Copyright WILEY‐VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2014. Supporting Information for Small, DOI: 10.1002/smll.201302854
Reductive Deprotection of Monolayer Protected Nanoclusters:
An Efficient Route to Supported Ultrasmall Au Nanocatalysts
for Selective Oxidation
Sayantani Das, Anandarup Goswami, Mahdi Hesari, Jafar F.
Al-Sharab, Eliška Mikmeková, Flavio Maran,* and Tewodros
Asefa*
Submitted to
Supporting Information for
Reductive Deprotection of Monolayer Protected Nanoclusters: An Efficient
Route to Supported Ultrasmall Au Nanocatalysts for Selective Oxidation
Table of Contents:
1. Materials and Reagents
2. Instrumentation
3. Synthesis of Mesoporous Silica, SBA-15
4. Synthesis of Mercaptopropyl-Functionalized Mesoporous Silica
5. Synthesis of Au25(SCH2CH2Ph)18
6. Synthesis of Au144(SCH2CH2Ph)60
7. Ligand Exchange in the monolayer of Au25(SCH2CH2Ph)18 with MercaptopropylFunctionalized Mesoporous Silica
8. Synthesis of Ext-SBA-15-Au25-1
9. Synthesis of Ext-SBA-15-Au25-5
10. Ligand Exchange in the Monolayer of Au144(SCH2CH2Ph)60 with MercaptopropylFunctionalized Mesoporous Silica
11. Synthesis of Ext-SBA-15-Au144-1
12. Synthesis of Ext-SBA-15-Au144-5
13. Catalytic Styrene Oxidation
14. Results for Control Catalytic Tests of Styrene Oxidation
15. Recyclability Studies
16. Synthesis of Ext-SBA-15-Aun-OH
17. Figures and Tables
18. References
1. Materials and Reagents. Poly(ethylene glycol)-block-poly(propylene glycol)-blockpoly(ethylene glycol) triblock copolymer (Pluronic®P 123, average molecular mass ~5800)
was obtained from BASF. Tetraethyl orthosilicate (TEOS), dichloromethane (DCM), toluene,
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2-phenylethanethiol, hydrogen tetrachloroaurate(III) trihydrate, sodium borohydride (NaBH4),
and tetrahydrofuran (THF) were purchased from Sigma-Aldrich. Hydrochloric acid (36.5%)
was received from Fischer Scientific. 3-Mercaptopropyltrimethoxysilane (MPTS) was
obtained
from
Gelest,
Inc.
Toluene
(99.8%),
methanol
(HPLC
grade,
99.8%),
dichloromethane (DCM) (99.8%), and chloroform (99.8%) were purchased from VWR.
Ethanol (99.8%) was received from Fluka. Tetra-n-butylammonium hexafluorophosphate
(TBAH, 99%, Fluka) was recrystallized from ethanol. Low conductivity water used was
milliQ Water pro analysis (Merck) or AnalaR Normapur (NDH).
