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Caitlin Callaghan Barry Grace Orest Skoplyak Ilie Fishtik Ravindra Datta

CO x -Free Hydrogen by Catalytic Decomposition of Ammonia on Commercial Fe and Ru Catalysts: An Experimental and Theoretical Study. Caitlin Callaghan Barry Grace Orest Skoplyak Ilie Fishtik Ravindra Datta. Fuel Cell Center Chemical Engineering Department Worcester Polytechnic Institute

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Caitlin Callaghan Barry Grace Orest Skoplyak Ilie Fishtik Ravindra Datta

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  1. COx-Free Hydrogen by Catalytic Decomposition of Ammonia on Commercial Fe and Ru Catalysts: An Experimental and Theoretical Study Caitlin Callaghan Barry Grace Orest Skoplyak Ilie Fishtik Ravindra Datta Fuel Cell Center Chemical Engineering Department Worcester Polytechnic Institute Worcester, MA 01609

  2. Motivation • Prospect of PEM Fuel Cells • Environmental benefit • Limited oil reserves • Need for Suitable Hydrogen Source • Hydrogen content/ energy density • Fuel processing • Storage / transportation

  3. Comparison of H2 Sources

  4. Objectives • Study the Decomposition of Ammonia on an Fe Synthesis Catalyst and a Supported Ruthenium Catalyst • Develop a Predictive Microkinetic Model • Design a Reactor to Produce Hydrogen for a PEM Fuel Cell Vehicle

  5. Kinetics • Rate Limiting Step • Rate Expression Derived using L-H Analysis [Chellappa et al., App. Catal. A: Gen. 227 (2002)] • Temkin-Pyzhev [Temkin, Adv. Cat. 26 (1979)]

  6. Experimental Setup

  7. Experimental • Catalysts • Triply-Promoted Fe (AS-4F), (40-60 mesh) Sud-Chemie • 0.5 wt% Ru on 1/8” Al2O3 pellets, Engelhard • Reduction/Stabilization Procedure • 3:1 H2/N2 Diluted to 50% in Ar, 500 ºC for 4 hours • 20% NH3 in Ar at 350 ºC 18 hours • Experimental Conditions • Fe: W/F (1.84 - 4.91 g hr/mol), T (325 – 550 ºC) • Ru: W/F (0.0928-0.186 g hr/mol), T (225 – 500 ºC)

  8. UBI-QEP Method • Predicts Surface Energetics • Diand Qi – Only Experimental Inputs • Atomic, weak, and strong binding chemisorption energies

  9. Microkinetic Model

  10. Dominant Reaction Routes

  11. Reaction Route 5 (Dominant) Quasi-Equilibrium and Quasi-Steady State Assumptions

  12. Reaction Rate Expression

  13. Surface Coverages on Fe Catalyst

  14. Surface Coverages on Ru Catalyst

  15. Apparent Activation Energy

  16. Model vs. Experimental Data on Fe Catalyst

  17. Model vs. Experimental Data on Ru Catalyst

  18. Experimental Activation Energy on Fe and Ru Catalyst

  19. Comparison of Iron and Ruthenium Activity

  20. Reactor Design for a PEM Operated Automobile • 10.5% of H2 is consumed to provide heat of reaction • 5.40 kg/hr of NH3 required to operate at 55 mph • Capable of traveling 434 miles at 55 mph, compared to 592 miles for gasoline powered vehicle • 150 g of Fe catalyst required to obtain 600 ppm NH3 effluent at 600 C

  21. Conclusions • It is possible to predict activity of transition metal catalysts for ammonia decomposition • Experimental activation energies for Fe and Ru are 29.8 kcal/mol and 21.4 kcal/mol, respectively, compared to predicted values of 47.9 kcal/mol and 43.0 kcal/mol • Ru catalyst is 10 times more active than Fe catalyst • A fuel cell operated automobile requires 5.40 kg/hr of NH3 • An absorber is required to remove trace levels (600 ppm) of NH3 from H2 stream

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