An in-depth understanding of the effects of metal particle sizes on reactions is crucial for tailoring and designing catalysts. Herein, the Pd/CNT catalysts with different Pd particle sizes were prepared and employed to explore the size effects on the Pd-catalyzed hydrogenation of 2,6-diamino-3,5-dinitropyridine (DADNP). The apparent turnover frequencies for DADNP conversion and target 2,3,5,6-tetraaminopyridine (TAP) formation are found to exhibit strong dependence on the Pd particle sizes, indicating that the hydrogenation of DADNP to TAP is typically structure-sensitive. The size-insensitive activation energies extracted from the kinetics studies for DADNP conversion on ≥2.6 nm-sized Pd catalysts with similar electronic properties suggest the presence of only one type of active site mainly dominating the reaction. Further combining model calculations based on the cuboctahedron shape for Pd nanoparticles characterized by electron microscopy, the (111) sites are demonstrated as the dominant active sites for DADNP conversion on the ≥2.6 nm-sized Pd catalysts. However, for the Pd catalyst size <2.6 nm, the reaction is shown to be mainly dominated by the Pd electronic properties.

中文翻译：

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2,6-二氨基-3,5-二硝基吡啶钯催化加氢的尺寸依赖性

深入了解金属粒度对反应的影响对于定制和设计催化剂至关重要。在此，制备了具有不同 Pd 粒径的 Pd/CNT 催化剂，并用于探索尺寸对 Pd 催化的 2,6-二氨基-3,5-二硝基吡啶 (DADNP) 加氢的影响。发现 DADNP 转化和目标 2,3,5,6-四氨基吡啶 (TAP) 形成的表观转换频率表现出对 Pd 粒径的强烈依赖性，表明 DADNP 氢化为 TAP 通常是结构敏感的。从具有相似电子特性的≥2.6 nm 尺寸 Pd 催化剂上 DADNP 转化的动力学研究中提取的尺寸不敏感活化能表明，仅存在一种主要主导反应的活性位点。进一步结合基于电子显微镜表征的 Pd 纳米颗粒的立方八面体形状的模型计算，证明 (111) 位点是≥2.6 nm 尺寸 Pd 催化剂上 DADNP 转化的主要活性位点。然而，对于 <2.6 nm 的 Pd 催化剂尺寸，反应主要受 Pd 电子性质支配。