Observation and Rationalization of Nitrogen Oxidation Enabled Only by Coupled Plasma and Catalyst

Heterogeneous catalysts coupled with non-thermal plasma (NTP) are known to achieve reaction yields that exceed the contributions of the individual components. Rationalization of the enhancing potential of catalysts, however, remains challenging because the background contributions from NTP are often non-negligible. Here, we first demonstrate nitrogen (N2) oxidation by radio frequency plasma and platinum (Pt) combination at conditions in which nitric oxide (NO) yield from plasma or Pt is vanishingly small. We then develop reactor models based on reduced NTP- and surface-microkinetic mechanisms to identify the features of each that lead to the synergy between NTP and Pt. At experimental conditions, NO yields from NTP and thermal catalysis are suppressed by radical reactions and inhibited by high N2 dissociation barrier, respectively. Pt catalyzes NTP-generated radicals and vibrationally excited molecules to produce NO. The model construction further illustrates that the optimization of yield and energy efficiency involves tuning of plasma species, catalysts properties, and the reactor configurations to couple the two. These results provide unambiguous evidence of the benefits of combining plasma and catalysts and open approaches to design the coupled system.