负载型金属催化剂的金属-氧化物界面原子级精准调控研究

Preferential oxidation of CO in hydrogen (PROX) has been considered as one of the most promising approaches for removing trace amount of CO from H2 gas to provide CO-free hydrogen fuel for proton-exchange membrane fuel cells (PEMFCs), so that the Pt anode can be protected from the CO poisoning. Supported Pt-based metal catalysts have received extensive attention. However, conventional methods including ion-exchange, impregnation, and precipitation, often lack precise control over the interfaces between Pt-based metal particles and reducible oxide promotor, which causes difficulties to establish the relationship between metal-oxide interface structure and activity, and to maximize its catalytic performance. . Atomic layer deposition (ALD) is a new promising method of catalyst synthesis. It is a sequence (usually binary) of self-limiting surface reactions between the precursor vapors and the substrate in a layer-by-layer fashion at the atomic level. As an alternative to the wet-chemistry based conventional methods, ALD provides a cycle-by-cycle “bottom-up” approach for nanostructuring supported catalysts with near atomic precision. . In this project, our idea is to selectively deposit reducible oxides including FeOx and CoOx onto the surface of Pt-based metal nanoparticles but not on the catalyst support, wherein metal-oxide promoter interfaces are precisely tuned by carefully varying the oxide dispersions on metal nanoparticles. By employing the advanced characterization techniques including aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), in situ x-ray adsorption fine spectroscopy (XAFS), and in situ x-ray photoelectron spectroscopy (XPS), we will mainly focus on: (1) investigation of the morphology and electronic structures of the oxide promoter species on the surfaces of Pt-based metal particles with different dispersions in various environments, especially under the PROX reaction conditions; (2) establishment of the relations between the structure of metal-oxide promoter interface and activity in the PROX reaction, as well as an atomic-level understanding of the reaction mechanism. This gained knowledge would guide us to design and synthesis new catalytic materials with high performance in PROX reaction. Finally, we expect that there will be about five to ten papers in the catalytic top journals as an output of this project.

富氢气氛下CO优先氧化（PROX）是去除氢气中微量CO，防止氢燃料电池电极中毒的有效方法之一。Pt系催化剂在该方面具有较大的潜在应用前景。然而常规催化剂制备方法很难对该类催化剂中的金属-氧化物助剂界面进行精准调控，以实现催化性能的最佳优化。本项目拟利用原子层沉积（ALD）“自下而上”原子级精准调控的技术优势，并根据选择性沉积策略，在负载型Pt系催化剂中的贵金属纳米颗粒表面，选择性地精准沉积不同分散度的FeOx或CoOx助剂，实现对金属-氧化物助剂界面的原子级精准调控。采用球差矫正扫描透射电镜、原位X射线吸收谱和原位X-射线光电子能谱等技术方法，重点研究PROX反应过程中，Pt系金属纳米颗粒表面上不同分散度氧化物助剂的电子和几何结构特征；探索分散度不同引起的金属-氧化物助剂界面结构调变与PROX催化活性的关系；并在原子层面上揭示其催化反应机制，为未来设计与制备高效PROX催化剂提供新思路。

富氢气氛下CO优先氧化（PROX）是去除氢气中微量CO，防止氢燃料电池电极中毒的有效方法之一。本项目利用原子层沉积（ALD）“自下而上”原子级精准调控的技术优势，在负载型Pt系催化剂中的贵金属纳米颗粒表面，选择性地精准沉积不同分散度的FeOx或CoOx助剂，实现对金属-氧化物助剂界面的原子级精准调控，继而实现CO高效优先氧化。主要研究成果如下：.1. 成功地构筑出倒置型Fe1(OH)x-Pt单点界面催化剂。在PROX反应中，该催化剂表现出极高的催化活性：首次在-75°C至107°C的超宽温度区间，实现了CO高效选择性去除，为延长氢燃料电池寿命、避免CO中毒，提供了一种解决方案。多方位原位表征手段确定了PROX工况下Fe物种的配位结构为Fe1(OH)3。理论合作者进一步明确了Fe1(OH)3在Pt表面上的空间构型，并揭示了该催化反应的分子机理。.2. 原位XAFS和性能测试进一步研究发现，Pt颗粒尺寸对于Fe1(OH)x-Pt单位点界面催化剂的本征活性有重要影响。当Pt尺寸为2.7 nm时，PROX催化活性性能最佳，降低或增加Pt尺寸，均显著降低PROX催化性能。.3. 利用静电强相互作用和氧化物包裹，成功制备出亚纳米二维结构Pt-CoOx复合团簇催化剂；该催化剂在 20至140 °C极宽温区内，实现CO高效选择性去除。其本证活性是对应的三维结构Pt-CoOx复合团簇的8倍。.4. 通过调控FeOx覆盖度和Ir颗粒尺寸，大大优化了Ir-FeOx/SiO2催化剂PROX性能。其中两个ALD循环FeOx 包裹1.5 nm的Ir颗粒催化剂时，PROX性能最佳，可以在60-180°C的宽温度区间实现的CO完全转化。. 至该项目实施以来，以通讯作者发表SCI论文19篇，其中基金第一标注的文章14篇，包括Nature 1篇、JACS 1篇、Nat. Commun. 1篇、Science Adv. 1篇、ACS Catal. 2篇、Small 1篇和受邀综述、论文或展望5篇。申请中国专利2项和国际PCT专利1项、授权中国专利1项。其中，《“界面单位点”新型催化剂结构设计与氢气中微量CO的高效去除》工作，入选了教育部科技委2019年度“中国高等学校十大科技进展”。执行本项目发展的倒置型单点界面新型催化剂结构，必将为金属-氧化物界面设计提供了一新思路、新机遇。