Supporting Information for

Transcription

1 Supporting Information for Discriminating catalytically active FeN x species of atomically dispersed Fe-N-C catalyst for selective oxidation of C-H bond Wengang Liu,,, Leilei Zhang,, Xin Liu, Xiaoyan Liu, Xiaofeng Yang, Shu Miao, Wentao Wang, Aiqin Wang,*,Tao Zhang,* State Key Laboratory of Catalysis, ichem (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, , China. University of Chinese Academy of Sciences, Beijing, , China. * Correspondence to: aqwang@dicp.ac.cn; taozhang@dicp.ac.cn S1

2 Chemicals and materials. Fe(OAc)2 was purchased from Sinopharm Chemical Reagent Co., Ltd., and other chemicals were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. All the chemicals were in analytical grade and used as received without further purification. Catalyst preparation. A mixture of Fe(OAc)2 (0.5 mmol, 106 mg) and 1,10-phenanthroline monohydrate (1.5 mmol, 330 mg) was added to 50 ml ethanol and sonicated for 10 min, followed by addition of 3.16 g MgO-nano and sonicated for another 10 min. Then the mixture was stirred under reflux at 60 o C overnight. After ethanol was removed by rotary evaporation, the remaining solid was dried at 60 o C for 12 h and then transferred to a quartz boat in the oven and fluxed with N2 for 30 min. The oven was then heated to 700 o C in nitrogen atmosphere at a ramp of 2 o C/min and was held at 700 o C for 2 h. The obtained black solid was stirred with 100 ml 1 mol/l HNO3 solution at room temperature for 2 h and this leaching procedure was repeated for 3 times to remove the MgO support. The recovered solid was washed with water until the filtrate became neutral and then dried at 60 o C for 12 h. The resultant sample is labeled as Fe-N-C. Samples pyrolyzed at different temperatures are denoted as Fe-N-C-X (X = pyrolysis temperature). XAS measurements. The X-ray absorption spectra (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) of the samples at Co K-edge were collected at the BL 14W1 of Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Institute of Applied Physics (SINAP), China. A double Si(111)-crystal monochromator was used for energy selection. Co foil was employed to calibrate the energy. The spectra were collected at transmission mode at room temperature. The Athena software package was used to analyze the data. X-ray diffraction (XRD) analysis was carried out on a PANalytical X pert diffractometer using nickel-filtered Cu Kα radiation with a scanning angle (2θ) of 10 o - 80 o, operated at 40 kv and 40 ma. ICP-AES. The metal loadings of the catalysts were determined with Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) on an IRIS Intrepid Ⅱ XSP instrument (Thermo Electron Corp.). Before analysis, a proper amount of powder sample was treated by hot aqua regia to get a clear solution. Scanning electron microscopy(sem) characterization was carried out with a field-emission JSM-7800F microscope under backscattered electron imaging mode with 15.0 kv accelerating voltage. X-ray photoelectron spectroscopy (XPS) was measured on a Thermo ESCALAB 250Xi spectrometer equipped with an Al anode (Al Kα = ev), operated at 15 kv and 10.8 ma. The background pressure in the analysis chamber was lower than Pa, and the operating pressure was around Pa. The survey and spectra were acquired at a pass-energy of 20 ev. Energy calibration was carried out using the C1s peak of adventitious C at ev. Subångström-resolution HAADF-STEM characterization was conducted on a JEOL JEM-ARM200F STEM/TEM with a guaranteed resolution of 0.08 nm. Prior to being examined, catalyst powders were S2

