Hammoud Leila, Strebler Claire, Toufaily Joumana, Hamieh Tayssir, Keller Valérie, Caps Valérie
ICPEES (CNRS UMR 7515/Université de Strasbourg), 25 rue Becquerel, 67087 Strasbourg, Cedex 02, France.
Laboratory of Materials, Catalysis, Environment and Analytical Methods Laboratory (MCEMA), Faculty of Sciences, Lebanese University, Rafic Hariri Campus, Hadath, Lebanon.
Faraday Discuss. 2023 Jan 31;242(0):443-463. doi: 10.1039/d2fd00094f.
Bimetallic gold-platinum nanoparticles have been widely studied in the fields of nanoalloys, catalysis and plasmonics. Many preparation methods can lead to the formation of these bimetallic nanoparticles (NPs), and the structure and related properties of the nanoalloy often depend on the preparation method used. Here we investigate the ability of thermal dimethylformamide (DMF) reduction to prepare bimetallic gold-platinum sub-nm clusters supported on titania. We find that deposition of Pt preferentially occurs on gold. Formation of sub-nm clusters ( NPs) appears to be dependent on the metal concentration used: clusters can be obtained for metal loadings up to 4 wt% but 7-8 nm NPs are formed for metal loadings above 8 wt%, as shown using high resolution transmission electron microscopy (HRTEM). X-ray photoelectron spectroscopy (XPS) shows electron-rich Au and Pt components in a pure metallic form and significant platinum enrichment of the surface, which increases with increasing Pt/Au ratio and suggests the presence of Au@Pt core-shell type structures. By contrast, titania-supported bimetallic particles (typically >7 nm) obtained by sodium borohydride (NaBH) reduction in DMF, contain Au/Pt Janus-type objects in addition to oxidized forms of Pt as evidenced by HRTEM, which is in agreement with the lower Pt surface enrichment found by XPS. Both types of supported nanostructures contain a gold-platinum interface, as shown by the chemical interface damping, gold plasmon damping by Pt, found using UV-visible spectroscopy. Evaluation of the materials for plasmon-induced continuous flow CO reduction with water, shows that: (1) subnanometer metallic clusters are not suitable for CO reduction with water, producing hydrogen from the competing water reduction instead, thereby highlighting the plasmonic nature of the reaction; (2) the highest methane production rates are obtained for the highest Pt enrichments of the surface, the core-shell-like structures achieved by the thermal DMF reduction method; (3) selectivity towards CO reduction the competing water reduction is enhanced by loading of the plasmonic NPs, coverage of the titania semi-conductor by plasmonic NPs. Full selectivity is achieved for loadings above 6 wt%, regardless of the NPs composition and alloy structure.
双金属金铂纳米粒子在纳米合金、催化和等离子体学领域得到了广泛研究。许多制备方法都能导致这些双金属纳米粒子（NPs）的形成，纳米合金的结构和相关性质往往取决于所使用的制备方法。在此，我们研究了热二甲基甲酰胺（DMF）还原法制备负载在二氧化钛上的双金属金铂亚纳米团簇的能力。我们发现铂优先沉积在金上。亚纳米团簇（NPs）的形成似乎取决于所使用的金属浓度：对于金属负载量高达4 wt%的情况可以获得团簇，但对于金属负载量高于8 wt%的情况会形成7 - 8 nm的NPs，这是使用高分辨率透射电子显微镜（HRTEM）显示的。X射线光电子能谱（XPS）显示以纯金属形式存在的富电子金和铂成分以及表面显著的铂富集，其随着Pt/Au比的增加而增加，表明存在Au@Pt核壳型结构。相比之下，通过在DMF中用硼氢化钠（NaBH）还原得到的负载在二氧化钛上的双金属粒子（通常>7 nm），除了Pt的氧化形式外还包含Au/Pt 型双面体，HRTEM证明了这一点，这与XPS发现的较低的Pt表面富集一致。如使用紫外可见光谱法发现的通过化学界面阻尼、Pt对金等离子体的阻尼所示，这两种负载型纳米结构都包含金铂界面。对用于等离子体诱导的水连续流CO还原的材料进行评估表明：（1）亚纳米金属团簇不适合用于水的CO还原，而是通过竞争性的水还原产生氢气，从而突出了反应的等离子体性质；（2）对于表面铂富集程度最高的情况，即通过热DMF还原法实现的核壳状结构，获得了最高的甲烷生成速率；（3）等离子体NPs的负载、等离子体NPs对二氧化钛半导体的覆盖增强了对CO还原而非竞争性水还原的选择性。对于负载量高于6 wt%的情况实现了完全选择性，而与NPs组成和合金结构无关。
