SUPPORTING INFORMATION. Synergistic Effect of Segregated Pd and Au Nanoparticles on Semiconducting SiC

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1 SUPPORTING INFORMATION Synergistic Effect of Segregated Pd and Au Nanoparticles on Semiconducting SiC for Efficient Photocatalytic Hydrogenation of Nitroarenes Cai-Hong Hao, 1,5 Xiao-Ning Guo, 1 * Meenakshisundaram Sankar, 2 * Hong Yang, 3 Ben Ma, 1,5 Yue-Fei Zhang, 4 Xi-Li Tong, 1 Guo-Qiang Jin, 1 and Xiang-Yun Guo 1* 1 State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi , China 2 Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, UK 3 Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign, 206 Roger Adams Laboratory, MC-712, 600 South Mathews Avenue, Urbana, Illinois 61801, United States 4 Beijing University of Technology, Institute of Microstructure & Property of Advanced Materials, Beijing , China. 5 University of the Chinese Academy of Sciences, Beijing , China Corresponding Authors * guoxiaoning@sxicc.ac.cn (XNG); Sankar@cardiff.ac.uk (MS); xyguo@sxicc.ac.cn (XYG). S-1

2 Supplementary Tables Table S1. Summary of reaction conditions and catalytic activity of selective hydrogenation of nitroarenes over various supported catalysts. Entry Reactant Catalyst T ( o C) Hydrogen source TOF (h -1 ) Reference 1 Pd/reduced graphene oxide RT NaBH 4 (2.6 eq.) 1.34 Appl. Catal. A- Gen 2015, 503, Pd/PEG RT H 2 balloon 83 J. Catal. 2012, 286,184 Appl. Catal. A- 3 1%Pd/meso-γ-Fe 2 O MPa 982 Gen 2015, 502, 105 Appl. Catal. A- 4 5% Pd/C MPa -- Gen 2005, 286, 167 Appl. Catal. A- 5 Pd-B/SiO MPa -- Gen 2000, 202, 17 6 Au/SiO MPa 208 J. Catal. 2006, 242, 227 S-2

3 7 Au/CeO MPa -- ChemCatChem 2012, 4, MPa 68 8 Au/TiO MPa MPa MPa 52 Science 2006, 313, Au 2.6 Cu 2 40 (CH 3 ) 2 CH OH ACS Catal. 2016, 6, γ-fe 2 O 3 /C 85 N 2 H 4 H 2 O (4 eq.) 13.3 Chem.Commun. 2016, 52, 4199 Appl. Catal. A- 11 Pt/TiO MPa 2457 Gen. 2016, 509, 38 S-3

4 12 Fe-Phen/C MPa 1.7 Science 2013, 342, eosin Y RT (HOCH 2 C H 2 ) 3 N (6 eq.) 4.1 Green Chem. 2014, 16, %Co25%Mo 2 C/AC 80 N 2 H 4 H 2 O 3.2 Green Chem. 2014, 16, Co 3 O 4 -NGr/C 100 HCOOH (3.5 eq.) 23.8 Green Chem. 2015, 17, Ir/SiO MPa 40.7 Nanoscale 2016, 8, J. Am. Chem % Au/TiO MPa 365 Soc. 2007, 129, Pd 13 Pb 9 /SiO RhPb 2 /SiO CH 3 OH Pd 13 Pb 9 /SiO ACS Catal. 2014, 4, 1441 RhPb 2 /SiO Co/NCNT-grown vol% H 2 flow rate ACS Catal. 2014, 4, 1478 S-4

5 ml/min 20 CeO 2 80 N 2 H 4 H 2 O (2.5 eq.) -- Nanoscale 2013, 5, PbBiO 2 X RT (HOCH 2 C H 2 ) 3 N (10 eq.) -- Green Chem. 2011, 13, Ni/SiO N 2 H 4 H 2 O (8 eq.) ACS Catal. 2015, 5, Ind. Eng. 23 Ni/SiO MPa 54.9 Chem. Res. 2010, 49, 4664 S-5

6 Table S2. The saturation adsorption capacity of H 2 on different catalysts at room temperature. Entry Catalyst H 2 (µmol g -1 ) 1 SiC Au 0.5 /SiC Pd 3 /SiC Pd 3 Au 0.5 /SiC Pd 3 Au 1 /SiC Pd 3 Au 1.5 /SiC Pd 3 Au 2 /SiC Pd 3 Au 2.5 /SiC Pd 3 Au 3 /SiC S-6

7 Table S3. Values of adsorption energy calculated from different slabs and adsorption modes on the SiC(111) surface. Mode 1R/3L 2R/3L 3R/3L 1R/4L 2R/4L Paralleled adsorption (ev) Monodentate configurations (ev) Bidentate configurations (ev) We test two slab (6 5) models in different thicknesses and different relaxed surface layers to check the influence of the slab thickness on the adsorption energy. The first slab model has three layers (3L). We relax the top one (1R), top two and top three layers, respectively, and other layers are fixed at the same time (1R/3L, 2R/3L, 3R/3L, respectively). The second slab model has four layers; in which only top layer and top two layers are relaxed and the other layers are fixed (1R/4L and 2R/4L). Using these slab models, we compute the adsorption energies of nitrobenzene in paralleled and vertical adsorption modes. For various numbers of relaxed layers, the same adsorption energies are obtained by using the three-layer or four-layer model. For example, the energy of 2R/3L model is close to those of 3R/3L, 1R/4L and 2R/4L models in both paralleled and vertical adsorption modes. Hence, we employ the 2R/3L model for computing the potential energy surfaces of nitrobenzene reduction. S-7

