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，我们工作在超纳米领域，包括尺寸通常在1-10纳米(0.001-0.01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极其重要，因为设备的小型化程度提高到纳米级，有利于减少制造设备时使用的原材料，因此有利于环境，是迈向技术可持续发展的一步。我们已经在日常生活中以广泛的方式利用纳米技术--从化妆品到电子设备，从医学到汽车燃料。后者是由于使用了含有直径仅为3 nm的微小铂颗粒的催化剂。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。它尤其涉及纳米氧化铁颗粒的制备、表征和反应活性，可用于甲醇的选择性氧化生成甲醛。甲醛的生产是一项全球主要业务和技术，因为甲醛被广泛用于从厨房的桌面和地板，甚至到保存身体的防腐液(即我们从摇篮到坟墓都使用它)！它的生产包括使用催化剂使氧气和甲醇反应，后者使反应以更环保的方式进行，与非催化过程相比，使用更低的能量(更低的温度)和产生更少的副产品。然而，这种催化被称为选择性氧化，在所有情况下都会产生二氧化碳和水。这些物质的生产意味着这一过程的经济效率的损失，但也许更重要的是，它会导致大气中额外的二氧化碳负担，从而对全球变暖产生负面影响。因此，重要的是使所有这些进程更有效率和更有选择性，包括我们在这里审议的进程。目前的工艺具有大约95%的选择性，这意味着每年大约有35万吨二氧化碳排放到大气中，大约相当于10万辆汽车的排放量。因此，选择性仅提高1%，将导致全球节省2万辆汽车，相当于大气中的二氧化碳负担。减少这些排放的一个重要因素是了解所涉及的催化和FeMo催化剂的性质，因为在此基础上我们可以设计出更高效的材料。这项工作的目的是首次在氧化铁晶体表面制造出定义明确的钼酸铁颗粒。我们用后者在其表面形成的钼酸铁上诱导结晶有序，从而制作钼酸铁催化剂的模型。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钼酸铁晶体的表面结构。扫描隧道显微镜的重要之处在于它具有原子分辨的能力，从而使我们能够直接识别分子在表面吸附的原子结构和位置。我们将把这种结构技术与XPS(X射线光电子能谱)的使用结合起来，XPS是一种分析技术，可以告诉我们三种元素(Fe、Mo、O)中有多少存在于表面。然后，我们将继续确定表面反应中心的性质，这是目前尚不清楚的；甲醇是否会与铁中心、钼中心或表面层中的缺陷(例如，缺失的氧)结合？根据对活性中心的了解，我们预计有能力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.