Ultraviolet Raman spectroscopy of catalysts: Adsorption and coke formation in zeolites and vibrational spectra of supported metal oxides

The primary goal of this dissertation is to study the physicochemical and catalytic properties of zeolites and supported metal oxide catalysts using UV Raman spectroscopy.; In order to reduce the thermal degradation and possible photodecomposition of adsorbates by UV radiation, we have developed a novel fluidized bed method for measuring the UV Raman spectra of catalysts and adsorbates. The UV Raman spectra of various organic compounds adsorbed in zeolites H-USY and H-ZSM-5 are recorded. When measurements are performed on stationary and spinning samples, the Raman spectra show the presence of coke, a typical end product of heat and photochemistry. In contrast, the Raman peaks of the unreacted adsorbates dominate the spectra measured using the fluidized bed method. These results indicate that the fluidized bed technique is a good method for measuring UV Raman spectra of catalysts and adsorbates.; The formation of coke in the methanol-to-gasoline conversion over zeolite H-ZSM-5 causes deactivation of the catalyst. To gain insight into the formation of coke, we have studied this reaction using UV Raman spectroscopy. The Raman spectral changes suggest coke is produced from conjugated olefins via cyclopentadiene intermediates. Aromatic compounds in gasoline may also be produced from cyclopentadienes.; The adsorbate-induced structural changes of zeolites may alter the molecular sieving characteristics of these materials which ultimately affect their performance as catalysts and adsorbents. We have quantified the adsorbate-induced structural changes of zeolite H-RHO using UV Raman spectroscopy. The Raman spectra of the zeolite after the adsorption of water, methanol or acetonitrile are consistent with an increase in the average T-O-T angle of the zeolite of 5–8°. The adsorption of ammonia, on the other hand, decreases the average T-O-T angle by 5°.; Because of certain advantages of UV Raman spectroscopy over visible Raman spectroscopy, recently there is a strong interest in using the former technique for studying the properties of supported metal oxide catalysts. We have made a careful comparison between the UV and visible Raman spectra of CrO ₃/Al₂O₃, V₂O₅/Al₂O ₃ and MoO₃/Al₂O₃. Generally the relative Raman band intensities in these two sets of spectra are different. These differences are attributed to UV resonance enhancement effects.