3 ultrasonicated in ethanol and then dispersed onto TEM copper grids covered with a lacey carbon film and dried at room temperature. Nitrogen sorption isotherms were obtained at -196 o C on a Micromeritics ASAP 2460 apparatus (Quadrasorb SI Automate Surface Area & Pore Size Analyzer). The samples were outgassed at 200 o C and 1 mtorr for 4 h prior to the measurements. Brunauer-Emmett-Teller (BET) surface areas were evaluated from the adsorption isotherm within the pressure range 0.05 <P/P0< 0.3. Pore size distribution was obtained from the adsorption isotherm using the Barrett-Joyner-Halenda (BJH) method. Catalyst evaluation. Unless otherwise noted, the reactions were carried out as following: The reaction was conducted in a flask equipped with a dropwise addition system. Before the reaction test, 10 mg catalyst and substrate (0.5 mmol) were put into the flask. Then TBHP (500 μl, 70 wt % in water) and water (6.5 ml) were added to the titration control system. The reaction mixture was stirred with TBHP titration feedstock at room temperature for 7 h. After the reaction, the solid catalyst was recovered by filtration, while the filtrate was extracted with 30 ml ethyl acetate (10 ml each time). The identification of products was conducted by using a Varian G 450/320 GC/MS system. The products were quantitatively analyzed by using an Agilent 7890A GC system equipped with a HP-5 capillary column and a FID detector. Dodecane was used as an internal standard. Reusability test. After each reaction, the catalyst was separated from the reaction system by centrifugation. Then the collected catalyst was successively washed by water (100 ml*3) and ethanol (100 ml*2), and then dried at 80 o C for 4 h. The obtained powder was submitted to the next batch of reaction. Titration experiment with KSCN. The titration experiment was performed with Fe-N-C-700 catalyst within a kinetically controlled region, that is, the catalyst amount was reduced to 2 mg (corresponding to mmol Fe) while the reaction time was shortened to 5 min. Before the reaction, a specified equivalent of KSCN aqueous solution (1 mg/ml) was injected into the reaction system containing catalyst, then the system was stirred for 10 min. After that, the substrate and oxidant were added as that for normal reaction conditions. Calculation of TOFs based on KSCN titration experiment. Different activity sites can be discriminated based on the rate of activity decrease with addition of KSCN. According to Figure 5, the activity decreasing curve can be divided into three stages: 1 First stage TOF D % 0.5 mmol 60 1 = 5350 h mmol 5 min 0.2 equiv. 2 Second stage TOF D % 0.5 mmol 60 1 = 533 h mmol 5 min 0.3 equiv. 3 Third stage S3

4 TOF D % 0.5 mmol 60 1 = 160 h mmol 5 min 0.5 equiv. 57 Fe Mössbauer spectra of the catalysts were carried out on a Topologic 500A spectrometer driving with a proportional counter at room temperature. The radioactive source was 57 Co (Rh) moving in a constant acceleration mode. Data analyses were performed assuming a Lorentzian line shape for computer folding and fitting. The components of iron phases were identified based on their Mössbauer parameters including isomer shift (δiso), quadruple splitting (ΔEQ) and magnetic hyperfine field. Calculation intrinsic activity of different active site (including D1, D2, and D4 moieties) based on the TOFs per Fe atom as well as their respective fractions of Mössbauer spectra in Figure 5b. TOF can be calculated with the equation: TOF Numbers of products molecules Numbers of Fe atoms reaction time Intrinsic activity of different active site(tof D1, TOF D2 and TOF D4) can be calculated with these equations: TOF Area % TOF Area % TOF D1 D1 D2 D2 600 TOF Area % TOF Area % TOF D2 D2 D4 D4 700 TOF Area % TOF Area % TOF TOF TOF TOF TOF TOF TOF D2 D2 D4 D4 800 D1 D2 D2 D4 D2 D4 D1 D2 D4 14.2% TOF 66.3% % TOF 17.9% % TOF 7.8% Characterization of the Fe-N-C catalyst. S4

5 Intensity(a.u) Scheme S1. Schematic preparation of atomically dispersed Fe-N-C catalyst using a template-sacrificial approach. C(002) C(004) Fe-N-C-600 Fe-N-C-700 Fe-N-C Figure S1. Powder XRD patterns of synthesized Fe-N-C catalyst. Only two broadened peaks centered at 25 o and 43 o were observed, corresponding to the (002) and (004) planes of carbon materials. No diffraction peak of crystalline metal/metal oxide phases can be found. S5

