Process aims to strip ammonia from wastewater
Ruthenium and copper catalyze a more environmentally friendly way to
produce essential chemical

Date:
May 2, 2022
Source:
Rice University
Summary:
Engineers have developed a high-performance nanowire catalyst that
pulls ammonia and solid ammonia (fertilizer) from nitrate, a common
contaminant in industrial wastewater and polluted groundwater.



FULL STORY ==========================================================================
A dash of ruthenium atoms on a mesh of copper nanowires could be one
step toward a revolution in the global ammonia industry that also helps
the environment.


========================================================================== Collaborators at Rice University's George R. Brown School of Engineering, Arizona State University and Pacific Northwest National Laboratory
developed the high-performance catalyst that can, with near 100%
efficiency, pull ammonia and solid ammonia -- aka fertilizer -- from
low levels of nitrates that are widespread in industrial wastewater and polluted groundwater.

A study led by Rice chemical and biomolecular engineer Haotian Wang
shows the process converts nitrate levels of 2,000 parts per million
into ammonia, followed by an efficient gas stripping process for ammonia product collection.

The remaining nitrogen contents after these treatments can be brought
down to "drinkable" levels as defined by the World Health Organization.

"We fulfilled a complete water denitrification process," said graduate
student Feng-Yang Chen. "With further water treatment on other
contaminants, we can potentially turn industrial wastewater back to
drinking water." Chen is one of three lead authors of the paper that
appears in Nature Nanotechnology.

The study shows a promising alternative toward efficient processes for
an industry that depends upon an energy-intensive process to produce
more than 170 million tons of ammonia per year.



==========================================================================
The researchers knew from previous studies that ruthenium atoms are
champs at catalyzing nitrate-rich wastewater. Their twist was combining
it with copper that suppresses the hydrogen evolution reaction, a way to produce hydrogen from water that in this case is an unwanted side effect.

"We knew that ruthenium was a good metal candidate for nitrate reduction,
but we also knew there was a big problem, that it could easily have a
competing reaction, which is hydrogen evolution," Chen said. "When we
applied current, a lot of the electrons would just go to hydrogen, not the product we want." "We borrowed a concept from other fields like carbon
dioxide reduction, which uses copper to suppress hydrogen evolution,"
added Wang. "Then we had to find a way to organically combine ruthenium
and copper. It turns out that dispersing single ruthenium atoms into
the copper matrix works the best." The team used density functional
theory calculations to explain why ruthenium atoms make the chemical
path that connects nitrate and ammonia easier to cross, according to co-corresponding author Christopher Muhich, an assistant professor of
chemical engineering at Arizona State.

"When there is only ruthenium, the water gets in the way," Muhich
said. "When there is only copper, there isn't enough water to provide
hydrogen atoms. But on the single ruthenium sites water doesn't compete as well, providing just enough hydrogen without taking up spots for nitrate
to react." The process works at room temperature and under ambient
pressure, and at what the researchers called an "industrial-relevant"
nitrate reduction current of 1 amp per square centimeter, the amount of electricity needed to maximize catalysis rate. That should make it easy
to scale up, Chen said.



==========================================================================
"I think this has big potential, but it's been ignored because it's been
hard for previous studies to reach such a good current density while
still maintaining good product selectivity, especially under low nitrate concentrations," he said. "But now we're demonstrating just that. I'm
confident we'll have opportunities to push this process for industrial applications, especially because it doesn't require big infrastructure."
A prime benefit of the process is the reduction of carbon dioxide
emissions from traditional industrial production of ammonia. These are
not insignificant, amounting to 1.4% of the world's annual emissions,
the researchers noted.

"While we understood that converting nitrate wastes to ammonia may not
be able to fully replace the existing ammonia industry in the short
term, we believe this process could make significant contributions to decentralized ammonia production, especially in places with high nitrate sources," Wang said.

Alongside the new study, Wang's lab and that of Rice environmental
engineer Pedro Alvarez, director of the Nanotechnology Enabled Water
Treatment (NEWT) Center, recently published a paper in the Journal of
Physical Chemistry C detailing the use of cobalt-copper nanoparticles on
a 3D carbon fiber paper substrate as an efficient catalyst to synthesize ammonia from nitrate reduction. This low-cost catalyst also showed great promise for the denitrification in wastewater.

Co-lead authors of the Nature Nanotechnology paper are Rice postdoctoral
fellow Zhen-Yu Wu and Srishti Gupta, a graduate student at Arizona
State University.

Co-authors are graduate student Daniel Rivera of Arizona State; Sten
Lambeets of the Pacific Northwest National Laboratory, Richland,
Washington; research scientist Guanhui Gao, undergraduate Stephanie
Pecaut, graduate students Jung Yoon Kim and Peng Zhu, and Yimo Han, an assistant professor of materials science and nanoengineering, at Rice;
Zou Finfrock, Hua Zhou and Wenqian Xu of Argonne National Laboratory,
Lemont, Illinois; Debora Motta Meira and Graham King of Canadian Light
Source, Saskatoon, Saskatchewan; and David Cullen of Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Daniel Perea of the Pacific Northwest lab is a co-corresponding author of
the paper. Wang is the William March Rice Trustee Chair and an assistant professor of chemical and biomolecular engineering.

The National Science Foundation Nanosystems Engineering Research Center
for Nanotechnology Enabled Water Treatment (1449500) and the Welch
Foundation (C- 2051-20200401, C-2065-20210327) supported the research.


========================================================================== Story Source: Materials provided by Rice_University. Original written
by Mike Williams. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Feng-Yang Chen, Zhen-Yu Wu, Srishti Gupta, Daniel J. Rivera, Sten V.

Lambeets, Stephanie Pecaut, Jung Yoon Timothy Kim, Peng Zhu,
Y. Zou Finfrock, Debora Motta Meira, Graham King, Guanhui Gao,
Wenqian Xu, David A. Cullen, Hua Zhou, Yimo Han, Daniel E. Perea,
Christopher L. Muhich, Haotian Wang. Efficient conversion of
low-concentration nitrate sources into ammonia on a Ru-dispersed
Cu nanowire electrocatalyst. Nature Nanotechnology, 2022; DOI:
10.1038/s41565-022-01121-4 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220502170905.htm

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