1. Nat. Commun.:PdSn 纳米线上的层状 Pd 氧化物用于促进 H2O2直接合成
第一作者：Hong-chao Li, Qiang Wan
通讯作者：熊海峰 教授，黄小青 教授，Sen Lin
通讯单位：厦门大学，福州大学
Nature Communications | ( 2022) 13:60721 https://doi.org/10.1038/s41467-022-33757-0
背景介绍
过氧化氢 (H2O2) 与其他氧化剂（例如含氯氧化剂和硝酸）, 相比，过氧化氢 (H2O2) 对环境友好且副产物仅涉及 H2O 和 O2，因此在许多领域被广泛用作氧化剂。目前，工业上采用蒽醌氧化法（AO法）作为生产H2O2的方法，而AO法需要大量的能源消耗和添加烷基苯等有毒有机溶剂。因此，需要开发可持续的工艺和更有效的 H2O2生产方法。
由 H2 和 O2 直接合成H2O2(DHS) 是小规模和现场H2O2 生产的有效替代方案，通常使用 Pd 基催化剂进行。然而，当使用纯钯基催化剂时，由于加氢和分解等高副反应，催化活性受到限制，导致净产率下降。 许多努力致力于开发用于 DHS 的高性能催化剂，例如使用双金属 Pd-Au、三金属 Pd-Au-Pt、酸和卤化物添加剂。然而，这些 Pd 催化剂含有昂贵的金，而 H2O2 的产率仍远低于 AO 工艺。将 Sn 添加到 Pd 催化剂中由于其高稳定性和惰性加氢用于 H2O2 合成的 Sn 组分而引起了广泛关注。特别是，PdSn 纳米催化剂的合成涉及氧化-还原-氧化 (O-RO) 的多步骤方案，形成了封装富含 Pd 的小颗粒的氧化锡表面层，同时暴露了较大的 PdSn 合金颗粒。通过 O-R-O 制备的 PdSn 纳米催化剂以 >95% 的高选择性生产 H2O2，而 H2O2的生产能力仅为~70mmol·gcat-1·h-1。
金属纳米线 (NWs) 是一维 (1D) 结构材料，广泛用于光、电和等离子体相关的应用。与纳米颗粒或块状材料相比，这些一维纳米线结构可以加速可定向的电子或离子转移和扩散，从而促进催化动力学。因此，纳米线可以提供一个独特的平台来研究催化。例如，在纳米线-细菌混合系统中，纳米线可以捕获电子并将其传递给细菌，从而使细菌能够确保 CO2 的转化。另一方面，据报道，氧化钴 (CoO) 纳米棒/纳米线会在表面产生氧空位纳米面。由于通过模拟揭示了钴氧化物纳米棒/纳米线的调制电子结构，该催化剂表现出优异的电催化 ORR/OER 性能
本文要点
1. 开发了一种制备 PdSn 纳米线以直接生产 H2O2 的方法，并发现通过两步合成（图 1）制备的 Pd4Sn 合金纳米线（NW）上的一层 Pd 氧化物在直接生产 H2O2中表现出有效的反应活性。
2.该方法首先通过溶剂热法合成表面粗糙的 Pd4Sn 纳米线（PdSn-NW，Sn:Pd 摩尔比为 4）。然后，将金属 Pd 前体沉积在 Pd4Sn 纳米线上，然后分散在 TiO2 载体上。在空气中对材料进行快速退火后，获得了一种用于直接 H2O2 合成的有效催化剂。
3.无支撑的 PdL/PdSn-NW 呈现蠕虫状纳米线的形态，一些纳米线相互连接形成互连结构。合成并测试了通过一步合成制备的TiO2负载的PdSn纳米线催化剂（表示为 PdSn-NW）。
4. PdL/PdSn-NW 在零摄氏度时在 DHS 中表现出优异的反应性，H2O2 的生产能力为 528mol kgcat-1·h-1 和H2O2 的选择性 > 95%。
5.H2O2在 PdL/PdSn-NW 上的弱吸附有助于低活化能和高 H2O2 产率。这种表面工程方法，在金属纳米线上沉积金属层，为合理设计用于 DHS 的高效催化剂提供了新的见解。
图文介绍
Fig. 1 | Schematic illustrationof the synthesis of the unsupported PdSn-NWandPdL/PdSn-NW.The supported PdSn-NWand PdL/PdSn-NWcatalysts are supported on TiO2.The two-step protocol involving an annealing process was used for thesynthesis of PdL/PdSn-NW. PdSn nanowire (NW) was prepared with a Pd: Sn molar ratio of 4 firstly and then, Pd precursor was deposited on the as-prepared PdSnnanowires again, followed by depositing on TiO2 and a rapid annealing in air. A PdSn-NW catalyst with Pd:Sn ratio of 4 was also synthesized for the purpose ofcomparison via one-step method by mixing Sn2+, Pd2+, PVP, EG, and NH4Br.
