Supporting Information

Transcription

1 Supporting Information Highly stable bimetallic AuIr/TiO 2 catalyst: physical origins of the intrinsic high stability against sintering Chang Wan Han 1, Paulami Majumdar 2, Ernesto E. Marinero 1, Antonio Aguilar-Tapia 3, Rodolfo Zanella 3, Jeffrey Greeley 2, and Volkan Ortalan 1* 1. School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA School of Chemical Engineering, Purdue University, West Lafayette, IN, USA Centro de Ciencias Aplicadas y Desarrollo Technologico, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico * Corresponding author: vortalan@purdue.edu

2 1. Methods 1.1. HRTEM and HAADF-STEM imaging for particle size measurement The high-resolution transmission electron microscopy (HRTEM) imaging and high-angle annular dark-field (HAADF) STEM imaging were performed at 300 kv using an FEI Titan microscope at the Birck Nanotechnology Center, Purdue University and FEI Titan S probe corrected microscope at Oak Ridge National Laboratory. The microscopy images acquired from the bimetallic AuIr and monometallic Au supported on TiO 2 characterize the steady state (long-term) stability of the catalyst samples. Particle size measurements for AuIr nanoparticles and Au nanoparticles were performed using the ImageJ software 1 from the collected HRTEM and HAADF-STEM images HAADF-STEM Tomography Two HAADF-STEM tilt series and one tilt-series were collected from the Au/TiO 2 and AuIr/TiO 2 using an FEI Titan microscope at the Birck Nanotechnology Center, Purdue University. Since Au nanoparticles were highly sintered, the number of Au nanoparticles found at high magnification tilt-series was too low to get a good statistic information. Therefore, we collected a low magnification tilt-series from the Au/TiO 2 having enough number of Au nanoparticles. The collected HAADF-STEM tilt series were aligned by the fiducial marker alignment implemented in the IMOD software package. 2 STEM-tomograms were reconstructed from the aligned tilt-series using TEMBIR method, 3 which provides less missing wedge artifacts and better signal to noise (SNR) ratio compared to those obtained by conventional weighted back projection (WBP) and simultaneous iterative reconstruction technique (SIRT). The reconstructed

3 tomograms were segmented by thresholding and manual inspection. Segmented tomograms were visualized by surface-rendering method and quantified by VGS Avizo software to get inter-particle nearest neighbor distance. Surface rendered tomogram of Au/TiO 2 (high mag.), Au/TiO 2 (low mag.), and AuIr/TiO 2 are shown in Figure S1, S2, and S3, respectively. Tomogram movies are also available.

4 2. Tomogram Movie Captions Movie S1. Surface rendered tomogram of Au/TiO 2 (Magnification: 320,000x, Voxel size: Å 3, Tilt series collection range: 70 to + 70 (5 increment)). Movie S2. Surface rendered tomogram of Au/TiO 2 (Magnification: 115,000x, Voxel size: Å 3, Tilt series collection range: 68 to + 70 (1 increment)) Movie S3. Surface rendered tomogram of AuIr/TiO 2 (Magnification: 320,000x, Voxel size: Å 3, 58 to 70 (2 increment))

5 3. Supplementary Figures Figure S1: Selected frames from the surface rendered tomogram movie (Movie S1) of Au/TiO 2 (High mag.).

6 Figure S2: Selected frames from the surface rendered tomogram movie (Movie S2) of Au/TiO 2 (Low mag.). For better visibility of Au nanoparticles, TiO 2 supports are transparently rendered.

7 Figure S3: Selected frames from the surface rendered tomogram movie (Movie S3) of AuIr/TiO 2.

8 References 1. Schneider, C. a, Rasband, W. S. & Eliceiri, K. W. NIH Image to ImageJ: 25 years of image analysis. Nat. Methods 9, (2012). 2. Kremer, J. R., Mastronarde, D. N. & McIntosh, J. R. Computer visualization of three-dimensional image data using IMOD. J. Struct. Biol. 116, (1996). 3. Venkatakrishnan, S., Drummy, L. F., Jackson, M. A., De graef, M. & Bouman, C. A. A Model Based Iterative Reconstruction Algorithm For High Angle Annular Dark Field-Scanning Transmission Electron Microscope. IEEE Trans. Image Process. 22, (2013).