Fundamental study of base catalysts for aldol condensation reaction

Zeolites containing cesium beyond ion-exchange capacity have been recognized as strong solid base over last few decades. They demonstrated excellent catalytic activity and selectivity in important reactions such as olefin double-bond isomerization. However, the local structure and composition of the active site in supported cesium catalysts is still undetermined. Experimental evidence suggests that the active site is located inside the zeolite micropore, but the detailed structure of the occluded species is not known. One of the objectives of this project was to study the local structure of cesium oxide with density functional theory (DFT). The bulk crystals and low index surfaces of three cesium oxides (Cs2O, Cs2O2, and CsO 2) were constructed and examined by gradient-corrected periodic density functional theory. Mulliken charge analysis ranked the basic strength of the three oxides as: Cs2O > Cs2O2 > CsO2. The adsorption of CO2 on the surfaces of the oxide was also investigated. Results showed that a cesium-terminated Cs2O {lcub}001{rcub} surface weakly adsorbed CO2 with an adsorption energy of -4.1 kJ mol-1. The oxidized Cs2O {lcub}001{rcub} surface showed much stronger adsorption energy of -95 kJ mol-1. The Cs 2O {lcub}010{rcub} surface with both Cs and O atoms exposed adsorbed CO2 strongly, with an adsorption energy of -284 kJ mol-1. The adsorption of CO2 on the {lcub}001{rcub}and the {lcub}100{rcub} surfaces of Cs 2O2 had adsorption energy of -101 and -186 kJ mol -1, respectively. The CsO2 surface failed to adsorb CO 2. Although the adsorption energy of CO2 on a Cs2O 2 surface calculated by DFT closely matches other's results from microcalorimetry measurements on cesium-loaded zeolites, there is no experimental evidence for peroxide in zeolite cages. DFT cluster calculations were used to determine the lowest energy structure of a candidate cesium oxycarbonate.; Alkali metal oxides and alkali-modified oxides and zeolites catalyze the vapor phase aldol condensation of propionic acid (PA) with formaldehyde (FA). The product of this reaction is methacrylic acid (MAA), a high demand intermediate in the production of commercial polymers (polymethyl methacrylate). State-of-the-art catalysts for this reaction include cesium supported on silica with bismuth added as promoter (Cs/Bi/SiO2) and niobium oxide impregnated silica (Nb2O5/SiO2). However, both catalysts suffer from loss of activity in the presence of water. Thus, another objective of this dissertation was to explore the catalytic activities and water tolerance of various metal oxides in the aldol condensation of PA with FA. (Abstract shortened by UMI.)...