(506g) Transcending the Volcano Plot: Enhancing NH3 Synthesis with Dynamic Catalysis
Above 400 oC, NH3 synthesis rates exhibit a volcano plot relationship with the binding energy of N* as a descriptor. The NH3 synthesis speed limit exists at the volcano peak, which has been attributed to the trade-off between the rate of N2 adsorption and N2 dissociation for a catalyst with static binding properties. In this talk, we demonstrate that these kinetic and thermodynamic constraints can be surpassed by varying catalyst binding properties as a function of time . Using CSTR and batch reactor models in Matlab, a model system with A â B and three elementary steps: (i) adsorption of A, (ii) reaction of A*â B*, and (iii) desorption of B was simulated. Binding energies were varied using square, sinusoidal, triangle, or saw-tooth waveform with specified oscillation frequencies (fosc , [=] Hz) and amplitudes (ÎU, [=] eV). Dynamic steady state rates were found to be highly dependent on the frequency and amplitude. Rate enhancement over the Sabatier maximum was observed for a system with BrÃ¸nsted-Evans-Polanyi parameters comparable to NH3 synthesis.
 M. A. Ardagh, O. A. Abdelrahman, P. J. Dauenhauer, âPrinciples of Dynamic Heterogeneous Catalysis: Surface Resonance and Turnover Frequency Responseâ ChemRxiv Preprint, 2019. doi.org/10.26434/chemrxiv.7790009.v1