International R&D on sustainable ammonia synthesis technologies

Over the last few weeks, I’ve written extensively about sustainable ammonia synthesis projects funded by the US Department of Energy (DOE). While these projects are important, the US has no monopoly on technology development. Indeed, given the current uncertainty regarding energy policy under the Trump administration, the US may be at risk of stepping away from its assumed role as an industry leader in this area.

This article introduces seven international projects, representing research coming out of eight countries spread across four continents. These projects span the breadth of next-generation ammonia synthesis research, from nanotechnology and electrocatalysis to plasmas and ionic liquids.

US federal funding for ammonia synthesis technology development is by no means over, however. Just this week, the DOE’s Office of Energy Efficiency and Renewable Energy (EERE) closed a new funding call for Advanced Manufacturing Projects. Unfortunately, unlike the other DOE funding I’ve written about, including six projects funded by the DOE’s Office of Basic Energy Sciences and another eight projects funded under ARPA-E’s “REFUEL” program, the $35 million anticipated funding by the EERE remains “subject to appropriations.”

This EERE funding opportunity is focused “on advancing transformational next-generation processes and technologies not bound by limitations of current processes.” In its full program description, the funding opportunity specifically includes “Ammonia production alternatives to the Haber Bosch process” (Subtopic 2.1 – Approaches to Cost‐Effective Hydrogen Use in Manufacturing Processes), and more generally encourages “Innovations in new catalyst materials to replace noble metal catalysts” as well as advances in biocatalysis and studies on “biomimetic catalyst design to better understand the extent that high stability atomically precise, enzyme‐like active sites can be designed and deployed” (Subtopic 1.4 – Novel Materials for New Highly-Effective Chemical Catalysts). Any ammonia projects awarded funding under this program won’t be announced until September 2017.

In the meantime, sustainable ammonia continues to make progress around the world.

Coupling Solid Oxide Electrolyser (SOE) and ammonia production plant
A group of Italian researchers recently published a comparative study of “efficiency, energy flows and greenhouse gas emissions” for a range of ammonia synthesis pathways that combine Haber-Bosch with a renewable hydrogen feedstock, using existing technologies. I write in more depth about this analysis in my article on Comparative studies of ammonia production, combining renewable hydrogen with Haber-Bosch.

That study concluded that, of all the existing renewable hydrogen pathways, electrolytic hydrogen produced from renewable electricity was the most advantageous technology “due to the high conversion efficiencies, … the potential absence of GHG emissions, but also … it is the only layout that could allow the complete use and storage of electricity from renewables into energy vectors like hydrogen (in form of the purge gas) and ammonia.”

It makes sense, therefore, that the same team has also developed a sustainable ammonia synthesis technology using electrolytic hydrogen.

In their “innovative” design of an NH3 production plant, “high temperature electrolysis allows [them] to achieve high efficiency and heat recovery [and] permits storage of electricity into a liquid carbon free chemical.”

This concept couples Solid Oxide Electrolysis (SOE), for the production of hydrogen, with an improved Haber Bosch Reactor (HBR) … SOE operates with extremely high efficiency recovering high temperature heat from the Haber-Bosch reactor … Both the SOE and the HBR operate at 650 °C. Ammonia production with zero emission of CO2 can be obtained with a reduction of 40% of power input compared to equivalent plants.
Cinti, et al: Coupling Solid Oxide Electrolyser and ammonia production plant, September 2016

Combining theory and experiment in electrocatalysis: Insights into materials design
Examining a similar pathway to sustainable ammonia production, an international team of researchers from the Technical University of Denmark, the Institute of Materials Research and Engineering in Singapore, and Stanford University in the US, recently published a review of “progress in electrocatalyst development to accelerate water-splitting” in Science Magazine.

However, this work looks beyond catalysts for hydrogen electrolysis because it also examines “the reverse reactions that underlie fuel cells, and related oxygen, nitrogen, and carbon dioxide reductions.” Their aim is to develop “sustainable, fossil-free pathways to produce fuels and chemicals of global importance.”

Today’s electrocatalysts, however, are inadequate. The grand challenge is to develop advanced electrocatalysts with the enhanced performance needed to enable widespread penetration of clean energy technologies …

A systematic framework of combining theory and experiment in electrocatalysis helps to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations … Although current paradigms for catalyst development have been helpful to date, a number of challenges need to be successfully addressed in order to achieve major breakthroughs. One important frontier, for example, is the development of both experimental and computational methods that can rapidly elucidate reaction mechanisms on broad classes of materials and in a wide range of operating conditions …

The long-term goal is to continue improving the activity and selectivity of these catalysts in order to realize the prospects of using renewable energy to provide the fuels and chemicals that we need for a sustainable energy future.
Jaramillo et al: Combining theory and experiment in electrocatalysis, January 2017

I note that this closely echoes the “grand challenge” described in the DOE’s recent Roundtable on Sustainable Ammonia.

As a detailed interview with the researchers on phys.org explains, referring to industrial ammonia production, “If we could simplify the process and use electrocatalysis, we could have a more decentralized supply of artificial fertilizers — powered by a nearby solar plant using nitrogen taken from the air.”

Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon-Nanotube-Based Electrocatalyst
Last week, another international group of researchers, from Italy and China, published a new study on electrochemical ammonia synthesis.

