Plasma-assisted catalytic formation of ammonia in N₂–H₂plasma on a tungsten surface

Abstract

Ammonia synthesis from hydrogen and nitrogen gases by low-temperature radio frequency plasma catalysis.

Harnessing Plasma Environments for Ammonia Catalysis: Mechanistic Insights from Experiments and Large-Scale Ab Initio Molecular Dynamics

“…Reasonably high degrees of nitrogen conversion to ammonia have been reported for a broad range of reactor designs, varying from atmospheric pressure dielectric barrier discharges (DBDs) in contact with a catalyst bed 6,20 to low-pressure plasmas driven by radio-frequency excitation. [21][22] No external heating is required in any of these cases, and good degrees of nitrogen fixation, even with the catalyst at nominally room temperature, are observed. The exact mechanism leading to the reasonably efficient fixation of nitrogen in these systems is still under intense debate.…”

Plasma-driven catalysis: green ammonia synthesis with intermittent electricity

“…Over the past decades, research on plasma-catalytic ammonia synthesis has transitioned from exploratory and trial-and-error approaches to more fundamental understanding based on experimental and modelling work, as described in detail in this review paper. Operando plasma and catalyst diagnostics, such as surface techniques such as XPS and FTIR, 193,195 pic labelling 326 and spectroscopy 194,327 will aid in further improving our understanding of how plasma and catalyst interact at the molecular level, rather than on the macroscopic level.…”

“…Reactors operating under radiofrequency (RF) plasma excitation have been researched to a lesser extent, as compared to DBD reactors, 261 but have recently gained substantial attention in several research groups. [190][191][192][193][194][195][196]298 In the late 1980s and early 1990s, Uyama et al and Tanaka et al used zeolite 182,187 as well as Fe 183,188 and Mo 183 wires as catalyst in the downstream of their low pressure (650 Pa) RF plasma apparatus. Fe catalysts resulted in the highest product yield.…”

“…They are the only authors to report the formation of both ammonia and hydrazine 182,183,188 and speculated that the H and NH x radicals formed in the discharge are the main adsorbates. 183 Recently, Ben Yaala et al 193,195 placed W and stainless steel catalysts in their low pressure (2 Pa) RF plasma reactor. They reported the thermal decomposition of ammonia at high temperature (above 830 K on W) and the creation of stables nitrides (starting at 650 K on stainless steel), inhibiting ammonia formation.…”

“…The subsequent hydrogenation steps primarily occur over the Fe catalyst via a Langmuir-Hinshelwood mechanism, 191 while the contribution of Eley-Rideal-like mechanisms may increase with increasing plasma power and pressure. Ben Yaala et al 193 performed a series of chemical looping experiments to gain insight in the mechanisms of ammonia synthesis in low pressure RF plasma on a W catalyst. They reported the highest yields for the H 2 : N 2 = 1 : 1 gas fraction and concluded that the Eley-Rideal reaction H + N* → NH* is a crucial step for the formation of ammonia under these circumstances.…”