Supporting Information Au@ZIF-8: CO Oxidation over Gold ...
Supporting Information
Au@ZIF-8: CO Oxidation over Gold Nanoparticles Deposited to Metal-Organic Framework Hai-Long Jiang, Bo Liu, Tomoki Akita, Masatake Haruta, Hiroaki Sakurai, and Qiang Xu
National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan, CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan, Graduate School of Science and Technology, Kobe University, Nada Ku, Kobe, Hyogo 657-8501, Japan, and Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan E-mail: [email protected]
Materials and Instrumentation. All chemicals were from commercial and used without further purification: zinc(II) nitrate tetrahydrate (Zn(NO3)2·4H2O, 98 %, Merck), 2-methylimidazole (>97.0 %, TCI), dimethyl Au(III) acetylacetonato ((CH3)2Au(C5H7O2), 99 %, Tri Chemical Laboratories Inc.), ZIF-8 (Zn(MeIM)2·(DMF)·(H2O)3 MeIM = 2-methylimidazole, Sigma-Aldrich) and N,N-dimethylformamide (HCON(CH3)2, Kishida Chemical Co., Ltd). Powder X-ray diffraction (PXRD) was carried out with a X-ray diffractometer of Rigaku, Rint 2000. The UV-vis absorption spectra were recorded on a Shimadzu UV-2550 spectrophotometer in the wavelength range of 400-800 nm. The nitrogen sorption isotherms were measured by using an automatic volumetric adsorption equipment (Mircomeritics, ASAP2010). The size and morphology of Au@ZIF-8 were
1
investigated by using a scanning electron microscope (SEM, Hitachi, S-5000) at 10 or 3 kV and a transmission electron microscope (TEM, JEOL, JEM-3000F) at 300 kV, respectively. The catalytic oxidation of CO was conducted by using a fixed bed plug flow reactor system equipped with an on-line mass spectrometer (MS). Typically, pure CO, O2 and He were supplied through mass flow controllers and mixed with each other, and then the final reactant gas (100 ml·min-1) was passed through the catalyst bed (0.1 g). Reaction gas was composed of CO (1 vol.%), O2 (21 vol.%) and He (78 vol.%), and hourly space velocity (SV) was 60,000 h-1·ml·g-catal-1. The catalyst was diluted by quartz sand (30-50 mesh) and the mixture was passed through the reactor made of stainless steel. The as-prepared Au@ZIF-8 was reduced in 10 vol.% H2/He at the defined temperature for 2.5 h or followed by calcination in 8 vol.% O2/He for 2 h before the catalytic reaction. The reaction temperature was programmed and it was monitored by a thermocouple extending into the catalyst bed inside the reactor. Carbon monoxide and CO2 were monitored by an on-line QMS analyzer (OmnistarTM, Pfeiffer Vacuum, model: GSD301 O type). Data acquisition of QMS signal was performed online every ten seconds to computer, and CO and CO2 concentrations were calculated. After repeated catalytic runs, CO+CO2 concentrations became almost constant during reaction and equal to reactant CO concentration, and then we calculated CO conversion for each data point as follows. CO conversion (%) = (1 – [CO]/([CO]+[CO2])*100 Temperature was programmed from room temperature to preset temperatures
2
(315-340 ºC) for each catalytic run with increasing temperature. Temperature was increased linearly with 3 ºC/min, and remained for 30 min at middle and final temperatures. All the catalytic activity curves finally obtained (Figure 2 left in main text) were nearly smooth despite including both rising and constant part of temperature, which means that the curves should agree with that obtained from steady-state measurement, and indicates the temperature rising rate of 3 ºC/min was not too fast for the measuring conditions.
