Catalyst for the carbon-free production of hydrogen gas from ammonia

May 19, 2017 by Heather Zeiger report
Credit: Katsutoshi Nagaoka

(Phys.org)—Hydrogen has the potential to provide an alternative, clean energy source, particularly as applied to fuel cell technology. Current fuel sources involve carbon-containing fossil fuels or carbon-containing organic molecules, which result in the production of excess CO2, a greenhouse gas. Several initiatives, including a national initiative in Japan, seek to create a low-carbon usage society by using alternative fuel sources.

The Energy Carriers initiative in Japan is a national project that is specifically looking at ways to efficiently store and transport hydrogen. One way to do this is to use ammonia as a hydrogen source. However, discovery of an efficient process for breaking down ammonia has proved difficult, largely because the catalytic process to break down ammonia requires the continuous addition of heat, which can be prohibitively expensive.

Katsutoshi Nagaoka, Takaaki Eboshi, Yuma Takeishi, Ryo Tasaki, Kyoto Honda, Kazuya Imamura, and Katsutoshi Sato of Oita University in Japan have developed a method using a novel for producing hydrogen from ammonia without the addition of external heat through the catalytic cycle. Their work appears in Science Advances.

The decomposition of ammonia into hydrogen and nitrogen is an endothermic process, meaning that it requires the addition of energy to obtain products. This means that traditional catalytic decomposition reactions require the addition of a large amount of heat to obtain a useful amount of hydrogen gas.

Nagaoka et al. developed a catalyst that is made of a RuO2 nanoparticle supported on γ-Al2O3 catalyst bed. After purging their catalyst of H2O and CO2, ammonia and oxygen were added to the reaction vessel where ammonia was adsorbed onto the catalytic surface, resulting in an increase in temperature. This increase in temperature catalyzed the oxidative decomposition of ammonia, an exothermic process. This heated up the reaction, which in turn, provided the energy for the endothermic decomposition of ammonia into hydrogen and nitrogen.

The catalyst pre-treatment did require heating to remove water and carbon dioxide, but it did not require subsequent re-heating. Tests on catalyst cycling showed that after the initial pre-treatment of the RuO2/γ-Al2O3 catalyst with helium at 300oC, the catalyst was able to cycle three times and still produce hydrogen in maximum yields. Furthermore, these studies included oxidative passivation to ensure that no heat was produced from oxidation of Ru to RuO2. In practice, oxidative passivation will not be necessary. So, even though heating is required to pre-treat the catalyst, heating is not required for additional cycles of the catalyst.

In an effort to understand how the RuO2/γ-Al2O3 catalyst works, Nagaoka et al. compared the maximum catalytic bed temperature that results from self-heating of RuO2/ γ-Al2O3 to RuO2/La2O3, a known ammonia decomposition catalyst. They found that the aluminum-based catalyst heated to a maximum temperature of 97oC, while the lanthanum-based catalyst heated to a maximum temperature of 53oC. This is important because the auto-ignition temperature for the oxidative combustion of ammonia is 90oC, and it explains why better reaction yields were seen with RuO2/ γ-Al2O3.

The authors point out that this difference in adsorption temperature is likely due to the favorable interaction between ammonia, a basic molecule, and Al2O3, which is a Lewis acid. La2O3, on the other hand, is a Lewis base.

Additionally, the authors looked at the difference between using bare γ-Al2O3 as a catalyst and RuO2/ γ-Al2O3. They found that 90% of the ammonia adsorbs onto bare γ-Al2O3 compared to the catalyst bed and the RuO2 nanoparticle. This implies that ammonia is chemisorbed onto the nanoparticle and γ-Al2O3, which then promotes multilayer physisorption.

Overall, this type of catalyst is helpful in providing enough heat to overcome the needed heat requirements for the endothermic decomposition of ammonia into hydrogen and nitrogen gas. This study shows that self-heating catalysis is a viable option for exploring solutions to the practical difficulties in using as a fuel source.

Explore further: Discovery of a facile process for H2 production using ammonia as a carrier

More information: Katsutoshi Nagaoka et al. Carbon-free Hproduction from ammonia triggered at room temperature with an acidic RuO/γ-AlOcatalyst, Science Advances (2017). DOI: 10.1126/sciadv.1602747

Abstract
Ammonia has been suggested as a carbon-free hydrogen source, but a convenient method for producing hydrogen from ammonia with rapid initiation has not been developed. Ideally, this method would require no external energy input. We demonstrate hydrogen production by exposing ammonia and O2 at room temperature to an acidic RuO2/γ-Al2O3 catalyst. Because adsorption of ammonia onto the catalyst is exothermic, the catalyst bed is rapidly heated to the catalytic ammonia autoignition temperature, and subsequent oxidative decomposition of ammonia produces hydrogen. A differential calorimeter combined with a volumetric gas adsorption analyzer revealed a large quantity of heat evolved both with chemisorption of ammonia onto RuO2 and acidic sites on the γ-Al2O3 and with physisorption of multiple ammonia molecules.

