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1 Platinum-Cobalt bimetallic nanoparticles in hollow carbon nanospheres for hydrogenolysis of 5-hydroxymethylfurfural Guang-Hui Wang, Jakob Hilgert, Felix Herrmann Richter, Feng Wang, Hans-Josef Bongard, Bernd Spliethoff, Claudia Weidenthaler, Ferdi Schüth* Max-Planck-Institut für Kohlenforschung, D Mülheim an der Ruhr, Germany * Tel: +49(0)208/ NATURE MATERIALS 1

2 Synthesis of PtCo/activated carbon (PtCo/AC) and PtCo/graphitized carbon (PtCo/GC). Pt/AC (platinum on activated carbon, 10 wt% loading, product number: ) and Pt/GC (platinum on graphitized carbon, 10 wt% loading, product number: ) were purchased from Sigma-Aldrich directly. The PtCo bimetallic catalysts supported on activated carbon and graphitized carbon were prepared by impregnation method using Pt/AC and Pt/GC as supports. Typically, 400 µl of ethanol containing 100 mg of Co(NO 3 ) 2 6H 2 O was impregnated into 200 mg of Pt/AC (Pt/GC), dried at room temperature for 8 h. Then, the PtCo/AC (PtCo/GC) was obtained by pyrolysis under the same procedure with PtCo@HCS. According to the AAS analysis, the amounts of Pt and Co in PtCo/AC (PtCo/GC) are 7.91 wt% and 8.18 wt% (8.70 wt% and 8.52 wt%), respectively. Characterization. Transmission electron microscopy (TEM) and Scanning transmission electron microscopy (STEM) analyses were carried out with Hitachi HF 2000 and Hitachi S-5500 microscopes, respectively. All samples were prepared by dipping the carbon-coated copper or nickel grids into the ethanol solutions of the products and drying at room temperature. In order to directly observe the bimetallic nanoparticles in the hollow cores by HRSEM, STEM and EDX analysis, PtCo@HCS was embedded in Spurr-resin and then cut by a LEICA-Ultracut microtome with a 35 diamond knife. Powder X-ray diffraction (XRD) was performed on a Stoe STADI P diffractometer operating in reflection mode with Cu Kα radiation, using a secondary graphite monochromator. Nitrogen adsorption isotherms were measured with a Micromeritics ASAP2010 adsorption analyzer at 77 K. Prior to the measurements, the sample was degassed at a temperature of 200 C for 6 h. The specific surface areas were calculated from the adsorption data in the relative pressure range of 0.05 to 0.3 using the Brunauer-Emmett-Teller (BET) method. Pore size distribution curves were 2 NATURE MATERIALS

3 SUPPLEMENTARY INFORMATION calculated by using the Barrett-Joyner-Halenda (BJH) method from the adsorption branch (desorption data which are normally recommended, can be influenced by capillary criticality effects). X-ray photoelectron spectroscopy (XPS) measurements were carried out with a Kratos HSi spectrometer with a hemispherical analyzer. The monochromatized Al Kα X-ray source (E = ev) was operated at 15 kv and 15 ma. An analyzer pass energy of 40 ev was applied for the narrow scans. The hybrid mode was used as lens mode. The base pressure during the experiment in the analysis chamber was Pa. To account for charging effects of carbonized samples, the binding energy values were referred to C 1s at ev. Thermogravimetry (TG) measurements were performed on a Netzsch STA 449C thermal analyzer with a heating rate of 10 C min -1. The dynamic light scattering (DLS) measurements were recorded on a Malvern Zetasizer Nano-ZS using laser radiation with a wavelength of 633 nm and a power of 4 mw. The scattered light was measured at a backscattering angle of 173. NATURE MATERIALS 3

4 Table S1. Synthetic conditions of the hollow polymer nanospheres (HPS). No DA (mmol) HMT (mmol) SO (mmol) P123 (mmol) T ( C) Size (nm) Shell thickness (nm) Hollow core size (nm) HPS ±19 36±4 105 HPS ±14 29±3 75 HPS ±14 23±3 66 HPS ±18 38±5 83 HPS ±16 36±5 93 HPS ±25 62±5 164 Contr Contr Contr Contr Contr Contr NATURE MATERIALS

5 SUPPLEMENTARY INFORMATION Figure S1. Photographs of reaction solutions before hydrothermal treatment and the size distributions of micelle/emulsion in H 2 O and DA/HMT solution. The sizes of SO and P123 micelles in H 2 O are ~2.5 nm and ~20 nm, respectively. When adding SO into the P123 micellar solution, the micelle size decreases from 20 nm to 2.5 nm, which indicates the formation of mixed SO/P123 micelles. After mixing with the acidic DA/HMT solution, the size of the P123 micelles increases from ~20 nm to ~30 nm, while the solution is still clear and transparent (Contr-1). For SO, a white emulsion with an average aggregate size of 160 nm was formed after mixing with DA/HMT solution (Contr-4). When mixing SO/P123 solution with DA/HMT solution, the translucent emulsion with an average aggregate size of 60 nm was generated (HPS-1), indicating that the P123 can exert control in the formation of the emulsion. NATURE MATERIALS 5

