Nature of alkali zeolites in base catalysis and oxidation catalysis

Alkali-loaded zeolites have been recognized over the last two decades as strong base catalysts. However, the nature of the basic sites in these materials is still unclear. One of the main objectives of this research was to probe number density; basic strength, chemical composition and atomic structure of the basic sites in alkali-loaded zeolites. In particular, cesium-exchanged zeolite X was impregnated with cesium acetate (Cs(Ac)/CsX) or cesium carbonate (Cs2CO3/CsX) and subsequently calcined to yield a basic zeolite catalyst. The Raman spectra of calcined Cs(Ac)/CsX and Cs2CO 3/CsX exhibited a new peak at 1036 cm-1 associated with the occluded species. No evidence for cesium peroxide or superoxide was observed. Adsorption and step-wise temperature programmed desorption of CO 2 revealed an adsorption stoichiometry of 1 CO2 per 4 occluded cesium atoms. Results from these characterization studies suggest that the occluded cesium species in both samples is an oxycarbonate, which is a metastable intermediate between cesium carbonate and stoichiometric cesium oxide.; The isomerization of 1-butene to cis- and trans-2-butene was catalyzed by the basic zeolites as well as MgO and Cs(Ac)/gamma-Al2O 3. Although CO2 poisoned the active base sites for catalysis, pretreatment of a basic catalyst with O2 at 373 K did not. Co-feeding O2 with 1-butene at 373 K, however, completely deactivated the base sites. Analysis of the reactor effluent at 473 K and the IR spectrum of the catalyst indicated the formation of carbon dioxide, which irreversibly adsorbed on the basic sites of the catalyst. Deactivation of basic catalysts by O2 is proposed to occur through low temperature oxidation of 1-butene to carbon dioxide, which strongly adsorbed on the active sites.; Exploration of butane and butene oxidation with O2 over various zeolites revealed that ion-exchanged samples were responsible for oxidation activity. The occluded oxycarbonate did not catalyze the oxidation reaction. Among the ion-exchanged zeolites, CsX and NaX exhibited the highest reaction rates in butene oxidation. The butane oxidation rate on CsX and NaX was much lower than that of butene oxidation, which is consistent with the lower ionization potentials and C-H bond energies of alkenes compared to those of alkenes. An intriguing aspect of the hydrocarbon oxidation studies is that CO was not observed. Therefore, the oxidation of CO to form CO2 was also explored over ion-exchanged zeolites.; The preferential oxidation (PROX) of CO in H2 with high selectivity is a commercially relevant and challenging reaction. The reaction kinetics of CO oxidation suggest that CO and O2 competitively adsorb on the active sites and that the exchangeable cation has great effect on the rate of oxidation. The selectivity of the PROX reaction (CO:O2:H 2 = 1:1:21.5) was 100% to CO2 in the temperature range from 423 K to 473 K. However, the selectivity decreased to 40% at 573 K. The presence of CO severely inhibited H2 oxidation over zeolites, which accounts for the high selectivity of zeolites in preferential CO oxidation.