be seen from the Fig S3, three obvious absorption peaks were found at 38.3°, 44.0°
and 58.4°, which was corresponding to the crystal {100}, {101}, {102} faces,
respectively. The diffraction peak position was consistent with the standard card
(JCPDS NO. 6-0663), which illustrated the Ru nanoparticles were formed as the
hexagonal-close-packed (hcp) structure.
(101)
(100)
(102)
30
40
50
60
70
80
2θ (degree)
Fig S3. XRD spectra of Ru nanoparticles
S2.4 The influence of various reaction media: A series of Ru nanoparticles
protected by F127 was prepared with various reaction media, and the TEM images
were shown in Fig S4. Just one day time, Ru nanoparticles had gathered into clumps
when the reaction medium was organic solvents.
Fig S4. TEM images of Ru nanoparticles in various reaction media
A: ethanol, B: methanol, C: ethyl acetate
S2.5 The influence of various volumes water: In the procedure of Ru nanoparticles
preparation, the amount of water influenced on the catalytic activity and selectivity of
Ru nanoparticles was studied, and the data were plotted in Table S1. When the amount
of water increased from 1 mL to 2 mL, the conversion of α-pinene rose from 81.3% to
91.3%. The conversions decreased with further increases in the amount of water. The
selectivity for cis-pinane was almost unchanged when the water amount increased
from 1 mL to 3 mL. We hence selected 2 mL water for subsequent experiments.
Table S1. The influence of various volumes of water on α-pinene hydrogenation
Volume of water
(mL)
Conversion (%)
1
1.5
2
2.5
3
81.3
88.9
91.3
90.2
87.1
Selectivity (%)
Cis-pinane
Trans-pinane
98.8
98.9
99.1
98.9
99.0
1.2
1.1
0.9
1.1
1.0
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; F127: 20 mg; reaction medium: water;
stirring rate: 500 r/min; 40 °C; 0.3 MPa H2; 2.0 h.
S2.6 The influence of various metal precursors: A series of Ru nanoparticles
protected by F127 was prepared with various metal precursors, and the TEM images
were shown in Fig S5.
Fig S5. TEM images of Ru nanoparticles in various metal precursors
A: RuCl3, B: PtCl4, C: PdCl2, D: RhCl3
S2.7 The influence of various surfactants: The activity and selectivity depended
strongly on the property of the surfactants in a given chemical reaction [4]. We
examined the influence of various surfactants on α-pinene hydrogenation, and the
results were shown in Table S2. The conversion of α-pinene was low without
surfactant (Table S2, Entry 1), because some of nanoparticles gathered into clumps,
which decreased the numbers of active sites of the catalyst and reduced the catalytic
activity. The conversion and selectivity in an amphiphilic triblock copolymer (entry 6)
was better than that in an amphiphilic ionic surfactant (entries 2, 3), hydrophilic
polymers (entry 4) and amphiphilic copolymer (entry 5). We hence selected F127 as
the stabilizer for subsequent experiments.
Table S2. Hydrogenation of α-pinene under various surfactants
Entry
Surfactant
Conversion (%)
1
2
3
4
5
6
SDS
CTAC
PVP
Octoxinol
F127
19.3
82.5
80.1
76.8
89.1
91.3
Selectivity (%)
Cis-pinane
Trans-pinane
92.3
93.5
94.6
98.0
98.7
99.1
7.7
6.5
5.4
2.0
1.3
0.9
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; surfactant: 20 mg; water: 2 mL; stirring
rate: 500 r/min; 40 °C; 0.3 MPa H2; 2.0 h.