2. Instrumentation. Analytical thin layer chromatography was performed on EM Reagent,
0.25 mm silica gel 60 F254 plates obtained from VWR. Visualization was accomplished with
UV light as well as with KMnO4 stain. Mass spectra were obtained on a Finnigan LCQ-DUO
mass spectrometer. The powder X-ray diffraction of the material was measured by a Histar
diffractometer at 295 K using monochromatized Cu Kα (λ = 1.54 Å) radiation. Transmission
electron microscope (TEM) images were obtained with a Topcon 002B TEM microscope
operating at 200 KeV. X-ray photoelectron spectroscopy (XPS) was performed using a
Thermo K-Alpha XPS system (Thermo Scientific, USA) equipped with an Al Kα radiation as
a source, with an energy resolution of 1 eV for the survey scans and 0.1 eV for high resolution
scans of the individual peaks. The X-ray gun produced a 400 μm spot size, and an electron
flood gun was used to minimize charging. The spectrometer was calibrated based on the
binding energy of Ag 3d5/2 peak (368.02 eV) at a given pass energy (PE = 50) and the
residual binding energies were corrected by assigning to the C1s peak associated with the
methylene groups a value of 285.0 eV. The system’s vacuum level was below 10-9 Torr
during the data collection. Raman spectroscopy was performed on a Renishaw inVia Raman
microscope with a 532 nm He–Ne laser. Typically, a laser power of 2.0 mW and an exposure
time was 10 s were used at the sample position. For the differential pulse voltammetry
experiments, we used a CHI 660c electrochemical workstation, by following the same
experimental conditions already described in detail previously.[S1] The experiments were
carried out using a glassy carbon microdiskelectrode (area = 9.64 x 10-3 cm2) in DCM/0.1 M
TBAH solution under an Ar atmosphere at 25 °C. Using these methods, the materials or
catalysts synthesized were characterized. The characterization results and data are included in
Figures 1, 2 and S1-S6 and Table S1 and S2. The STEM images were obtained by using a
high resolution scanning transmission electron microscope (STEM, Magellan 400, FEI). The
instrument is equipped with segments of STEM detector that enable transmitted electron2
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based imaging in bright field (BF), dark field (DF) and high angle annular dark field
(HAADF) modes. Each mode provides a different view of the specimen: the BF detector
collects electrons transmitted trough the sample, DF detector detects electrons diffracted in
crystalline areas and incoherent Rutherford scattering electrons, and the HAADF detector
collects impacted electrons scattered to high angles, where the scattering is roughly
proportional to the square of the atomic number (Z) and the images contrast increases with
decreasing electron energy. For imaging of the materials in STEM, we used a maximum
accelerating voltage 30 keV, a beam current 50 pA and the work distance was kept on 4.5 mm
which enabled us to get a high material contrast.
The catalytic reaction mixtures were analyzed by GC (HP 6850) equipped with FID
detector and an HP-1, 30 m long x 0.25 mm ID column. The 1H NMR spectra were obtained
in CDCl3 using a Brüker model Avance DRX-400 MHz spectrometer, and the UV-Vis spectra
were recorded with a Thermo Scientific Evolution 60S spectrophotometer using cuvettes with
an optical path length of 1 cm. The results are depicted in Figures 3 and S8 and Table S3.
3. Synthesis of SBA-15 Mesoporous Silica (Ext-SBA-15). Surfactant-extracted mesoporous
SBA-15 (Ext-SBA-15) was synthesized as reported previously[S2] by using Pluronic® P 123
as a templating agent in acidic solution. Typically a solution of Pluronic® P 123 : HCl :
TEOS : H2O = 2 : 12 : 4.3 : 52 (mass ratio in g) was stirred at 40 °C for 24 h and then aged at
65 °C for another 24 h. The resulting solution was filtered, and the solid was washed with
copious amounts of water producing a material labeled as “as-synthesized SBA-15”. The assynthesized SBA-15 (4 g) was then dispersed in ethanol (400 mL) and diethyl ether (400 mL)
and stirred at 50 °C for 5 h to remove the organic templates from it. The solid material was
separated by filtration and was dried in oven at 40 C for 2 h. This produced a surfactantextracted mesoporous silica material, labeled as “Ext-SBA-15”.
4. Synthesis of Mercaptopropyl-Functionalized SBA-15 Mesoporous Silica (Ext-SBA-15SH). 500 mg of the dried Ext-SBA-15 sample was stirred with excess MPTS (0.64 mL, 3.68
mmol) in toluene at 80 °C for 6 h. The solution was filtered, and the residue was quickly
washed with toluene (3 x 20 mL) and then with ethanol (3 x 20 mL) and air-dried. The
resulting dried sample was denoted as “Ext-SBA-15-SH”.
5. Synthesis of Au25(SCH2CH2Ph)18. Au25(SCH2CH2Ph)18 MPCs (monolayer protected
clusters or nanoparticles) containing 25 Au atoms in the clusters were synthesized according
3
to an established procedure.
