Supporting Information

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1 Supporting Information Highly Active and Selective Hydrogenation of CO 2 to Ethanol by Ordered Pd-Cu Nanoparticles Shuxing Bai, Qi Shao, Pengtang Wang, Qiguang Dai, Xingyi Wang, Xiaoqing Huang * College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Jiangsu , China. Research Institute of Industrial Catalysis, School of Chemistry & Molecular Engineering, East China University of Science & Technology, Shanghai , China hxq006@suda.edu.cn Experimental section Synthesis of ordered Pd-Cu nanoparticles (NPs). In a typical preparation of ordered Pd 2 Cu NPs, palladium (II) acetylacetonate (Pd(acac) 2, 10.0 mg), copper (II) acetylacetonate (Cu(acac) 2, 6.7 mg), ferric chloride hexahydrate (FeCl 3 6H 2 O, 5.4 mg), ascorbic acid (AA, 35.6 mg) and 5 ml oleylamine were added into a vial (volume: 35 ml). After the vial had been capped, the mixture was ultrasonicated for 120 min. The resulting homogeneous mixture was heated from room temperature to 160 ºC in 30 min and maintained at 160 ºC for 5 h and then heated from 160 ºC to 180 ºC in 10 min and maintained at 180 ºC for 3 h in an oil bath, before it cooled to room temperature. The resulting colloidal products were collected by centrifugation and washed three times with a cyclohexane/ethanol mixture. The synthetic conditions for Pd 1.5 Cu NPs and Pd 1 Cu NPs were similar to that of Pd 2 Cu NPs except changing the amounts of Cu(acac) 2 to 10.0 and 13.3 mg, respectively. Synthesis of Pd NPs. Pd(acac) 2 (10.0 mg), tri-n-octylphosphine (TOP, 0.05 ml), l ml oleic acid and 4 ml oleylamine were added into a vial (volume: 35 ml). After the vial had been capped, the mixture was ultrasonicated for 120 min. The resulting homogeneous mixture was heated from room temperature to 160 ºC in 30 min and maintained at 160 ºC for 5 h in an oil bath, before it cooled to room temperature. The resulting colloidal products were collected by centrifugation and washed three times with a cyclohexane/ethanol mixture. Preparations of supported catalysts. Pd-Cu NPs and support (CeO 2 (Inoke), Al 2 O 3 (Alfa Aesar), P25 (Degussa) or SiO 2 (Degussa)) were mixed in 5 ml of chloroform and stirred for 3 h to load the S1

2 Pd-Cu NPs on different supports. The products were separated by centrifugation and washed with acetone for three times. The Pd-Cu NPs/support were subjected to thermal annealing in Air at 300 ºC for 1 h and then in 5% H 2 /N 2 atmosphere at 300 ºC for 1 h. The resulting products were denoted as Pd-Cu NPs/CeO 2, Pd-Cu NPs/Al 2 O 3, Pd-Cu NPs/P25, and Pd-Cu NPs/SiO 2, respectively. Characterizations. Powder X-ray diffraction (PXRD) patterns were collected using an X Pert-Pro X-ray powder diffractometer equipped with a Cu radiation source (λ = nm). The morphologies and sizes of the NPs were determined by transmission electron microscope (TEM) (Hitachi, HT7700) at 120 kv. High resolution transmission electron microscopy (HRTEM), and elemental line scans were conducted on a JEOL-2100F transmission electron microscope at an acceleration voltage of 200 kv. Energy dispersive X-ray spectroscopy (EDS) was performed on a scanning electron microscope (Hitachi, S-4700). All the X-ray photoelectron spectroscopy (XPS) spectra of the Pd-Cu NPs were collected by XPS (Thermo Scientific, ESCALAB 250 XI). The concentrations of all the catalysts were determined by the inductively coupled plasma atomic emission spectroscopy (ICP-AES) (710-ES, Varian). Electron spin resonance (ESR) measurements have been performed on a BRUKER EMX-8/2.7C X-band spectrometer with 100 khz modulation at low temperature (77 K). The microwave frequency was 9.85 GHz. Catalytic tests. The catalysts were prepared by loading Pd-based NPs on different supports (CeO 2, Al 2 O 3, P25, and SiO 2 ). The CO 2 hydrogenation was performed in a 60 ml stainless-steel autoclave. After the additions of 5 ml H 2 O and 5 mg catalysts into a Teflon inlet, the autoclave was pressurized with CO 2 (0.8 MPa) and H 2 (2.4 MPa). The reaction was performed at 200 ºC with stirring at 300 rpm for 5 h. After completion of the reaction, the gaseous mixture was analyzed using a gas chromatograph (Shiweipx GC-7806) equipped with a GDX-502 column connected to a thermal conductivity detector. The liquid mixture was collected by centrifugation at rpm for 3 min. 5 μl of acetone was introduced into 1 ml of the reaction mixture as an internal standard. The liquid mixture was analyzed using a gas chromatograph (Persee G5) equipped with a KB-5 column connected to a flame ionization detector. The tests were repeated three times for each catalyst. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) test. DRIFTS experiments were conducted at 200 ºC by a Nicolet 6700 Fourier transform infrared (FTIR) equipped with the liquid nitrogen cooled mercury-cadmium-telluride detector (MCT). The wavenumber resolution is 4 cm -1. The DRIFTS cell (Harrick, HVC-DRP) fitted with ZnSe windows was used as the reaction chamber. After flowing Ar (50 ml min -1 ) for 0.5 h, the background spectrum of the sample was acquired. CO 2 /Ar (3.3/46.7 ml min -1 ), CO 2 /H 2 /Ar (3.3/10/36.7 ml min -1 ) and Ar (50 ml min -1 ) were then allowed to flow into the cell in turn at 200 ºC for 0.5 h, respectively. The spectras were recorded after the exposure of Pd-Cu NPs/P25 to these three gas flows. With CH 3 OH, C 2 H 5 OH and S2

