March30, 2023
By Tokyo
Institute of Technology
![](images/images_03_31_2023/breaking-the-barrier-l.jpg)
The Haber-Bosch (HB) process is one of the most important industrial
chemical reactions. It combines nitrogen and hydrogen gases in the
presence of an iron-based catalyst at high temperatures and pressures
to produce ammonia fertilizer which helps provide food for over five
billion people.
Over the decades, researchers have tried to bring down the
reaction temperature of the HB process to increase the ammonia yield
while reducing energy consumption. To this end, they have recently
developed new catalysts based on other transition metals, such as
ruthenium, cobalt, and nickel, which exhibit much higher catalytic
activity than iron.
However, these catalysts preferentially adsorb hydrogen atoms
onto their surface at low temperatures of 100–150oC, which reduces
nitrogen adsorption and thus hampers ammonia production. This
phenomenon, known as hydrogen poisoning, poses an obstacle to the
low-temperature HB process.
In this light, researchers led by Professor Michikazu Hara of
the Laboratory for Materials and Structures at Tokyo Institute of
Technology (Tokyo Tech), have refocused on iron-based catalysts and
modified them to produce ammonia at 100oC. Their work is all set to be
published in the Journal of the American Chemical Society.
Prof. Hara explains the motivation behind the research.
"Hydrogen poisoning is not strong for iron-based catalysts. Therefore,
they may be used for the low-temperature HB process but only when
combined with an appropriate promoter that increases their catalytic
activity." In this work, the researchers prepared metallic iron (Fe)
nanoparticles on calcium hydride (CaH2) particles, with a mixture of
barium oxide (BaO) and barium hydride (BaH2) deposited on them.
A set of experiments revealed that the iron nanoparticles
interact strongly with the hydride ions of both hydrides. As a result,
hydrogen atoms move from the hydrides to the nanoparticles and get
desorbed as hydrogen gas, leaving behind electrons. The hydrides
donate these electrons to the iron nanoparticles. It facilitates the
breaking of nitrogen gas into atoms, resulting in enhanced catalytic
activity for ammonia production even at low temperatures.
The BaH2–BaO/Fe/CaH2 catalyst exhibited a turnover frequency of
0.23 s-1 at 100oC and 12.3 s-1 at 300oC under a moderate pressure of
0.9 MPa. These values, orders of magnitude higher than those for
catalysts based on other transition metals, result from the ability of
iron to prevent hydrogen poisoning by desorbing the adsorbed hydrogen
atoms as hydrogen gas at low temperatures.
Discussing the future potential of their work, Prof. Hara
observes, "The BaH2–BaO/Fe/CaH2 catalyst facilitates low-temperature
HB process, which consumes less energy. As such, it can reduce the use
of fossil fuels and potentially lower global carbon emissions. In
addition, iron is abundant and inexpensive, which makes the HB process
more sustainable."
Green Play Ammonia™, Yielder® NFuel Energy.
Spokane, Washington. 99212
www.exactrix.com
509 995 1879 cell, Pacific.
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