[S3]
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Briefly, to a solution of HAuCl4.3H2O (2.6 mmol) in 100 mL
of THF, 15.6 mmol 2-phenylethanethiol (6 equiv.) was added dropwise under slow stirring at
room temperature. The mixture was stirred for 45 min until the color of solution changed
from yellow to milky white, indicative of reduction of Au(III) ions to Au(I) species. NaBH 4
(26.0 mmol), dissolved in 20 mL of icy water, was then added under vigorous stirring to the
mixture. A black color, indicative of the formation of AuNPs, immediately produced in the
solution while a gas, presumably H2, was evolved. After one week, the reaction mixture was
filtered on filtration membrane, and the THF in the reaction mixture was removed using a
rotary evaporator. The excess 2-phenylethanethiol was removed from the crude product by
washing the materials several times with mixtures of 70/30, and then 80/20, methanol–water
solutions. The powdered material was collected on a Gooch G4 filter and washed with ethanol.
The resulting powdered materials was further collected off the frit by dissolution in DCM and
then the solution was rotary evaporated to yield the Au25(SCH2CH2Ph)18 MPCs, which are
denoted here as Au25. The typical yield of the purified product was ca. 20%.
6. Synthesis of Au144(SCH2CH2Ph)60. For the synthesis of Au144(SCH2CH2Ph)60 MPCs
(which were denoted here as Au144), we used the Brust-Schifrin two-phase synthetic
approach[S4] as implemented by Donkers et al.[S5] In a 500 mL three-neck round-bottom flask,
1.55 g (3.94 mmol) HAuCl4.3H2O was dissolved in 50 mL water. While stirring, 100 mL
toluene and 2.56 g (4.68 mmol) of tetra-n-octylammonium bromide were added to the
solution. After 30 min of vigorous stirring of the biphasic mixture, the clear aqueous phase
was removed and the remaining dark-red organic solution was cooled to 0 °C using an icebath. 2-Phenylethanethiol (2.6 mL, 19.4 mmol) was then added to the solution, under slow
stirring. The solution turned to light yellow, and after 1.5 h, to opaque white. To the solution,
1.89 g NaBH4 (50.0 mmol), dissolved in 30 mL of ice-cold water, was added under vigorous
stirring, resulting in a black solution. The reaction mixture was warmed to room temperature
and stirred for another 24 h. The crude sample was transferred to a separatory funnel and
washed thrice with 50 mL water. Toluene was then evaporated under reduced-pressure
yielding a black product. Excess thiol was removed by adding methanol (200 mL) to the
crude product. After 4 h, the supernatant was discarded and the solid dispersed in 200 mL
methanol and left in a fridge overnight. This step was repeated thrice. Smaller nanoparticles,
namely Au25, which exist as byproduct, were removed from the solid by washing it with
acetonitrile (10 x 10 mL). A crystalline black powdered material consisting of pure
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Au144(SCH2CH2Ph)60
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was then finally obtained, whose purity was checked by
electrochemistry and UV-Vis and 1H NMR spectroscopy.
7. Ligand Exchange in the Monolayer of Au 25(SCH2CH2Ph)18 with MercaptopropylFunctionalized SBA-15 Mesoporous Silica. A dried Ext-SBA-15-SH sample (300 mg) was
dispersed in 30 mL of a 2 M Au25(SCH2CH2Ph)18 solution in DCM and stirred at room
temperature for 3 h. The solution was centrifuged, and the residue was washed with DCM (3
x 10 mL). The resulting pale beige colored solid sample (Figure S1A) was air-dried. The final
material obtained was labeled as “Ext-SBA-15-SH-Au25”. The successful encapsulation of the
AuNPs in the pores of the SBA-15 by ligand-place exchange was evidenced by the typical
smell of phenylethanethiol, along with loss of the Au MPCs’ color in the solution and
subsequent change of the color of the Ext-SBA-15-SH samples from white into purple and red.