S2.8 Optimal conditions of α-pinene hydrogenation: To further study the influence
of the catalyst on the hydrogenation of α-pinene, several parameters such as
temperature, H2 pressure, reaction time, and stirring rate were studied, and the results
were shown in Fig S6. The conversion of α-pinene increased with increasing
temperature. When the temperature was higher than 40 °C, the influence of
temperature on the conversion was not obvious. Furthermore, low temperature
favored the production of cis-pinane from α-pinene [5,6]. Thus, we selected the
temperature of 40 °C for subsequent experiments. The conversion and selectivity
increased with increasing H2 pressure. When the H2 pressure was higher than 0.3 MPa,
the influence of H2 pressure on the conversion was not obvious. Furthermore, the
influence of stirring rate on α-pinene hydrogenation was also studied. The conversion
of α-pinene markedly increased with increasing stirring rate, and the experiment
showed that 500 r/min was the best stirring rate. The amount of catalysts were also
studied, the results showed the best amount of RuCl3 was 2.1 mg. Under these
conditions, the conversion of α-pinene was 99.9% after 3 h, and the selectivity of
cis-pinane was 99.0%. Further increased of reaction time was not necessary.
Considering the analysis results of these five factors, the optimum conditions were
determined to be: 40 °C, 0.3 MPa H2, stirring rate 500 r/min, 0.21 mg RuCl3, 3.0 h.
100
100
80
80
80
80
60
40
40
20
20
25
30
35
40
45
conversion
selectivity
60
40
40
20
20
50
0.0
0.2
0.4
Temperature (C)
0.6
0.8
Pressure (MPa)
100
80
80
40
40
20
100
80
80
conversion
selectivity
60
60
40
40
Selectivity (%)
60
conversion
selectivity
Selectivity (%)
60
100
Conversion (%)
100
Conversion (%)
60
Selectivity (%)
60
Selectivity (%)
conversion
selectivity
Conversion (%)
100
Conversion (%)
100
20
20
100
200
300
400
500
20
0.5
600
1.5
2.0
2.5
100
100
80
80
conversion
selectivity
60
60
40
Selectivity (%)
Conversion (%)
1.0
Amount of catalysts (mg)
Stirring rate (r/min)
40
20
20
0.5
1.0
1.5
2.0
2.5
3.0
Time (h)
Fig S6. Optimal conditions of α-pinene hydrogenation
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 0.5-2.5 mg; F127: 20 mg; water: 2 mL; stirring
rate: 100-600 r/min; 25-50 °C; 0.1-0.8 MPa H2; 0.5-3.0 h.
S2.9 Reproducibility of the reaction: The curves of the reaction were separately
determined three times under same conditions, and the results were shown in Fig S7.
At all the reaction times, the selectivity to cis-pinane was better than 98.5% in all of
the repeated experiments up to complete conversion of pinene. The maximum
deviation of the conversion was ±4%, which was satisfactory.
Conversion & selectivity (%)
100
80
60
40
20
0
0.5
1.0
1.5
2.0
2.5
3.0
Time (h)
Fig S7. Three kinetic curves of the reaction under same conditions determined separately.
Open symbols: conversion; Solid symbols: selectivity.
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate:
500 r/min; 40 °C; 0.3 MPa H2.
S2.10 Ru leaching in the process of recycling experiment: In the process of
catalytic recycling experiment, the amount of Ru leaching into organic phase was
measured using ICP-AES. A certain amount of sample was dissolved in 5 mL aqua
regia. The mixture was then transferred to a 10 mL volumetric flask, diluted to 10 mL,
and tested by ICP-AES analysis.
Table S3. Ru leaching tested by ICP analysis
Sample
Sample amount (g)
Percentage of Ru leaching (%) b
after 1 cycle a
after 1 cycle
after 6 cycles
after 10 cycles
1.14
1.14
1.14
1.14
0.77
0.13
0.51
1.21
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate:
500 r/min; 40 °C; 0.3 MPa H2; 3h.
a: Without F127; b: Ratio of the leaching of Ru and the concentration of Ru in fresh catalyst.
S2.11 The influence of n-heptane on α-pinene hydrogenation: A set of experiments
was designed to explore whether the residual n-heptane had an influence on the
activity of catalyst. The aforementioned prepared catalyst with an additional 0.5-2.0
mL n-heptane was used to catalyze the hydrogenation of α-pinene under the same
experimental conditions.
