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Stanford researchers make ammonia from air and water microdroplets

Stanford researchers, with a colleague from King Fahd University of Petroleum and Minerals, have developed a simple and environmentally sound way to make ammonia with tiny droplets of water and nitrogen from the air. An open-access paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

Water (H2O) microdroplets are sprayed onto a magnetic iron oxide (Fe3O4) and Nafion-coated graphite mesh using compressed N2 or air as the nebulizing gas. The resulting splash of microdroplets enters a mass spectrometer and is found to contain ammonia (NH3). This gas–liquid–solid heterogeneous catalytic system synthesizes ammonia in 0.2 ms.

The conversion rate reaches 32.9 ± 1.38 nmol s−1 cm−2 at room temperature without application of an external electric potential and without irradiation.

Water microdroplets are the hydrogen source for N2 in contact with Fe3O4. Hydrazine (H2NNH2) is also observed as a by-product and is suspected to be an intermediate in the formation of ammonia. This one-step nitrogen-fixation strategy to produce ammonia is eco-friendly and low cost, which converts widely available starting materials into a value-added product.

—Song et al.

Pnas

Catalytic mechanism for ammonia formation from N2 and water droplets striking Fe3O4. (A) Diagrams of the reaction steps and (B) corresponding free energy changes found from DFT calculations. Song et al., PNAS


For more than a century, the world has relied on the Haber-Bosch process to yield ammonia in bulk; however, the industrial procedure is energy intensive. To break nitrogen’s strong bonds, the Haber-Bosch process requires roughly 80-300 atmospheres of pressure and temperatures around 572-1000 ˚F (300-500 ˚C). The steam-treating of natural gas involved in the process also releases ample amounts of carbon dioxide.

All told, to satisfy the current annual worldwide demand for 150 million metric tons of ammonia, the Haber-Bosch process consumes more than 2% of global energy and accounts for about 1% of the carbon dioxide emitted into the atmosphere.

In contrast, the innovative method debuted by the Stanford researchers requires less specialized circumstances.

We were shocked to see that we could generate ammonia in benign, everyday temperature-and-pressure environments with just air and water and using something as basic as a sprayer. If this process can be scaled up, it would represent an eco-friendly new way of making ammonia, which is one of the most important chemical processes that takes place in the world.

—senior author Richard Zare

The new method also uses little energy and at low cost, thus pointing a way forward to potentially producing the valuable chemical in a sustainable manner. Xiaowei Song, a postdoctoral scholar in chemistry at Stanford, is the lead author of the study.

The new chemistry discovered follows pioneering work by Zare’s lab in recent years examining the long-overlooked and surprisingly high reactivity of water microdroplets. In a 2019 study, Zare and colleagues novelly demonstrated that caustic hydrogen peroxide spontaneously forms in microdroplets in contact with surfaces. Experiments since have borne out a mechanism of electric charge jumping between the liquid and solid materials and generating molecular fragments, known as reactive oxygen species.

While promising, the ammonia production method is only at the demonstration stage. The researchers plan to explore how to concentrate the produced ammonia as well as gauge how the process could potentially be scaled up to commercially viable levels.

While Haber-Bosch is only efficient when pursued at huge facilities, the new ammonia-making method could be portable and done on-site or even on-demand at farms. That, in turn, would slash the greenhouse gas emissions related to the transportation of ammonia from far-off factories.

Resources

  • Xiaowei Song, Chanbasha Basheer and Richard N. Zare (2023) “Making ammonia from nitrogen and water microdroplets” PNAS doi: 10.1073/pnas.2301206120

Comments

Davemart

The potential implications of this are staggering.

Rightly so, the authors modestly talk about replacing current ammonia production, which is pretty substantial.

But that is nothing compared to how it could be used in volume if production was cheap enough both in economic and energy terms.

' The conversion rate reaches 32.9 ± 1.38 nmol s−1 cm−2 at room temperature without application of an external electric potential and without irradiation. '

The current plan in Europe is to import vast quantities of hydrogen, likely as ammonia, precisely because of a lack of this 'irradiation' in Hamburg in midwinter.

There is however plenty of water.

'Easy' early targets in addition to present production for fertiliser etc would include ammonia production for low carbon steel, where it is just as good as hydrogen, but potential uses include just about everything to power society.

