(537f) Ammonia Synthesis Using Plasma Assisted Catalysis: Understanding Rate Enhancements By Excited Species

The industrial Haber-Bosch process for catalytic ammonia synthesis from nitrogen and hydrogen is carried out at high pressures (100-200 bar) and temperatures (400-500 °C). The robust N-N triple bond is the fundamental barrier for this reaction, and there has been a longstanding desire to develop ways to activate this bond under less extreme conditions. A few reports in the literature [1-4], as well as recent experiments performed by us, have demonstrated that is possible to produce ammonia at atmospheric pressure and temperatures between 100-300°C by coupling the catalyst with a non-thermal plasma. It is speculated that the plasma assists in activating the source gas by generating reactive species, such as vibrationally or electronically excited N2*, ions, and radicals, which interact on the catalyst surface to produce NH3. In this talk, we explore the limits of ammonia synthesis rate enhancements on transition metal surfaces by plasma activated intermediates using a simple microkinetic model based on density functional theory calculations. Our model predicts that plasma-assisted catalysis could lead to low temperature and pressure reaction rates that are competitive with the Haber-Bosch process, but the optimal metal catalysts and active-site motifs are distinct from those predicted to be most active for thermal catalysis. The models are useful for interpreting literature results and guiding new experiments.

References

1. Peng, P., Li, Y., Cheng, Y., Deng, S., Chen, P., & Ruan, R. Plasma Chemistry and Plasma Processing, 36(5), 1201–1210 (2016).

2. Xie, D., Sun, Y., Zhu, T., Fan, X., Hong, X., & Yang, W. RSC Advances, 6(107), 105338–105346 (2016).

3. Kim, H., Teramoto, Y., Ogata, A., Takagi, H., & Nanba, T. Plasma Processes and Polymers, Published online: DOI:10.1002/ppap.201600157 (2016).

4. Akay, G., and Zhang, K. Industrial & Engineering Chemistry Research, 56(2), 457–468 (2017).