Preparation of Au@ZIF-8: ZIF-8 was purchased from Sigma-Aldrich directly or synthesized according to the literature.1 Prior to gold loading, the as-synthesized or commercial ZIF-8 samples were pretreated as follows: ZIF-8 were immersed in methanol at ambient temperature for 48 h, evacuated at ambient temperature for over 10 h, then at 300 ºC for 2 h to obtain optimally evacuated sample. In a typical synthesis, the pretreated ZIF-8 samples with desired quantitative Me2Au(acac) (acac = acetylacetonate) in weight ratio of 1:100 for Au/ZIF-8, were ground in an agate mortar in air for about 30 min at room temperature. Then the mixture was treated in a stream of 10 vol.% H2 in He at 230 ºC for 2.5 h to yield 1.0 wt% Au@ZIF-8. Gold catalysts containing 0.5, 2.0 and 5.0 wt% Au with respect to ZIF-8 were also prepared in the similar procedure except for different Au/ZIF-8 weight ratios.
3
N2 adsorption examination: N2 adsorption was examined for ZIF-8 and Au@ZIF-8 with different Au loadings. Before the measurements, ZIF-8 was pretreated under the same condition as that used for preparing Au@ZIF-8 (mentioned in detail below), and the Au@ZIF-8 samples were evacuated again at 250 °C. The surface area decreased obviously after Au loading. The BET surface areas of blank ZIF-8, 0.5, 1.0, 2.0, 5.0 and 10.0 wt% Au@ZIF-8 were 1413, 911, 891, 905, 1012 and 1237 m2/g, respectively.
Comparative Study of Catalytic Properties: For comparison, the following catalytic tests were also performed: a) the evacuated ZIF-8 blank sample was used as a catalyst for CO oxidation, but CO conversion was negligible between room temperature and 300 ºC. b) as-prepared Au@ZIF-8 samples with different Au loadings were reduced by H2/He at 230 ºC, followed by calcination in O2/He at around 325 ºC before catalytic activity measurements. However, no more satisfactory catalytic activity was obtained. c) 1.8 wt% and 3.5 wt% Au@ZIF-8 samples were also prepared by incipient wetness impregnation method: the pretreated ZIF-8 was dispersed in HAuCl4·4H2O aqueous solution over 2 h in evacuated condition until no air bubble appeared, followed by drying in a vacuum drying oven. The as-prepared Au@ZIF-8 was reduced in 10 vol.% H2 in He at 230 ºC for 2 h. Catalytic activity examination for both catalysts indicated the temperature for half conversion exceeded 250 ºC. d) In the case of Au@ZIF-8 catalysts, the CO oxidation activity depends on both the
4
amount and size of Au NPs. Loading with more Au NPs could enhance the activity whereas that also gives rise to aggregation of Au NPs, which will lower the activity. The 10.0 wt% Au@ZIF-8 sample has also been prepared under similar conditions in order to investigate the influences. CO oxidation experiments show that its activity (50 % conversion: around 230 ºC) is obviously lower than that of 5.0 wt% sample (50 % conversion: around 170 ºC). The fact should be attributed to the formation of larger Au NPs based on powder XRD studies (Figure S1f).
The stability of host framework: Powder XRD of Au@ZIF-8 samples having different Au loadings was investigated for as-prepared, after H2 reduction and after several runs of reaction. Strong low-angle peaks at 2θ = 5-20 deg appeared in each diffraction pattern (although the diffractions after catalytic reaction were weaker than before), indicating that the framework of ZIF-8 host matrix is not destroyed after Au loading and even after several runs of catalytic reaction. The broad diffraction around 2θ of 38.1 deg was detected clearly by powder XRD in 5.0 wt% Au@ZIF-8 after 7 runs of CO oxidation, which is possibly attributed to the ZIF-8 framework (weak diffraction peak locates around 38.12 deg) or/and aggregations of Au NPs (the strongest diffraction peak locates around 38.27 deg) Reference (1) Park, K. S.; Ni, Z.; Côté, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Proc. Natl. Acad. Sci., 2006, 103, 10186-10191.
