Towards a deeper understanding of catalytic activity in supported precious metal catalysts

Supported heterogeneous catalysts comprising nano-sized metals/metal oxides such as Cr, Ni, Co, Au, Pd, Pt and Ag dispersed on an oxide support (i.e. SiO2/Al2O3), play a central role in an industry estimated to be worth ca. 1500 billion $US/annum. They are the principle protagonists in the conversion of fractions from natural oil and gas to produce, via core catalytic processes (i.e. polymerisation, isomerisation, reduction and oxidation), a wide variety of chemicals for everyday use. A combination of dwindling supply and increasing demand on these feedstocks means it is vital that catalysts and catalytic processes operate as efficiently as possible. Optimal efficiency is normally achieved by rationalisation of structure with function and forms the basis for much catalysis research. However the characterisation performed is often incomplete and rarely performed under reaction conditions leading to contrasting conclusions as to what makes a catalyst active. This project will develop more robust structure-activity relationships by correlating how parameters that influence catalyst performance i.e. nanoparticle size, shape, redox functionality and metal-support interactions, affect and evolve in core catalytic processes of hydrogenation and oxidation. The project adopts a novel approach drawing on skills in catalyst preparation and in situ catalyst characterisation to prepare size-controlled monometallic nanoparticles, deposited on a flat oxide supports and to characterise them in operando using simultaneous time-resolved grazing incidence X-ray scattering (GIXRS) techniques. In particular small angle/wide angle grazing incidence scattering methods (GISAXS/GIWAXS) will be used although attempts will also be made to extract pair distribution function ((GI)PDF) from the data to enable a more complete characterisation of the catalyst. Such a thorough characterisation has never been previously employed and will be used to determine the salient characteristics of catalytic nanoparticles in both two-phase (hydrogenation) and three-phase (oxidation) catalytic systems. It is expected that these measurements will prove invaluable for understanding what makes a supported nanoparticle tick and an important basis for future catalyst optimisation and design.

Chemicals are one of the UK's chief exports and central to the success of this industry are heterogeneous catalysts. The catalysis industry therefore fulfills an important economic role and through the development of pharmaceuticals, hygiene products and emission control systems an important societal one too. Central to the success of this field in the UK has been the strong investment in R & D in both industrial and academic settings rendering it internationally competitive. Investment and growth in this area, particularly through the creation of research centres, is vitally important in order to not only maintain the status quo but also to strengthen it in light of growing, stiff international competition. At the heart of UK excellence in catalysis is the combination of a strong fundamental understanding applied to real catalytic problems; a research environment that is complementary to the approach adopted in this project and one very much in line with current UK Science policy. By utilising a targeted approach to tackle specific, industrially important applications of hydrogenation and oxidation it is expected that the results generated will be of direct interest to companies that operate such processes. As such even modest gains in their understanding could result in an immediate impact on current industrial practice in the UK and beyond, via the application of new, targeted preparation methods or else via the optimisation of catalytic processes. However, since these reactions are core catalytic processes used across the chemical industry, the findings in this project are also likely to be of interest to a wider audience. A more thorough understanding of these catalytic processes will also allow us to identify the key traits for activity so as to design and develop new, more efficient catalysts and catalytic processes altogether. Ultimately it is hoped that the information provided in this study/approach could provide the basis for tackling two major issues that we as a global society currently face, i.e. to find alternative, more sustainable fuel sources (i.e. biomass, fuel cells, etc) and to find alternatives to the scarce yet heavily-in-demand platinum group metals used in many catalytic processes (notably, emission control). Meanwhile the developments in the characterisation methodologies employed here will also result in an expansion in the catalysis scientist's toolbox, with these developments (and others) expected to demonstrate the benefits of locating the Catalysis Centre close to central measurement facilities and serving as a powerful magnet for attracting future investment from academic and industrial sources, nationally and internationally. This need not be limited to catalysis since such techniques can provide insight to scientific problems across a number of research areas where structure-activity relationships are valued such as nanotechnology, energy and cultural heritage where, for example, the study of nanoparticles present in artefacts and paintings under variable atmospheres is important in understanding aging. Finally by providing a combination of necessary skills set, research know how and innovation experience the project will ensure that the co-researchers on the project (post docs) obtain an excellent grounding for a career in catalysis, materials science or synchrotron radiation in an industrial or academic setting, so that they may continue to contribute to the knowledge economy of the UK. As such the benefits of this project could be very broad in both economic and societal terms in the short and longer term.