3 CO as probes, CH 3 OH/Ar, C 2 H 5 OH/Ar or CO/Ar (5/45 ml min -1 ) and Ar (50 ml min -1 ) were allowed to flow into the cell in turn at 200 ºC for 0.5 h, respectively. The adsorption spectras were recorded after CH 3 OH, C 2 H 5 OH and CO absorbed on the Pd 2 Cu NPs/P25. Figures and tables Figure S1. TEM images of (a, b) Pd 1.5 Cu NPs and (c, d) Pd 1 Cu NPs. The scale bars in (a) and (c) are 20 nm. The scale bars in (b) and (d) are 100 nm. S3

4 Figure S2. SEM-EDS spectra of the Pd 2 Cu NPs, Pd 1.5 Cu NPs and Pd 1 Cu NPs. Figure S3. TEM images of (a) Pd 1.5 Cu NPs/P25 and (b) Pd 1 Cu NPs/P25. The scale bars are 20 nm. S4

5 Figure S4. TEM images of (a) Pd 2 Cu NPs/Al 2 O 3, (b) Pd 2 Cu NPs/CeO 2 and (c) Pd 2 Cu NPs/SiO 2. The scale bars are 20 nm. Figure S5. XRD patterns of P25, Pd NPs/P25, Pd 2 Cu NPs/P25, Pd 1.5 Cu NPs/P25, and Pd 1 Cu NPs/P25. S5

6 Figure S6. The GC-TCD spectra of H 2, CO 2, CO, CH 4, and gas mixture before and after reaction (Left). The magnified GC spectra of gas mixture before and after reaction (Right). Figure S7. The GC-FID spectra of CH 3 OH, C 2 H 5 OH, and reaction liquid. S6

7 Figure S8. TOF Pd values of CH 3 OH and C 2 H 5 OH over (a) Pd 2 Cu NPs with different loadings on P25 and (b) Pd 2 Cu NPs supported on different support. Figure S9. ESR spectra with the values of (a) magnetic field and (b) the g-factor of P25, Pd NPs/P25, Pd 2 Cu NPS/P25, Pd 1.5 Cu NPs/P25 and Pd 1 Cu NPs/P25. S7

8 Figure S10. XPS curves of Ti 2p of (a) P25, (b) Pd NPs/P25, (c) Pd 2 Cu NPS/P25, (d) Pd 1.5 Cu NPs/P25, and (e) Pd 1 Cu NPs/P25. (f) The Ti 3+ ratios on the surface of these samples. Figure S11. TEM images of (a, b) Pd NPs. The scale bars in (a) and (b) are 20 nm and 100 nm, respectively. S8

9 Figure S12. TOF Pd values of CH 3 OH and C 2 H 5 OH over 1.23 wt% Pd 2 Cu NPs/P25 at different temperatures for 5h. Figure S13. Product yields of CH 3 OH and C 2 H 5 OH and selectivity of C 2 H 5 OH achieved with (a) 1.23 wt% Pd 2 Cu NPs/P25 and (b) 10 wt% Pd/C over six rounds of successive reactions. S9

10 Figure S14. TEM images (a, b) of 1.23 wt% Pd 2 Cu NPs/P25 after six rounds of successive reactions. The scale bars in (a) and (b) are 20 nm and 50 nm, respectively. Figure S15. TEM images of 10 wt% Pd/C catalyst before (a, b) and after (c, d) six rounds of successive reactions. The scale bars in (a) and (c) are 20 nm. The scale bars in (b) and (d) are 100 nm. S10

11 Figure S16. XPS curves of Pd 3d of Pd NPs/P25, Pd 2 Cu NPs/P25, Pd 1.5 Cu NPs/P25 and Pd 1 Cu NPs/P25. Figure S17. XPS curves of Cu 2p of (a) Pd 2 Cu NPs/P25, (b) Pd 1.5 Cu NPs/P25 and (c) Pd 1 Cu NPs/P25. S11

