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Role of Support in the Spontaneous Oxidation of Ultra-small Platinum Nanoparticles

This study investigates the effect of support materials on the spontaneous oxidation of ultra-small platinum nanoparticles. The results show that nanoparticle size, support porosity, and metal loading all play a role in the extent of oxidation. The findings have implications for the design of catalyst materials.

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Role of Support in the Spontaneous Oxidation of Ultra-small Platinum Nanoparticles

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  1. Role of Support in the Spontaneous Oxidation of Ultra-small Platinum Nanoparticles Ritubarna Banerjee Qiuli Liu, John M.M.Tengco, JadidSamad, John R. Regalbuto SECS Symposium 09/19/2016

  2. Background 2c Pt-Al2O3 PtOx • It has been reported that ultra-small supported nanoparticles of • Pt tend to be oxidized either completely or partially when exposed • to air at room temperature following the reduction • Tang et al reported oxidation in Pt nanoparticles: • Oxide content decreased with increasing particle size 2c Pt-CNT 5c Pt-Al2O3 James R. Gallagher, Tao Li, Haiyan Zhao, JingjingLiu, Yu Lei, Xiaoyi Zhang, Yang Ren, Jeffrey W. Elam, Randall J. Meyer, Randall E. Winansand Jeffrey T. Miller, Catal. Sci. Technol., 2014, 4, 3053 Yawen Tang , Lingling Zhang , Yanen Wang , Yiming Zhou, Ying Gao, Changpeng Liu , Wei Xing , Tianhong Lu, Journal of Power Sources 162 (2006) 124–131

  3. XRD: Solid State Detectors Scintillation Detector D-Tex Ultra Detector • Advantages: • Ability to detect ultra-small nanoparticles (≥ 0.8 nm) at low weight loadings • 2 orders of magnitude more sensitive than scintillation detectors (Limit 2-2.5 nm) • Easy availability compared to limited accessibility to synchrotron sources • 1. Kerry O’Connell , John R. Regalbuto(2015) CatalLett 145:777– 783

  4. Proposed Hypothesis (> 50 nm) (> 2 nm and < 50 nm) (< 2 nm) Hypothesis:Enhanced Pt/C interaction in micropores assumed to stabilize the metal

  5. Pore Distribution: Micropore Analysis • Carbon and silica supports chosen with varying porosity

  6. Strong Electrostatic Adsorption (SEA)

  7. Detection of Oxide : Carbon Supports • XRD deconvolutions show metallic Pt and Pt3O4 peaks • STEM Volume average sizes indicate a combination of the metal and oxide phases

  8. Detection of Oxide : Silica Supports • Metal and oxide peaks detected in XRD • STEM Volume average sizes indicate a combination of the metal and oxide phases

  9. Carbon supported Platinum: FFT Studies • Nanoparticles > 2.5 nm were found to be in metallic state whereas < 1.5 nm, were oxide: nanoparticles in between 1.5 nm to 2.5 nm were found to exist as a combination of the two phases

  10. Oxidation States of Platinum • Pt0, Pt+2 and Pt+4 oxidation states in air exposed samples • The larger size distribution particles with high standard deviation less prone to oxidation: • smaller particles oxidized while larger ones remain metallic

  11. Binding Energy Shifts Pt0 Pt4f O1s • Pt4f peaks shift to higher binding energies with increasing air exposure times

  12. Nanoparticle Size Variations High Micropore Volume Low Micropore Volume • At high weight loadings (>10%), high micropore volume (>0.6 cc/gm) gives large particles; • at low weight loadings, micropore volume has no effect on size • For carbons with the same micropore volume, increase in weight loadings increases • the particle sizes • Nanoparticle size has a coupled dependence on metal weight loadings and micropore • volumes seen only for carbons: for silica, no such effect found

  13. Oxide Content in Nanoparticles • Low weight loadings : At the same weight loadings and particle sizes, increase in • micropore volume has a negligible effect on oxide content • High weight loadings (>10%) : Increase in micropore volume causes increase in size and • decrease in oxide content • Smaller particles have a higher oxide content than larger particles

  14. Conclusions • Platinum nanoparticles were found to undergo spontaneous oxidation on exposure to ambient air: oxide phases detected in XRD and XPS • Oxidation was size sensitive • >2.5nm: Metal • <1.5nm: Oxide • <1.5 nm and > 2.5 nm: Metal + Oxide • At low weight loadings, micropore volume did not effect the particle size but at higher weight loadings, high micropore volumes caused nanoparticle sintering: • LARGER PARTICLES MORE METALLIC THAN SMALLER PARTICLES • An inter-dependence was found between microporosity, metal loading and nanoparticle sizes that affected the extent of oxidation on carbon supports

  15. Acknowledgements 1. Group Members at the Center of Catalysis for Renewable Fuels 2. Job Group at the University of Liège, Belgium Thank you !

  16. ADDITIONAL SLIDE

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