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24 comments

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Shootist
2 / 5 (4) May 19, 2017
Making H2 from ammonia (which is primarily made from petroleum) is not optimal.

100 1000 megawatt fission plants would allow us to produce all the H2, fresh water and electricity, we will need to charge our battery powered cars, power fuel cells and provide fresh water for drinking, agriculture, fracking and fresh water injection wells.

Fission, it is the 21st century after all.
Whydening Gyre
5 / 5 (1) May 19, 2017
Making H2 from ammonia (which is primarily made from petroleum) is not optimal.


And here, I always thought it was made from urine...
(which is ANY century...:-))

Dingbone
3 / 5 (4) May 19, 2017
The article author must be an idiot - or he believes, that his readers are idiots. Production of ammonia requires 2% of energy budget of civilization (which is currently composed of more than 85% fossil fuels) - so I seriously doubt it's carbon free. But this is what the renewables propaganda is all about from its very beginning.
Dingbone
3 / 5 (2) May 19, 2017
The ammonia gas is flammable and it was itself tested as a hydrogen-rich fuel. The proposed catalyst is made of extremely rare and expensive ruthenium (only 12 tonnes of ruthenium are mined each year with world with compare to 3500 tonnes of gold, for example) and the ammonia gets partially burned during production of hydrogen and 30% of its hydrogen gets wasted at place in this way.
MR166
1 / 5 (2) May 19, 2017
Also it appears that some of the H2 is turned into water. I suppose that is where the necessary heat comes from. All in all this looks to be another case of feel good science.
manfredparticleboard
5 / 5 (2) May 19, 2017
Ok ammonia requires energy to make. But then so does fuel mining, cleaning, refining and it's distribution chain. Ammonia to hydrogen cuts out many of the energy hungry middle men in the carbon fuel cycle. And at least its a closed cycle even if it does come close to the energy budget of carbon fuels; which at the moment carries some measure of importance.
I doubt the industrial form of this process will rely on Ru. An expedited catalyst will likely be found to do the same job, even if it is less efficient.
manfredparticleboard
5 / 5 (1) May 19, 2017
Ammonia is a terrible fuel, it's flammable, but barely. It doesn't generate enough heat to support it's own combustion as a flame. Maybe with a very complex fuel cell you could get ammonia to supply energy via an oxidation reaction.
MR166
5 / 5 (1) May 19, 2017
This article just highlights how difficult it is to store and transport H2 gas as a transportation fuel. H2 gas might make sense when used as an renewable energy storage medium for stationary power plants providing that solar and wind costs are so low that the conversion inefficiencies can be disregarded.
MR166
not rated yet May 19, 2017
As I understand it, ammonia is a viable alternative automotive fuel. Just as a side note it will destroy brass.
rrrander
5 / 5 (1) May 20, 2017
Hydrogen, propane, all these alternatives COST more than traditional fossil fuels and have much lower energy density than hydrogen. The West is spending itself into mass bankruptcy. It's been estimated that we are living at least 40% beyond the capacity to generate new wealth. We need to be economizing and that means no high-priced fuels.
manfredparticleboard
not rated yet May 20, 2017
Hydrogen, propane, all these alternatives COST more than traditional fossil fuels and have much lower energy density than hydrogen. The West is spending itself into mass bankruptcy. It's been estimated that we are living at least 40% beyond the capacity to generate new wealth. We need to be economizing and that means no high-priced fuels.

Or you can stop borrowing money and spending it on military and bullshit walls to prop up a failing voter base. Deferring to growth economy at all costs philosophies is another failed experiment that has fed the banks and speculators but done nothing to actually improve overall quality of living. Stop making shit you don't need can cut out enormous quantities of the energy being consumed. Do you need another cheaply made piece of crap from China? Really? This game of money go round has kept the West sufficiently addicted for long enough and there's not many hands left to play.
MR166
5 / 5 (3) May 20, 2017
".....and bullshit walls to prop up a failing voter base. "

Show me other countries that do not control their border. Border control is a major part of a governments duties. The progressive movement wants to eliminate all national governments and replace them with a one world government. Uncontrolled migration is just one part of that plan. I live in an area with a large population of immigrants and many work off the books, pay no taxes and get government benefits to boot. Also much of out law enforcement cost are directly related to them. Hospitals in our area were put out of business because they had no way to collect for services provided to them.
Dingbone
5 / 5 (3) May 20, 2017
Ironically the ammonia (i.e. the nitrogen hydride) is the better and more concentrated source of energy than the hydrogen itself. Hydrogen is difficult to compress and liquefy with compare to ammonia and it explodes in contact with air in wide range of concentrations. Whereas the ammonia is relatively safe and because of its smell its leaks can be easily detected. It's conversion to hydrogen has absolutely no meaning here and it has many other uses (fertilizers). The production of ammonia consumes 2% of total energy of civilization so its production represents an ideal storage of surplus of energy from unstable wind and solar sources. It can be burned in gas plants directly. But if you would search for even better storage of hydrogen, then the carbon hydrides (i.e. the gasoline) are even more concentrated and safer source of hydrogen. We don't need to utilize nitrogen for temporal fixation and storage of hydrogen, we can simply use carbon too.
Eikka
5 / 5 (1) May 20, 2017
Ok ammonia requires energy to make. But then so does fuel mining, cleaning, refining and it's distribution chain.


