Prof Adam Lee - BA PhD (Cantab) CChem FRSC
- Development and application of novel clean catalytic technologies
- Operando X-ray spectroscopies for dynamic studies of solid surfaces
- Physico-chemical properties of metal and oxide nanoparticles
- Design of hierarchical porous inorganic solids
My research uses advanced thin-film synthetic and surface analytical techniques to obtain molecular level insight into important surface phenomena including alloying, adsorption and catalytic chemistry. The importance of surface chemistry in everyday life is reflected in the diversity of research undertaken within our group, ranging from designer catalysts for clean chemical synthesis, to improved magnetic materials for high density data storage and even novel antibacterial wound dressings. A particular focus of my research is the rational design of new heterogeneous catalysts and the associated development of high power instrumental techniques for investigating dynamic structural and chemical changes within such catalytically-active materials.
Time-resolved XPS is an extremely powerful method for investigating chemical transformations catalysed by solid surfaces in real-time (Figure 1). XPS represents a chemically specific, surface sensitive and quantitative technique for characterising both adsorbates species and the underlying interface. Synchrotron X-ray radiation allows us to tune into different chemical elements at a solid surface (e.g. adsorbed molecules or metal dopants) and probe their local environment. There are two principle modes of operation: spectra can be recorded as a function of time while exposing the surface to an adsorbate at constant temperature shedding insight into adsorption kinetics; alternatively spectra can be recorded continuously while heating a reactant adlayer to deconstruct reaction mechanism and identify metastable reaction intermediates.
The ability to observe dynamic structural changes of working catalysts under reaction conditions is invaluable to understanding key promotion and poisoning phenomena and tailoring the design of next-generation catalysts. EXAFS is a perfect spectroscopic tool for probing the local chemical environment and oxidation state of atoms within catalysts over a wide range of temperatures and pressures. A key advantage of this technique is that the high penetration depth of X-rays allows solid catalysts to be studied while exposed to either vapour or liquid reaction mixtures.
The selective oxidation of alcohols is an important step in synthesising many valuable intermediates for the food, fragrance and pharmaceutical industries. This chemistry traditionally uses stoichiometric amounts of hazardous and toxic oxidants such as peroxides and chromates and generates large quantities of harmful waste. We have recently developed a range of supported platinum-group metals which are effective for the aerobic selective oxidation of allylic alcohols to the corresponding aldehydes under mild conditions. Use of templated mesoporous enables the genesis of single-site Pd catalysts which exhibit exceptionally high activity, for crotyl and cinnamyl alcohol oxidation.
Combinatorial Materials Synthesis
The sequential or simultaneous synthetic preparation of potentially vast numbers of related compounds is termed Combinatorial Chemistry and this approach has been widely used for drug discovery in the pharmaceutical industry. In general combinatorial techniques describe any protocol that allows a large number of compounds to be prepared in a fraction of the time required if they were prepared individually by classical methods. The discovery of complex solid materials with desirable chemical or physical properties is an obvious target for the application of simultaneous preparation techniques.
We use in vacuo sputter deposition (Figure 3) to generate libraries of thin metal alloy or mixed metal oxide films spanning an entire 3-phase diagram. These planar library arrays effectively span millions of different compositions allowing a vast number of new materials with desirable catalytic, electronic, or magnetic properties to be generated in a single experiment.
Gradiated sputtered Pt/Cu library
We are also interested in developing new high-throughput screening techniques such as IR thermography, for real-time, parallel imaging of the catalytic activity or thermal emissivity of an entire library (Figure 4). This allows us to rapidly identify new promising catalyst formulations and search for cheaper, replacement components for precious metals widely used in the chemical industry.