6 Fe-N-C-600 Fe-N-C-700 Fe-N-C-800 G Intensity(a.u) D Raman shift (cm ) Figure S2. Raman spectra of Fe-N-C samples. No any peaks except for the characteristic carbon resonances at 1600 cm-1(g band) and 1350 cm-1(d band) were observed in the Fe-N-C samples. Figure S3. N2 sorption isotherms and pore size distribution of Fe-N-C catalysts. The BET surface area plots and pore size distribution of Fe-N-C catalysts indicated the existence of micropores and mesopores. Specifically, the surface areas were as high as 620 m2/g (Fe-N-C-600), 835 m2/g (Fe-N-C-700) and 748 m2/g (Fe-N-C-800), respectively. These features are favorable for active site exposure and mass transfer. S6

7 Figure S4. Representative SEM images of Fe-N-C-600/700/800 catalysts under different detector modes (left images: UED; right images: BED-C). Fe nanoparticles are absent in the SEM images. S7

8 Figure S5. STEM-DF images (a,b) and HRTEM images (c,d) of Fe-N-C-800 catalyst. Nanoparticles of Fe or Fe x C are indicated with red circles. The white arrow indicates the carbon layers with thickness of 3-5 nm. S8

9 Figure S6. STEM-DF images of Fe-N-C-600 (a, b) and Fe-N-C-700 (c, d) catalysts. No any Fe-containing nanoparticles are observed. S9

10 Signal intensity(a.u) g=4.24 Fe-N-C K Fe-N-C K Fe-N-C K g=4.24 g= B/Guass Figure S7. The EPR spectra of Fe-N-C samples measured at 100 K. The isotropic signal at g=4.24 is assigned to high-spin ferric species corresponding to X-(Fe III N 4 )-Y (D2) moieties. S10

11 Abs(%) FePc Velocity/mms -1 Figure S8. Mössbauer spectra of FePc at 293 K. Figure S9. Conversion-time profiles of different catalysts for selective ethylbenzene oxidation. S11

12 Figure S10. The O1s spectra of the Fe-N-C catalysts. Two peaks at binding energies of ev and ev are ascribed to ketonic C=O groups and C O groups, respectively. S12

13 Figure S11. The structure of the hemoglobin molecule in organism. The simplify structure of hemoglobin molecule is that central ion coordinated with the four nitrogen atoms in the center of the ring at one plane and bonded to the fifth N atom of the imidazole ring of histidine residue in the axial direction while the sixth position of the iron center can reversibly bind oxygen by a coordinate covalent bond. Therefore, our single Fe atom centered clusters could be regarded as a mimic of the enzyme. Figure S12. The XRD patterns (a) and N 2 adsorption isotherms (b) of the Fe-N-C-700 catalyst before and after five cycles of reaction. Figure S13. (a) The normalized XANES spectra at Fe K-edge of the Fe-N-C-700 catalyst before and after five cycles of reaction; (b) The k 2 -weighted Fourier transform spectra of Fe-N-C-700 catalyst before and after five cycles of reaction, as S13

14 well as the reference sample Fe foil. Table S1. The relative concentrations of different N species based on XPS of the three Fe-N-C samples. Catalyst Total N (atom %) Relative concentrations of different N species ( area %) Pyridinic N Pyrrolic N Graphitic N N-oxide Fe-N-C % 45.7% 7.2% 4.2% Fe-N-C % 41.0% 15.0% 12.4% Fe-N-C % 49.7% 14.0% 6.1% Table S2. E 0 Values of the Fe-N-C Samples as well as Reference Samples. Sample Fe foil FeO Fe 3 O 4 α-fe 2 O 3 γ-fe 2 O 3 E 0 (ev) Fe porphyrins Fe(II)Pc Fe(phen) x Fe-N-C-600 Fe-N-C-700 Fe-N-C Table S3. Mössbauer Parameters of FePc. δ iso = Chemical Shift a, ΔE Q = Quadrupole splitting. Doublet δ iso /mm s -1 ΔE Q /mm s -1 Area(%) D D D a Relative to α-iron. The Mössbauer parameters of doublet (D1) correspond well with the pristine Fe II Pc with large quadruple splitting. The doublets D2 and D3 can be associated with Fe III -oxygen adducts in low spin (LS) and high spin (HS) states, respectively. S14

