[kmm]

Of course it is not an energy negative. The production of ammonia from hydrogen and nitrogen gas is an exothermic process. At room temperature it's even a spontaneous process.

The reason we need these complicated processes is the massive activation energy of the reaction, making it extremely slow uncatalyzed.

These are professional chemists, publishing in a serious journal. Did you really think they didn't take into account the basic energy balance of their equation?

[ryanmt]

I'd like to remind you that the process we are discussing is currently responsible for 1% of the world's energy consumption annually. That's clearly a "net-negative" cost. Feel free to review the Haber-Bosch process to confirm.

[kmm]

Ammonia has a negative enthalpy of formation of about -46 kJ/mol [0]. If you read the wikipedia page of the Haber process [1] it explicitly states the reaction is exothermic.

The reason the Haber process is so costly is because it uses very high pressures and temperatures to overcome the activation energy, even with the best catalysts we have. Not because creating ammonia from nitrogen and hydrogen needs energy. It's in effect wasted energy.

Enzymes can't change the cost equation, but luckily it's in our favor. If they can reduce the activation energy without wasting a ton of energy, it can be a net energy producer.

0: https://en.wikipedia.org/wiki/Ammonia 1: https://en.wikipedia.org/wiki/Haber_process

[rasmusei]

Yes, it can be a net energy producer given a source of hydrogen, but hydrogen is typically not available for free. See my other comment.

[kmm]

Nobody is saying hydrogen is free. Nor will the production of ammonia from compounds we have in abundance (i.e. water, air and rock) ever produce energy, as it's a high energy compound, releasing quite a bit of energy when combusted. But that is absolutely not what this is about.

However, I was refuting the GP's wrong assertion that the energy cost equation of this reaction shows that it cannot be a net energy producer.

It makes sense to optimize this step, because the energy equation shows the energy is just wasted as heat, as it's not contained in the compound itself.

[rasmusei]

I agree 100%. Thanks for the clarification!

[nickjarboe]

Not sure where you get a pure hydrogen source on this planet without using some energy. I'd like to own such a source. Sort of like owning an oil well.

[kmm]

That's moving the goalposts. The point of this is to reduce the energy cost of making ammonia, assuming you already have hydrogen gas available.

The article is not purporting to have conceived of a new energy source, only to have found a way to recuperate some of the cost of making ammonia, by extracting some energy from a step that ought to be a net energy producer.

[nickjarboe]

I was thinking that producing the hydrogen feed stock would be most of the energy used in the process. This site [1] states that, using the current global feed stock mix of light carbon and heavy carbon sources, about half the energy used in production is feed stock energy and half is added energy. Maybe an industrial chemist could estimate how much energy this new tech could save if it could be used at the scale needed?

[1] http://ietd.iipnetwork.org/content/ammonia