Linde Type-A zeolite synthesis and effect of crystallization on its surface acidity

摘要

An alumino-silicate zeolite, Linde Type-A (LTA) has been prepared from aluminium powder and sodium metasilicate by hydrothermal process. The zeolite was characterized by FTIR and X-ray diffraction (XRD) analysis and by measuring the surface acidity using KOH as adsorbate. The surface acidity of LTA zeolite varied greatly with varying synthesized conditions such as crystallization temperature, crystallization time and K~+ ion adsorption period. The Bronsted acid site on the zeolite surface increased with increasing crystallization temperature and the maximum surface acidity was obtained at 100°C Crystal growth was also dependent on the crystallization time. The surface acidity increased with increasing crystallization time. The maximum surface acidity due to the maximum consumption of the K~+ ion was observed at 48 h adsorption time and the value was found to be 0.9 meq/g when Si:Al was 50:50. It was seen that the surface acidity was more pronounced when ammonium hydroxide solution as adsorbate and agitated crystallization condition were used. The surface acidity of the commercial LTA zeolite was compared with the surface acidity of the synthesized LTA zeolite. It was found that the surface acidity of synthesized LTA zeolite is slightly greater than commercial LTA zeolite.