Fabrication and Reactivity of Model Mixed Oxide Nanoparticles

本申请的重点是纳米科学的一个方面，后者被定义为与尺寸小于1微米的材料有关的科学领域。事实上，我们正在超纳米领域工作，涉及尺寸通常在1- 10 nm（0.001至0.01微米）之间的结构。纳米科学和技术对我国当前和未来的福祉至关重要，因为将设备的尺寸提高到纳米级，可以减少制造设备时使用的原材料，因此对环境有利，并且是迈向技术可持续性的一步。我们已经在日常生活中广泛使用纳米技术--从化妆品到电子设备，从药品到我们汽车的燃料。后者来自于使用含有直径仅约3 nm的微小Pt颗粒的催化剂。纳米粒子的表面反应性和纳米科学与催化的相关性是这一应用的重点。特别地，本发明涉及纳米级FeMo氧化物颗粒的制造、表征和反应性，所述纳米级FeMo氧化物颗粒可用于甲醇的选择性氧化以产生甲醛。甲醛的生产是主要的全球商业和技术，因为甲醛用于覆盖我们厨房的台面和地板的广泛产品中，甚至用于保存尸体的防腐液（我们从摇篮到坟墓都用它）！它的生产涉及使用催化剂使氧气与甲醇反应，后者使反应能够以更环保的方式进行，使用更低的能量（更低的温度），产生更少的副产物，而不是非催化过程。然而，这种催化作用被称为选择性氧化，在所有情况下也会产生CO2和水。生产这些意味着该工艺的经济效率损失，但也许更重要的是，它会给大气带来额外的CO2负担，对全球变暖产生负面影响。因此，重要的是使所有这些进程，包括我们在此考虑的进程，更有效率和更有选择性。目前的工艺在约95%的选择性下工作，这意味着每年约有350，000吨CO2排放到大气中，大约相当于100，000辆汽车的排放量。因此，选择性仅提高1%，将导致全球大气中减少20，000汽车当量的CO2负担。减少这些排放的一个重要推动因素是了解催化剂和所涉及的FeMo催化剂的性质，因为根据这些知识，我们可以设计出更高效的材料。这项工作的目的是第一次在氧化铁晶体的表面上制造出轮廓分明的铁颗粒。我们用后者诱导其表面形成的铁氧化物的晶体学有序性，并以此方式制作铁氧化物催化剂模型。我们将使用相对较新的扫描隧道显微镜技术来成像氧化铁和氧化铁晶体的表面结构。STM最重要的一点是它具有原子分辨率，从而使我们能够直接识别表面的原子结构和分子吸附位置。我们将联合收割机这种结构技术与XPS（X射线光电子能谱）的使用相结合，XPS是一种分析技术，可以告诉我们三种元素（Fe，Mo，O）中的每一种在表面上存在多少。然后，我们将继续确定在表面的反应中心的性质，这是目前未知的;甲醇将结合到铁中心，钼中心或缺陷的表面层（例如，缺少氧）？根据对活性位点的了解，我们预期能够利用这些知识来定制更有效的催化剂。

The focus of this application is an aspect of nanoscience, the latter being defined as that area of science concerned with materials of dimensions of less than 1 micron. In fact we are working in the ultra-nano regime involving structures typically between 1-10nm in size (0.001 to 0.01 microns). Nanoscience and technology are extremely important for the current and future well-being of our country because increased miniaturisation of devices down to the nanosize regime offers benefits of reduced usage of raw materials in constructing devices, which is therefore beneficial to the environment and is a step towards sustainability of technology. We already make use of nanotechnology in a wide range of ways in everyday life - from cosmetics to electronic devices, from medicine to the fuel in our cars. The latter derives from the use of catalysts containing tiny Pt particles of only ~3nm diameter. It is the surface reactivity of nanoparticles and the relevance of nanoscience to catalysis, that is the focus of this application. In particular it concerns the fabrication, characterisation and reactivity of nanosized FeMo oxide particles which may be used for the selective oxidation of methanol to produce formaldehyde.The production of formaldehyde is a major global business and technology, since formaldehyde is used in a wide range of products from the worktops and flooring which cover our kitchens, and even to embalming fluid for preserving dead bodies (ie we use it from cradle to grave)! Its production involves reacting oxygen with methanol using a catalyst, the latter enables the reaction to proceed in a more environmentally-friendly way, using lower energy (lower temperature) and producing less by-products, than would otherwise be the case for a non-catalysed process. However, this kind of catalysis is called selective oxidation, and in all cases CO2 and water are also produced. Production of these means a loss of economic efficiency for the process, but perhaps more importantly it results in an additional CO2 burden to the atmosphere with negative consequences for global warming. Thus it is important to make all such processes more efficient and more selective, including the one we are considering here. Current processes work at about 95% selectivity, which means that about 350,000 tonnes per year of CO2 are emitted to the atmosphere, approximately equivalent to the emissions from 100,000 cars. Thus an improvement of selectivity of only 1%, will result in a saving of 20,000 cars equivalent of CO2 burden on the atmosphere globally. An important enabler to reduce these emissions is to understand the nature of the catalysis and the FeMo catalyst involved, because from that basis of knowledge we can engineer the material to be more efficient. The aim of the work proposed here is to make well-defined particles of iron molybdate on the surface of an iron oxide crystal FOR THE FIRST TIME. We use the latter to induce crystallographic order on the iron molybdate formed on its surface, and in this way to make models of iron molybdate catalysts. We will use the relatively new technique of scanning tunnelling microscopy to image the surface structure of the iron oxide and iron molybdate crystals. The important point about STM is that it is capable of atomic resolution, thereby enabling us the DIRECTLY identify the atomic structures and sites for molecule adsorption at the surface. We will combine this structural technique with the use of XPS (X-ray Photoelectron Spectroscopy) which is an analytical technique to tell us how much of each of the three elements (Fe, Mo, O) is present AT THE SURFACE. We will then go on to identify the nature of the reactive centre at the surface, something which is currently unknown; will methanol bind to Fe centres, Mo centres or defects in the surface layer (e.g. missing oxygens)? From knowledge of the active site we anticipate the ability to use that knowledge to tailor more efficient catalysts.