12 Figure S18. (a) DRIFTS spectra of Pd 2 Cu NPs/P25 after the exposure to CO 2 + Ar at 150 ºC and after the exposures to CO 2 + Ar, CO 2 + H 2 + Ar and after aerofluxus to Ar in turn at 200 ºC. (b) Adsorption spectra after CH 3 OH, C 2 H 5 OH, CO, and CH 4 absorbed on the Pd 2 Cu NPs/P25. DRIFTS spectra of Pd-based NPs/P25 after (c) CO 2 + H 2 + Ar and (d) CO + Ar aerofluxus at 200 ºC. S12

13 Figure S19. DRIFTS spectra of Pd NPs/P25, Pd 2 Cu NPS/P25, Pd 1.5 Cu NPs/P25, and Pd 1 Cu NPs/P25 after the exposures to (a) CO 2 /Ar, (b) CO 2 /H 2 /Ar at 200 ºC. Table S1. CO 2 hydrogenation activities over different catalysts. Entry Catalysts Pd Contents Product Yields /mmol g -1 h -1 TOFs Pd /h -1 C 2 H 5 OH /wt %, ICP CH 3 OH C 2 H 5 OH CH 3 OH C 2 H 5 OH Selectivities /% 1 Pd 2 Cu NPs/P ± ± ± ± Pd 2 Cu NPs/P ± ± ± ± Pd 2 Cu NPs/P ± ± ± ± Pd 2 Cu NPs/P ± ± ± ± Pd 2 Cu NPs/SiO ± ± ± ± Pd 2 Cu NPs/CeO ± ± ± ± Pd 2 Cu NPs/Al 2 O ± ± ± ± Pd/C ± ± ± ± Pd NPs/P ± ± ± ± Pd 1.5 Cu NPs/P ± ± ± ± Pd 1 Cu NPs/P ± ± ± ± S13

14 Table S2. The C 2 H 5 OH synthesis from CO x hydrogenation activities over different catalysts. Catalysts CO x T /ºC P /Mpa Product Yields /mmol g -1 h -1 C 2 H 5 OH Selectivities /% TOFs /h -1 Refs. 1.23%Pd 2 Cu NPs/P25 CO This work 1%Pt/Co 3 O 4 CO [1] 1%Ru/Co 3 O 4 CO [1] 1%Rh/Co 3 O 4 CO [1] 1%Pd/Co 3 O 4 CO [1] 1.2%RhMnLiFe-in-CNTs CO [2] Rh/SiO 2 CO [3] CuCoMo CO [4] Au/TiO 2 CO > [5] 8.7%Pd-10%Cu/SiO 2 CO (CH 3 OH) 1.4 [6] Ru 3(CO) 12, Co 4(CO) 12, PPNCl CO [7] Table S3. XPS results of Pd NPs/P25, Pd 2 Cu NPs/P25, Pd 1.5 Cu NPs/P25 and Pd 1 Cu NPs/P25. Catalysts Pd/Cu /at% / at% Pd 0 3d 5/2 /ev Pd 2+ 3d 5/2 /ev Pd 0 /at% Pd 2+ /at% Cu 0 2p 3/2 /ev Cu 2+ 2p 3/2 Pd NPs/P Pd 2 Cu NPs/P25 48 / Pd 1.5 Cu NPs/P25 37 / Pd 1 Cu NPs/P25 28 / /ev Cu 0 /at% Cu 2+ /at% 3 H H 2 H 2CO 2 CO 2 HOCO 2 CO + 2 HO CHO + CO + 2H O * 2 * * * 2 * * H CH OH + CO + 2H O CH + OH + CO + 2H O CH + CO + 3H O * * * * * 2 * * H H CH CO + 3H O CH CH O + 3H O 2 CH CH OH + 3H O * * Scheme S1 Conceivable reaction mechanism of CO 2 hydrogenation to C 2 H 5 OH on Pd-Cu NPs/P25. [1] Z. He, Q. Qian, J. Ma, Q. Meng, H. Zhou, J. Song, Z. Liu, B. Han, Angew. Chem. Int. Ed. 2016, 55, [2] X. Pan, Z. Fan, W. Chen, Y. Ding, H. Luo, X. Bao, Nat. Mater. 2007, 6, [3] N. Yang, A. J. Medford, X. Liu, F. Studt, T. Bligaard, S. F. Bent, J. K. Nørskov, J. Am. Chem. Soc. 2016, 138, [4] G. Prieto, S. Beijer, M. L. Smith, M. He, Y. Au, Z. Wang, D. A. Bruce, K. P. Jong, J. J. Spivey, P. E. Jongh, Angew. Chem. Int. Ed. 2014, 53, [5] D. Wang, Q. Bi, G. Yin, W. Zhao, F. Huang, X. Xie, M. Jiang, Chem. Commun., 2016, 52, [6] X. Jiang, N. Koizumi, X. Guo, C. Song, Appl. Catal. B: Environ. 2015, 170, [7] M. Cui, Q. Qian, Z. He, Z. Zhang, J. Ma, T. Wu, G. Yang, B. Han, Chem. Sci., 2016, 7, S14