Plasma‐Driven Nitrogen Fixation on Sodium Hydride

Abstract

The development of alternative approaches to the conventional Haber–Bosch ammonia synthesis process is an imperative but very challenging task. Extrinsic stimuli such as plasma could provide greater flexibility in materials selection and process innovation for nitrogen fixation. Hydride (hydrogen anion, H‾)‐containing materials have recently shown promise in thermal ammonia synthesis, whereas the interactions of hydrides and N2 under plasma have rarely been investigated. Herein we explore plasma‐driven nitrogen fixation to NH3 mediated by an inexpensive and common reagent sodium hydride, which does not react with N2 under normal thermal conditions. Nitrogen plasma can produce reactive nitrogen species and also induce the dehydriding of NaH, which result in the activation and hydrogenation of N2 to surface NaNH2 species. The subsequent thermal‐hydrogenation of NaNH2 produces NH3 facilely. The stepwise chemical loop prevents ammonia from plasma‐induced cracking. This NaH‐mediated chemistry broadens the scope of hydrides as well as many other materials for N2 fixation, and also has prospect for other chemical transformations.

Strategies for avoiding the scaling relationship in ammonia synthesis with non-thermal plasma methods – the “shift” or “break” approach

“…Zen et al 142 further optimized the non-thermal plasma indirect NH 3 synthesis system by using DBD plasma to nitride MgO under a mixed atmosphere of N 2 and H 2 . Wu et al 140 presented a plasma-coupled CLAS process based on sodium hydride-mediated synthesis. NaNH 2 was formed on the surface of NaH under the action of N 2 plasma with the simultaneous release of H 2 .…”

Towards green and efficient chemical looping ammonia synthesis: design principles and advanced redox catalysts

“…46 Therefore, there are also some redox cycling processes for ammonia production similar to CLAS including electrolytic-chemical cycle, 48,49 as well as some external field-assisted chemical loops for ammonia production, such as plasma-assisted CLAS. 20,50,51…”

“…60 Recently, Chen and co-workers proposed an external-field-assisted H 2 -CLAS process for low-temperature operation. 51,61…”

“…59iThe ammonia productivity of this redox catalyst (20 wt%NaH/MgO) in a single loop is estimated to be half of the ammonia production rate (∼2080 μmol NH 3 g NaH −1 h −1 at 250 °C and ∼1530 μmol NH 3 g NaH −1 h −1 , which is equal to 416 μmol NH 3 g cat −1 h −1 and 153 μmol NH 3 g cat −1 h −1 , respectively) in thermal hydrogenation, because the reaction time of the nitrogen fixation step is not mentioned in this study. 51 jThe ammonia productivity of this redox catalyst is calculated through dividing the amount of ammonia produced (2379 μmol g −1 ) by the total reaction time (17 min) of nitridation (2 min) and hydrogenation (15 min) in a single loop. The data is from Fig.…”

Advances in Nitrogen Carriers for Chemical Looping Processes for Sustainable and Carbon-Free Ammonia Synthesis

“…Numerous alternative processes have been developed to address the current challenges in ammonia production. These include enzymatic catalysis, organometallic approaches, − electrochemical and electrocatalytic methods, − photochemical and photocatalytic systems, − plasma-driven transformations − and chemical looping. ,− Among these options, chemical looping stands out due to its ability to decouple the synthetic process into two or three steps, including (1) N 2 activation via formation of nitrides, imides or nitrogen-rich intermediates as nitrogen carriers, (2) NH 3 formation via reaction between H 2 or H 2 O and nitrogen carriers, and (3) regeneration of intermediates via reduction process. This unique feature enables the optimization of reaction conditions at each step of the chemical looping process.…”