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首页> 外文学位 >Design of novel catalysts by infusion of presynthesized nanocrystals into mesoporous supports.
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Design of novel catalysts by infusion of presynthesized nanocrystals into mesoporous supports.

机译：通过将预合成的纳米晶体注入介孔载体中来设计新型催化剂。

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Traditionally, supported metal catalysts have been synthesized by reduction of precursors directly over the support. In these techniques, it is challenging to control the metal cluster size, composition and crystal structure. Herein, we have developed a novel approach to design catalysts with controlled morphologies by infusing presynthesized nanocrystals into the supports. High surface area mesoporous materials, including graphitic carbons, have been utilized for obtaining a high degree of metal dispersion to enhance catalyst stabilities and activities. Gold and iridium nanocrystals have been infused in mesoporous silica with loadings up to 2 wt% using supercritical CO2 as an antisolvent in toluene to enhance the van der Waals interactions between nanocrystals and the silica. The iridium catalysts show high catalytic activity and do not require high temperature annealing for ligand removal, as ligands bind weakly to the iridium surface. To further enhance metal loadings to >10% in the catalysts, short-ranged interactions between the metal nanocrystals and the support are further strengthened with weakly binding ligands to expose more of the metal surface to the support. For pre-synthesized FePt nanocrystals, coated with oleic acid and oleylamine ligands, high loadings >10 wt% in mesoporous silica are achieved, without using CO2. The strong metal-support interactions favor FePt adsorption on the support and also enhance stability against sintering at high temperatures. High resistance to sintering favors formation of the FePt intermetallic crystal structure with 4 nm size upon thermal annealing at 700°C. The fundamental understanding of the metal-support interactions gained from these studies is then utilized in the design of highly stable Pt and Pt-Cu electrocatalysts with controlled size, composition and alloy structure supported on graphitized mesoporous carbons for oxygen reduction. The resistance of the graphitic carbons to oxidation coupled with strong metal-support interactions mitigate nanoparticle isolation from the support, nanoparticle coalescence, Pt dissolution and subsequent Ostwald ripening and thus enhance catalyst stability. The control of the Pt nanocrystal morphology with high concentrations of highly active (111) surface leads to 25% higher activities than commercial Pt catalysts. Furthermore, the catalyst activities obtained for Pt-Cu catalysts are 4-fold higher than Pt catalysts due to strained Pt shell generated from electrochemical dealloying of copper from the nanoparticle surface.
机译：传统上，已经通过在载体上直接还原前体来合成载体金属催化剂。在这些技术中，控制金属簇的大小，组成和晶体结构具有挑战性。在这里，我们已经开发出一种新颖的方法，通过将预先合成的纳米晶体注入载体中来设计具有可控形态的催化剂。高表面积的介孔材料，包括石墨碳，已被用于获得高度的金属分散性，以增强催化剂的稳定性和活性。使用超临界CO2作为甲苯中的反溶剂，可以将金和铱纳米晶体注入到介孔二氧化硅中，其载量高达2 wt％，以增强纳米晶体与二氧化硅之间的范德华相互作用。铱催化剂显示出高催化活性，并且不需要高温退火来去除配体，因为配体与铱表面的结合力弱。为了将催化剂中的金属负载进一步提高到> 10％，金属纳米晶体与载体之间的短程相互作用通过弱结合配体进一步增强，以使更多的金属表面暴露于载体。对于用油酸和油胺配体涂覆的预合成FePt纳米晶体，无需使用CO2，即可在介孔二氧化硅中实现> 10 wt％的高负载量。强烈的金属-载体相互作用有利于FePt在载体上的吸附，并增强了高温下烧结的稳定性。在700°C下进行热退火时，高的抗烧结性有助于形成尺寸小于4 nm的FePt金属间晶体结构。然后，将从这些研究中获得的对金属-载体相互作用的基本理解，用于设计高度稳定的Pt和Pt-Cu电催化剂，并控制尺寸，组成和合金结构，并负载在石墨化的介孔碳上以减少氧。石墨碳的抗氧化性以及强大的金属-载体相互作用可减轻纳米粒子与载体的分离，纳米粒子的聚结，Pt的溶解和随后的奥斯特瓦尔德熟化，从而增强催化剂的稳定性。高浓度的高活性（111）表面对Pt纳米晶体形态的控制导致活性比市售Pt催化剂高25％。此外，由于从纳米粒子表面进行铜的电化学脱合金而产生的应变的Pt壳层，使Pt-Cu催化剂获得的催化剂活性比Pt催化剂高4倍。

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