Nitrate (NO₃⁻) contamination has dramatically increased owing to extensive human activities, which may cause severe problems on human health and the environment. Recently, catalytic denitrification of NO₃⁻ to N₂ has attracted much attention owing to its highly fast reaction with high N₂ selectivity. However, only a few studies have investigated the effect of natural substances in real groundwater on catalytic denitrification, particularly the type of natural organic matter (NOM) and combined effect of NOM and ionic ions. Herein, we investigated the effects of natural dissolved inorganic and organic matter on catalytic denitrification of contaminated groundwater using a novel Pd–In bimetallic catalyst supported on kaolin-derived zeolite (ZK). Pd–In/ZK showed a highly enhanced performance for denitrification, resulting in a high turnover frequency (18.9 × 10⁻³ s⁻¹) and N₂ selectivity (98%). Various surface analyses confirmed that the rejuvenation of In by active H on Pd sites is the key factor that controls the enhanced NO₃⁻ reduction and high N₂ selectivity. Applying the optimized Pd–In/ZK catalyst to NO₃⁻ contaminated groundwater revealed that its catalytic activity was significantly affected by various constituents in groundwater. Particularly, the results from fluorescence excitation emission matrix spectroscopy showed that humic-like and fulvic-like organic substances potentially inhibited the catalytic NO₃⁻ reduction owing to their adsorption onto the catalyst surface. Furthermore, some inorganic ions inhibited the catalytic NO₃⁻ reduction via different inhibitory mechanisms, i.e. the competitive adsorption of Cl⁻ and SO₄²⁻ with NO₃⁻ and catalyst fouling induced by formation of CaCO_3(s). The novel findings from this study highlight the potential applicability of ZK as a value-adding support material for catalytic denitrification and emphasize the effect of dissolved organic and inorganic matters in groundwater on the catalytic activity of bimetallic catalysts.

中文翻译：

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负载在高岭土的沸石上的新型双金属催化剂增强了对地下水的反硝化作用：天然溶解的无机和有机物的作用

硝酸盐（NO ₃ ^- ）污染，由于大量的人类活动，这可能会导致对人类健康和环境的严重问题急剧增加。近日，NO的催化脱硝₃ ^-到N ₂吸引，由于非常重视与高氮高反应快₂选择性。但是，只有很少的研究调查了真实地下水中天然物质对催化反硝化的影响，特别是天然有机物（NOM）的类型以及NOM和离子离子的联合作用。在本文中，我们研究了负载在高岭土衍生沸石（ZK）上的新型Pd-In双金属催化剂对天然溶解的无机和有机物对受污染的地下水的催化脱氮的影响。Pd-In / ZK的反硝化性能大大增强，从而导致高周转频率（18.9×10 ^-3 s ^-1）和N ₂选择性（98％）。各种表面分析证实，活性H在Pd位点上使In再生是控制增强NO ₃的关键因素。^-还原和高N ₂选择性。应用优化的Pd-IN / ZK催化剂为NO ₃ ^-受污染的地下水透露，其催化活性显著受地下水中的各种成分。特别地，从荧光光谱特征的结果表明，类腐殖质和富里状有机物质潜在地抑制催化NO ₃ ^-还原由于其吸附到催化剂表面上。此外，一些无机离子抑制了催化NO ₃ ^-还原经由不同抑制机制，即Cl组成的竞争吸附^-和SO ₄ ^2-与NO ₃ ^-和催化剂结垢诱导形成碳酸钙的_3（S） 。这项研究的新发现突出了ZK作为催化反硝化增值载体材料的潜在适用性，并强调了地下水中溶解的有机和无机物对双金属催化剂催化活性的影响。