The nature of loading-dependent reaction barrier over mixed

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1 Supporting Information The nature of loading-dependent reaction barrier over mixed RuO2/TiO2 catalysts Hao Li, 1,2 Shenjun Zha, 1,2 Zhi-Jian Zhao, 1,2 Hao Tian, 1,2 Sai Chen, 1,2 Zhongmiao Gong, 3 Weiting Cai, 1,2 Yanan Wang, 1,2 Yi Cui, 3 Liang Zeng, 1,2 Rentao Mu, 1,2 * and Jinlong Gong 1,2 * 1 Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Tianjin , China; 2 Collaborative Innovation Center of Chemical Science and Engineering, Tianjin , China; 3 Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano- Bionics, Chinese Academy of Sciences, Suzhou , China. * murt@tju.edu.cn; jlgong@tju.edu.cn S1

2 Materials and Methods Preparation and Characterization of Catalysts For comparison, r-tio2 (Alfa Aeaser, 99.5%) and a-tio2 (J&K chemical, 99%) with similar textual structure and surface area were selected as the supports (Table S2), which were calcined at 400 C for 8 h in pure oxygen atmosphere to eliminate the oxygen vacancy and possible contaminants. All the catalysts were prepared via wetness impregnation method using RuCl3 xh2o (Energy Chemical Co. LTD, 99%) as precursor. For preparation of RuO2/TiO2 catalysts with different calcined temperatures, the Ru loading was fixed to 2 wt%. Firstly, 0.8 g TiO2 was added to 3.72 ml RuCl3 solution with the Ru concentration of 4.3 mg/ml. Subsequently, the mixture was dried using water bath heating at ~60 C. After further drying at 70 C for 12 h, the solid was calcined at 200, 300, 450, 600 or 750 C respectively in muffle oven with heating rate of 5 C/min. The total calcined time was controlled for 5 h. For preparation of RuO2/TiO2 catalysts with different Ru loadings, the same wetness impregnation method was used by adding 0.8 g TiO2 to 3.72 ml RuCl3 solution with different Ru concentrations. After drying, the catalysts were calcined at 300 C for 5 h. As the loading of Ru increasing, the catalysts become dark in color (Figure S5), indicating more and more RuO2 can be deposited on TiO2. The BET surface areas of the catalysts was measured by nitrogen adsorption at -196 C using a micrometrics tristar II 3020 apparatus. The thermo-gravimetric analysis were conducted under a 50 ml/min air stream with a heating rate of 10 C/min. XRD were performed with 2θ value between 20º and 60º via Rigaku C/max-2500 diffractometer using the Cu Kα radiation (λ = Å). The morphology of catalysts was recorded using Jeol JEM 2010F microscope. Raman spectra were collected by Renishaw invia Reex system using a 532 nm Ar-ion laser beam. S2

3 XPS experiments were taken on a PHI-1600 ESCA instrument (PE Company) employing an Al Kα X-ray radiation source ( hv= ev). In-situ XPS experiments were performed in customized system of Near Ambient Pressure XPS (SPECS GmbH, Germany) equipped with analyzer of PHOIBOS 150 NAP 1D-DLD and monochromatic X-ray of XR 50 MF. During and after CO oxidation, the XPS Ru3d peaks of RuO2/r-TiO2 were collected. CO oxidation was conducted under 1 mbar mixed gas of CO and O2 (CO:O2 = 2:1) at 327 C for 30 min. The binding energy was calibrated by the C1s at ev. Reactivity Test CO oxidation reaction was carried out in a quartz fixed-bed reactor (8 mm inner diameter) loaded with 100 mg catalysts (20-40 mesh) mixed with 1 ml of quartz particles at atmospheric pressure. Before the reactivity test, each catalyst was pretreated in flow 20% O2/N2 (45 ml/min) at 300 C for 2 h and then cooled to room temperature. At room temperature, the reactants (1% CO, 0.5% O2, He balance) were introduced into reactor at a total flow of 50 ml/min. The gas hourly space velocity is set to 30,000 ml h -1 gcat -1. Then the temperature was ramped with a rate of 1 C/min to test reactivity or with a rate of 0.5 C/min to measure the Ea. The tail gas was analyzed by gas chromatograph (GC 2060 Shanghai Instrument) employing thermal conductivity detector (TDX-01 column). The conversion of CO was determined by following equation. XX CCCC = CC CCCC(iiii) CC CCCC (oooooo) CC CCCC (iiii) 100 The Ea was obtained based on the catalytic reactivity under CO conversion less than 20% to exclude diffusion effect and the turnover frequency (molco molru -1 h -1 ) was calculated based on the nominal Ru loading.(1) S3

