Studies of tartaric acid modified nickel supported catalysts for enantioselective hydrogenation reactions

摘要

This thesis investigates the catalytic properties of tartaric acid‐nickel supported catalysts, obtained from hydrotalcite‐like compound precursors, in the enantioselective hydrogenation of methyl acetoacetate to methyl 3‐hydroxybutyrate. Variables of reaction during modification such as pH and tartaric acid concentration, as well as Ni particle size above a minimum threshold of ca. 20 nm, proved not to have a major effect on enantioselectivity. However, the nature of the cations constituting the catalyst support was found to influence the enantioselectivity observed. Specifically, when iron or chromium were constituents of the supporting oxide matrix, enantioselectivities were found to be much higher. For systems containing nickel, magnesium (or zinc) and aluminium as the cations present in the parent hydrotalcite phase, when a series of materials of the same composition obtained from different synthetic methods, the urea hydrolysis method leads to catalysts with enantiodifferentiation ability, whereas materials prepared by the coprecipitation method does not. Also, this thesis researches the use of different types of ordered mesoporous silicas as supports of tartaric‐acid nickel in the aforementioned reaction. Even though the techniques of metal deposition explored did not allow incorporation of Ni in the internal surface of the materials, it was found that the morphology of the support plays an important role in enantioselectivity. In addition, for a given material, the incorporation of Ni via solid state reaction resulted in a catalyst with improved catalytic properties compared to one prepared by wet impregnation techniques.