Catalytic denitrification over Pd-based catalysts under mild conditions has received significant attention as an emerging technology. However, the Pd particle size effect has been much less systematically investigated. Herein, carbon-supported Pd nanoparticles (NPs) with particle sizes ranging from 2.1 to 22.1 nm were synthesized and characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), CO-chemisorption, and X-ray photoelectron spectroscopy (XPS). Catalytic nitrite reduction experiments were conducted in a semi-batch reactor at room temperature. The results showed that the highest mass catalytic activity of 603.6 mg g_Pd⁻¹ min⁻¹ was obtained at the Pd size of 2.7 nm. The turnover frequency (TOF) and the N₂ selectivity increased gradually with the increasing Pd NP size. Considering both the mass catalytic activity and N₂ selectivity, the Pd catalyst with a size of approximately 5 nm had a better comprehensive performance. Mechanism studies showed that the enhanced TOF of larger Pd NPs could be ascribed to the formation of more β-hydride, which has a higher reducing activity than α-hydride. Compared with the terraces, the edges and corners of Pd NPs are the major active sites where ammonia is generated, most likely because of their low-coordination and electron-deficient properties. This indicated that the NO₂⁻ catalytic reduction is a size sensitive reaction in terms of both activity and selectivity, and may provide new insight into tailoring Pd NP size of Pd-based catalysts to improve catalytic activity and selectivity for nitrate and nitrite reduction in water.

中文翻译：

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洞悉Pd纳米颗粒对Pd / C催化剂上水中亚硝酸盐催化还原的尺寸效应

钯基催化剂在温和条件下的催化反硝化作为一种​​新兴技术受到了广泛的关注。但是，对Pd粒度效应的研究还很少。本文中，合成并使用高分辨率透射电子显微镜（HR-TEM），X射线衍射（XRD），CO化学吸附和X表征了粒径为2.1至22.1 nm的碳载Pd纳米颗粒（NP）。射线光电子能谱（XPS）。在室温下在半间歇反应器中进行催化亚硝酸盐还原实验。结果表明，在2.7nm的Pd尺寸下获得了最高的603.6mg g _Pd ^-1 min ^-1的质量催化活性。周转频率（TOF）和N ₂选择性随着Pd NP尺寸的增加而逐渐增加。考虑到质量催化活性和N ₂选择性，尺寸约5nm的Pd催化剂具有更好的综合性能。机理研究表明，较大的Pd NPs的TOF增强可以归因于更多的β-氢化物的形成，其具有比α-氢化物更高的还原活性。与梯田相比，Pd NP的边缘和角落是产生氨的主要活性部位，这很可能是由于它们的低配位和电子不足特性。这表明，NO ₂ ^- 催化还原在活性和选择性方面都是对尺寸敏感的反应，可以为调整Pd基催化剂的Pd NP尺寸提供新的见解，以提高催化活性和选择性，以减少水中的硝酸盐和亚硝酸盐。