Table S4. The influence of n-heptane on α-pinene hydrogenation
Entry
Volume of n-heptane
(mL)
Conversion (%)
1
2
3
4
5
0
0.5
1.0
1.5
2.0
99.9
88.7
82.5
78.1
72.3
Selectivity (%)
Cis-pinane
Cis-pinane
99.0
98.5
98.4
98.1
98.0
1.0
1.5
1.6
1.9
2.0
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate:
500 r/min; 40 °C; 0.3 MPa H2; 3h.
S2.12 Images of vesicles during the hydrogenation of α-pinene: To confirm the
status of the aqueous-organic phases in the hydrogenation of α-pinene, the
micro-circumstance was observed by CLSM. As clearly shown in Fig S8, the vesicles
were formed in the reaction system when the hydrogenation of α-pinene occurred.
This structure significantly increased the biphasic interface area, and the energy
barrier of phase transfer was effectively minimized.
Fig S8. Images of vesicles during the hydrogenation of α-pinene
S2.13 F127 micelles tested by DLS: In the procedure of catalyst preparation, F127
was added into the water. When the concentration reached its CMC, F127 micelles
were formed in the reaction system. Ru3+ was added into the mixture and reduced to
Ru0, and the size of F127 micelles might be changed. DLS was employed to
determine the sizes of the obtained F127 micelles. As shown in Table S5, the average
size of F127 micelles (24.8 nm) was almost unchanged after Ru3+ was added into the
mixture (25.0 nm). When the Ru nanoparticles were formed, Ru nanoparticles were
embedded in the core of the F127 micelles, and F127 micelles were enlarged (29.8
nm).
Table S5. F127 micelles tested by DLS
F127 micelles a
F127-Ru3+
micelles a
F127-Ru0
micelles a
Ru nanoparticles b
24.8
25.0
29.8
2.8±0.5
Average diameter
(nm)
Reaction conditions: RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate: 500 r/min; 40 °C; 0.2
MPa H2; 2h.
a: Measured using DLS; b: Measured using TEM.
S2.14 Preliminary kinetics: The kinetic curves of α-pinene hydrogenation at some
typical conditions are presented in Figure S9. As expected, the conversion increases
with the reaction time and temperature up to complete conversion. The ln(c0/c) vs.
reaction time curves in the figures up to complete conversion are also given. c0 and c
are the concentrations of α-pinene before the reaction and at a certain reaction time,
respectively. The straight line indicates that the reaction follows standard
pseudo-first-order kinetics for α-pinene at the experimental conditions, which is the
same as those reported by many other authors [7,8].
2.5
100
2.0
80
1.5
ln (c0/c)
60
%
conversion
selectivity
40
1.0
0.5
20
0.0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
Time (h)
0.5
1.0
1.5
Time (h)
(a) 35 °C, 0.3 MPa H2
2.0
2.5
3.0
3.5
100
3.0
80
2.5
2.0
ln (c0/c)
60
%
conversion
selectivity
40
1.5
1.0
0.5
20
0.0
0
0.0
0.5
1.0
1.5
2.0
2.5
-0.5
3.0
0.0
0.5
1.0
Time (h)
1.5
2.0
2.5
Time (h)
(b) 40 °C, 0.3 MPa H2
100
3.0
2.5
80
2.0
ln (c0/c)
%
60
conversion
selectivity
40
1.5
1.0
0.5
20
0.0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
Time (h)
1.5
2.0
Time (h)
(c) 45 °C, 0.3 MPa H2
100
2.0
80
1.5
ln (c0/c)
60
%
conversion
selectivity
40
1.0
0.5
20
0.0
0
0.0
0.5
1.0
1.5
2.0
2.5
0.0
0.5
Time (h)
1.0
1.5
Time (h)
(d) 40 °C, 0.6 MPa H2
Fig S9. The kinetic curves of α-pinene hydrogenation under some typical conditions
Reaction conditions: α-pinene: 0.2730 g; RuCl3: 2.1 mg; F127: 20 mg; water: 2 mL; stirring rate:
500 r/min.
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