6 Figure S2. TEM images of the hollow polymer nanospheres synthesized at different conditions. a-c, The HPS synthesized at 160 C with HMT amount of 0.5 mmol (a, HPS-1), 0.75 mmol (b, HPS-2) and 1 mmol (c, HPS-3). d-e, The HPS synthesized at 120 C (d, HPS-4) and 140 C (e, HPS-5) with HMT amount of 0.5 mmol. f, The HPS-6 synthesized at 160 C with higher concentration of DA compared with HPS-1. g-l, The control samples Contr-1, Contr-2, Contr-3, Contr-4, Contr-5, and Contr-6. 6 NATURE MATERIALS

7 SUPPLEMENTARY INFORMATION By increasing the amount of HMT, as shown in Fig. S2a-c, the diameters of HPS decrease from 177 ± 19 nm (HPS-1) to 133 ± 14 nm (HPS-2) and 112 ± 14 nm (HPS-3); the shell thickness of the three samples decreases from 36 ± 4 nm to 29 ± 3 nm and to 23 ± 3 nm, respectively. Calculated from the diameter and shell thickness, the diameters of the hollow cores are 105 nm, 75 nm and 66 nm, respectively (Table S1). In the hydrothermal process, HMT decomposed into formaldehyde and ammonia. With increasing amounts of HMT, the concentration of ammonia increases proportionately and leads to increased ph of the reaction system, possibly leading to shrinkage of the emulsion droplets. Thus, the diameters of the HPS and of the hollow cores decrease with increasing amount of HMT. The reaction temperature also has a slight effect on the diameter of the HPS. As shown in Fig. S2d, e and a, when increasing the temperature from 120 C to 140 C and 160 C, the diameter of the product increases from 159 ± 18 nm (HPS-4) to 165 ± 16 nm (HPS-5) and 177 ± 19 nm (HPS-1). With almost constant shell thickness sizes of the hollow core sizes of 83 nm, 93 nm, and 105 nm can be calculated. This increase size with temperature may be explained by expansion of the emulsion droplets at higher temperature. The concentration of the polymer precursors affects the sizes of HPS as well. When the concentration of DA increases from 1.2 to 2.0 mmol (the molar ratios of DA/HMT were kept constant at 2.4), as shown in Fig. S2a and f, the diameter and shell thickness of the products increases to 288 ± 25 nm and 62 ± 5 nm, respectively. This corresponds to an increased core size of 164 nm, which may also be attributed to the change of the system ph. Some contrast experiments with different molar ratios of SO and P123 were carried out, while keeping the other reaction conditions identical to the ones of HPS-1. As shown in Fig. S2g, using only P123 as surfactant (Contr-1) does not lead to formation of regular hollow structures; adding NATURE MATERIALS 7

8 SO (Contr-2) results in formation of more regular hollow structures, due to formation of mixed emulsions (Fig. S2h), too much SO (Contr-3) results in the generation of polymer networks besides HPS (Fig. S2i). If only SO is used (Contr-4), the size distribution of the as-obtained HPS is very broad (Fig. S2j). Adding P123 results in a uniform and stable emulsion with, from which HPS with narrow size distribution can be obtained (Fig. S2a). However, too much P123 leads to the formation of hollow polymer hemispheres (Contr-5 and 6) because of the instability of the emulsions in hydrothermal process (Fig. S2k-l). 8 NATURE MATERIALS

9 SUPPLEMENTARY INFORMATION Figure S3. TG curves of different samples. a, The TG curves of and oleic acid under argon. b, The TG curves of and under air. NATURE MATERIALS 9

10 Figure S4. TEM images of the treated at different conditions. a-b, The after pyrolysis at 800 C under Ar. c-d, The Pt@HPS with low Pt loading in the hollow cores (0.02 mmol K 2 PtCl 4 used in the synthesis step) after pyrolysis at 800 C. e-f, The Pt@HPS after pyrolysis at 500 C under 5% H 2 /95% Ar. 10 NATURE MATERIALS

11 SUPPLEMENTARY INFORMATION Figure S5. TEM image and size distributions of the metal nanoparticles in a, TEM image of the b, The size distribution of metal nanoparticles in the hollow cores; the average particle size is 3.6 ± 0.7 nm. c, The size distribution of metal nanoparticles in the shells; the average particle size is 1.5 ± 0.3 nm. NATURE MATERIALS 11

12 Figure S6. XPS spectra of a, XPS survey spectra. b, The high-resolution Pt 4f spectra. c, The high-resolution Co 2p spectra. 12 NATURE MATERIALS

13 SUPPLEMENTARY INFORMATION Figure S7. TEM images, XRD pattern and XPS spectra of the sample prepared by the same procedure with but in absence of Pt in the hollow cores. a-b, TEM images of the sample; the size of metal particles is 1.7 ± 0.3 nm. c, The XRD pattern of the sample, indicating that the nanoparticles are Co 3 O 4. d, The Co2p spectrum of the sample, showing the characteristic of a Co 3 O 4 phase. NATURE MATERIALS 13

