Advances in Performance Evaluation Indices, Characterization Methods, and Simulation of Non-Thermal Plasma-Catalyzed Ammonia Synthesis
Feng Yue1, Fan Jieping1, Liu Dingxin1, Tu Xin2, Zhou Renwu1
1. Centre for Plasma Biomedicine Xi'an Jiaotong University Xi'an 710049 China; 2. Department of Electrical Engineering and Electronics University of Liverpool Liverpool L69 3GJ UK
Abstract:Ammonia is a critical industrial chemical, predominantly synthesized through the Haber-Bosch (H-B) process. While this method has enabled large-scale fertilizer production and sustained food security worldwide, it is highly energy-intensive and carbon-emitting, accounting for 1%~2% of global energy consumption and approximately 1.44% of total CO2 emissions. As the world accelerates its transition to low-carbon energy systems, there is growing demand for sustainable and decentralized ammonia synthesis technologies that can integrate flexibly with intermittent renewable power sources such as solar and wind. In this context, non-thermal plasma (NTP)-catalyzed ammonia synthesis has emerged as a promising alternative owing to its operation under ambient conditions, fast dynamic response, and compatibility with distributed energy networks. This review systematically summarizes recent advances in performance evaluation criteria, physicochemical characterization techniques, and simulation methods in the field of plasma-catalyzed ammonia synthesis. It highlights the fundamental principles of NTP-catalyzed processes, in which high-energy electrons and reactive species such as radicals and vibrationally excited molecules synergistically activate inert N2 molecules at low temperatures. This non-equilibrium environment facilitates reaction pathways that are inaccessible in conventional thermal systems. Moreover, when coupled with suitable catalysts, the plasma can enhance reaction rates and energy efficiencies. Reported ammonia synthesis rates typically range from 300 to 5 000 μmol/(g·h), with energy efficiencies between 0.3 and 2 g/(kW·h), depending on plasma configuration and catalyst formulation. A key aspect of advancing this technology lies in the establishment of standardized performance metrics. Current evaluation practices focus on ammonia yield, energy consumption, and catalyst activity, enabling cross-comparison among different plasma setups. However, disparities in reactor design and testing methods often hinder data comparability. Thus, the development of universally accepted performance benchmarks is essential for guiding reactor optimization and accelerating technological maturation. Equally important is the in-depth characterization of plasma and catalyst properties. On the plasma side, diagnostic tools such as optical emission spectroscopy (OES), intensified charge-coupled devices (ICCD), femtosecond-resolved two-photon laser-induced fluorescence (fs-TALIF), and coherent anti-Stokes Raman spectroscopy (CARS) allow researchers to probe electron temperature, species distribution, and transient discharge behavior. On the catalyst side, surface-sensitive techniques including XPS, XRD, SEM/HRTEM, BET, and TPD/TPR provide insights into structural features, active sites, and surface reactivity. Despite their utility, many of these techniques are ex-situ or offline, lacking real-time temporal resolution. To overcome this limitation, emerging in situ diagnostic methods such as infrared spectroscopy and electron-impact molecular beam mass spectrometry (EI-MBMS) are gaining attention for their potential to identify intermediate species and elucidate reaction mechanisms. Complementing experimental approaches, modeling and simulation play an increasingly vital role in understanding plasma-catalyst interactions. Multiphysics simulations, kinetic models, and density functional theory (DFT) calculations offer powerful tools for exploring reaction energetics, species transport, and surface reaction pathways. While current models have made significant progress, they often fall short in capturing the complex coupling between plasma species and catalyst surfaces. Future work should integrate experimental in situ data with dynamic simulations to develop predictive models that accurately reflect real reactor behavior. In conclusion, plasma-catalyzed ammonia synthesis presents a viable and flexible route for decentralized, low-carbon ammonia production. By advancing performance evaluation standards, refining real-time diagnostic capabilities, and enhancing simulation fidelity, the field is moving toward more energy-efficient and scalable solutions. Furthermore, the chemical energy stored in ammonia can serve as a means of grid-level energy storage, offering benefits such as high hydrogen density, safe transport, and zero-carbon utilization. This positions plasma-catalyzed ammonia synthesis not only as a replacement for the H-B process but also as a strategic enabler of the renewable energy ecosystem, paving the way for sustainable nitrogen fixation and a cleaner energy future.
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