Eco-Design of Hydrogenation Catalysts for Oxyanion Reduction: The Overlooked Roles of Nitrogen-Containing Groups on the Catalyst Supports

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Toxic oxyanions such as nitrate (NO3−) and perchlorate (ClO4−) are persistent pollutants that have been detected in groundwater, surface water, and drinking water sources in the United States and worldwide. The consumption of drinking water containing toxic oxyanions can adversely impact human health. Ion exchange (IX) and reverse osmosis (RO) are the best commercially available technologies for removing toxic oxyanions from drinking water sources. However, IX and RO do not destroy contaminants. In addition, they generate residuals including concentrated waste brines that need to be treated and/or disposed of. Water treatment by catalytic hydrogenation has emerged as a promising technology that can rapidly and effectively destroy toxic oxyanions in contaminated aqueous solutions including concentrated waste brines. The most effective oxyanion hydrogenation catalysts (e.g., Pd) are in the form of nanoparticles. Anchoring catalytic nanoparticles on supports such as activated carbon can facilitate their use in water treatment. In this project, the Principal Investigators (PIs) propose to carry out a fundamental study of the activity and reactivity of Pd nanoparticles immobilized onto supports that contain nitrogen groups in aqueous solutions and brines contaminated by toxic oxyanions with the goal of improving their performance. The successful completion of this research will benefit society through the development of new fundamental knowledge to advance the design and development of more efficient and cost-effective oxyanion hydrogenation catalysts for water treatment. Additional benefits to society will be achieved through student education and training including the mentoring of one graduate student and one undergraduate student at the South Dakota School of Mines and Technology and one postdoctoral researcher at the University of Alabama.Palladium (Pd) nanoparticles have emerged as promising catalysts for reducing toxic oxyanions such as nitrate (NO3−) in aqueous solutions/brines and converting them to harmless by-products such as dinitrogen (N2) gas. Pd nanocatalysts are immobilized on support materials to 1) reduce nanoparticle aggregation and leaching and 2) facilitate catalyst handling and reuse. The presence of nitrogen-containing groups (e.g., amines) on the supports of Pd nanocatalysts have been found to significantly enhance catalyst performance (including activity, selectivity, and stability) during the hydrogenation of oxyanions in aqueous solutions. However, a fundamental understanding of the role of nitrogen-containing groups (NCGs) on the structure and performance of Pd hydrogenation nanocatalysts has remained elusive. To address these knowledge gaps, the Principal Investigators (PIs) of this project propose to carry out fundamental studies of the structure and performance of Pd nanocatalysts immobilized onto supports with NCGs. The specific objectives of the research are to 1) characterize and unravel the relationships between NCG support and catalyst structure and physicochemical properties; 2) investigate the impact of NCG support on the performance of Pd nanocatalysts for the reduction and conversion of oxyanions in model aqueous solutions and complex water matrices using hydrogen (H2) as reducing agent ; and 3) leverage the data collected in this project to develop machine learning (ML)-informed life cycle assessment (LCA) to guide catalyst design, synthesis, and optimization. The successful completion of this project has the potential to advance the practical implementation of Pd-based catalysts and reactors for the treatment of drinking water sources and concentrated waste brines contaminated with toxic oxyanions. To implement the education and training goals of the project, the PIs propose to leverage existing programs at the South Dakota School of Mines and Technology and the University of Alabama to 1) recruit and mentor graduate and undergraduate students from underrepresented groups to work on the project and 2) develop and implement outreach activities to advance diversity, equity, and inclusion in STEM education.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.