Nonthermal Plasma Catalytic Ammonia Synthesis over a Ni Catalyst Supported on MgO/SBA-15

Abstract

Nonthermal plasma (NTP)-enabled ammonia synthesis has been recently considered a sustainable technique as compared to the Haber−Bosch (HB) process. Herein, we demonstrated the NTP catalytic ammonia synthesis using mesoporous silica (SBA-15)-supported Ni catalysts under ambient conditions. Specifically, two types of MgO-modified SBA-15 were developed (as the catalyst support) by the in situ doping and incipient wetness impregnation (IWI) methods, respectively. Experimental results demonstrated that the addition of Mg in SBA-15 via the IWI method favored the ammonia synthesis rate under NTP conditions. The developed Ni-Mg 0.02 /SBA-15-IWI catalyst exhibited the highest ammonia synthesis rate and energy efficiency value of 4.4 mmol h −1 g cat −1 and 1.05 g NH3 kWh −1 , respectively, outperforming the Ni/ SBA-15 and Ni-Mg 0.02 /SBA-15-In situ catalysts (i.e., the doping of Mg via the in situ method). High-resolution transmission electron microscopy (HRTEM) and energy-dispersive system (EDS) mapping analysis showed that the addition of Mg (on SBA-15) via the IWI method favored the dispersion of Ni active sites on the surface of the catalyst and the interaction between Ni and the SBA-15 support, i.e., uniform distribution of Ni nanoparticles of 5.1 ± 1.1 nm in the Ni-Mg 0.02 /SBA-15-IWI catalyst, which enhanced the ammonia synthesis performance. Finally, the developed Ni-Mg 0.02 /SBA-15-IWI catalyst displayed a slight decrease in the ammonia synthesis rate from ∼4.42 to ∼3.89 mmol h −1 g cat −1 over 40 h on stream, which could be attributed to the aggregation of Ni particles based on the postreaction HRTEM analysis.

Shielding Protection by Mesoporous Catalysts for Improving Plasma-Catalytic Ambient Ammonia Synthesis

“…In non-catalytic systems, inert porous packing (such as zeolite 5A and 4A 23 ) was recently found to be beneficial in improving NH 3 synthesis rates, most likely due to in situ NH 3 adsorption by the porous packing. 22 Furthermore, the supported metal catalysts on mesoporous materials (e.g., Ru/MCM-41 24 and Ni−Mg/SBA-15 25 ) were also found to be very effective in promoting plasma-catalytic NH 3 synthesis. Despite the fact that using porous materials or catalysts in plasma discharge improves the NH 3 yield, the mechanism underlying such hybrid systems remains unclear.…”

Sustainable Hydrogen and Ammonia Technologies with Nonthermal Plasma Catalysis: Mechanistic Insights and Technoeconomic Analysis

“…Research in plasma-assisted catalytic ammonia synthesis began in 1980 when Botchway and Venugopalan first investigated the effect of an iron catalyst on cold DBD plasma for ammonia production and, subsequently, plasma-assisted ammonia synthesis have been explored over various catalytic materials such as metal oxides, transition metals, porous catalysts, bimetallic materials, and perovskites . Besides experimental works, mechanistic studies on the reaction scheme of plasma-catalytic ammonia synthesis were conducted using analytical methods .…”

“…There are three ways to cleave the nitrogen triple bond N�N: (1) using a reducing catalyst that is electron-donating to dinitrogen (e.g., Fe catalyst in Haber−Bosch process), (2) using an oxidizing catalyst that accepts electrons from the electron-rich nitrogen triple bond N�N, but such material has not been discovered given that the nitrogen triple bond is very stable, and (3) excitation of the nitrogen triple bond by external energy sources (e.g., electrochemical potential, electromagnetic energy, energetic species including photons and electrons, etc.) 71 Research in plasma-assisted catalytic ammonia synthesis began in 1980 when Botchway and Venugopalan first investigated the effect of an iron catalyst on cold DBD plasma for ammonia production 72 and, subsequently, plasma-assisted ammonia synthesis have been explored over various catalytic materials such as metal oxides, 73 transition metals, 74 porous catalysts, 75 bimetallic materials, 76 and perovskites. 77 Besides experimental works, mechanistic studies on the reaction scheme of plasma-catalytic ammonia synthesis were conducted using analytical methods.…”

Energy-Efficient Pathways for Pulsed-Plasma-Activated Sustainable Ammonia Synthesis

“…The above experimental and simulation results show that increasing the gainful utilization of the energy associated with vibrational excitation in the gas phase can potentially promote ammonia synthesis by nonthermal plasmas. Li et al 33 proved that the doping of Mg can accelerate the desorption of NH 3 by enhancing the Ni species dispersion and the Ni−support interaction. This shows that the surface characteristics of the catalyst have a great influence on the plasma synthesis of ammonia.…”