In situ Raman spectroscopy studies of catalysts

In situ Raman spectroscopy is rapidly becoming a very popular catalyst char acterization method because Raman cells are being designed that can combine in situ molecular characterization studies with simultaneous fundamental q uantitative kinetic studies. The dynamic nature of catalyst surfaces requir es that both sets of information be obtained for a complete fundamental und erstanding of catalytic phenomena under practical reaction conditions. Seve ral examples are chosen to highlight the capabilities of in situ Raman spec troscopy to problems in heterogeneous catalysis: the structural determinati on of the number of terminal M=O bonds in surface metal oxide species that are present in supported metal oxide catalysts; structural transformations of the MoO3/SiO2 and MoO3/TiO2 supported metal oxide catalysts under variou s environmental conditions, which contrast the markedly different oxide-oxi de interactions in these two catalytic systems; the location and relative r eactivity of the different surface M-OCH3 intermediates present during CH3O H oxidation over V2O5/SiO2 catalysts; the different types of atomic oxygen species present in metallic silver catalysts and their role during CH3OH ox idation to H2CO and C2H4 epoxidation to C2H4O; and information about the ox idized and reduced surface metal oxide species, isolated as well as polymer ized species, present in supported metal oxide catalysts during reaction co nditions. In summary, in situ Raman spectroscopy is a very powerful catalys t characterization technique because it can provide fundamental molecular-l evel information about catalyst surface structure and reactive surface inte rmediates under practical reaction conditions.