15 Table S4. Comparison of the catalytic performance of Fe-N-C-700 catalyst with those reported in literatures. Catalyst Reactant Reaction conditions Product 25 o C, H 2 O solvent, Fe-N-C TBHP (2-6 equiv.), 0.5mmol substrate (0.6mol% Fe). 25 o C, H 2 O solvent, Fe-N-C TBHP (2-6 equiv.), 0.5mmol substrate (0.6mol% Fe) 140 o C, TBHP (3mol%) + Au/LDH 3 MPaO 2, 47mmol substrate. (0.002mol% Au) 25 o C, CH 3 CN solvent, H 2 O 2 (10 equiv.), 1mmol substrate. (1mol% Cu) 2.3% 150 o C, 1 MPa O 2, Cu/ 20 ml cyclohexane, SBA-15 (50 mg catalyst) 80 o C, H 2 O solvent, N-doped TBHP (3 equiv.), Carbon 1mmol substrate. (10 mg catalyst) 60 o C, CH 3 CN solvent, Graphene H 2 O 2 (20 equiv.), 1.2 mmol substrate. (20 mg catalyst) 80 o C, H 2 O solvent, N/P/S- TBHP (6-7 equiv.) doped 0.5 mmol substrate. Carbon (10 mg catalyst) 150 o C, B,F-doped H 2 O 2 (0.7 equiv.) Carbon 0.8mL substrate. (50 mg catalyst) Conv. Sel. Ref. % % This work This work ref ref ref ref ref ref ref.7 S15

16 Co- SAPO-5 FePc/ graphene Co/ACsalen o C, 1 MPa O 2, 4 g substrate. (20 mg catalyst) 25 o C, CH 3 CN solvent, H 2 O 2 (13.4 equiv.), 0.4 ml substrate. (50 mg catalyst) 80 o C, CH 3 CN solvent, TBHP (0.4 equiv.), 1 mmol substrate. (0.76 mmol% Co) ref ref ref.10 (1) Wang, L.; Zhu, Y.; Wang, J. Q.; Liu, F.; Huang, J.; Meng, X.; Basset, J. M.; Han, Y.; Xiao, F. S. Nat. Commun. 2015, 6, (2) Isaac G. B.; Siegler, M. A. Angew. Chem., Int. Ed. 2016, 55, (3) Duan X. G., Liu W., Yue L., Fu W., Ha M. N., Li J., Lu G. Dalton Trans., 2015,44, (4) Gao, Y.; Hu, G.; Zhong, J.; Shi, Z.; Zhu, Y.; Su, D. S.; Wang, J.; Bao, X.; Ma, D. Angew. Chem., Int. Ed. 2013, 52, (5) Yang, J.-H.; Sun, G.; Gao, Y.; Zhao, H.; Tang, P.; Tan, J.; Lu, A.-H.; Ma, D. Energy Environ. Sci. 2013, 6, (6) Yang, S.; Peng, L.; Huang, P.; Wang, X.; Sun, Y.; Cao, C.; Song, W. Angew. Chem., Int. Ed. 2016, 55, (7) Wang, Y.; Zhang, J.; Wang, X.; Antonietti, M.; Li, H. Angew. Chem., Int. Ed. 2010, 49, (8) Zhu, X.; Zhan, W.; Gao, Y.; Guo, Y.; Guo, X.; Lu, G. Chin. J. Catal., 2016, 37: (9) Deng, D.; Chen, X.; Yu, L.; Wu, X.; Liu, Q.; Liu, Y.; Yang, H.; Tian, H.; Hu, Y.; Du, P.; Si, R.; Wang, J.; Cui, X.; Li, H.; Xiao, J.; Xu, T.; Deng, J.; Yang, F.; Duchesne, P. N.; Zhang, P.; Zhou, J.; Sun, L.; Li, J.; Pan, X.; Bao, X. Sci. Adv. 2015, 1, e (10) Nakatsuka, K.; Yoshii, T.; Kuwahara, Y.; Mori, K.; Yamashita, H. Phys. Chem. Chem. Phys. 2017, 19, S16