8 Table S4. Calculated energy barrier Ea (ev), reaction energy E (ev) and rate constant κ (393 K) of all steps for aniline formation via the direct route on the clean and four-hydrogen-atom (4H) precovered SiC(111) surfaces. It can be seen that the rate constants for all reactions on 4H surface have evident increase. Reaction clean SiC(111) surface 4H SiC(111) surface E a (ev) E (ev) κ E a (ev) E (ev) κ PhNO 2 + H PhNOOH PhNOOH + H PhNO + H 2 O PhNO + H PhNOH PhNOH + H PhNHOH PhNHOH+ H PhNH + H 2 O PhNH + H PhNH S-8

9 Supplementary Figures Figure S1. (a) Recyclability in the hydrogenation of nitrobenzene, (b) TEM image and (c) XRD of the Pd 3 Au 0.5 /SiC catalyst after five catalytic cycles. The recyclability of Pd 3 Au 0.5 /SiC catalyst was investigated by reusing it for five runs under the identical conditions. The catalyst can be reused with no measureable loss in both the catalytic activity and selectivity, suggesting the excellent stability of this catalyst. TEM image of the used catalyst shows no obvious change in morphology and aggregation of both Au and Pd nanoparticles. The XRD results of the used catalyst also suggest that the Pd and Au nanoparticles still exist on the SiC surface as metallic phase. These well explain the good recyclability of the Pd 3 Au 0.5 /SiC catalyst. S-9

10 Figure S2. TEM images of the (a) Pd 3 Au 0.5 /SiC, (b) Au 0.5 /SiC, and (c) Pd 3 /SiC catalysts. In (a), the nanoparticles in white circles are Au nanoparticles, the rest are Pd nanoparticles. Figure S3.The size distributions of (a) Pd and (b) Au nanoparticles in the Pd 3 Au 0.5 /SiC catalyst. The statistical results of hundreds of particles show that the average diameters of Pd and Au nanoparticles are 3.9 nm and 8.2 nm, respectively. S-10

11 Figure S4. XRD patterns of SiC, Au 0.5 /SiC, Pd 3 /SiC, Pd 3 Au 0.5 /SiC and Pd 3 Au 0.5 /SiC-heat catalysts. The Pd 3 Au 0.5 /SiC-heat catalyst was obtained by calcinated Pd 3 Au 0.5 /SiC at 400 o C in Ar for 2 h. In the XRD patterns shown in Figure S4, the diffraction peaks detected at 35.6 o, 41.4 o, 60.0 o, 71.8 o, 75.5 o correspond to (111), (200), (220), (311) and (222) planes of β-sic. The peak at 33.6 o is due to stacking faults. The sample of Au 0.5 /SiC shows a diffraction peak at 38.2 o indexed to (111) plane of cubic Au. The sample of Pd 3 /SiC shows a diffraction peak at 46.7 o indexed to (200) plane of cubic Pd. For Pd 3 Au 0.5 /SiC bimetallic catalyst, the diffraction peaks of face-centered cubic Au and Pd are clearly visible, and the positions of Pd or Au diffraction peaks do not shift compared with the corresponding monometallic catalysts. For conventional Pd nanoparticles, the (111) diffraction peak usually is most intensive, however we did not observe the (111) diffraction peak on Pd/SiC or PdAu/SiC catalysts. We think that it is related to the growth of Pd nanocrystallines on SiC. After the Pd 3 Au 0.5 /SiC catalysts were calcinated at 400 o C in Ar for 2 h, the (111) diffraction peak of Pd particles appeared (Pd 3 Au 0.5 /SiC-heat). S-11

12 Figure S5. (a) HAADF-STEM of the alloyed Pd 3 -Au 0.5 /SiC catalyst and (b) the EDX linear scan for a typical Au-Pd nanoparticle indicated by the orange line in (a). The preparation of the alloyed Pd 3 -Au 0.5 /SiC catalyst: 965 mg of SiC powder was dispersed in 28.2 ml of Pd(NO 3 ) 2 aqueous solution (0.01 M) and 4.3 ml of HAuCl 4 aqueous solution (2 mg/ml). After stirring for 30 min, 20 ml of lysine aqueous solution (0.53 M) was dropwise added in the above suspension. After stirring for another 30 min, 10 ml of NaBH 4 solution (0.35 M) was added in 20 min, then 10 ml of 0.3 M HCl was dropwise added in the above suspension. The mixture was placed under stirring for 24 h. Finally, the mixture was separated, washed and dried to obtain Pd 3 -Au 0.5 /SiC catalyst. Figure S5 shows that the nanoparticles consist of both Pd and Au distributed spherically around a common center, which means that the two metals exist as binary alloy nanoparticles in this sample. S-12