4 Computational Methods Vienna ab initio simulation package was used to perform calculations with the PBE exchange-correlation functional.(2) Valence electrons were described by a plane-wave basis set with the cut-off energy of 400 ev. Meanwhile, core electrons were treated using projector augmented-wave method.(3) The Monkhorst-Pack k-points grid (2 2 1) was used to sample the Brillouin zone of the surface.(4) The electronic occupancies were determined according to the Gaussian scheme with an energy smearing of 0.05 ev and the total energies were evaluated by extrapolating to zero broadening. The dipole correction was included in the direction perpendicular to the slab surface. The four-layer slab was built with top two layers relaxed and the size of slab was supplied. All structures were optimized until the force on each atom has been less than 0.05 ev/å. Based on the three structures shown in Figure 6, the Bader Charge of Ru atoms is calculated by DFT.(5) S4

5 Table S1. The Raman shift of RuO2/TiO2 with different Ru loading. Ru loading / wt% E g E g B 1g RuO 2 /a-tio 2 RuO 2 /r-tio 2 A 1g + B 1g E g B 1g Two-phonon scattering E g A 1g Table S2. The textures of TiO2 supports and RuO2/TiO2. Ru RuO 2 /a-tio 2 RuO 2 /r-tio 2 loading / wt% Specific surface area a / m 2 /g Pore volumes b / cm 3 /g Specific surface area a / m 2 /g Pore volumes b / cm 3 /g a: Derived from BET. b: Derived from BJH adsorption pore distribution. S5

6 Figure S1. (A-D) The reactivity of RuO2/TiO2 with 2 wt% Ru loading calcined at different temperature and (E) the temperatures for 100 % CO conversion as a function of calcined temperature. S6

7 Figure S2. The thermo-gravimetric analysis (solid lines) and derivative thermogravimetry (dash lines) of RuCl3/TiO2 with 2 wt% Ru. S7

8 Figure S3. TEM images of pure TiO2 and RuO2/TiO2 with 2 wt% Ru loading calcined at 300 o C. S8

9 Figure S4. (A) Survey XPS and (B) enlarged Cl2p peaks from pure r-tio2 and RuO2/r- TiO2 with 1 wt% Ru loading calcined at 300 C. S9

10 Figure S5. Pictures of RuO2/TiO2 catalysts with different Ru loadings. S10

11 Figure S6. (A and B) The reactivity of RuO2/TiO2 with different Ru loadings and (C) the dependence of temperature at 100% CO conversion on Ru loadings. S11

12 Figure S7. XRD patterns of (A) spent RuO2/r-TiO2 and (B) spent RuO2/a-TiO2 with different Ru loading. The Figures on right in (A) or (B) show the enlarged XRD patterns. S12

13 References (1). Zheng, Y.; Li, K.; Wang, H.; Wang, Y.; Tian, D.; Wei, Y.; Zhu, X.; Zeng, C.; Luo, Y. Structure Dependence and Reaction Mechanism of CO Oxidation: A Model Study on Macroporous CeO 2 and CeO 2 -ZrO 2 Catalysts. J. Catal. 2016, 344, (2). Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, (3). Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, (4). Monkhorst, H. J.; Pack, J. D. Special Points for Brillouin-Zone Integrations. Phys. Rev. B 1976, 13, (5). Tang, W.; Sanville, E.; Henkelman, G. A Grid-Based Bader Analysis Algorithm Without Lattice Bias. J. Phys.: Condens. Matter 2009, 21, S13