TOUCAN: TOwards an Understanding of CAtalysis on Nanoalloys

纳米粒子在许多方面与它们的“块状”或“液体”结构不同。过渡金属纳米粒子因其高的表面积体积比和当团簇尺寸减小到几十纳米时增加表面能而被广泛用于加速重要的化学反应。特别令人感兴趣的是双金属和多金属纳米粒子(所谓的“纳米合金”)，因为它们可以表现出丰富的结构和混合模式，以及由此提供的化学和物理性能的控制。计算工具在纳米材料的设计和定制中发挥着核心作用，使我们能够找到目标应用的“神奇”纳米粒子，因为计算能力将在实验条件下重新创建和研究，以便向工业合作伙伴建议最佳候选者。第一性原理模拟在纳米合金科学中的基本应用集中在它们引起的化学反应上。实验表明，异质外延生长的应变覆盖层可以呈现出与相同元素的非应变表面不同的化学性质。这一事实已被第一性原理计算所证实。然而，在纳米尺度上，由于其特殊的表面和体相几何结构以及不同的化学顺序，即使是表征纳米合金上的化学吸附位置也不是一件容易的事情。在这个拟议的研究计划中，二元纳米合金将被研究其潜在的催化性能。本项目将主要集中于铂合金(即PtAg和PTAu)、镍合金(即AgNi、NiPt)、Pd合金(即PdAg和PdPT)、钴合金(即AGCO和CoPT)和铁合金(即FePT和FeCo)。在可持续能源领域具有强大影响力的特定化学反应将被考虑，如二氧化碳捕获、生物质过程--例如，涉及CO和CH4的解离，以及用于制氢的NH3解离。要在实验室发生自发化学反应，必须满足两个条件：(1)最终状态必须具有比初始状态更低的自由能，(2)必须至少有一条途径允许在合理的时间内发生转变。在简单的化学反应中，转化路径(反应坐标)通常被很好地理解，这使得计算反应速率和预测外部影响(如催化剂)将如何影响这些速率成为可能。然而，存在许多变换，包括固体中的结构松弛和成核，其中轨迹可以遵循与多个自由度的协作或顺序运动相对应的复杂路径。从计算机模拟的角度来看，这样的路径对应于罕见的事件，因为与事件本身所花费的时间相比，发生感兴趣的过程所需的等待时间非常长。为了在微观层面上理解和控制这种复杂的转变，我们需要描述潜在的、高维的势能格局，并直接对罕见事件进行采样。基于这些知识，我们的目标是预测相关的转型路径和比率，并更雄心勃勃地了解我们如何影响这些比率。该项目由四个相互关联的项目组成，它们与上述目的和目标保持一致：P1。纳米合金数据库数据库P2的构建纳米合金同分异构体P3热稳定性的测定化学吸附图谱P4。纳米合金上分子解离的反应速率

Nanoparticles differ in many ways from their "bulk" or "liquid" structures. Nanoparticles of transition metals have been widely used for accelerating important chemical reactions, thanks to their high surface to volume ratios and increasing surface energy when the cluster size decreases to a few tens of nanometers. Of particular interest are bi- and multi-metallic nanoparticles (the so-called "nanoalloys") due to the richness of structures and mixing patterns that they can exhibit and the control of chemical and physical properties that this affords. Computational tools play a central role in designing and tailoring of nanomaterials, allowing us to find the "magic" nanoparticles for target applications, since the computing power will recreate and investigate in-silico the experimental conditions in order to suggest optimal candidates to industrial partners. A fundamental use of first-principles simulations in nanoalloy science focuses on the chemical reactions that they induce. It has been experimentally shown that heteroepitaxial grown strained over-layers can present chemical properties different than those of the unstrained surface of the same elements. This fact has been confirmed by first-principles calculations. However, at the nanoscale, due to their peculiar surface and bulk geometries, as well as various chemical orderings, even the characterization of chemisorption sites on nanoalloys is not an easy task.In this proposed research programme, binary nanoalloys will be investigated for their potential catalytic properties. This project will focus mainly on Pt- alloys (i.e. PtAg and PtAu), Ni-alloys (i.e. AgNi, NiPt), Pd-alloys (i.e. PdAg, and PdPt), Co-alloys (i.e. AgCo and CoPt) and Fe-alloys (i.e. FePt and FeCo). Specific chemical reactions with a strong influence in the field of sustainable energy will be considered, such as CO2-capture, biomass processes - e.g. involving dissociation of CO and CH4, and NH3 dissociation for hydrogen production.Two conditions must be fulfilled for a spontaneous chemical transformation to occur in the laboratory: (1) the final state must have a lower free energy than the initial state, and (2) there must be at least one pathway that allows the transformation to take place within a reasonable time. In simple chemical reactions, the transformation pathway (the reaction coordinate) is often well understood, which makes it possible to compute reaction rates and predict how external influences (such as catalysts) will affect these rates. However, there are many transformations, includingstructural relaxation and nucleation in solids, where the trajectory can follow complex paths that correspond to cooperative or sequential motion of many degrees of freedom. From the point of view of computer simulation, such pathways correspond to rare events, because the waiting time required for the process of interest to occur is very large compared to the time taken for the event itself. To understand and control such complex transformations at the microscopic level, we need to characterise the underlying, high-dimensional potential energy landscape and sample the rare events directly. Based on this knowledge, we aim to predict the relevant transformation pathways and rates and, more ambitiously, to understand how we can influence these rates.The project is comprised of four inter-linked projects which are aligned with the aims and objectives set out above:P1. Construction of the Nanoalloy DatabaseP2. Determination of Thermal Stabilities of Nanoalloy IsomersP3. Chemisorption MapsP4. Reaction Rates for Molecular Dissociation on Nanoalloys