5
Relative Intensity
blank ZIF-8
after 7 runs of catalysis experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta / degrees
50
60
(a)
Relative Intensity
0.5 wt% Au@ZIF-8
after H2 reduction and 6 runs of catalyis
after H2 reduction at 230 degC for 2h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(b)
Relative Intensity
1.0 wt% Au@ZIF-8
after H2 reduction and 5 runs of catalysis after H2 reduction at 230 degC for 2.5h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(c)
6
Relative Intensity
2.0 wt% Au@ZIF-8
after H2 reduction and 5 runs of catalysis after H2 reduction at 230 degC for 2.5h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(d) *
5.0 wt% Au@ZIF-8
Relative Intensity
* the peak come from silica + the peak comes from Au NPs
*
after H2 reduction and 7 runs of catalysis + after H2 reduction at 230 degC for 2.5h experimental ZIF-8 simulated ZIF-8
10
20
30 40 2 theta (degrees)
50
60
(e) 10.0 wt% Au@ZIF-8
Relative Intensity
* the peaks assigned to Au species
after H2 reduction and 5 runs of catalysis
* *
*
experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(f) Figure S1. Powder XRD patterns for ZIF-8 and Au@ZIF-8 samples recorded during whole prepared process and after catalytic reaction.
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Absorbance (a.u.)
ZIF-8 0.5 wt% Au@ZIF-8 1.0 wt% Au@ZIF-8 2.0 wt% Au@ZIF-8 5.0 wt% Au@ZIF-8
400
500
600 Wavelength (nm)
700
800
Figure S2. UV-vis spectra of the ethanol solution of ZIF-8 and Au@ZIF-8 samples with different Au loadings.
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(a)
50 1.0wt% Au@ZIF-8 Mean Size 3.43nm SD 1.42
40
1.0wt% Au@ZIF-8 after catalysis Mean Size 3.09nm SD 0.90
25
Counts
Counts
20 30
20
10
15 10
5
0 0
1
2
3
4
5
6
Diameter (nm)
7
8
9
0
10
0
1
2
3
4
5
6
7
8
9
10
Diameter (nm)
(b)
9
100
5.0wt% Au@ZIF-8 Mean Size4.17nm SD 2.56
100 80
60
Counts
Counts
80
5.0wt% Au@ZIF-8 after catalysis Mean Size3.47nm SD 2.37
120
40
60 40
20
20 0
0 0
2
4
6
8
10
12
14
Diameter (nm)
16
18
20
22
0
2
4
6
8
10
12
14
16
18
Diameter (nm)
(c) Figure S3. large-scale TEM images of 0.5 wt% (a), 1.0 wt% (b) and 5.0 wt% (c) Au@ZIF-8 and corresponding size distributions of Au NPs, left and right images represent before and after catalytic reaction, respectively.
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Figure S4. SEM micrographs of representative 1.0 wt% Au@ZIF-8 samples before (a and b) and after (c and d) catalytic reaction.
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Figure S5. Color change before (left) and after (right) catalytic reaction of ZIF-8 (a), 0.5 wt% (b), 1.0 wt% (c), 2.0 wt% (d) and 5.0 wt% (e) Au@ZIF-8 samples.
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100
100 0.5 wt% Au@ZIF-8
80 CO conversion (%)
80 CO conversion (%)
1.0 wt% Au@ZIF-8
60
40
60
40
20
20
4th run 5th run
5th run 6th run
0 50
100
150 200 250 o Temperature ( C)
300
0 50
350
100
(a)
300
350
(b) 100
100 2.0 wt% Au@ZIF-8
5.0 wt% Au@ZIF-8
80 CO conversion (%)
80 CO conversion (%)
150 200 250 o Temperature ( C)
60
40
60
40
20
20 4th run 5th run
0 50
100
150 200 250 o Temperature ( C)
300
350
5th run 6th run
0 50
100
150 200 250 o Temperature ( C)
300
350
(c) (d) Figure S6. Reproducible activities for (a) 0.5 wt%, (b) 1.0 wt%, (c) 2.0 wt% and (d) 5.0 wt% Au@ZIF-8 catalysts.
