Characterisation of Metal Nanoclusters and Catalytic Mechanisms by Microwave Spectroscopy

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The speed at which an object rotates depends upon its mass and the way that mass is distributed in the object. Thus, it is harder to set a roundabout turning when somebody is riding at the edge but easier if that person stands right in the middle. It is easy to set a frisbee spinning but hard to flip a javelin end-over-end. These observations are a consequence of the relationship between mass, geometrical structure and inertia. The same relationship allows study of the structure of a molecule through measurements of its molecular rotation. Microwave spectroscopy works by causing molecules to spin and then seeing how fast they rotate. Is a given molecule shaped more like a frisbee or a javelin? The technique can also be used to determine how atoms are arranged within a molecule and to accurately measure bond distances and angles between bonds. It can tell us whether a molecule is flexible or rigid. It can say how charge is distributed, telling us about the strength and nature of chemical bonds. In a novel application, I propose to use a new tool in microwave spectroscopy to determine whether reactions are catalysed on the surface of selected metal nanoclusters. The development of more efficient, selective and greener catalysts is a key challenge of modern research in chemistry. Catalysts are often used to accelerate chemical reactions and processes of commercial significance. Industry employs the surface environment provided by solid metals to catalyse the manufacture of a wide variety of chemical products, materials and foods. For example, margarine is produced using nickel metal as a catalyst. Researchers have already described how nanoclusters of metal atoms supported on surfaces can be highly effective catalysts. It is known that the size and topology (molecular landscape of the surface) of these units can have a profound influence on their catalytic properties. This proposal seeks to contribute fundamental information on the molecular mechanisms of catalysis on metal nanoclusters on the smallest possible scale. Carbon monoxide is known to poison catalytic materials, reducing their efficiency. Metal nanoclusters with adsorbed carbon monoxide will be one target of studies. H2O and CO yield H2 and CO2 in an industrially-important catalysed reaction that is a useful source of hydrogen fuel (the water gas shift reaction). I will study whether this reaction can occur on very small metal nanoclusters, and if so, whether its efficiency is a function of cluster size. Conventional Balle-Flygare Fourier transform microwave (FTMW) spectrometers possess a narrow, 1 MHz bandwidth and are unsuitable for collecting data rapidly. The proposed research will exploit the latest 21st century digital technology for the construction of a novel chirped pulse Fourier transform microwave (CP-FTMW)spectrometer. The new CP-FTMW instrument will be broadband and allow the collection of data over an 11 GHz frequency range simultaneously. Given that it will be possible to monitor the concentration of many different components in a gas sample simultaneously, this instrument may ultimately find applications in analytical science. It will also be perfectly suited to probe the microwave spectra of many biologically-significant molecules.