Fig. 2 | Representative TEM image and the catalytic performances of the PdSn nanowire catalysts in the direct H2O2 synthesis (DHS). a Representative TEM image of the unsupported PdSn nanowire catalyst prepared by two-step (unsupported PdL/PdSn-NW). b H2O2 producibility of the supported PdL/PdSn-NW and Snx/PdSn-NW catalysts with different Pd/Sn ratios after annealing in air (350 °C, 8min), demonstrating the addition of Sn has negative effect on the producibility of H2O2. c H2O2 producibility, hydrogenation, and decomposition of the supported PdL/PdSn-NW catalyst annealing at different temperatures in air, showing that the supported PdL/PdSn-NW annealing at 400 °C did not catalyze the hydrogenation and decomposition. d The comparison of the H2O2 producibility, hydrogenation, and decomposition of supported PdL/PdSn-NW catalyst with other Pd catalysts (Table 1). The error bars in b–d show the standard deviation in the measurements. The standard deviation was achieved from the repeated runs of three to five times using fresh catalyst each time. The error bars refers to the standard deviation of multiple times measurements of hydrogen peroxide productivity.
Fig. 3 | Structural characterization of the unsupported and supported PdL/PdSn-NWcatalysts before and after annealing in air at 400 °C. a XRD patterns of the unsupported and supported PdL/PdSn-NWcatalysts before and after annealing in air. b HRTEMimage of the unsupported PdL/PdSn-NWsample showing the lattice fringes of the PdSn phase. c STEM image and STEM-EDSmapping of the supported PdL/PdSn-NW showing the close proximity of both Pd and Sn elements, indicating the successful synthesis of Pd4Sn alloy. d XPS spectra of Pd 3d core level of the supported PdL/PdSn-NW catalyst before and after annealing in air. e Surface valence band photoemission spectra of the supported PdL/PdSn-NW catalysts annealing at different temperatures in air. f HAADF-STEM image of the supported PdL/PdSn-NW catalyst after annealing showing a layer of Pd oxide on the PdSn nanowires.
Fig. 4 | EXAFS spectra of the PdK edge of PdSn catalysts and reference samples, and NAP-XPS of Pd 3d spectra for PdSn catalysts under different treatment conditions. a EXAFS spectra of the PdK edge of PdSn catalysts after annealing in air. b In situ NAP-XPS of Pd 3d spectra for PdSn-NW in the presence of O2, H2, and O2/H2. c In situ NAP-XPS of Pd 3d spectra for PdL/PdSn-NW after annealing in air in the presence of O2, H2 and O2/H2. d In situ NAP-XPS of Pd 3d spectra for PdSn-NP after annealing in air in the presence of O2, H2 and O2/H2.
Fig. 5 | Adsorption energy of key species and proposed mechanism. a DFT optimized structures of PdO(101), Pd4Sn, and PdO@Pd4Sn with b adsorption energies of H2, O2, H2+O2, and H2O2, c free energy profiles for H2 activation, and d free energy profiles for O2 reduction by the surface hydrides on these three models. TS transition state. Color code: Pd, blue; O, red; H, white; Sn, yellow.
