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Southeastern Catalysis Society 2014 Annual Meeting September 15, 2014

Chemisorption – XRD Particle Size Discrepancy of Carbon Supported Palladium: Carbon Decoration of Pd?. John Meynard Tengco , Ritubarna Banerjee, Yuliana Lugo-José, John Monnier , John Regalbuto. Southeastern Catalysis Society 2014 Annual Meeting September 15, 2014.

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Southeastern Catalysis Society 2014 Annual Meeting September 15, 2014

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  1. Chemisorption – XRD Particle Size Discrepancy of Carbon Supported Palladium: Carbon Decoration of Pd? John MeynardTengco, Ritubarna Banerjee, Yuliana Lugo-José, John Monnier, John Regalbuto Southeastern Catalysis Society 2014 Annual Meeting September 15, 2014

  2. Catalyst performance is dependent on available catalytic sites for desired reaction, measured as dispersion • Decoration (covering of surface) decreases dispersion • Dispersion is obtained from characterization by probing active surface like chemisorption or from size estimates by XRD or STEM • Systematic discrepancy of size estimate for carbon supported catalysts: X-ray diffraction (XRD) < Chemisorption

  3. A survey of size discrepancy in literature • Loss of active sites hypothesized to be due to decoration by carbon support

  4. Catalyst Preparation • Pd/C catalysts were prepared using the method of Strong Electrostatic Adsorption (SEA) • BASF Carbon (identified as CP-97) with a surface area of 615m2/g and PZC of 8.5 • Sodium tetrachloropalladate was used as the precursor salt • optimal pH for the adsorption: 2.5 • Nominal loading: 10%Pd/C Uptake of [PdCl4]2- on CP-97 carbon support as a function of equilibrium pH. Treatments: Pd/CP97:Reduced 150°C, 2.5°C/min 1hr, and 350°C 5°C/min, 2 hrs Pd/CP97-A: He Annealed 300°C 1hr, Reduced 350°C 5°C/min, 2 hrs Pd/CP97-C: Air Calcined 300°C 1hr, Reduced 350°C 5°C/min, 2 hrs

  5. Dispersion and Size Estimation • Autochem II 2920 chemisorption analyzer • Hydrogen titration of oxygen pre-covered catalysts

  6. Size Estimation of Pd/Carbon Samples XRD profiles of the catalyst series directly reduced - Pd/CP97 annealed - Pd/CP97-A calcined- Pd/CP97-C.

  7. STEM of Pd/CP97-C

  8. Temperature Programmed Oxidation (TPO) • Custom TPX system fitted with InficonTranspector 2 Mass spectrometer • 0.2g of samples pretreated in He at 200°C until H2O signal is diminished • 10% O2 in He flow set at 20sccm • 5°C/min ramp

  9. TPO of CP97 Support • Burn-off of carbon powder at around 500°C

  10. TPO of Pd/CP97

  11. TPO of Pd/CP97-A

  12. TPO of Pd/CP97-C

  13. Carbon Burn-off Data burn off surface carbon carbon “decorated” catalyst Data for deconvoluted low temperature carbon burn-off peaks.

  14. Cycled TPO of Pd/CP97-C Helium Purge burn off surface carbon carbon “decorated” catalyst further oxidation

  15. Cycled TPO of Pd/CP97-C with in situ reduction Helium Purge In Situ Reduction @ 50°C Helium Purge

  16. Cycled TPO of Pd/CP97-C with in situ reduction Helium Purge In Situ Reduction @ 200°C Helium Purge

  17. Cycled TPO of Pd/CP97-C with in situ reduction Helium Purge In Situ Reduction @ 350°C Helium Purge burn off surface carbon carbon “decorated” catalyst cleaned catalyst surface reduction

  18. Chemisorption of Pd/CP97-C after burn-off. • Possible sintering burn off surface carbon carbon “decorated” catalyst cleaned catalyst surface reduction

  19. TPO as a technique to probe carbon decoration Pd Pd signal signal signal Carbon Temperature Temperature Temperature - bulk carbon - proximate carbon - surface carbon (on Pd) - subsurface carbon (on Pd)

  20. burn off surface carbon carbon “decorated” catalyst Summary further oxidation calcined catalyst reduction cleaned catalyst surface

  21. Application on another Pd/C catalyst: 2.7% Palladium on Oxidized Vulcan XC72 Prepared by SEA, direct reduced at 180°C Chemisorption size of fresh catalyst: 6.3nm No Pdpeaks, Size <2.0 nm

  22. TPO of VXC72Ox Support TPO of Pd/VXC72Ox • Chemisorption with Oxidation pretreatment at 300°C gives 3.5nm particle size. • Possible incomplete removal of decorating carbon or sintering of Pd nanoparticles (300°C vs reduction at 180°C )

  23. Conclusions • TPO can be used to probe presence of decorating carbon on carbon supported catalysts. • Oxidative treatment can be formulated to recover metal nanoparticle surface, however with possible trade-offs. • Reduction of the catalyst is not direct cause of decoration, however chlorine is being looked at as possible cause. • STEM particle size analysis (or other size estimation technique) needed to support XRD size data.

  24. Thank You!

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