Martin Makosch [a] , Václav Bumbálek [a] , Jacinto Sá [b] , Jeroen A. van Bokhoven *[a,b] a
Institute for Chemical and Bioengineering ETH Zurich, Wolfgang-Pauli Strasse, 8093 Zurich,
Switzerland. b Laboratory for Catalysis and Sustainable Chemistry, Paul Scherrer Institute (PSI), Villigen
(Switzerland).
*E-mail: jeroen.vanbokhoven@chem.ethz.ch

Supplementary Information
Synthesis of materials
1wt% Au/Al
2
O
3
colloid-precursor were synthesized by deposition precipitation with urea of the gold onto the surface of Al
2
O
3
according to 1 . Prior to the synthesis, the Al
2
O
3
was calcined at 500 °C to remove all residuals from the synthesis. In a teflon container, 3 g of the support was dissolved in 300 ml of water containing 0.9 g of urea. To this solution 50.97 mg of HAuCl
4
.
3H
2
O (Au: 49 %, 99.9 % metal basis, ABCR-Chemicals) was added.
Subsequently, the mixture was stirred for 16 h at 80 °C under the exclusion of light. The precipitate was filtered, washed 3 times with water to prevent chloride contamination and dried in vacuum over night. The resulting precursor is referred to as “as prepared”. Before modification with the organic thiols, all colloid precursors were pretreated as follows: 300 mg of the catalyst were heated to 300 °C in a flow of 100 ml/min of 5% H
2
in He. After reaching
300 °C, the catalyst was kept at that temperature for 60 min and then cooled down to room temperature in the same flow. A total of 300 mg of the freshly reduced Au/Al
2
O
3 precursor was added to 100 ml of a 20 mM solution of the corresponding thiol in ethanol (ethanol absolute, analytical grade, Scharlau) to obtain a nominal Au/thiol ratio of 1:20. For dilution experiments Au/thiol ratios of 75:1, 50:1, 25:1 and 10:1 were employed. The ratio Au/thiol was varied by changing the molarity of the solution. Prior to the addition of the catalyst the thiol/ethanol solution was always purged with nitrogen under magnetic stirring for 30 min.
After the addition of the Au/Al
2
O
3
precursor the suspension was stirred for 16 h under nitrogen purging at room temperature, filtered and washed three times with 125 ml ethanol and dried in vacuum overnight. A total of 100 mg precursor was suspended in 40 ml toluene and heated under reflux at 80 °C for 20 h. The colorless toluene turned red upon heating. The colloid in toluene was obtained by filtering the Al
2
O
3
.
Colloid characterization
Atomic absorption spectroscopy (AAS)
Using a Varian SpectrAA 220 FS, atomic absorption spectrometry (AAS) analysis was used to determine the wt% of gold in the Au/Al
2
O
3
precursor and the Au-colloid. For that, 100 mg precursor was dissolved in 6 ml aqua regia over night and then water was added to a total volume of 50 ml. The Au-colloids in toluene were used as is. The solutions were compared to a standard calibration row.

