The objective of the proposed work is to obtain fundamental information which will be relevant to the technology required to convert stocks of CFCs such as CFC-113 and CFC-12 to CFC-alternatives, the hydrofluorocarbons HFC-134a and HFC-32. Catalytic routes will be developed that involve the generic reactions, isomerization, dismutation and hydrodechlorination, all to be performed under heterogeneous conditions. Although these are known reaction types, currently used catalysts have significant drawbacks and an important aspect of the work will be the development, characteriszation and evaluation of new catalytic materials. The routes chosen have environmetal advantages since the use of toxic reagents such as anhydrous hydrogen fluoride is avoided and, in contrast to the destruction of CFCs by incineration or by catalytic oxygenation, emission of carbon dioxide is avoided.
Catalysts for isomerization or for dismutation reactions are derived from metal oxides, oxofluorides or fluorides, candidate materials being chosen on the basis of their perceived Lewis acid surface properties. Particular attention will be given to aluminium-containing compounds, as opposed to the more toxic chromium analogues and a novel feature is the use that will be made of aerogel and xerogel preparations. An integral part of the project will involve radiotracer studies of the dynamic behaviour of CFCs on a catalyst's surface, of the events involved in catalyst pretreatment and of the lability of surface halogen-containing species. The combination of this mechanistically-oriented work and the studies of catalytic activity will enable different catalysts to be compared in a definite manner.
Hydrodechlorination of CFCs is a process that has received considerable technological and academic attention, however the fundamentals of the process are still not well-understood.
Deactivation of currently used supported palladium catalysts is a major drawback. In this project emphasis will be given to this aspect by exermining the support material. By these methods it will be possible to determine the mechanism of deactivation and hence design better catalysts.