Effects of Supported Catalyst on the Plasma in a Packed-Bed Dielectric Barrier Discharge Reactor for Ammonia Synthesis

Abstract

Ammonia, a precursor for fertilizers, is crucial to feed the world's population but also it has the potential to be used as an alternative fuel or as a chemical store for renewable energy technologies. The most common process of ammonia production is the Haber-Bosh (H-B) process, a well-optimized method that requires high temperature (~ 700 K) and pressure (~ 1 00 atm) to operate under equilibrium conditions (using thermal catalysis). Alternatively, ammonia can be produced less efficiently close to standard conditions by combining non-thermal plasmas and catalysts (plasma catalysis). Unlike thermal catalysis, in plasma catalysis the non-equilibrium state of the plasma $(T_{electrons}\gg T_{ions},T_{neutrals}$ produces reactive species, such as excited species, that may play an important role in the production of ammonia. The interaction between the plasma and the catalyst can be characterized in two categories: the effect of the plasma on catalysis and the effect of the catalyst on the plasma state. This work focuses on the latter. We use a laboratory-scale, packed bed, dielectric barrier discharge (DBD) reactor to investigate the effects of different supported metal catalysts on the plasma. Optical emission spectroscopy (OES) and electrical measurements are used to estimate various system parameters, including rotational and vibrational temperatures and electron densities, for various supported catalyst configurations (e.g., alumina supported nickel). These parameters are correlated with measurements of ammonia synthesis under identical conditions to assess whether there are significant differences in the plasma under conditions where ammonia synthesis is enhanced.