The Use of Ion Beam Techniques in Catalysis

It has become increasingly obvious recently that ion beam methods can make a significant contribution to the preparation and characterisation of heterogeneous catalysts. Normally such catalysts are composed of one or more metals or compounds dispersed over a high surface area support material, such as alumina or silica. It is important to be able to measure the relative concentrations of the catalytic components (and any associated impurities) over the support, and, to some extent, within the support. Proton Induced X-ray Emission is particularly appropriate for this purpose. It may be used also to identify the presence of poisoning elements which have been responsible for catalyst deactivation. However, one of the most common causes of catalyst deactivation is carbon deposition on to its exposed surfaces. In this case, a particularly useful diagnostic technique is Prompt Nuclear Activation Analysis, since it can be rendered specific for carbon to the exclusion of other associated elements. So far as catalyst preparation is concerned, there are of course many conventional chemical routes: for example, these may involve impregnating the support with suitable catalytic metal salts, thereby utilising the high surface area properties of the support to create the dispersion of the catalytic elements. However, it has now been realised that two ion beam techniques, namely ion implantation and sputtering, provide an alternative method of producing novel catalysts.