Isolated Single-Atomic Ru Catalyst Bound on a Layered. Double Hydroxide for Hydrogenation of CO 2 to Formic Acid

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1 Supporting Information Isolated Single-Atomic Ru Catalyst Bound on a Layered Double Hydroxide for Hydrogenation of CO 2 to Formic Acid Kohsuke Mori *,,,, Tomohisa Taga, and Hiromi Yamashita *,, Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka , Japan JST, PRESTO, HonCho, Kawaguchi, Saitama, , Japan Unit of Elements Strategy Initiative for Catalysts & Batteries, Kyoto University, Katsura, Kyoto , Japan Corresponding Author *K. M. mori@mat.eng.osaka-u.ac.jp *H. Y. yamashita@mat.eng.osaka-u.ac.jp

2 General procedure for preparation of LDHs: A typical example for Mg 10 Al 2 (OH) 24 CO 3 is as follows. Al(NO 3 ) 3 9H 2 O (0.01 mol) and Mg(NO 3 ) 2 6H 2 O (0.05 mol) were dissolved in deionized water (100 ml), and a second aqueous solution (60 ml) of Na 2 CO 3 (0.03 mol) and NaOH (0.07 mol) was prepared. After slow addition of the first solution to the second one, the resulting mixture was heated at 65 C for 18 h with vigorous stirring. The white slurry was then cooled to room temperature, filtered, washed with large amount of deionized water, and dried overnight at 110 C. Synthesis of catalyst: RuCl 3 nh 2 O (6.80 mg) was placed in a flask and dissolved in deionized water (85 ml) and 0.2 M NaOH solution (10 ml). LDH (0.5 g) was added to the resulting precursor solution and stirred at 50 C for 8 h. The resulting slurry was recovered by centrifugation, washed with deionized water, and dried overnight under vacuum, yielding Ru/LDH as a gray powder. Characterization: BET surface area measurements were performed using an N 2 adsorption-desorption instrument (BEL-SORP max, BEL Japan, Inc.) at 77 K. The sample was degassed under vacuum at 80 C for 24 h prior to data collection. Inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements were performed using a Nippon Jarrell-Ash ICAP-575 Mark II spectrometer. TEM micrographs were obtained using a field emission (FE)-TEM (Hf-2000, Hitachi) instrument equipped with an energy-dispersive X-ray detector (Kevex) operated at 200 kv. HAADF-STEM was obtained using JEOL JEM-2100F microscopes. XPS spectra were measured using a Shimadzu AXIS-ULTRA DLD instrument. Ru K-edge XAFS spectra were recorded in fluorescence-yield collection technique mode at the beam line 01B1 station with an attached Si(111) monochromator. In a typical experiment, a pellet sample was placed into a batch-type in situ XAFS cell. XAFS data were examined using the REX2000 program (Rigaku). General procedure for catalytic hydrogenation of CO 2 : The catalyst (0.1 g) and 1 M NaHCO 3 aqueous solution (10 ml) were loaded into an autoclave, and the pressure was increased to 1.0 MPa of CO 2 and then increased to 2.0 MPa with H 2. The system was heated to 100 C and stirred for 24 h. The yield of formic acid was determined by HPLC using a Shimazu HPLC instrument equipped with a Bio-rad Aminerganic Analysis Column and an Aminex HPX-87H Ion Exclusion Column. 5 mm H 2 SO 4 (0.500 ml/min) was used as mobile phase at 40 C.

3 Measurement of CO 2 adsorption capacity: CO 2 adsorption was determined using TG-DTA (Rigaku, Thermo Plus EVO II). The sample (0.05 g) was heated to 110 C, and this temperature was maintained for 3 h under a N 2 flow (100 ml/min) to remove the physically adsorbed water. The sample was then cooled down to 30 C, and this temperature was held for 60 min to stabilize the sample weight and temperature. The amount of adsorbed CO 2 was monitored for 13 h under a flow of CO 2 (10 ml/min) and N 2 (90 ml/min). This adsorption time was sufficient to allow consideration of the amount of adsorbed CO 2 in a pseudo-equilibrium capacity.

4 Figure S1. UV-vis spectra of RuCl 3 aqueous solution and RuCl 3aq with NaOH.

5 Figure S2. Ru K-edge (A) XANES spectra and (B) FT-EXAFS spectra of RuCl 3 aqueous solution and RuCl 3aq with NaOH.

6 Figure S3. XRD pattern of (a) Ru/LDH and (b) LDH.

7 Figure S4. Cl 2p XPS spectra of (a) Ru/LDH and (b) RuCl/LDH.

8 Figure S5. Ru K-edge XANES spectra of Ru/LDH and reference samples.

9 Figure S6. (A) FT-EXAFS spectra of Ru/LDH Ru/LDH before and after desorption treatment, (B) Inverse-FT of Ru K-edge k 3 -weighted EXAFS and Curve-fitting result for Ru/LDH after desorption treatment, (C) Inverse-FT of Ru K-edge k 3 -weighted EXAFS and Curve-fitting result for as-synthesized Ru/LDH without desorption treatment, and (D) Inverse-FT of Ru K-edge k 3 -weighted EXAFS for RuCl 3, RuO 2, and Ru foil.

10 Figure S7. 13 C NMR spectrum of the product solution after the hydrogenation of 13 CO 2 by Ru/LDH catalyst in D 2 O solvent (0.5 M NaOH).

11 Figure S8. Ru K-edge FT-EXAFS of (a) fresh Ru/LDH (red line) and (b) recovered Ru/LDH (dotted black line).

12 Figure S9. Ru K-edge FT-EXAFS of various Ru samples.

13 Figure S10. Ru 3p XPS spectra of various Ru samples.

14 Figure S11. Effect of temperature and Arrhenius plots of lnk vs. 1/T for Ru/LDH.

15 Figure S12. Effect of (A) H 2 and (B) CO 2 pressure and (C) (D) their log plots at 100 C

16 Table S1. Results of curve-fitting analysis of Ru/LDH. sample shell N R/Å Δσ 2 /Å 2 Desorbed Ru/LDH As synthesized Ru/LDH Ru O (1) Ru O (2) Ru O (1) Ru O (2) N: Coordination number, R: distance, Δσ 2 : Debye-Waller factor