FT-IR studies of zeolite materials: characterization and environmental applications

Synthetic zeolites are used widely throughout the petroleum refining and chemical process industries as selective adsorbents, catalysts and ion exchangers. The research described in this thesis focuses on the characterization and environmental applications of faujasite zeolites, including nanocrystalline Y zeolites that have particle sizes less than 100 nm.

In Chapter 3, photooxidation of cyclohexane and cyclohexene using molecular oxygen in BaY is investigated as a green chemical process. The reactivity and selectivity in photooxidation reactions are examined as a function of reactant, oxidant and irradiation wavelength. A major portion of this thesis involves the use of nanocrystalline zeolite catalysts in deNOx reactions. Nanocrystalline zeolites with increased external surface areas are synthesized and characterized with a variety of techniques, including transmission FT-IR spectroscopy, sorption of probe molecules and microscopy (Chapter 4). There are a greater number of silanol groups and extra framework aluminum (EFAL) species, which are important in applications as adsorbents and catalysts, on the external surface of nanocrystalline NaY zeolites relative to commercial micrometer-sized NaY.

In the absence of oxygen, the selective catalytic reduction (SCR) of NO2 with propylene at low temperature results in the complete reduction of NO2 to N2 and O2 in nanocrystalline NaY zeolite with a particle size of 80±30 nm (Chapter 5). It is revealed that silanol groups and EFAL sites on the external surface of nanocrystalline NaY provide additional adsorption sites for propylene and NO2. EFAL species are found to be important for SCR reactions. This is further supported by the studies using nanocrystalline NaY with a particle size of 23 nm as a deNOx catalyst with propylene (Chapter 6) and urea (Chapter 7) as reducing reagents. In the presence of an excess amount of oxygen, nanocrystalline NaY appears to be a better SCR catalyst than commercial NaY. Silanol groups and EFAL species are found to be responsible for the better performance of nanocrystalline NaY relative to commercial NaY zeolite. Thus the increased external surface of nanocrystalline zeolites can be utilized as a reactive surface with unique active sites for catalysis.