Surface Topography, Molecular Beams, and Transitory Species

4 Surface Topography, Molecular Beams, and Transitory Species 

This section of the review deals with three major areas of catalysis. The first is the characterization of surfaces and the different effects produced in adsorption and reaction rates by the selection of different surfaces. Controversy is not absent in this field and this is reflected by papers on the H2/D2 exchange. The second major area chosen is that of molecular beams where the example chosen shows the wealth of information which can be obtained, admittedly for the decomposition of a simple molecule. The final paper chosen for this section has information on a transient intermediate which may, or may not, be of great significance to catalysis. 

Before beginning with specific examples, however, it is worth noting the paucity of papers on co-adsorption. There are some examples in this review, e.g. CO + NO. Within this field of co-adsorption, which must represent one of the keys to catalysis, there is a significant observation by Conrad et al. They point out that in UPS the occurrence of new features arising from co-adsorption is very unusual. Thus in their study of the C2N2/H2/Pt(100) system the appearance of a new feature in the spectrum leads them to wonder if they are observing a surface intermediate in the reaction which produces HCN. 

Another example of the effect of a co-adsorbed species on adsorption can be found in Kunimori et al. on high resolution AES of NH3 on Pd. At 25 °C NH3 adsorbs in molecular form, but when O2 is present a NH,(ads) species is produced. 

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