## 4 Conclusions  
In this work, NTP-assisted ammonia synthesis by the addition of noble gases in a DBD reactor driven with nanosecond pulsed power supply is investigated. The addition of He produces a more uniform and diffuse plasma than the addition of Ar. The addition of noble gases significantly improves the ammonia synthesis effect, and the addition of moderate amounts of noble gases accelerates the production of key reactive particles through penning excitation and ionization reactions. The excessive noble gas additions can lead to ammonia decomposition, as well as more energy wasted on Ar and He excitation and ionization, and reduced energy utilization. By optimizing the reaction conditions, i.e., 40% addition of Ar, gas ratio of H\({}_{2}\):N\({}_{2}\) = 2, 40% addition of He, gas ratio of H\({}_{2}\):N\({}_{2}\) = 3, and the optimum parameters of the pulses, i.e., pulse voltage of 13 kV, pulse repetition rate of 1200 Hz, pulse width of 120 ns, and pulse rise time of 50 ns, the addition of Ar can increase the ammonia synthesis energy yield by 45.1%, and the addition of He can increase it by 47%. The energy yield was increased by 45.1% with the addition of Ar and 47% with the addition of He. We have studied the key reactive particles by OES and found that the number of particles of both N\({}_{2}\)\({}^{+}\) and N\({}_{2}\)\({}^{\star}\) in the rate-limiting step of the reaction increases with the addition of noble gases. To further investigate the process, the reaction involving Ar active particles was simulated using the 0D plasma chemical dynamic model. The addition of Ar adds new gas-phase reaction pathways, and as the addition increases, the rate of electron transfer reactions and intermediate reactive species increases, which can facilitate ammonia synthesis.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14073001/s1](https://www.mdpi.com/article/10.3390/app14073001/s1)]([https://www.mdpi.com/article/10.3390/app14073001/s1](https://www.mdpi.com/article/10.3390/app14073001/s1)). The supplementary materials include settings for gas flow rate parameters, the impact of gas flow rate on ammonia synthesis, the effect of discharge power on ammonia synthesis, additional information on OES, changes in the density of main active species over time, and relevant content involved in modeling. Table S1: Flow rate of additive gases under various conditions. Table S2: Species considered in the N\({}_{2}\)-H\({}_{2}\)-Ar plasma model. Table S3: Gas-phase reactions. Figure S1: Effect of Gas Flow Rate on Ammonia Synthesis Efficiency. Figure S2: Effect of different Ar and He additions on the discharge power at different gas ratios. Figure S3: OES plots for the addition of Ar and the addition of He. Figure S4: Variation of the density of the main active particles in the reaction as a function of time.  
**Author Contributions:** Methodology and investigation, D.Y. and Y.X.; data curation, and writing--original draft preparation, Y.X.; writing--review and editing, H.Y., H.W. and K.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study is supported by the National Natural Science Foundations of China (Grant Nos. 52077026, 12305279 and 52307163), and the China Postdoctoral Science Foundation (2022M710590).  
Figure 10: Effect of different additions of Ar on chemical reaction rates.  
Data Availability Statement: Data is contained within the article or supplementary material. Conflicts of Interest: The authors declare no conflicts of interest.