纳米空间限域的金属合金粒子的晶相调控及其催化性能研究

The microstructure of catalysts at the nano-scale, such as size, morphology, crystallite phase is the key issue in heterogenous catalysis to achieve the desired performance. The size/morphology-dependent effects of nanoparticles have been intensively and extensively studied in the past decades; whereas the impact of the crystalline phase has received less concern, primarily because the metastable phases, usually being more reactive, tend to convert into thermodynamically stables one during the synthesis process or under working conditions. This project was proposed to tune the crystallite phase of Pd、Au、Pt based nanoalloys in the confined nanospace, which could prohibit the sintering or leaching of nanoparticles during the solid-phase conversion. The key issue is to modify the crystallite phase of nanoalloys (PdCu、AuCu、PtFe etc.) with the similar particle size and chemical compositions. The selective hydrogenation of nitrobenzene and α, β-unsaturated aldehyde or ketones was applied as probe reactions to elucidate the crystallite phase effect of the obtained nanoalloys. Moreover, the dynamical characterization by ETEM and spectroscopic techniques was also performed to follow the evolution of surficial structure and coordination environment, which might be helpful to clarify the active sites and the phase transformation of alloy at nanometer scale.

尺寸、形貌和晶相是决定金属合金纳米粒子催化性能的关键因素。近年来，金属纳米粒子催化剂的尺寸和形貌效应已经有了系统深入的研究，但晶相效应的研究还较少涉及。这主要是由于金属纳米粒子介稳态晶相在合成过程或反应条件下容易转化为热力学稳定的晶相。本项目针对多相催化中广泛应用的Pd、Au、Pt基金属合金催化剂，利用纳米空间限域条件下的金属合金纳米粒子的固相转化法，实现化学组成相同、尺寸相近、形貌相似但晶相不同的纳米合金催化剂（PdCu、AuCu、PtFe等）的高效合成。以重要的加氢过程为探针反应，结合结构表征，深入研究催化剂的表面结构及原子配位环境，强化纳米尺度下合金粒子晶相转化机制和纳米催化晶相效应的认知。

尺寸、形貌和晶相是决定金属合金纳米粒子催化性能的关键因素。近年来，金属纳米粒子催化剂的尺寸和形貌效应已经有了系统深入的研究，但晶相效应的研究还较少涉及。这主要是由于金属纳米粒子介稳态晶相在合成过程或反应条件下容易转化为热力学稳定的晶相。本项目针对多相催化中广泛应用的Pd、Au、Pt基金属合金催化剂，发展了一系列溶液体系中制备组成、尺寸和结构可控的金属催化剂（PdCu、AuCu、PtFe等）的新方法；发展了一种反相微乳体系制备SiO2包覆合金纳米粒子的合成方法，利用纳米空间限域条件下的金属合金纳米粒子的固相转化法，在化学组成、尺寸和形貌保持不变的前提下实现了合金纳米粒子的晶相调控；项目通过探针分子的低温吸附红外光谱技术、X射线吸收精细结构和STEM研究了不同晶相的合金纳米粒子的空间分布和原子排布；项目利用这类新型催化剂中金属材料的独特的空间分布，实现温和条件下加氢反应的高活性和高选择性，强化纳米尺度下合金粒子晶相转化机制和纳米催化晶相效应的认知。