13 Figure S6. XPS results of (a) Pd 3 /SiC and (b) Au 0.5 /SiC catalysts. Figure S7. (a) PL spectra under 320 nm excitation wavelength at room temperature and (b) time-resolved transient PL decay (TR-PL) spectra under 375 nm excitation wavelength and 460 nm emission wavelength of SiC, Au 0.5 /SiC, Pd 3 /SiC, Pd 3 Au 0.5 /SiC. S-13

14 Figure S8. Dependences of the catalytic activity of Pd 3 Au 0.5 /SiC for nitrobenzene hydrogenation to aniline on the (a) irradiation intensity and (b) wavelength. The red line in (b) is the absorption spectrum of Pd 3 Au 0.5 /SiC catalyst. When performing the reaction in dark, the Pd 3 Au 0.5 /SiC catalyst yields a nitrobenzene conversion of only 19% (TOF, 290 h -1 ), indicating the crucial role of light to the catalytic activity. Further experiment showed a linear increase in the catalytic activity (TOF, from 900 to 1715 h -1 ) with light intensity (from 0.3 to 0.8 Wcm -2 ) over Pd 3 Au 0.5 /SiC (Figure S8a). The damping of catalytic activity is due to the decrease in the number of energized electrons at low irradiation intensity. The dependence of catalytic activity on the irradiation wavelength was also investigated by using different optical filters. The TOF value is 1715, 1305, 1020, and 393 h -1 for the wavelength range of , , , and nm respectively. Since the TOF value is only 290 h -1 in the dark reaction, the light-induced conversion within each wavelength range contributes about 29% for nm, 20% for nm, 44% for nm, and 7% for nm (Figure S8b). These values are consistent with the UV-visible absorption of the Pd 3 Au 0.5 /SiC catalyst. The light absorption below 460 nm mainly generates separated electrons and holes in the conduction and valence bands of SiC, respectively. Meanwhile, the LSPR absorption of Au nanoparticles in S-14

15 nm also produces energetic hot electrons that will be injected to the conduction band (CB) of SiC. These energetic electrons in CB can effectively activate the nitro group in nitrobenzene adsorbed on the SiC surface. Therefore, the irradiation with wavelengths in these ranges has the largest contribution on the reaction. The near infrared light from nm appears to have smaller impact on the reaction because it is mainly converted into thermal energy and enhances the reaction via heating the reaction system. Figure S9. (a) Dependence of the catalytic activity (C) on the adsorption quantity of atomic hydrogen (Q H ) and (b) H 2 -TPD profile obtained from SiC. S-15

16 Figure S10. Linear sweeping voltammetry curves of SiC, Au 0.5 /SiC, Pd 3 /SiC and Pd 3 Au 0.5 /SiC. Electrochemical measurements were performed on a CHI 760D electrochemical workstation with a standard three electrode cell. The platinum plate and saturated Ag/AgCl electrode were used as the counter and reference electrodes, respectively. A glassy carbon electrode (GCE, 5 mm diameter) was used as the substrate for the working electrode. To prepare the working electrodes, 5.0 mg catalyst powder was dispersed into 1.0 ml ethanol and 10 μl Nafion solutions. After sonication for 30 min, 5 μl of catalyst suspension was dropped on the surface of GCE, and dried at ambient temperature. Linear sweep voltammetry (LSV) was conducted in H 2 SO 4 solution (0.5 M), beginning at 0.5 V and ending at -0.5V with a scan rate of 5 mv/s. S-16

17 Figure S11. XPS spectra of C 1s (a, c) and Si 2p (b, d) in samples of SiC and Pd 3 Au 0.5 /SiC. Figure S12. PL spectra under 320 nm excitation wavelength at room temperature of Pd 3 /SiC (a) and Pd 3 Au 0.5 /SiC (b) before and after H 2 adsorption. S-17

18 Figure S13. In-situ diffuse reflectance FT-IR spectra of Pd 3 Au 0.5 /SiC before and after H 2 adsorption at 300 o C (The spectrum of Pd 3 Au 0.5 /SiC was used as the background). S-18

19 Figure S14. Top views of the optimized intermediate geometries (initial state/is, transition state/ts, final state/fs) and the potential energy surfaces (in ev) for nitrobenzene hydrogenation to aniline on SiC(111) surface via direct route (Ph represents the benzene ring, C/gray, Si/yellow, N/blue, O/red, H/green, C in benzene ring/black; Ph represents the benzene ring). S-19

20 Figure S15. Top views of the optimized intermediate geometries and the potential energy surfaces (in ev) for nitrobenzene hydrogenation to aniline on SiC(111) surface via condensation route (Ph represents the benzene ring, C/gray, Si/yellow, N/blue, O/red, H/green, C in benzene ring/black; Ph represents the benzene ring). S-20

21 Figure S16. The catalytic performances of pure SiC for nitrobenzene hydrogenation at different H 2 pressures at 120 o C. With the increase of H 2 pressure, the aniline selectivity increases. S-21