8. Synthesis of Ext-SBA-15-Au25-1. 250 mg of Ext-SBA-15-Au25 was dispersed in 25 mL
distilled water. Then, 1 mM NaBH4 solution (10 mL) was added into the solution. After 30
min of stirring, the solid solution was centrifuged, and the precipitate was washed with
distilled water (3 x 10 mL). The resulting pale beige colored solid was air-dried and denoted
as “Ext-SBA-15-SH-Au25-1”.
9. Synthesis of Ext-SBA-15-Au25-5. 250 mg of Ext-SBA-15- Au25 was dispersed in 25 mL
distilled water. To this solution, 5 mM NaBH4 solution (10 mL) was added. After stirring at
room temperature for 30 min, the solution was centrifuged, and the precipitate was washed
with distilled water (3 x 10 mL). The resulting pale beige colored solid material was air-dried.
The material finally obtained was labeled as “Ext-SBA-15-SH-Au25-5”.
10. Ligand Exchange in the Monolayer of Au 144(SCH2CH2Ph)60 with MercaptopropylFunctionalized Mesoporous Silica. A dried Ext-SBA-15-SH sample (200 mg) was dispersed
in 5 mL of 2 M Au144 solution in DCM and stirred at room temperature for 3 h. The solution
was centrifuged and the residue was washed with DCM (3 x 10 mL). The resulting pale
purple colored solid (Figure S1B) was air-dried. The resulting sample was labeled as “ExtSBA-15-SH-Au144”, and its TEM image is shown in Figure S2.
11. Synthesis of Ext-SBA-15-Au144-1. 250 mg of “Ext-SBA-15-Au144” was dispersed in 25
mL distilled water. Then, 1 mM NaBH4 solution (10 mL) was added into the mixture. After
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stirring at room temperature for 30 min, the solution was centrifuged and the precipitate was
washed with distilled water (3 x 10 mL). The resulting pale purple colored solid was air-dried
and labeled as “Ext-SBA-15-SH-Au144-1”.
12. Synthesis of Ext-SBA-15-Au144-5. 250 mg of Ext-SBA-15-Au144 was dispersed in 25 mL
distilled water. Then, 5 mM NaBH4 solution (10 mL) was added, and the solution was stirred
at room temperature for 30 min. The solution was centrifuged and the residue was washed
with distilled water (3 x 10 mL). The resulting pale purple colored solid was air-dried. This
sample was denoted as “Ext-SBA-15-SH-Au144-5”, and its TEM image is shown in Figure S2.
13. Catalytic Styrene Oxidation. In a typical styrene oxidation reaction, the catalyst (25 mg)
was added to a solution of styrene (0.1 mmol), TBHP (5.5 M in decane, 76 L), and
anhydrous toluene (1 mL) in a round-bottom flask. Toluene was used as the solvent for the
reaction in this case. The solution was stirred at 80 °C in nitrogen atmosphere. The progress
of the reaction was monitored with TLC using 1:4 ratio of ethyl acetate / hexane solution as
eluent, and also with gas chromatography-mass spectrometry (GC-MS). The percentage
conversion of the reactants and the yields of the products were calculated based on the
respective areas of the compound peaks as obtained by gas chromatography (GC).
14. Results for Control Catalytic Tests of Styrene Oxidation. First, a blank reaction
without any material / catalyst was run in anhydrous toluene with TBHP as oxidant. The
reaction showed 42% conversion of styrene in 24 h, with the reaction product consisting of
86% benzaldehyde and 14% styrene oxide. A control experiment of styrene oxidation was
then studied using Ext-SBA-15 as catalyst, which showed 46% conversion in 24 h. Also in
this case, the reaction favored benzaldehyde product (85%) more than styrene oxide product
(15%). The fact that similar results were obtained for the blank reaction and the reaction
containing Ext-SBA-15 proved that the support material, Ext-SBA-15, behaves just as a
spectator, without taking an active part in the reaction. An additional control experiment using
Ext-SBA-15-SH as catalyst gave even lower % conversion of styrene (32% in 24 h), with
benzaldehyde being the major product. The results of these control reactions are summarized
in Table S3 (below).
