5 CONCLUSIONS

In-situ experiments are now available probing the bulk and surface reactivity of "real" catalysts. They yield detailed information on geometric and electronic structure of working systems. It is of minor relevance that a pressure gap still exists between a few millibars and atmospheric pressure. Significant conversions are achieved during in-situ experimentation under a few millibar pressures, at reaction temperature, and in the correct feed gas composition. Thus, all processes affecting the structure of the surface and of the sub surface region are operative. As the geometry of the gas-solid interaction is far from that in a practical catalytic reactor it cannot be expected that the kinetic parameters match between macrokinetic experiments and the in-situ experiments. Reservation is required for this reason when interpreting structure-function correlations in quantitative ways. The experiments prove, however, very clearly how dynamically bulk and surface of catalytically active systems behave. The findings underline that surface science model systems are rigorous boundary condition states of a system and the corresponding results should not be extrapolated quantitatively to practical operation. The present findings indicate, however, that the qualitative conclusions drawn from model studies are valid in pictures of the complex practical situation. There should be a co-operation between surface science giving insight into the mode of operation of catalysts and a combined in-situ analytical-preparative effort providing the relevant systems. In such a way, the gaps between model and real catalysts can be bridged effectively and there is no room left for speculations...