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 Worcester, MA 01609

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

Comparison of H 2 Sources

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

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)]

Experimental Setup

Experimental Catalysts Triply-Promoted Fe (AS-4F), (40-60 mesh) Sud-Chemie 0.5 wt% Ru on 1/8” Al 2 O 3 pellets, Engelhard Reduction/Stabilization Procedure 3:1 H 2 /N 2 Diluted to 50% in Ar, 500 ºC for 4 hours 20% NH 3 in Ar at 350 ºC 18 hours Experimental Conditions Fe: W/F ( g hr/mol), T (325 – 550 ºC) Ru: W/F ( g hr/mol), T (225 – 500 ºC)

UBI-QEP Method Predicts Surface Energetics D i and Q i – Only Experimental Inputs Atomic, weak, and strong binding chemisorption energies

Microkinetic Model

Dominant Reaction Routes

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

Reaction Rate Expression

Surface Coverages on Fe Catalyst

Surface Coverages on Ru Catalyst

Apparent Activation Energy

Model vs. Experimental Data on Fe Catalyst

Model vs. Experimental Data on Ru Catalyst

Experimental Activation Energy on Fe and Ru Catalyst

Comparison of Iron and Ruthenium Activity

Reactor Design for a PEM Operated Automobile 10.5% of H 2 is consumed to provide heat of reaction 5.40 kg/hr of NH 3 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 NH 3 effluent at 600  C

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 NH 3 An absorber is required to remove trace levels (600 ppm) of NH 3 from H 2 stream