The styrene oxidation reaction was also studied by using Ext-SBA-15-SH-Au25-5 as
catalyst and oxygen as oxidant, but without TBHP. The conversion of styrene here was only
6% in 3 days. Since the reaction was slow in toluene, the same reaction was tried under neat
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conditions (without using any solvent). In 24 h, the conversion of styrene was 28%, giving
benzaldehyde as the major product (75%) and styrene oxide as the minor product (11%),
besides a few other products (14%) (Table S4). When the reaction was catalyzed by Ext-SBA15-SH-Au144-5, the % conversion of styrene was also low (14% in 24 h), whose products were
composed of 71% benzaldehyde, 22% styrene oxide, and 7% other products.
15. Recyclability Studies. Performing recyclability studies for small amount of catalysts
could sometimes be tricky due to various external parameters (e.g., handling the very small
amount of dry catalyst during transfer, washing, etc.). To overcome any such problem during
our recyclability tests, we designed and used the following procedures, which are also
depicted in a flowchart in Figure S7 for clarity. Typically, 25 mg of Ext-SBA-15-SH-Au144-5
was added to each of four long-necked vials and suspended in toluene (1 mL). After adding
styrene and TBHP to each of them, the vials were stirred at 80 °C under nitrogen. The
reaction in one of the vials was monitored using GC. After 24 h, the other vials were also
centrifuged and thoroughly washed with toluene, acetone and ethanol and dried overnight (no
visible color change was observed). To these the recovered catalysts in the three vials, 1 mL
of toluene was added to each and the vials were sonicated for 1 h. Styrene and TBHP were
then added and the reactions were allowed to stir for 24 h at 80 °C. One of them was taken
and used for characterization of the catalytic reaction in the second cycle. The remaining two
vials were centrifuged and recovered and used for the next cycle in the same way as above.
After addition of styrene and TBHP, the reactions were once again stir for 24 h at 80 °C, and
the conversion of styrene and selectivity of the reaction were measured using GC. The results
of the recyclability studies and conversion-time profiles are depicted in Figure S8.
16. Synthesis of Ext-SBA-15-Aun-OH Catalysts by Treatment of Ext-SBA-15-Aun
Catalysts with NaOH Solutions: To determine the possible effect of surface OH- species in
the materials, if present after treatment with NaBH4, additional samples were synthesized by
treating Ext-SBA-15-Aun catalysts with NaOH solutions for further control experiments.
Specifically, 50 mg of “Ext-SBA-15-Aun” (n = 25 and 144) was dispersed in 5 mL distilled
water. Then, 0.1 mM KOH solution (2 mL) was added into the mixture. After stirring at room
temperature for 30 min, the solution was centrifuged and the supernatant was removed and the
precipitate was washed with distilled water (3 x 2 mL). The resulting pale purple colored solid
was air-dried and labeled as “Ext-SBA-15-SH-Aun-OH”.
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17. Figures and Tables
Figure S1. Digital images of AuNPs-immobilized 3-mercaptopropyl-functionalized
mesoporous silica wet samples in dichloromethane solution: (A) Ext-SBA-15-SH-Au25 and
(B) Ext-SBA-15-SH-Au144. The solid samples took the distinct color of the AuNPs (persistent
even after washing), while the supernatant became colorless.
50 nm
20 nm
nm
Figure S2. Low resolution TEM images of Ext-SBA-15-Au144 (left) and Ext-SBA-15-Au144-5
(right) clearly showing the mesoporous channels of the materials.
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Figure S3. UV-Vis spectra of the supernatant collected after treatment of (A) Ext-SBA-15SH-Au25 or (B) Ext-SBA-15-SH-Au144 with 1 mM and 5 mM NaBH4 and centrifugation of
the solutions. These solutions did not show absorption features of the original MPCs (cf.
Figure 1), indicating the absence of AuNPs in the supernatants after treatment of the ExtSBA-15-SH-Aun nanocatalysts with aqueous NaBH4 solutions.
