MSGID: 1:317/3 6270b034   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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.   
      
      
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   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.   
      
      
      
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   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.   
      
      
      
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   "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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