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Au@ZIF-8: CO Oxidation over Gold Nanoparticles Deposited to Metal-Organic Framework Hai-Long Jiang, Bo Liu, Tomoki Akita, Masatake Haruta, Hiroaki Sakurai, and Qiang Xu
National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan, CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan, Graduate School of Science and Technology, Kobe University, Nada Ku, Kobe, Hyogo 657-8501, Japan, and Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan E-mail: [email protected]
Materials and Instrumentation. All chemicals were from commercial and used without further purification: zinc(II) nitrate tetrahydrate (Zn(NO3)2·4H2O, 98 %, Merck), 2-methylimidazole (>97.0 %, TCI), dimethyl Au(III) acetylacetonato ((CH3)2Au(C5H7O2), 99 %, Tri Chemical Laboratories Inc.), ZIF-8 (Zn(MeIM)2·(DMF)·(H2O)3 MeIM = 2-methylimidazole, Sigma-Aldrich) and N,N-dimethylformamide (HCON(CH3)2, Kishida Chemical Co., Ltd). Powder X-ray diffraction (PXRD) was carried out with a X-ray diffractometer of Rigaku, Rint 2000. The UV-vis absorption spectra were recorded on a Shimadzu UV-2550 spectrophotometer in the wavelength range of 400-800 nm. The nitrogen sorption isotherms were measured by using an automatic volumetric adsorption equipment (Mircomeritics, ASAP2010). The size and morphology of Au@ZIF-8 were
1
investigated by using a scanning electron microscope (SEM, Hitachi, S-5000) at 10 or 3 kV and a transmission electron microscope (TEM, JEOL, JEM-3000F) at 300 kV, respectively. The catalytic oxidation of CO was conducted by using a fixed bed plug flow reactor system equipped with an on-line mass spectrometer (MS). Typically, pure CO, O2 and He were supplied through mass flow controllers and mixed with each other, and then the final reactant gas (100 ml·min-1) was passed through the catalyst bed (0.1 g). Reaction gas was composed of CO (1 vol.%), O2 (21 vol.%) and He (78 vol.%), and hourly space velocity (SV) was 60,000 h-1·ml·g-catal-1. The catalyst was diluted by quartz sand (30-50 mesh) and the mixture was passed through the reactor made of stainless steel. The as-prepared Au@ZIF-8 was reduced in 10 vol.% H2/He at the defined temperature for 2.5 h or followed by calcination in 8 vol.% O2/He for 2 h before the catalytic reaction. The reaction temperature was programmed and it was monitored by a thermocouple extending into the catalyst bed inside the reactor. Carbon monoxide and CO2 were monitored by an on-line QMS analyzer (OmnistarTM, Pfeiffer Vacuum, model: GSD301 O type). Data acquisition of QMS signal was performed online every ten seconds to computer, and CO and CO2 concentrations were calculated. After repeated catalytic runs, CO+CO2 concentrations became almost constant during reaction and equal to reactant CO concentration, and then we calculated CO conversion for each data point as follows. CO conversion (%) = (1 – [CO]/([CO]+[CO2])*100 Temperature was programmed from room temperature to preset temperatures
2
(315-340 ºC) for each catalytic run with increasing temperature. Temperature was increased linearly with 3 ºC/min, and remained for 30 min at middle and final temperatures. All the catalytic activity curves finally obtained (Figure 2 left in main text) were nearly smooth despite including both rising and constant part of temperature, which means that the curves should agree with that obtained from steady-state measurement, and indicates the temperature rising rate of 3 ºC/min was not too fast for the measuring conditions.
