Fabrication and Reactivity of Model Mixed Oxide Nanoparticles

Lead Research Organisation: Cardiff University
Department Name: Chemistry

Abstract

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.

Publications

10 25 50
 
Description The preferential segregation of Mo to the surface of iron oxide single crystals and the primary chemistry associated with methanol oxidation
Exploitation Route The development of new cheaper catalysts for methanol selective oxidation
Sectors Chemicals,Construction,Energy,Environment

URL http://www.cf.ac.uk/chemy/contactsandpeople/academicstaff/bowker-michael-overview_new.html
 
Description Fritz Haber Inst of the Max Planck Socie 
Organisation Max Planck Society
Department Fritz Haber Institute
Country Germany, Federal Republic of 
Sector Academic/University 
Start Year 2007