14 Figure S8. HMF Conversion and product yields as a function of time using PtCo@HCS and PtCo@HCS-crushed as catalysts. a, Time course of HMF conversion and product yields over PtCo@HCS and PtCo@HCS-crushed; reaction conditions: 2 mmol HMF (5 wt% in butanol), 50 mg catalysts, P = 10 bar H 2, T = 180 C; the red symbols indicate the catalytic result after reacting 40 min using PtCo@HCS-crushed as catalyst, the yield of DMF is comparable to the result of PtCo@HCS, indicating that the mass transfer limitation induced by the hollow shells is negligible. b-c, TEM images of the PtCo@HCS-crushed, indicating the hollow structures are crushed completely. 14 NATURE MATERIALS

15 SUPPLEMENTARY INFORMATION Figure S9. Characterization of after using 3 runs in hydrogenolysis of HMF. a-b, TEM images of PtCo@HCS-3runs and the corresponding EDX analysis; the PtCo alloy particles in the hollow cores are stable; some aggregates are formed outside of the shell, which mainly contain cobalt. c, The XRD pattern of PtCo@HCS before and after 3 runs, indicating that the PtCo alloy structure is stable. d, N 2 sorption isotherms of PtCo@HCS before and after using 3 runs; the surface area decreases from 542 m 2 g -1 to 413 m 2 g -1 (Table S3), indicating some blockage of the pore structures after 3 runs. NATURE MATERIALS 15

16 Figure S10. Characterization of Pt/AC and PtCo/AC. a-b, TEM images of Pt/AC, the region in the red square is magnified; the size of metal particles is nonuniform. C-d, TEM images of PtCo/AC, the region in the red square is magnified; the size of metal particles is nonuniform. e, XRD patterns of Pt/AC and PtCo/AC; the pattern of Pt/AC displays the reflections of pure Pt crystals with face-centered cubic (fcc) structure; the slight shift of peak positions for PtCo/AC indicates that Co is incorporated into the Pt fcc structure to form an alloy phase. f, N 2 sorption isotherms of Pt/AC and PtCo/AC; the surface area and pore volume are 1295 m 2 g -1 and 0.95 cm 3 g -1 for Pt/AC, 1045 m 2 g -1 and 0.83 cm 3 g -1 for PtCo/AC (Table S3). 16 NATURE MATERIALS

17 SUPPLEMENTARY INFORMATION Figure S11. Characterization of Pt/GC and PtCo/GC. a-b, TEM images of Pt/GC, the region in the red square is magnified; the size of metal particles is about 2 nm. C-d, TEM images of PtCo/GC, the region in the red square is magnified; some larger metal particles with diameter of 20~50 nm and smaller particles with diameter of about 3.5 nm are observed. e, XRD patterns of Pt/GC and PtCo/GC; the pattern of Pt/GC displays typical reflections of graphitic carbon and pure Pt crystals with face-centered cubic (fcc) structure; the pattern of PtCo/GC shows the reflections of graphitic carbon, Co crystals and PtCo alloy. f, N 2 sorption isotherms of Pt/GC and PtCo/GC; the surface area and pore volume are 228 m 2 g -1 and 0.31 cm 3 g -1 for Pt/GC, 187 m 2 g -1 and 0.26 cm 3 g -1 for PtCo/GC (Table S3). NATURE MATERIALS 17

18 Table S2. Hydrogenation of HMF to DMF reported in literature. Catalyst Temp/time (ºC/min) Hydrogen source Solvent Conversion (%) Yield of DMF (%) TOF (min -1 ) Ref CuRu/C 220/ bar H 2 1-butanol CuRu/C 220/ bar H 2 1-butanol a Pd/C 60/150 1 bar H 2 1-propanol Pd/C 120/60 62 bar H 2 EMIMCl and b acetonitrile Pd/C and H 2SO 4 THF refluxing/900 Formic acid THF - ~70-6 c Cu-PMO 260/180 Methanol Methanol Ru/C 190/360 2-propanol 2-propanol a crude HMF from corn stover was used as substrate. b TOF was calculated on the basis of the total Pd content using the molar ratio of the converted substrate over the catalyst divided by the reaction time. c GC analysis result. 18 NATURE MATERIALS

19 SUPPLEMENTARY INFORMATION Table S3. Textural parameters of samples. Sample S BET (m 2 g -1 ) S mic (m 2 g -1 ) V total (cm 3 g -1 ) V mic (cm 3 g -1 ) Pt@HCS PtCo@HCS PtCo@HCS, after 3 runs Pt/AC Pt/GC PtCo/AC PtCo/GC S BET = specific surface area calculated by the BET method, S mic = micropore surface area calculated by the t-plot method, V mic = micropore volume calculated by the t-plot method, and V total = total pore volume at P/P 0 = NATURE MATERIALS 19