Preparation of Au@ZIF-8: ZIF-8 was purchased from Sigma-Aldrich directly or synthesized according to the literature.1 Prior to gold loading, the as-synthesized or commercial ZIF-8 samples were pretreated as follows: ZIF-8 were immersed in methanol at ambient temperature for 48 h, evacuated at ambient temperature for over 10 h, then at 300 ºC for 2 h to obtain optimally evacuated sample. In a typical synthesis, the pretreated ZIF-8 samples with desired quantitative Me2Au(acac) (acac = acetylacetonate) in weight ratio of 1:100 for Au/ZIF-8, were ground in an agate mortar in air for about 30 min at room temperature. Then the mixture was treated in a stream of 10 vol.% H2 in He at 230 ºC for 2.5 h to yield 1.0 wt% Au@ZIF-8. Gold catalysts containing 0.5, 2.0 and 5.0 wt% Au with respect to ZIF-8 were also prepared in the similar procedure except for different Au/ZIF-8 weight ratios.
3
N2 adsorption examination: N2 adsorption was examined for ZIF-8 and Au@ZIF-8 with different Au loadings. Before the measurements, ZIF-8 was pretreated under the same condition as that used for preparing Au@ZIF-8 (mentioned in detail below), and the Au@ZIF-8 samples were evacuated again at 250 °C. The surface area decreased obviously after Au loading. The BET surface areas of blank ZIF-8, 0.5, 1.0, 2.0, 5.0 and 10.0 wt% Au@ZIF-8 were 1413, 911, 891, 905, 1012 and 1237 m2/g, respectively.
Comparative Study of Catalytic Properties: For comparison, the following catalytic tests were also performed: a) the evacuated ZIF-8 blank sample was used as a catalyst for CO oxidation, but CO conversion was negligible between room temperature and 300 ºC. b) as-prepared Au@ZIF-8 samples with different Au loadings were reduced by H2/He at 230 ºC, followed by calcination in O2/He at around 325 ºC before catalytic activity measurements. However, no more satisfactory catalytic activity was obtained. c) 1.8 wt% and 3.5 wt% Au@ZIF-8 samples were also prepared by incipient wetness impregnation method: the pretreated ZIF-8 was dispersed in HAuCl4·4H2O aqueous solution over 2 h in evacuated condition until no air bubble appeared, followed by drying in a vacuum drying oven. The as-prepared Au@ZIF-8 was reduced in 10 vol.% H2 in He at 230 ºC for 2 h. Catalytic activity examination for both catalysts indicated the temperature for half conversion exceeded 250 ºC. d) In the case of Au@ZIF-8 catalysts, the CO oxidation activity depends on both the
4
amount and size of Au NPs. Loading with more Au NPs could enhance the activity whereas that also gives rise to aggregation of Au NPs, which will lower the activity. The 10.0 wt% Au@ZIF-8 sample has also been prepared under similar conditions in order to investigate the influences. CO oxidation experiments show that its activity (50 % conversion: around 230 ºC) is obviously lower than that of 5.0 wt% sample (50 % conversion: around 170 ºC). The fact should be attributed to the formation of larger Au NPs based on powder XRD studies (Figure S1f).
The stability of host framework: Powder XRD of Au@ZIF-8 samples having different Au loadings was investigated for as-prepared, after H2 reduction and after several runs of reaction. Strong low-angle peaks at 2θ = 5-20 deg appeared in each diffraction pattern (although the diffractions after catalytic reaction were weaker than before), indicating that the framework of ZIF-8 host matrix is not destroyed after Au loading and even after several runs of catalytic reaction. The broad diffraction around 2θ of 38.1 deg was detected clearly by powder XRD in 5.0 wt% Au@ZIF-8 after 7 runs of CO oxidation, which is possibly attributed to the ZIF-8 framework (weak diffraction peak locates around 38.12 deg) or/and aggregations of Au NPs (the strongest diffraction peak locates around 38.27 deg) Reference (1) Park, K. S.; Ni, Z.; Côté, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Proc. Natl. Acad. Sci., 2006, 103, 10186-10191.
