In situ investigation of solid -liquid catalytic interfaces by attenuated total reflection infrared spectroscopy

In recent years, there has been an increased desire to implement heterogeneous catalysis in the fine chemicals and pharmaceuticals industries. This is being driven by the goal of developing environmentally friendly ("green") approaches for the production of such specialty products. One of the main obstacles in the establishment of heterogeneous catalysis in these industries is the difficulty in reproducing homogeneous catalyst properties, such as selectivity and product quality. Monitoring surfaces of solid catalysts in the liquid phase can provide much-needed insight into these reactions and help lead to implementation of heterogeneous catalysis in these industries.;One approach that is beginning to be used for surface studies of heterogeneous catalysts is attenuated total reflection infrared (ATR-IR) spectroscopy. The prospects of ATR-IR were tested and a thin (ca 10 mum) films of a 5 wt% Pt/gamma-Al2O3 catalyst were deposited onto the surface of a germanium waveguide. The very small support particles (average size 37 nm) form a stable film that does not peel from the waveguide when exposed to flowing liquid. The catalyst film is thick enough so that essentially all of the IR electric field is attenuated within the film, thus decreasing bulk liquid signals.;The objective of this dissertation was to further apply the ATR-IR approach for the study of surface chemistry at solid catalyst-liquid interfaces. We have extended the ATR-IR approach to examine adsorption and hydrogenation of CO, formaldehyde and nitriles (C2H3N, C4H 7N) in various liquid solvents (H2O, C2H 5OH, C6H14) on a Pt/Al2O3 powder catalyst. In situ ATR-IR studies under reaction conditions provide previously unavailable information about the nature of surface species and important solvent effects. The data was analyzed using multivariate analysis, which applies classical least squares (CLS) and partial least squares (PLS) in order to correlate spectral changes with known sources of experimental variation (i.e., time and concentration of solution species).;The main reaction emphasized was nitrile hydrogenation (i.e., butyronitrile and acetonitrile) to form various amines. Nitrile adsorption on Pt/Al 2O3 in hexane was tested in order to determine the effect of liquid-phase concentration on the adsorption mode (conformation) and coverage. The nitrites were found to adsorb on the Pt catalyst in both a linear and tilted configuration. The latter conformation was found to be reactive towards hydrogen, suggesting that it might play a role in nitrite hydrogenation. The introduction of hydrogen into the nitrite solution resulted in the formation of primary amines, which strongly adsorb the catalyst surface. Similar studies were performed on amine adsorption and hydrogenation, revealing a strong interaction of this species with both the Pt and the support.