Technical Challenges and Prospects in Sustainable Plasma Catalytic Ammonia Production from Methane and Nitrogen

Abstract

Ammonia is crucial for human life as an important ingredient for fertilizer, industrial and household chemicals, and is considered as a future fuel alternative and hydrogen storage molecule. There remain no viable alternatives to the energy‐and capital‐intensive Haber–Bosch (H−B) process. Efforts in the development of novel catalytic processes operated at milder conditions (low temperatures and ambient pressure), prominently electrochemistry and non‐thermal plasma (NTP), and utilization of lower‐cost H sources for ammonia formation than the ultrapure H2 have been witnessed in the last few years. Yet, limited progress from these routes has been made to date given unresolved low ammonia yield and technical challenges. Several rare works attempted to activate methane (CH4) and nitrogen (N2) by non‐thermal plasma to produce ammonia and valued‐added hydrocarbons have proven to be a promising research direction, rivalling the reaction between N2 and ultrapure H2 or water. The direct conversion of CH4 and N2 to ammonia is still at the beginning level, and it remains unclear that what extent these technologies must be improved to develop a commercial process. Toward this goal, this Perspective critiques current steps and miss‐steps of sustainable plasma catalytic ammonia production from CH4 and N2 in terms of technology, plasma‐catalyst synergy, mechanistic insights, and experimental protocols. We discuss mechanistic understandings of catalyst‐promoted ammonia production and translate such discussions as well as key metrics achieved in the field into recommendations of feasible processes for ammonia and value‐added hydrocarbons formation from CH4 and N2.

In‐Liquid Plasma Catalysis: Tools for Sustainable H2‐free Heavy Oils Upgrading

“…Processing both such plasma gas and heavy oils together enables the formation of highly energetic plasma species such as Ar * , He * , N 2 * (in the case of using Ar, He, or N 2 ) or H * and CH x * (in the case of using H 2 and/or CH 4 /H 2 mixture), promoting the conversion of heavy hydrocarbons into more valuable products such as H 2 and lighter fuel products. Compared to Ar and He, CH 4 offers lower cost and contains only hydrogen and carbon, directly into liquid fuels through plasma assisted gas‐to‐liquid conversion [10] . More importantly, noble gas such as Ar, He, or even N 2 are less readily available for on‐site petroleum applications compared to methane, posing challenges in the separation of non‐hydrocarbon components from products.…”

“…The utilization of natural gas, like CH 4 , as a source of active H and CH x species for the cleavage of hydrocarbon chains is applicable in on‐site petroleum applications, presenting convenient accessibility that merits consideration. NTP has recently emerged in many fields of chemical processes and reactions including gas and liquid‐phase reactions [10] . The reactivity of plasma, as the fourth state of matter, has gained traction in the chemical industry, generated either by gas heating or by subjecting gas to a strong electromagnetic or electrical field [11] .…”

Non-thermal plasma catalysis driven sustainable pyrolysis oil upgrading to jet fuel under near-ambient conditions

“…15 The utilization of pure H 2 for chemical processes is considered economically and environmentally unsustainable. 16 More importantly, the primary method for hydrogen production involves the energy-intensive reforming of natural gas. 17 Leveraging CH 4 directly as an active H 2 source has the potential to substantially lower operational expenses and decrease greenhouse gas emissions.…”

“…17 Leveraging CH 4 directly as an active H 2 source has the potential to substantially lower operational expenses and decrease greenhouse gas emissions. 16 Non-thermal plasma (NTP) catalysis emerges as a viable technique for dissociating hydrogen from CH 4 and breaking C–O and C–N bonds in pyrolysis oil under conditions closely approximating ambient parameters, including atmospheric pressure and low temperatures. This process is facilitated by the influence of high-energy electrons, reaching up to 10 eV.…”

Ammonia Synthesis via Nitrogen-Coupled Methane Conversion at Ambient Temperature and Plasma Conditions

“…Up until now, there have only been a few reports on the synthesis of ammonia from methane and nitrogen through a plasma-catalyst hybrid. 35 Tiwari et al 36 used CH 4 /N 2 = 3:1 as the feed gas and obtained an ammonia concentration of 417 ppm at 500 °C with microwave plasma combined with a K− Ru/γ-Al 2 O 3 catalyst. Ethane, ethylene, and acetylene form simultaneously at atmospheric pressure.…”