Catalytic converter technologies situated in the exhaust streams of vehicles are under continuing pressure to meet more stringent emissions standards that requires increasing longevity along with higher efficiencies. This investigation studied the fundamental factors known to contribute to catalyst deactivation, by developing the specific designs and by construction of ageing facilities that isolated the ageing factors under inspection. Various static ageing schedules were completed along with rapid ageing cycles with the aid of a custom built synthetic gas ageing machine named AutoCAS, (Automotive Catalyst Ageing System). Explicit characterisation techniques to help define the extent of catalyst degradation were also developed. These focused on use of scanning electron, microscopy and transmission electron microscopy to produce images of the catalyst which could then be analysed using image analysis software. The software program enabled statistical data to be collated, allowing conclusions to be drawn about the surface structure before and after ageing. Raman spectroscopy was used to probe the changes in catalyst substrate after the ageing process. Results uncovered that Platinum/Rhodium, (PtIRh), catalysts behave differently to Palladium, Pd, catalysts with respect to particle agglomeration. Pd loaded samples exhibited relationships with respect to ageing time and temperature whilst PtlRh catalysts were only susceptible to ageing temperature. Also, concluded was that PtlRh catalysts undergo agglomeration in an inert nitrogen environment which is in direct contradiction to mathematical expressions already published. Precious metal particle agglomeration was found to have a relatively insignificant role to play in overall catalyst deactivation. RATA ageing showed that the thermal stressing incurred by thermal cycling affected the catalyst activity more so than ageing at uniform temperature. Application ofthe current QUB catalyst model showed that there may be other factors contributing to deactivation rather than just washcoat sintering and precious metal agglomeration as measured in this research.