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Intensity (a.u.)
(A)
Ext-SBA-15-SH
809
2581
1482
2942
2995
965
3500 3000 2500 2000 1500 1000
500
Wavenumber (cm-1)
(C)
Ext-SBA-15-SH
Intensity (a.u.)
Intensity (a.u.)
(B)
Ext-SBA-15-SH-Au25
Ext-SBA-15-SH-Au25-1
Ext-SBA-15-SH-Au144
Ext-SBA-15-SH-Au144-1
Ext-SBA-15-SH-Au25-5
3500
3000
2500
2000
1500
Ext-SBA-15-SH
Ext-SBA-15-SH-Au144-5
1000
500
3500
Wavenumber (cm-1)
3000
2500 2000 1500
Wavenumber (cm-1)
1000
500
Figure S4. Solid state IR spectra of: (A)Ext-SBA-15-SH (showing different characteristic
peaks); (B) Ext-SBA-15-SH, Ext-SBA-15-SH-Au25, Ext-SBA-15-SH-Au25-1,andExt-SBA-15SH-Au25-5 nanocatalysts; and (C) Ext-SBA-15-SH, Ext-SBA-15-SH-Au144, Ext-SBA-15-SHAu144-1, and Ext-SBA-15-SH-Au144-5 nanocatalysts.
The presence of thiol group in the parent material was confirmed by FT-IR
spectroscopy, whose use for characterization of thiol-containing materials and compounds as
well as mesoporous silica-based material is well-documented in the literature.[S6]A very weak
vibration 2581 cm-1 in case of Ext-SBA-15-SH is indicative of S-H stretching vibration. While
the absorption bands at 2995 and 2942 cm-1 can be assigned to the asymmetric stretching of (CH2-), the band at ~1482 cm-1 stems from the bending of the same groups. The characteristic
Si-O-Si, Si-OH and Si-O stretching vibrations are observed at ~1000, ~965 and ~809 cm-1
respectively. In addition, the broad peak from 3000 to 4000 cm-1 can be attributed to the
stretching of O–H on the surface silanol groups (and the remaining adsorbed water molecules).
The peak at ~1600 cm-1 is possibly due to the deformation vibrations of adsorbed water (H-OH) molecules.
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(A)
3075
Ext-SBA-15-SH
2912
2575
Intensity (a.u.)
1116
980
500
1000
2500
3000
Wavenumber (cm-1)
(C)
(B)
Intensity (a.u.)
Ext-SBA-15-SH-Au25
Intensity (a.u.)
Ext-SBA-15-SH
Ext-SBA-15-SH
Ext-SBA-15-SH-Au144
Ext-SBA-15-SH-Au144-1
Ext-SBA-15-SH-Au144
750
2500
Ext-SBA-15-SH-Au144-5
3000
750
Wavenumber (cm-1)
2500
3000
Wavenumber (cm-1)
Figure S5. (A) Raman spectrum of Ext-SBA-15-SH (showing different characteristic peaks);
(B) Solid state Raman spectra of Ext-SBA-15-SH, Ext-SBA-15-SH-Au25, and Ext-SBA-15SH-Au144 nanocatalysts; and (C) Solid-state Raman spectra of Ext-SBA-15-SH, Ext-SBA-15SH-Au144, Ext-SBA-15-SH-Au144-1, and Ext-SBA-15-SH-Au144-5 nanocatalyst.
