Catalysis

Even though EXAFS is a young technique already quite a few very important results have been obtained in catalysis. Especially the results on Wilkinson’s catalyst (Section 8.3.1), the sulfided Co—Mo/A1203 catalyst (Section 8.3.3), bromine and krypton on graphite (Section 8.3.4), and the mono and bimetallic catalysts (Sections 8.4.1 and 8.4.2) are worth mentioning. In homogeneous catalysis the results have much in common with those reported on metal con taining enzymes in biochemistry and in situ EXAFS studies allow a detailed picture to be obtained of the environment of the metal atom. In heterogeneous catalysis the best studies published so far have provided information of about the same quality as that obtained by the SEXAFS technique on adsorbates on single crystal surfaces. Therefore, it is expected that studies on highly dispersed catalysts will aid in developing a detailed picture of catalyst support interfaces and of the interaction playing a role in the bonding of catalyst particles to the support. Great difficulties will lay ahead, though, because the normal EXAFS technique is a bulk technique and thus not only metal atoms in the interface between metal particle and support will be measured but also all other metal atoms on top of those in the interface. Furthermore, the support oxygen ions have a low backscattering amplitude. For these reasons especially catalysts with very high dispersions are of interest. Such catalysts can in general only be prepared at low metal loading, which brings us to the problem of signal-to-noise ratio. Therefore, the trend in the applications of EXAFS in catalysis in the coming years will undoubtedly be to try for lower and lower catalyst loadings, which experimentally means that one ultimately has to switch from normal transmission detection to fluorescence detection. Another area of interest for EXAFS in catalysis will be the morphology of catalyst particles with such a small size that they are not measurable with a