AVS 66th International Symposium & Exhibition
    Fundamental Discoveries in Heterogeneous Catalysis Focus Topic Wednesday Sessions
       Session HC+OX+SS-WeA

Paper HC+OX+SS-WeA1
Yittria-stabilized Zirconia (YSZ) Supports for Low Temperature Ammonia Synthesis

Wednesday, October 23, 2019, 2:20 pm, Room A213

Session: Metal-Support Interactions Driving Heterogeneously-Catalyzed Reactions
Presenter: Colin Wolden, Colorado School of Mines
Authors: Z. Zhang, Colorado School of Mines
S. Livingston, Colorado School of Mines
L. Fitzgerald, University College Dublin
J.D. Way, Colorado School of Mines
C.A. Wolden, Colorado School of Mines
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The use of renewable hydrogen for distributed synthesis of ammonia requires the development of efficient catalysts and processes that operate under mild conditions. Here we introduce yittria stabilized zirconia (YSZ) as a more active Ru catalyst support for NH3 synthesis than traditionally used supports such as Al2O3. The addition of Cs promoter increased rates an order of magnitude higher by reducing the apparent activation energy from 103 kJ/mol to 65 kJ/mol. The rate enhancement is largely insensitive to the amount of promoter addition, with Cs outperforming Ba and K by a factor of 2. At 400°C under 1.0 MPa, the synthesis rate was comparable with that of most active oxide-supported Ru catalysts. The rate becomes inhibited by H2 absorption at low temperature (< 350°C), but the use of lower H2:N2 ratios enables the rate to remain comparable to what is observed in stoichiometric mixtures at temperatures > 400°C. A detailed microkinetic model was developed that successfully captures the observed behavior, revealing that adsorption is coverage dependent. These results provide insight and direction into developing alternatives to Haber-Bosch for distributed synthesis of green ammonia.