5
Relative Intensity
blank ZIF-8
after 7 runs of catalysis experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta / degrees
50
60
(a)
Relative Intensity
0.5 wt% Au@ZIF-8
after H2 reduction and 6 runs of catalyis
after H2 reduction at 230 degC for 2h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(b)
Relative Intensity
1.0 wt% Au@ZIF-8
after H2 reduction and 5 runs of catalysis after H2 reduction at 230 degC for 2.5h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(c)
6
Relative Intensity
2.0 wt% Au@ZIF-8
after H2 reduction and 5 runs of catalysis after H2 reduction at 230 degC for 2.5h as prepared after loading Au precursor experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(d) *
5.0 wt% Au@ZIF-8
Relative Intensity
* the peak come from silica + the peak comes from Au NPs
*
after H2 reduction and 7 runs of catalysis + after H2 reduction at 230 degC for 2.5h experimental ZIF-8 simulated ZIF-8
10
20
30 40 2 theta (degrees)
50
60
(e) 10.0 wt% Au@ZIF-8
Relative Intensity
* the peaks assigned to Au species
after H2 reduction and 5 runs of catalysis
* *
*
experimental ZIF-8 simulated ZIF-8 10
20
30 40 2 theta (degrees)
50
60
(f) Figure S1. Powder XRD patterns for ZIF-8 and Au@ZIF-8 samples recorded during whole prepared process and after catalytic reaction.
7
Absorbance (a.u.)
ZIF-8 0.5 wt% Au@ZIF-8 1.0 wt% Au@ZIF-8 2.0 wt% Au@ZIF-8 5.0 wt% Au@ZIF-8
400
500
600 Wavelength (nm)
700
800
Figure S2. UV-vis spectra of the ethanol solution of ZIF-8 and Au@ZIF-8 samples with different Au loadings.
8
(a)
50 1.0wt% Au@ZIF-8 Mean Size 3.43nm SD 1.42
40
1.0wt% Au@ZIF-8 after catalysis Mean Size 3.09nm SD 0.90
25
Counts
Counts
20 30
20
10
15 10
5
0 0
1
2
3
4
5
6
Diameter (nm)
7
8
9
0
10
0
1
2
3
4
5
6
7
8
9
10
Diameter (nm)
(b)
9
100
5.0wt% Au@ZIF-8 Mean Size4.17nm SD 2.56
100 80
60
Counts
Counts
80
5.0wt% Au@ZIF-8 after catalysis Mean Size3.47nm SD 2.37
120
40
60 40
20
20 0
0 0
2
4
6
8
10
12
14
Diameter (nm)
16
18
20
22
0
2
4
6
8
10
12
14
16
18
Diameter (nm)
(c) Figure S3. large-scale TEM images of 0.5 wt% (a), 1.0 wt% (b) and 5.0 wt% (c) Au@ZIF-8 and corresponding size distributions of Au NPs, left and right images represent before and after catalytic reaction, respectively.
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Figure S4. SEM micrographs of representative 1.0 wt% Au@ZIF-8 samples before (a and b) and after (c and d) catalytic reaction.
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Figure S5. Color change before (left) and after (right) catalytic reaction of ZIF-8 (a), 0.5 wt% (b), 1.0 wt% (c), 2.0 wt% (d) and 5.0 wt% (e) Au@ZIF-8 samples.
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100
100 0.5 wt% Au@ZIF-8
80 CO conversion (%)
80 CO conversion (%)
1.0 wt% Au@ZIF-8
60
40
60
40
20
20
4th run 5th run
5th run 6th run
0 50
100
150 200 250 o Temperature ( C)
300
0 50
350
100
(a)
300
350
(b) 100
100 2.0 wt% Au@ZIF-8
5.0 wt% Au@ZIF-8
80 CO conversion (%)
80 CO conversion (%)
150 200 250 o Temperature ( C)
60
40
60
40
20
20 4th run 5th run
0 50
100
150 200 250 o Temperature ( C)
300
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5th run 6th run
0 50
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150 200 250 o Temperature ( C)
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(c) (d) Figure S6. Reproducible activities for (a) 0.5 wt%, (b) 1.0 wt%, (c) 2.0 wt% and (d) 5.0 wt% Au@ZIF-8 catalysts.
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