Maybe there are loads of 'gocha's' in scaling this, but on the face of it, this could be gigantic.

sd

When my company was in the startup and initial building stage, we used a water table plasma cutter to cut out steel sheet and plate parts. We later moved on to a faster and more efficient laser cutter. Anyway, periodically, we would shovel the wet pellets that formed from the molten steel hitting the water into barrels. One day, when our scrap company was dumping the barrels of the scrap from, they complained about the smell. I quickly identified the smell as ammonia. There was also some crystalline material which was probably ammonium nitrate. I guess I should have written a paper about this new energy efficient process for manufacturing ammonia as it only required wet iron pellets sitting in a barrel.

I think their research is interesting but is about as likely to result in a commercial process as having wet iron pellets sitting in a barrel.

Gorr

Im interrested in buying a small ammonia car.

mahonj

Lots of small hydrocarbon cars are already available ...

Davemart

@sd

' I think their research is interesting but is about as likely to result in a commercial process as having wet iron pellets sitting in a barrel.'

Or perhaps as likely as the idiotic notion that some small amounts of oil out of the ground could ever compete with wonderful, fully established whale oil.

I am hardly one to be unreservedly all on board about potential breakthroughs in anything, as they are just that, potential, but it seems as ill advised to wave them away as to jump on board until the facts are in.

I have no idea why you should seek to be so utterly dismissive.

Of course it may not work at any scale.

But then again, there is clearly an unexpected reaction which was not in the book, so it merits investigation to find out what is going on.

Who knows, perhaps if you had fully investigated the reaction you noted, you would now be a trillionaire!

I recall some other entirely serendipious and unexpected experimental results, which were sometimes ignored, and some which were instead exploited to great profit.

That is pretty much what experiments are about, to find out what is going on, instead of assuming this or that.

mahonj

@Dave etc, have you read "The Prize" by Daniel Yergin. (it is about the oil industry) and is a great read, whatever your views on propulsion fuels.
It was also made into a very good TV series.

Davemart

Hi Jim.

No, I haven't, but have just googled it to get an idea of its subject.

The issue with oil is that it is eminently suitable to being grabbed by elites, to the detriment of the general population, with the surpluses then available to finance, for instance, the invasion of the Donbass.

Whether or not this notion of producing ammonia and so its derivative hydrogen very cheaply and universally works, solar and wind hydrogen is already 'good enough' to disrupt this model and democratise power.

Like many before him, the 'Great Patriot' Putin has gone for a deeply stupid over extension.

When huge fossil fuel reserves were an increasingly dubious asset, pissing off and demonstrating how insecure access to those resources are to your biggest customer is the act of a child, who wants what he wants, now!

Perhaps here in the UK we ought to be considering reclaiming the United States, as our claim is about as good as Russia's for the Ukraine.

One way or another, fossil fuels are being marginalised and replaced, it might be a bit faster and more generalised if this potential breakthrough works at scale, but if not, then what we have will do just fine.

Nirmalkumar

Just yesterday IIT Gauhati India have discovered a new lab process with triple catalyst to make hydrogen from mythyl alcohol thru no carbon dioxide production and good biproduct. This could open up chiep way of making Hydrogen from mythyl alcohol.

sd

@ Davemart

In general, I believe in research, both basic and applied and sometimes you can get surprisingly good results. Most of the time, it takes years of doggedly hard work and even that is no guarantee. Just look at how long it took to go from a red LED to white light LED bulbs. In 1970, when I was a grad student, a researcher gave a lecture on a fluid where a magnetic field would change the viscosity but they did not have an application. Now GM uses it their high performance shock absorbers.

But the first thing to ask for this type of research is where does the energy come from? Unless you believe in magic, the energy for this transaction has to come from somewhere. You do not get something for nothing. If you know about entropy, energy only flows in one direction and you need energy to cause this reaction. There may be more efficient means than the Haber process but you still need to put in more energy than you will get back.

Davemart

Hi Nirmakumar!

Sounds interesting! Have you got a link?

Davemart

I found a video on the process here:

https://www.youtube.com/watch?v=GO9z13iHvnY

It is a bit tough to follow for those of us who are not accustomed to an Indian accent, but interesting.

I gather they are thinking first of processing biomass more efficiently, if I have followed it right.

Davemart

Hi sd:

I certainly don't think that they are some bunch of nutters claiming negative entropy, although the energy processes are not clear, and indeed they specifically say:

' The new method also uses little energy and at low cost,'

'Little energy' is not 'no energy' so your critique would appear to be without foundation, although they have not specified inputs etc, or rather the stuff they have specified in the diagrams etc are far too advanced to make any sense to the likes of me.

Entropy always rules, but can be tricky, so energy from the environment in marginal drops in temperature etc can play a part, as can fairly obscure changes of state, way, way above my pay grade.

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