Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.

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M.Sc. (Chemistry) / The usefulness of vibrational spectroscopy in identifying surface species, determining adsorbate structures and studying surface reactions has been widely demonstrated. Most of the infrared work on surface species is currently performed using the transmission technique with very thin pressed discs of self supported catalysts. This technique has several disadvantages of which the limited transmission of many catalysts and the loss of available surface area during sample preparation, are but a few. Because of these limitations, information obtained from conventional transmission studies has limited application in terms of understanding and/or improving commercial catalysts. An alternative method which does not suffer from these limitations is Diffuse Reflectance Infrared Fourier Transform Spectroscopy or DRIFTS as it is commonly known. This spectroscopic technique has only recently been extended into the infrared region because of the progress in FTIR instrumentation. Because this is a reflectance technique, the sample is most appropriately a powder, so a high surface area catalyst in its normal powder form can be examined directly without altering its state. A spectroscopic facility which is capable of obtaining DRIFT spectra of adsorbed species at high sensitivity and in situ operating conditions has been established. This facility consists of an FTIR instrument fitted with a diffuse reflectance unit, a heatable high pressure cell and the necessary attachments for gas flow, pressure and temperature control. The project work consisted of an investigation into CO-adsorption on supported rhodium catalysts. By using different combinations of the three parameters: reduction temperature, metal loading and support material, several different species of surface bonded CO have been identified. The three rnein species being: geminal dicarbonyl, linear and bridging CO. As each of these species is associated with a specific Rh-site, conclusions concerning the oxidation state and dispersion of the Rh on the surface could be made. The thermal stability of the different CO-species was studied by increasing the catalyst temperature in a linear fashion. It was found that the geminal dicarbonyl species was the most stable in an oxidising atmosphere. The interconversion of chemisorbed . CO-species at higher temperatures has been spectroscopically verified. A mechanism for CO-dissociation on Rh-catalysts was proposed. In additional experiments the sensitivity of DRIFTS for adsorbed hydrocarbons has been demonstrated. It is concluded that this spectroscopic technique has been proven to be of great significance in the study of surface species on heterogeneous catalysts.

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Optimization of capillary gas chromatography-Fourier Transform Infrared (GC-FTIR) spectrometry has been accomplished by studying various columns, lightpipe designs, FTIR detectors and spectroscopic parameters. For adequate separation of complex samples the efficiency of WCOT (Wall Coated Open Tubular) fused silica capillary columns was found to be unmatched by packed columns or wide bore glass capillaries. A consequence of using more narrow bore columns, however, is lower sample capacity and less IR detectability. Two 6 cm light pipes and a more narrow 40 cm lightpipe were compared with respect to both optical throughput and eluent band broadening. FTIR spectroscopic parameters such as mirror velocity and number of scans coadded were examined in order to achieve an optimum signal to noise ratio. The complexity of a particular sample has been shown to dictate certain spectroscopic parameters. The sensitivity differences of two liquid-nitrogen cooled FTIR detectors used in the GC-FTIR experiments have been determined with reference to using them with either a long or short lightpipe. The capability of optimized capillary GC-FTIR has been demonstrated in the analysis of model compound mixtures and comp lex petroleum products including test aviation jet fuels. Major attention was given to the detection and identification of aliphatic and aromatic components in the highly complex samples. Computerized library search routines have been used to tentatively identify eluting components by infrared spectral matching to quality vapor phase library file spectra. Gas chromatography-mass spectrometry (GC-MS) data are also included for the same jet fuel samples to directly compare extent of information provided and relative spectroscopic sensitivities. / Master of Science

High performance liquid chromatographic separations employing on-line flow cell Fourier transform infrared spectroscopic detection were developed for polar compounds including phenols, alcohols, amines and azaarenes. Detection by FTIR gave information concerning hydrogen bonding and solvent effects occurring during the separations in addition to giving structural information about eluted species to aid in identification. Both analytical size and microbore normal phase columns were employed. Such experimental considerations as column overload, injected minimum detectable quantities, the use of analytical vs. microbore columns and flow cell pathlength were examined. The developed HPLC-FTIR systems were applied to the analysis of several coal liquefaction samples for heteroatom content. Confirmatory and additional information concerning the samples were provided by field ionization mass spectrometry, gas chromatography/ mass spectrometry and reversed phase liquid chromatography employing UV detection. An equation relating reversed phase retention times to structural parameters was developed and applied to the analysis of the coal-derived samples. Two process solvents were found to contain primarily alkyl-substituted phenols in addition to azaarenes such as pyridine and quinoline. Some non-distillable coal-derived samples were found to contain azaarenes such as alkyl quinolines. Evidence was also found concerning the presence of hydroxypyridine type compounds and the incorporation of process solvent molecules into the coal structure during liquefaction. / Ph. D.

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