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

有毒的氧阴离子，如硝酸盐(NO3−)和高氯酸盐(ClO4−)，是在美国和世界各地的地下水、地表水和饮用水水源中检测到的持久性污染物。饮用含有有毒含氧阴离子的饮用水会对人体健康造成不利影响。离子交换(IX)和反渗透(RO)是去除饮用水水源中有毒氧离子的最佳商业技术。然而，IX和RO不会破坏污染物。此外，它们还会产生残留物，包括需要处理和/或处置的浓缩废盐水。催化加氢水处理技术是一种可以快速有效地去除包括浓盐水在内的受污染水溶液中有毒含氧阴离子的技术。最有效的氧阴离子加氢催化剂(如Pd)是以纳米颗粒的形式存在的。将催化纳米颗粒锚定在活性碳等载体上可以促进其在水处理中的使用。在这个项目中，首席调查员(PI)建议对固定在水溶液和被有毒氧离子污染的盐水中含有氮基的载体上的Pd纳米粒子的活性和反应性进行基础研究，以期提高它们的性能。这项研究的成功完成将通过发展新的基础知识来促进水处理用更高效和更具成本效益的氧阴离子加氢催化剂的设计和开发，从而造福社会。通过学生教育和培训还将为社会带来更多好处，包括指导南达科他州矿业与技术学院的一名研究生和一名本科生以及阿拉巴马大学的一名博士后研究员。钯(Pd)纳米颗粒已成为很有希望的催化剂，可用于减少水溶液/盐水中的硝酸盐(NO3−)等有毒氧离子，并将它们转化为无害的副产品，如二氮(N2)气体。Pd纳米催化剂被固定在载体材料上，以1)减少纳米粒子的聚集和浸出，2)促进催化剂的处理和重复使用。Pd纳米催化剂载体上含氮基团(如胺)的存在可以显著提高水溶液中含氧阴离子加氢反应的催化剂性能(包括活性、选择性和稳定性)。然而，对于含氮基团(NCGS)对钯加氢纳米催化剂的结构和性能的影响，人们仍然缺乏基本的了解。为了弥补这些知识空白，该项目的首席研究员建议对以NCGS固定在载体上的Pd纳米催化剂的结构和性能进行基础研究。该研究的具体目标是：1)表征和揭示NCG载体与催化剂结构和物理化学性质之间的关系；2)考察NCG载体对Pd纳米催化剂在模型水溶液和复杂水基质中以氢(H2)为还原剂还原和转化含氧阴离子的性能的影响；以及3)利用本项目收集的数据来开发基于机器学习(ML)的生命周期评估(LCA)，以指导催化剂的设计、合成和优化。该项目的成功完成有可能推动以钯为基础的催化剂和反应堆的实际实施，以处理受有毒氧离子污染的饮用水水源和浓缩废盐水。为了实现该项目的教育和培训目标，PIS建议利用南达科他州矿业与技术学院和阿拉巴马大学的现有计划来1)招募和指导来自代表性不足群体的研究生和本科生参与该项目，以及2)开发和实施外联活动，以促进STEM教育的多样性、公平性和包容性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.