Abstract
Post-synthesis modification of zeolite materials can be an effective way to enhance desirable physical and chemical properties. Specifically, altering the silicon to aluminum ratio and the introduction of a unique heteroatom are primary goals of the Crawford research group. The goal of this research project was to establish the necessary tools to modify zeolites, starting from Zeolite Y. Zeolite Y was used as the test material for studying hydrothermal dealumination and subsequent spontaneous realumination. These two processes were studied using FTIR and magic angle solid state NMR techniques. The degree of hydrothermal dealumination can be controlled based on the evidence presented for the dealumination of zeolite Y Si/Al 5.2 and 12. The rates of dealumination were calculated from FTIR measurements for zeolite Y Si/Al 5.2 and 12 to be ~1 Si/Al unit and ~3 Si/Al units per hour of hydrothermal treatment respectively. The degree of dealumination was shown to be dependent on the amount of time exposed to hydrothermal dealumination conditions. A pathway for dealumination is proposed for zeolite Y Si/Al 5.2 based on 29Si NMR data. The proposed pathway suggests that the rate of dealumination increases for silicon with a greater number of neighboring Al atoms compared to those with fewer Al neighbors. Spontaneous realumination, with ambient temperature and ambient relative humidity, was observed for both zeolite Y Si/Al 5.2 and 12 through use of FTIR measurements. Realumination was broken down into three periods; short-term 1, short-term 2, and long-term. All three phases were observed in FTIR and 29Si NMR spectra during realumination of zeolite Y Si/Al 5.2 and 12. The observation that aluminum readily reinserts into the formed dealumination defect sites strongly suggests that heteroatom insertion into dealuminated zeolites is possible. It was shown that metal ions could be inserted into defect sites created upon dealumination based on the increase in Si/Al ratios during spontaneous realumination.