Transmission electron microscopy measurements (TEM)
Transmission electron microscopy (TEM) measurements of the Au/Al
2
O
3
colloid precursors and the colloid were performed on a HD2700CS (Hitachie, aberration-corrected dedicated
STEM, cold FEG, 200 kV) and a Tecnai F30 ST (FEI, FEG, 300 kV) microscope. For that, the powder was suspended in ethanol and a drop of the suspension was supported on a copper grid by evaporation of the solvent. The colloid was directly used from the toluene phase. To determine the particle size distribution, TEM pictures were analyzed with the Image J software and 250 particles were taken into account for each measurement.
Fourier transform infrared spectroscopy measurements
Fourier transform infrared measurements were recorded on a Bruker Equinox 55 FTIR spectrometer. For that, a drop of the Au
C12
-colloid was measured between two KBr pellets.
Prior to the measurement, a background spectrum in air was recorded with 50 scans per spectrum. Samples were recorded between 4500 and 600 cm
-1 with a resolution of 1 cm
-1
.
1000 scans per spectrum were averaged.
In situ high energy resolution fluorescence detected X-ray absorption near edge spectroscopy measurements
In situ high energy resolution fluorescence detected X-ray absorption near edge spectroscopy
(HERFD XANES) measurements were performed in a cell previously described in
2
. The cell consisted of a standard 50 ml autoclave with an opening for irradiation of X-rays. A suspension of 300 mg Au
C12
/Al
2
O
3
colloid precursor and the Au/Al
2
O
3
precursor respectively in 35 g of toluene (puriss > 99 %, Fluka Analytical) were put into the cell. HERFD XANES spectra were recorded during the preparation of the Au-colloid while stirring at 80 °C with a time interval of 1 min per spectrum. All experiments were recorded at beamline ID26 of the
European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The ring operated in uniform mode at a ring current of 200 mA. Three coupled undulators using the third harmonic were employed for the HERFD XANES measurements. The incident energy was monochromatized by a pair of Si(111) crystals. Three Pd/Cr mirrors positioned at 2.5 mrad relative to the incident beam were used to suppress higher harmonics and focus the beam on the sample with a size of 600 µm horizontal by 200 µm vertical. The estimated flux was
8x10
13
photons s
-1
. HERFD XANES spectra were measured by using a vertical-plane
Rowland circle X-ray emission spectrometer in combination with an avalanche photodiode

(APD, Perkin Elmer).
3
The scattering angle in the horizontal plane was about 130°. The spectrometer was tuned to the Pt L
α1
fluorescence line (9442 eV) using the [660] reflection of four spherically bent Ge crystals, that is, working at a Bragg angle of about 80 °. A total resolution of 1.93 eV (FWHM) was obtained. The raw HERFD XANES spectra were treated with the Athena software. After background subtraction the raw data were normalized to the last point of each spectrum and 30 spectra were averaged. Exposure of the slurry to X-rays did not cause any changes to the spectra and thus beam damage did not occur.
Comments
FT-IR characterization of the Au
C12
-colloid in toluene showed that 1-dodecanethiol adsorbed on the Au nanoparticles via the sulphur group as the characteristic S-H vibration at 2570 cm
-1 was absent in the IR spectrum. Additionally IR characterization showed that 1-dodecanethiol was densely packed on the Au nanoparticle surface as the symmetric and asymmetric methylene C-H stretch vibration were shifted to lower wavenumbers characteristic for an ordered, crystalline-like structure (Supplementary information 1).
4
HERFD XANES measurements of the liquid phase revealed that 1-dodecanethiol adsorbed via the sulphur atom on the Au
C12
/Al
2
O
3
and the Au
C12
-colloid as indicated by higher whiteline intensity.
5
Characteristic features for Au nanoparticles did not change for the Au/Al
2
O
3
colloidprecursors, the Au
C12
/Al
2
O
3
catalyst and the Au
C12
-colloid implying that the structure of the
Au nanorparticles were the same in all of them (Supplementary information 2).
0.639
0.630
1 2
3
4
5
6
7
3200 3000 2800
-1
2600
Supplementary 1 FT-IR spectrum of the Au
C12
-colloid in toluene.

Supplementary Table 1 Mode assignments for Au
C12
-colloid in toluene.
Wavenumber / cm -1 Intensity
(1) 3085
(2) 3064
(3) 3029
(4) 3004
(5) 2958
(6) 2920
(7) 2852
(8) 2570 w w m sh w s m absent
Contribution
Toluene
Toluene
Toluene
Toluene
Toluene
1-dodecanethiol
1-dodecanethiol
-
Assignment according to 6
ν20b
ν20a
ν7b
ν13
νCH
3
νCH
2 as
νCH
2 s
-
Supplementary 2 HERFD XANES of the Au/Al
2
O
3 colloid-precursor (green), the Au
C12
/Al
2
O
3
catalyst (red) and the Au
C12
colloid in toluene (blue) after heating at 100 °C.
(1)
(2)
(3)
(4)
(5)
(6)
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