2. Nano Letters：富缺陷PdSn 纳米线用于ORR
Nano Lett. 2019, 19, 6894−6903；DOI: 10.1021/acs.nanolett.9b02137
贵金属纳米结构的缺陷工程至关重要，因为它可以提供一个额外的层来进一步促进催化，特别是对于具有高表面体积比的一维（1D）贵金属纳米结构，更重要的是具有工程设计的能力沿一维纳米结构纵向的缺陷。在这里，首次报道一维贵金属纳米结构中的缺陷是实现燃料电池反应的高活性和稳定电催化剂必不可少的因素。电催化结果表明，Pd-Sn 纳米线 (NWs) 表现出有趣的缺陷依赖性性能，其中富含缺陷的 Pd4Sn 波浪形 NWs 在甲醇氧化反应 (MOR) 和氧还原反应中表现出最高的活性和耐久性(ORR)。密度泛函理论 (DFT) 计算表明，大量表面空位/聚集空隙是在 Pd4Sn WNW 内形成表面晶界 (GB) 的驱动力。这些电子活性GB区域是保持Pd0位点数量的关键因素，这对于最小化固有的位点到位点电子转移势垒至关重要。通过这种缺陷工程，Pd4Sn WNW 最终产生了高效的碱性 ORR 和 MOR。目前的工作强调了缺陷工程在提高潜在实用燃料电池和能源应用的电催化剂性能方面的重要性。
Figure 1. (A, B) TEM images. (C) HAADF-STEM image and corresponding elemental mapping images of Pd4Sn NWs with red for Pd and green for Sn. (D) Line-scan analysis across the yellow arrow in image C. (E) PXRD pattern, (F) SEM-EDS spectrum, and (G) HRTEM images of Pd4Sn NWs. The inset in B shows a structural model of Pd4Sn NW. The scale bars in the insets of A−C are 50, 20, and 5 nm, respectively.
Figure 2. (A) HAADF-STEM image, (B) TEM image, and (C) corresponding elemental mapping images with red for Pd and green for Sn, respectively. (D) PXRD pattern and (E) SEM-EDS spectrum of Pd4Sn WNWs. (F−H) Cs-corrected TEM images of Pd4Sn WNWs. Dotted lines in F and G highlight the presence of twin defects cross-sectioning the WNW. Dashed arrows in (H) highlight the presence of distinct defects/grain boundaries. (I) Structural schematic diagram of the Pd4Sn WNWs. The scale bars in A, B, C and H, and F and G are 200, 20, 5, and 2 nm, respectively.
Figure 3. (A) CO-stripping measurements of different catalysts in 0.1 M HClO4 solution at a scan rate of 20 mV/s. (B) CVs of different catalysts in 0.1 M KOH and 0.5 M methanol solution at a sweep rate of 50 mV/s. (C) Histogram of mass and specific activities of different catalysts for MOR. (D) Changes in the electroxidation peak current densities on different catalysts during the cycles.
Figure 4. (A) ORR polarization curves, (B) half-wave potential, ORR mass activities, and specific activities of different catalysts at (C) 0.90 V and (D) 0.929 V versus RHE. The ORR polarization curves were recorded at room temperature in an O2-saturated 0.1 M KOH aqueous solution at a sweep rate of 10 mV/s and a rotational rate of 1600 rpm. (E) ORR polarization curves and (F) histograms of mass activities for different catalysts before and after 10 000 cycles of ADTs.
3. Small：空心 Pd-Sn 金属间化合物纳米粒子促进 H2O2 直接生成催化
Small 2018, 14, 1703990，
DOI: 10.1002/smll.201703990
尽管直接将氢气 (H2) 氧化为过氧化氢 (H2O2) 被认为是直接 H2O2 合成的一种有前途的策略，但理想的转化效率仍然是一个巨大的挑战。在此，通过使用中空 Pd-Sn 金属间化合物纳米粒子 (NPs) 作为催化剂，实现了高活性和选择性的 H2 直接氧化成 H2O2。通过调整催化溶剂和催化剂载体，可以很好地优化 H2 直接氧化为 H2O2 的效率，空心 Pd2Sn NPs/P25 表现出高达 80.7% 的 H2O2 选择性和 60.8 mol kgcat-1 h-1 的产率。CO吸附结果的原位漫反射红外傅里叶变换光谱证实了实心和空心Pd-Sn NPs之间不同的表面原子排列。X射线光电子能谱结果表明，Pd2Sn NPs/P25的较高效率是由于其较高的金属Pd含量和较高的Snx+比例，有利于H2O2的产生和选择性。
转自：“我要做科研”微信公众号
如有侵权，请联系本站删除！