In our Raman study for Ext-SBA-SH (Figure S8A), a peak at 2575 cm-1 shows the
presence of S-H stretching vibration. The peaks at ~3000 cm-1 was possibly stemmed from the
combinations of vibrations originated from either i) grafted thiol-ligands, ii) residual
surfactant molecules, or iii) SiO-H. The peaks at ~1116 cm-1 can be attributed to Si-OH, C-C
and C-S vibrations (it was difficult to deconvolute the signal intensities). Interestingly, the
peak intensity increases when Au-cluster was incorporated (Figure S8B), presumably because
of the SERS enhancement effect by the Au nanoparticles. Please note that these peaks were
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much lower in intensity ion samples containing no Au nanoparticles as expected. We have
recently reported that Au nanoparticles within mesoporous silica materials can result in the
significant enhancement of intensity of Raman peaks of mercapto compounds due to the
SERS enhancement effect by the former.[S7,S8] So, this results is actually also an indirect proof
of the presence of Au nanoparticles. Interestingly also, the peaks such as the one at ~1100 cm1
decreases as the materials were treated with NaBH4 solution, which is indicative of the
lower amount of thiolate groups in the materials as they are treated with increasing
concentration of NaBH4 solution.
Figure S6. Product distribution of styrene oxidation catalyzed by Ext-SBA-15-SH-Au25-5
under oxygen at 80 ºC (under solvent-free conditions).
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One of the vials and the solution in it
were used for characterization of the
catalytic reaction in the first cycle.
for studies of the
catalytic reaction
in the second
cycle.
Figure S7. Schematic diagram showing how the recyclability studies were performed.
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Figure S8. (A) Percent conversion versus time for styrene oxidation reaction catalyzed by
Ext-SBA-15-SH-Au144-5 nanocatalyst. (B) Percent conversion versus reaction time in a
leaching experiment. The black arrow indicates the time at which the solid Au nanocatalyst
was filtered and separated from the reaction mixture and the supernatant was then run by itself
without the solid catalyst. A decrease in the catalytic activity or reaction rate was observed on
going from the first cycle to the subsequent cycles, which is conceivably due to loss of
catalyst during handling and centrifugation from the very small amount of catalyst used in
these studies.
S2p
Intensity (a.u.)
Ext-SBA-15-SH
Ext-SBA-15-SH-Au25
Ext-SBA-15-SH-Au25-1
Ext-SBA-15-SH-Au25-5
162
164
166
Binding Energy (eV)
Figure S9. XPS spectra of (E) S2p and (F) Au4f peaks of Ext-SBA-15-SH, Ext-SBA-15-SHAu25, Ext-SBA-15-SH-Au25-1, and Ext-SBA-15-SH-Au25-5.
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Figure S10. Representative STEM pictures of Ext-SBA-15-SH-Au144.
Figure S11. Representative STEM images of Ext-SBA-15-SH-Au144-5, a sample treated with
5 mM of NaBH4 solution.
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BF
BF
DF
HAADF
DF
HAADF
Figure S12. Representative STEM images in in BF, DF and HAADF modes, showing Au
NPs within Ext-SBA-15-SH- Au144. Please note that the Au NPs look as dark spots in the BF
images and they look as bright spots in DF and HAADF. The particles are most visible in
HAADF detector due to their sensitivity to Z contrast. The results clearly show that the Au
NPs are within the channels of the SBA-15 material. The good contrast in BF is possble
because we employed low energy electron beam (30 keV).
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Figure S13. Representative HAADF-STEM image of Ext-SBA-15-SH-Au144.
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Figure S14. Representative HAADF-STEM image of Ext-SBA-15-SH-Au144.
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Figure S15. Representative HRTEM image showing Au NPs (marked by yellow arrow)
within Ext-SBA-15-SH- Au25 along with their size distribution.
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Figure S16. Representative HRTEM images showing Au NPs (marked by yellow arrow)
within Ext-SBA-15-SH- Au25.
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Figure S17. Representative HRTEM image showing Au NPs (marked by yellow arrow)
within Ext-SBA-15-SH- Au25-5 along with their size distribution. After treatment of ExtSBA-15-SH-Au25 with NaBH4, the sizes of the Au nanoclusters appeared to have decreased a
little bit. We suspect that the leaching of Au nanoparticles during NaBH4 might be responsible
for their change in size.
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Table S1. Precursor material and reagents employed to synthesize the two different types of
Ext-SBA-15-Aun materials used in the study.