The difference is the energy return: fossil fuels positive, ammonia negative.

Stop making shit you don't need can cut out enormous quantities of the energy being consumed. Do you need another cheaply made piece of crap from China? Really?


It's not that simple. 80% of the workforce is now in "services" which has turned into an enterprise based on selling goods for consumption and coming up with new ways to induce more consumption of resources to turn a buck in the middle. The vast majority of the population now falls into the category of unnecessary middle-men, selling unproductive luxuries.

If the flow of cheap pointless trinkets from china stops, half the people go on the dole because all the necessary food, clothes, housing etc. can be produced by the other 20% of people thanks to extensive automation.
MR166
not rated yet May 20, 2017
RRR you are 100% correct about our economic problems. The US national debt is doubling every 8 years and there looks to be no way to change this. At some point in time this will result in a huge inflation spike. Right now we finance this debt via artificially low interest rates and print money at will to fund new debt. Despite this debt real wages are still falling, this is a real problem.
Eikka
not rated yet May 20, 2017
That's the actual irony. If we were being completely rational and efficient about it, only one in five people would actually have to work while the rest can just sit and enjoy the spoils. The less they work, the better off everyone would be, because make-work is a waste of resources.

But the problem then becomes about the distribution of wealth, because almost everyone wants more than their equal share and nobody prefers to spend any effort to gain it. Hence, if the distribution of wealth is made a political question, as in the communist states, you get massive government corruption and nepotistic backstabbing, and eventually dictatorship.

Post-scarcity is already here - we're just wasting it.
Eikka
not rated yet May 20, 2017
The US national debt is doubling every 8 years and there looks to be no way to change this.


Technically, the growth of national debt is fine as long as it's internal debt - because of how fiat money works. The amount of debt always matches the amount of money in circulation because money exists due to the debt. As the government bonds mature, new bonds are issued to maintain the amount of debt and the amount of money.

As the economy grows, the debt must grow to create more money. Otherwise you get deflation which is a sign that people don't have enough money to exchange all the goods and services they're trying to, so money itself starts to become more valuable than the goods and services, which leads to money hoarding and a recession.

Though it's true that 8 years is too short for the doubling, when the economy is doubling every 35 years.
MR166
not rated yet May 20, 2017
Eikka it is the demise of the middle class that is worrisome. Besides our national debt there is also the huge trade deficit of about 1/2 trillion per year. My only guess is that the money is going to military expenditures and domestic entitlements. It can't be going only to the "Rich" because you could take ALL of their money and it would not put a dent in the problem.
manfredparticleboard
not rated yet May 20, 2017
That's the actual irony. If we were being completely rational and efficient about it, only one in five people would actually have to work while the rest can just sit and enjoy the spoils. The less they work, the better off everyone would be, because make-work is a waste of resources....


This point has been made many times over the years by economists. Only a small percentage of the workforce actually creates wealth. The rest are just sheltered workshops that need artificial support to sustain a workforce. It's just you can't call it charity because it's political dynamite. In the past when I had to deal with inept or poisonous personalities in the workforce I realised that paying my taxes to keep them on the dole and out of our industry made more economic sense, because the loss of productivity from their behavior was greater.
daqddyo
not rated yet May 21, 2017
Back to the ammonia article. Storage of ammonia gas is more hazardous than storing hydrogen.
Ammonia gas destroys lungs very quickly. Even small leaks would be deadly.

Let's focus on perfecting the electrolysis of water which is very abundant and the end product of the process is perfect for our atmosphere.
Dingbone
not rated yet May 21, 2017
gmarster
not rated yet May 21, 2017
Hydrogen is so 20th century, electrons are the 21st century power medium of choice.
FTCause
not rated yet May 21, 2017
Hydrogen is so 20th century, electrons are the 21st century power medium of choice.


Gmarster, How do you suggest we create and store the electrons for later use??? I'm pretty sure hydrogen fuel cells create a flow of electrons to be used by a variety of electric circuits.
Whydening Gyre
not rated yet May 21, 2017
Hydrogen is so 20th century, electrons are the 21st century power medium of choice.


Gmarster, How do you suggest we create and store the electrons for later use??? I'm pretty sure hydrogen fuel cells create a flow of electrons to be used by a variety of electric circuits.

FT,
I guess he missed that hydrogen IS an electron storage medium...

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