Accelerated ammonia synthesis holds promise for conversion of renewable
energy

Date:
February 15, 2022
Source:
Hiroshima University
Summary:
Scientists reveal a way to make ammonia from its constituent
molecules of nitrogen and hydrogen at ambient pressure.



FULL STORY ========================================================================== Research by Japanese scientists at Hiroshima University reveals a way
to make ammonia from its constituent molecules of nitrogen and hydrogen
at ambient pressure.


==========================================================================
The new study, published on Feb. 2 in the Journal of Physical Chemistry C, demonstrates a process with potential for use in renewable energy storage
and transfer, which relies on a dispersed and fluctuating network of
resources, such as sun and wind. "The ultimate goal of this work is to establish the small-scale NH3 production process to effectively utilize renewable energy" said study author and associate professor Hiroki
Miyaoka from Hiroshima University's Natural Science Center for Basic
Research and Development.

Ammonia (NH3) has recently been recognized as an outstanding energy
carrier molecule. In 1918, German chemist Fritz Haber won the Nobel
Prize for synthesis of ammonia from its elements, paving the way
for ammonia's significant role in industrial fertilizers. However,
use of ammonia in renewable energy applications has been limited by
the processes available to synthesize it. The Haber-Bosch process,
used in industrial production of ammonia, requires high temperature and pressure, conditions not typically available in renewable energy storage
and transport infrastructure.

The NH3 synthesis process via chemical looping using lithium hydride
(LiH) starts by combining LiH with N2 (molecular nitrogen) at ambient
pressure and temperatures up to 500DEGC to yield a lithium imide product (LiNH2). The lithium imide then reacts with hydrogen gas (H2) to yield
ammonia. The reaction time for ammonia synthesis from its constituent
molecules in this process is more than 1000 minutes. Its speed is limited
by the clumping up (agglomeration) of the products of the reaction into
large particles (more than 200 ?m) that don't have much surface area
exposed to the hydrogen gas. For its practical application in distributed renewable energy, this prolonged reaction, requiring extreme conditions,
is an impediment to ammonia production.

In the new study, researchers experimented with using lithium oxide
(Li2O) as a molecular scaffold to synthesize ammonia under ambient
pressure and temperatures below 400DEGC, conditions easy to mimic in nonindustrial settings.

They combined the reactant lithium hydride with lithium oxide and
found that the lithium hydride prevented clumping, leaving smaller
particles (less than 50 ?m) with more surface area exposed for chemical reactions. Using these non- agglomerated reactants and adding the gaseous hydrogen used in the final step of ammonia synthesis, they were able to
produce ammonia more quickly; the reaction substantially sped up.

If ammonia can be produced quickly with relatively simple equipment
under modest temperature and pressure conditions, it paves the way for smaller-scale ammonia production.

"The chemical looping process is useful to establish the small-scale
NH3 synthesis process, which can be operated under lower pressure and temperature with higher conversion yield than the conventional catalytic process," said Miyaoka. The new process also obviates the need for
expensive metal catalysts - - such as elemental ruthenium (Ru) -- used
in industrial synthesis of ammonia.

The results of this study are relevant to renewable energy generation,
which tends to be more distributed than industrial production. The
process pioneered in the Hiroshima lab to produce ammonia efficiently
under near-ambient conditions is the foundation for such applications.

"As a next step, the practical reaction processes to effectively control
the above NH3 synthesis should be considered from chemical engineering
points of view," Miyaoka said.

The Japan Society for the Promotion of Science funded this research.

========================================================================== Story Source: Materials provided by Hiroshima_University. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
*
Schematic_image_of_small-scale_and_distributed_NH3_synthesis_processes ========================================================================== Journal Reference:
1. Kentaro Tagawa, Hiroyuki Gi, Keita Shinzato, Hiroki Miyaoka,
Takayuki
Ichikawa. Improvement of Kinetics of Ammonia Synthesis at Ambient
Pressure by the Chemical Looping Process of Lithium Hydride. The
Journal of Physical Chemistry C, 2022; 126 (5): 2403 DOI: 10.1021/
acs.jpcc.1c09902 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215092519.htm

--- up 10 weeks, 3 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)