This team synthesized ammonia directly from atmospheric nitrogen and water, using a catalyst of “Iron supported on carbon nanotubes (CNTs),” under ambient conditions.

A rate of ammonia formation of 2.2×10⁻³ gNH₃ m⁻² h⁻¹ was obtained at room temperature and atmospheric pressure in a flow of N₂, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained.
Centi et al: Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon-Nanotube-Based Electrocatalyst, January 2017

In terms of the “grand challenge” of developing deeper understanding of catalyst behavior, the study also indicated that “the active sites in NH₃ electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N₂, making it more reactive towards hydrogenation.”

Plasma catalytic synthesis of ammonia using functionalized-carbon coatings in an atmospheric-pressure non-equilibrium discharge
In Australia, another electrocatalytic ammonia synthesis process has been developed using an entirely different carbon nanotechnology, specifically “using functionalized-nanodiamond and diamond-like-carbon coatings on α-Al₂O₃ spheres as catalysts.” This process takes place “in a non-equilibrium atmospheric-pressure plasma.”

Oxygenated nanodiamonds were found to increase the production yield of ammonia, while hydrogenated nanodiamonds decreased the yield. Neither type of nanodiamond affected the plasma properties significantly … the carbonyl group is associated with an efficient surface adsorption and desorption of hydrogen in ammonia synthesis on the surface of the nanodiamonds, and an increased production of ammonia. Conformal diamond-like-carbon coatings, deposited by plasma-enhanced chemical vapour deposition, led to a plasma with a higher electron density, and increased the production of ammonia.
Murphy et al: Plasma Catalytic Synthesis of Ammonia Using Functionalized-Carbon Coatings in an Atmospheric-Pressure Non-equilibrium Discharge, July 2016

Process Intensification in Ammonia Synthesis Using Novel Coassembled Supported Microporous Catalysts Promoted by Nonthermal Plasma
Another technology that utilizes both plasmas and nanotechnology has been developed by a group of researchers from Turkey and the UK, “using novel coassembled microporous silica supported nickel catalysts and nonthermal plasma reactors operating at ca. 140 ± 10 °C and ambient pressure.”

The conversion levels of nitrogen and hydrogen to ammonia are similar to that achieved by the current industrial best practice which is, however, carried out at 100–250 bar and the temperatures 350–550 °C. In order to achieve continuous plasma generation, a novel catalyst, which has a surface area of ca. 200 m²/g in the form of lamellae with ca. 2 nm thick plates of nickel catalyst sandwiched between the silica support, has been used in the presence of plasma catalysis promoters in the form of spheres made from high permittivity material … It is shown that the catalyst activity remained constant over a continuous period of 72 h when the reaction was terminated.
Akay and Zhang, Process Intensification in Ammonia Synthesis Using Novel Coassembled Supported Microporous Catalysts Promoted by Nonthermal Plasma, December 2016

This technology builds upon Akay’s detailed research, published in June 2016, on the Synthesis of Nano-Structured Supported Catalysts.

It won’t surprise regular readers to know that many other developments are underway in Japan, involving a range of advanced catalysts for ammonia synthesis technologies.

Direct Transformation of Molecular Dinitrogen into Ammonia Catalyzed by Cobalt Dinitrogen Complexes Bearing Anionic PNP Pincer Ligands
One recent project from Japan demonstrated the “direct formation of ammonia from molecular dinitrogen under mild reaction conditions,” utlitlizing “new cobalt dinitrogen complexes.” These and other researchers had previously demonstrated that “some cobalt complexes are effective catalysts for the reduction of dinitrogen gas … under ambient reaction conditions.” Unfortunately, “the cobalt-catalyzed direct formation of ammonia from molecular dinitrogen [had] not been reported to date.” Now, however:

These complexes were indeed found to work as catalysts for the direct reduction of dinitrogen gas into ammonia under mild reaction conditions. Up to 15.9 equiv of ammonia were produced based on the amount of catalyst together with 1.0 equiv of hydrazine (17.9 equiv of fixed N atoms). Herein, we detail the preparation and characterization of these novel cobalt dinitrogen complexes and their catalytic behavior.
Yoshizawa, Nishibayashi, et al: Direct Transformation of Molecular Dinitrogen into Ammonia Catalyzed by Cobalt Dinitrogen Complexes, August 2016

Electrochemical conversion of dinitrogen to ammonia induced by a metal complex–supported ionic liquid
Another team from Japan report progress in a completely different scientific arena: liquid state electrochemical ammonia synthesis, using an ionic liquid, which “is a salt in a liquid state under ambient conditions.” The ionic liquid represents an interesting avenue of scientific discovery in this area “because it has several unique properties such as low volatility, large electrochemical window, high thermal and chemical stabilities, and high electric conductivity.”

The reduction of N₂ in ionic liquid has never been reported. We have reported the first example of the electrochemical reduction of N₂ to NH₃ … When the controlled potential electrolysis was carried out at -1.5 V (vs. Ag/AgCl), the yield of NH₃ per Cp₂TiCl₂ and current efficiency were 27% and 0.2%, respectively, which are significantly higher in comparison with those reported previously.
Katayama et al: Electrochemical conversion of dinitrogen to ammonia induced by a metal complex–supported ionic liquid, October 2016

You can also read the full article at ammoniaindustry.com.