Characterising metal nanoparticle catalytic activity by the work function

我们将展示非接触原子力显微镜(NC-AFM)和开尔文探针力显微镜(KPFM)的结合可以用来在单纳米粒子(NP)水平上量化基本气体在多相催化中的吸附/解吸特性，作为NP尺寸、形状、组成和温度的函数，以及氧化物载体如何影响性质。此外，我们将明确证明KPFM能够量化单个NPs上的污染和溶解现象，这对许多催化过程是最重要的。虽然NC-AFM将用于揭示由NPs的尺寸、形状、分布和烧结决定的表面结构和形貌，但KPFM的任务将是监测由NP功函数(WF)的变化确定的局部电子结构，为NPs中吸附的分子物种或溶解的原子物种提供定量测量。这些技术将被确立为涉及金属纳米颗粒的多相模型催化中的校准标准工具。NC-AFM和KPFM的局部测量将得到X射线光电子能谱(XPS)和紫外光电子能谱(UPS)的分析，以获得分子-NP-表面体系的化学指纹和平均WF。实验将得到密度泛函理论(DFT)的支持，分析和预测反应物在NPs上的吸附和相关的WF变化。最终和具有挑战性的目标是观察和量化单个NPs上的简单反应，即CO的氧化和碳氢化合物的加氢。在本项目中，我们首先将重点放在铂族材料(PGMs)的纯NPs上，特别是工业催化转化器中常用的钯(Pd)和金(Au)。此外，我们考虑了双金属纳米粒子，重点是Pd和Au。在项目过程中，我们可以选择考虑其他金属，如铁、钴或铜。载体将是超薄和厚膜的CeO2。将详细研究CO、氧气、氢气和简单碳氢气体(如乙烯)的吸附和解吸；已知的物种吸附在PdNPs等金属纳米颗粒上。污染实验将特别关注碳污染和溶解，这一现象与许多催化反应最相关，如碳氢化合物加氢、费托工艺以及石墨烯或纳米管等碳结构的合成。

We will demonstrate that the combination of non-contact atomic force microscopy (NC-AFM) and Kelvin probe force microscopy (KPFM) can be used to quantify the adsorption/desorption characteristics of fundamental gases in heterogeneous catalysis at the single nanoparticle (NP) level as a function of NP size, shape, composition and temperature, and how properties are affected by the oxide support. Furthermore, we will explicitly demonstrate that KPFM is capable of quantifying phenomena of contamination and dissolution at single NPs that is most important for many catalytic processes.While NC-AFM will be used to reveal the surface structure and morphology determined by the size, shape, distribution and sintering of NPs, the task of KPFM will be to monitor the local electronic structure determined by changes in the NP's work function (WF) providing a quantitative measure for adsorbed molecular species or dissolved atomic species in NPs. The techniques will be established as calibrated standard tools in heterogeneous model catalysis involving metal NPs. Local measurements by NC-AFM and KPFM will be supported by an analysis with X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoelectron spectroscopy (UPS) to obtain the chemical fingerprints and average WF of the molecule-NP- surface system. Experiments will be backed by density functional theory (DFT) analysing and predicting the adsorption of reactants on NPs and related WF changes. The ultimate and challenging goal is to observe and to quantify simple reactions at single NPs, namely the oxidation of CO and the hydrogenation of hydrocarbons.For the project, we will first focus on pure NPs of platinum group materials (PGMs), in particular on palladium (Pd) and gold (Au), commonly used for industrial catalytic converters. Furthermore, we consider bi-metallic NPs with the focus on Pd and Au. During the course of the project, we optionally consider other metals like Fe, Co or Cu. The support will be ultra-thin and thick films of cerium oxide (ceria).The adsorption and desorption of CO, oxygen, hydrogen and simple hydrocarbon gases (e.g. ethylene) will be investigated in detail; species that are known to adsorb at metal nanoparticles like PdNPs. Contamination experiments will focus in particular on carbon contamination and dissolution, phenomena most relevant for many catalytic reactions like the hydrogenation of hydrocarbons, Fischer-Tropsch process and in the synthesis of carbon structures like graphene or nanotubes.