6.4. Requirements for further research

The results of this thesis have shown that there is a clear need for a further development of laboratory scale ageing cycle which corresponds to the ageing-induced changes in the catalyst either after the engine bench ageing, or under vehicle operation. The results of this thesis can be utilized in this development work which, in the author’s opinion, requires the testing of a number of different catalyst compositions in order to guarantee the reliability of the ageing cycle and more realistic models of deactivation. This development and testing work has been initiated in parallel with this thesis, but outside the scope of it, as mentioned above.

In the course of this study, several characterization techniques were used to examine ageing-induced changes in the catalyst, and as shown in this work deactivation of a TWC cannot be understood on the basis of some separate characterization technique. Many properties affect the catalyst’s performance and the integration of the results of several characterization techniques are required for the fundamental understanding of the deactivation phenomena of the three-way catalysts. In the future, it would be informative to utilize TEM (Transmission Electron Microscopy) to study ageing-induced changes in the active metals. TEM would provide detailed information e.g. on metal particle size and shape of active metals after the ageings, and thus some additional information on the deactivation mechanisms of Pd/Rh monoliths. On the other hand, it would give few new insights into the deactivation correlation between laboratory scale ageings and engine bench/vehicle ageings.

Furthermore, the use of Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFT) would increase the information on the adsorption of NO on catalytically active sites on the surface (Keiski et al. 1995), and so assist the interpretation of the NO-TPD spectra. In this respect, characterizations were carried out with simplified model catalysts, which helped with the interpretation of the origin of desorption peaks of NO. The additional information obtained from the DRIFT technique would increase the understanding of deactivation phenomena at the molecular level, but it provides little or no new information concerning the deactivation correlations.