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

有毒的氧离子，如硝酸盐（NO3−）和高氯酸盐（ClO4−）是在美国和世界各地的地下水、地表水和饮用水源中检测到的持久性污染物。饮用含有有毒氧离子的饮用水会对人体健康产生不利影响。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不能破坏污染物。此外，它们还产生残留物，包括需要处理和/或处置的浓缩废盐水。催化加氢技术是一种很有前途的水处理技术，它可以快速有效地破坏污染水溶液中的有毒氧离子，包括高浓度的废盐水。最有效的氧阴离子加氢催化剂（如钯）以纳米粒子的形式存在。将催化纳米颗粒锚定在诸如活性炭之类的载体上可以促进它们在水处理中的使用。在本项目中，主要研究人员将钯纳米粒子固定在含氮基团的载体上，在有毒氧离子污染的水溶液和盐水中进行活性和反应性的基础研究，以提高其性能。这项研究的成功完成将通过发展新的基础知识来推动设计和开发更高效和更具成本效益的水处理氧阴离子加氢催化剂，从而造福社会。通过学生教育和培训，包括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的指导，将为社会带来额外的好处。钯（Pd）纳米颗粒已成为一种很有前景的催化剂，用于还原水溶液/盐水中的有毒氧离子，如硝酸盐（NO3−），并将其转化为无害的副产物，如二氮（N2）气体。钯纳米催化剂被固定在载体材料上，1)减少纳米颗粒的聚集和浸出，2)便于催化剂的处理和再利用。在钯纳米催化剂的载体上存在含氮基团（如胺），可以显著提高催化剂在水溶液中氧阴离子加氢过程中的性能（包括活性、选择性和稳定性）。然而，对含氮基团（NCGs）在Pd加氢纳米催化剂结构和性能中的作用的基本理解仍然是难以捉摸的。为了解决这些知识空白，该项目的首席研究员（pi）建议对固定化在NCGs载体上的钯纳米催化剂的结构和性能进行基础研究。本研究的具体目标是：1)表征和揭示NCG载体与催化剂结构和理化性质之间的关系；2)研究NCG载体对钯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氧阴离子性能的影响；3)利用该项目收集的数据开发基于机器学习（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进pd基催化剂和反应器的实际应用，用于处理受有毒氧离子污染的饮用水源和浓缩废盐水。为了实现该项目的教育和培训目标，项目负责人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项目，1)从代表性不足的群体中招募和指导研究生和本科生参与该项目，2)制定和实施外展活动，以促进STEM教育的多样性、公平性和包容性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.