The role of heterogeneous catalysts in the plasma-catalytic ammonia synthesis

Patil, Bhaskar S; Cherkasov, Nikolay; Srinath, Nadadur Veeraraghavan; Lang, Juergen; Ibhadon, Alex O.; Wang, Qi; Hessel, Volker

Abstract

Ammonia, being the second largest produced industrial chemical, is used as a raw material for many chemicals. Besides, there is a growing interest in the applications of ammonia as electrical energy storage chemical, as fuel, and in selective catalytic reduction of NOx. These applications demand on-site distributed ammonia production under mild process conditions. In this paper, we investigated 16 different transition metal and oxide catalysts supported on γ-Al2O3 for plasma-catalytic ammonia production in a dielectric barrier discharge (DBD) reactor. This paper discusses the influence of the feed ratio (N2/H2), specific energy input, reaction temperature, metal loading, and gas flow rates on the yield and energy efficiency of ammonia production. The optimum N2/H2 feed flow ratio was either 1 or 2 depending on the catalyst-substantially above ammonia stoichiometry of 0.33. The concentration of ammonia formed was proportional to the specific energy input. Increasing the reaction temperature or decreasing gas flow rates resulted in a lower specific production due to ammonia decomposition. The most efficient catalysts were found to be 2 wt% Rh/Al2O3 among platinum-group metals and 5 wt% Ni/Al2O3 among transitional metals. With the 2 wt% Rh catalyst, 1.43 vol% ammonia was produced with an energy efficiency of 0.94 g kWh-1. The observed behaviour was explained by a combination of gas phase and catalytic ammonia formation reactions with plasma-activated nitrogen species. Plasma catalysts provide a synergetic effect by activation of hydrogen on the surface requiring lower-energy nitrogen species.

Citation

Patil, B. S., Cherkasov, N., Srinath, N. V., Lang, J., Ibhadon, A. O., Wang, Q., & Hessel, V. (in press). The role of heterogeneous catalysts in the plasma-catalytic ammonia synthesis. Catalysis Today, https://doi.org/10.1016/j.cattod.2020.06.074

• Journal Article Type: Article
• Acceptance Date: Jun 28, 2020
• Online Publication Date: Jul 25, 2020
• Deposit Date: Sep 6, 2020
• Publicly Available Date: Jul 26, 2021
• Journal: Catalysis Today
• Print ISSN: 0920-5861
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• DOI: https://doi.org/10.1016/j.cattod.2020.06.074
• Keywords: Plasma catalysis; Ammonia production; Catalytic DBD reactor; Supported transition metal oxides; Energy efficiency; Haber-Bosch
• Public URL: https://hull-repository.worktribe.com/output/3428022
• Publisher URL: https://www.sciencedirect.com/science/article/abs/pii/S0920586120304661?via%3Dihub