5. Main reactions for characterizing metal catalysts

Model reactions are mainly used to characterize metal catalysts in terms of dispersion. Electron microscopy is the method of choice for measuring the size of metal clusters. However, the use of model reactions becomes indispensable when dispersion is high (small particle sizes), as it may be difficult to observe particles by electron microscopy, to have peaks detectable by XRD or to obtain precise information on the quantity of chemisorbed molecules (limited by gas detection). In order to measure metal dispersion, we choose a model reaction that is insensitive to structure, i.e. all exposed sites will exhibit the same intrinsic activity, and therefore the activity per site is independent of particle size (Boudart). Aromatic hydrogenation and cycloalkane dehydrogenation are structure-insensitive reactions. Structure-sensitive model reactions are also used to characterize the nature of the...