Department of Chemical and Biomolecular Engineering , University of Notre Dame , Notre Dame , Indiana 46556 , United States.
School of Environmental Science and Technology , Nankai University , Tianjin 300350 , PR China.
Environ Sci Technol. 2019 Jul 2;53(13):7551-7563. doi: 10.1021/acs.est.9b01425. Epub 2019 Jun 24.
Pd-catalyzed reduction has emerged as a promising treatment strategy to remove the recalcitrant disinfection byproduct N-nitrosodimethylamine (NDMA). However, the reaction pathways remain unexplored, and questions remain about how water solvent influences NDMA reduction mechanisms and selectivity. Here, we compute the energies and barriers of all relevant elementary steps in NDMA reduction by H on Pd(111) using density functional theory. We further calculate water-assisted H-shuttling for all hydrogenation reactions explicitly and include water solvation for all elementary reactions implicitly. We parametrize microkinetic models to predict product formation rates and selectivities over a wide range of NDMA concentrations. We show that HO-mediated H-shuttling lowers the reaction barriers for all hydrogenation reactions involved in NDMA reduction while implicit solvation has negligible impact on the reaction and activation energies. We further conduct batch experiments with SiO-supported Pd nanoparticles and compare them with the microkinetic models. The predicted rates, selectivity, and apparent activation energy from the model parametrized with both explicit HO-mediated H-shuttling and implicit solvation correspond well with experimental observations. Models that ignore water as an H-shuttle or solvent fail to recover the experimental rates and apparent activation energy. We identified the rate-determining steps of the reaction and show the reaction flow pathways of the complicated reaction network. Finally, we demonstrate that water-mediated H-shuttling changes the rate-determining steps and reaction flows of elementary reactions.
钯催化还原已成为去除顽固消毒副产物 N-亚硝基二甲胺 (NDMA) 的有前途的治疗策略。然而，反应途径仍未得到探索，关于水溶剂如何影响 NDMA 还原机制和选择性的问题仍然存在。在这里，我们使用密度泛函理论计算了 H 在 Pd(111)上还原 NDMA 的所有相关基元步骤的能量和势垒。我们进一步明确计算了所有加氢反应的水辅助 H 穿梭，并隐式考虑了所有基元反应的水溶剂化。我们参数化微观动力学模型以预测广泛 NDMA 浓度范围内的产物形成速率和选择性。我们表明，HO 介导的 H 穿梭降低了 NDMA 还原中所有加氢反应的反应势垒，而隐式溶剂化对反应和活化能几乎没有影响。我们进一步进行了 SiO 负载钯纳米粒子的批量实验，并将其与微观动力学模型进行了比较。通过同时考虑显式 HO 介导的 H 穿梭和隐式溶剂化对模型进行参数化，预测的速率、选择性和表观活化能与实验观察结果非常吻合。忽略水作为 H 穿梭或溶剂的模型无法恢复实验速率和表观活化能。我们确定了反应的速率决定步骤，并展示了复杂反应网络的反应流途径。最后，我们证明了水介导的 H 穿梭改变了基元反应的速率决定步骤和反应流。