Sample
SBA15
Used
(mg)
Ext-SBA-Au25
300
Au Nanocluster Used
Au25(SCH2CH2Ph)18
Approx.
Amount of
thiol/thiolate
(mol/gSBA15)
Volume
(mL)
Conc.
(M)
Approx. Amount
of Au
Nanoclusters
(mol/g SBA-15)
30
2
20
360
5
2
0.05
3
(MW = 7394.21 g/mol)
Ext-SBAAu144
Au144(SCH2CH2Ph)60
200
(MW = 36596.88
g/mol)
Table S2. Catalyst loading (from ICP-MS and XPS) and turnover frequency (TOF) of the
catalysts for styrene oxidation.
Catalyst
Sulfur Analysis
Gold Analysis
TOF (h-1)
ICP-MS
(wt. %)
XPS
(At. %)
ICP-MS
(ppm)
XPS
(At. %)
(based on Au
ICP-MS)
Ext-SBA-15-SH
5.06
3.3
-
-
-
SBA-15-SH-Au25
-
3.3
10
-
984.80
SBA-15-SH-Au25-5
-
3.5
19
-
1727.72
SBA-15-SH-Au144
4.52
3.0
487
0.16
21.57
SBA-15-SH-Au144-5
4.57
3.1
138
0.16
237.87
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Table S3. Experimental results of styrene oxidation reaction in the presence of the different
catalysts synthesized here and their corresponding parent materials used as reference or in
absence of any material/catalyst.a
Oxidant
(Reaction time)
Conversion of
Styrene (%) b
Selectivity to
Benzaldehydeb
Selectivity to
Styrene Oxide b
Blank
TBHP (24 h)
42
86
14
Ext-SBA-15
TBHP (24 h)
46
85
15
Ext-SBA-15-SH
TBHP (24 h)
32
~100
~0
SBA-15-SH-Au25
TBHP (24 h)
30
~100
~0
SBA-15-SH-Au25-1
TBHP (24 h)
38
~100
~0
SBA-15-SH-Au25-5
TBHP (24 h)
~100
~100
~0
SBA-15-SH-Au144
TBHP (24 h)
32
~100
~0
SBA-15-SH-Au144-1
TBHP (24 h)
68
~100
~0
SBA-15-SH-Au144-5
TBHP (24 h)
~100
~100
~0
SBA-15-SH-Au25-5
O2 (3 days)
6
-
-
SBA-15-SH-Au25-5
O2, Neat (24 h)
28
75
11
SBA-15-SH-Au144-5
O2, Neat (24 h)
14
71
22
SBA-15-SH-Au25-OH
TBHP (24 h)
25
~100
~0
SBA-15-SH-Au144-OH
TBHP (24 h)
28
~100
~0
Catalyst
a
All experiments were carried out at 80 °C.
b
Percentage.
c
The experimental data were
-
obtained to determine the possible effect of surface OH species around the Au NPs (if present
after treatment with NaBH4) on the catalytic properties of the materials (see Experimental
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Submitted to
details above for the synthesis of the materials or catalysts). Specifically, after treating the
Ext-SBA-SH-Aun with 0.1 mM NaOH solution, and then washing the resulting materials, the
catalytic oxidation experiments using the OH--treated materials as catalyst were performed.
The OH--treated materials, Ext-SBA-15-Au25-OH and Ext-SBA-15-Au144-OH, gave 25% and
28% conversion after 24 h while the parent materials gave 30 and 32% conversions,
respectively. Thus, it was concluded that surface adsorbed OH- species have no discernible
effect on the catalytic properties of both Ext-SBA-15-SH-Au144-1 and Ext-SBA-15-SH-Au1445.
Table S4. Elemental analysis of the solid SBA-15-SH-Au144-5 and the solution recovered
after the 3rd reaction cycle.
Entry
Au (ppm)
Au (%)
Au (mmol)
Catalyst
107
0.01
3.1 x 10-5
Reaction solution recovered from 3rd cycle
4
0.0004
1.26 x 10-6
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Submitted to
18. References
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