Syntéza a charakterizace hydrotalcit - zeolitových sloučenin

Abstract

This thesis was focused on the synthesis and characterization of novel hybrid materials composed of hydrotalcites and zeolites, aimed at application in environmental catalysis. The materials were synthesized via the co-precipitation method and subsequently calcined to form catalysts of the desired structure. The in-situ thermal decomposition of hydrotalcites on the zeolite surface was expected to allow the formation of well-dispersed copper oxides (CuO) supported on the zeolite. Both, hydrotalcites derived mixed metal oxides and zeolites show promising performance in the field of environmental catalysis. Therefore, the synthesis of novel hybrid materials and their calcination aim to combine the high surface area of zeolitic supports with the catalytic efficiency of copper oxides. As similar materials are not reported in the literature, the synthesis procedure requires careful optimization. Initially, the stability of zeolite structures in an alkaline environment under hydrotalcite synthesis conditions was evaluated. The main goal was to prepare hydrotalcite–zeolite compounds by combining two types of hydrotalcites with different copper loadings (25 and 35 mol.%) and with four different types of zeolites (ZSM-5 with theoretical Si/Al ratios of 6, 11.5, and 25, and zeolite Y with theoretical Si/Al ratio of 5.2) Characterization of the prepared materials was performed using the following methods: atomic absorption spectrometry (AAS), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), low-temperature sorption of dinitrogen, scanning electron microscopy (SEM), and hydrogen temperature-programmed reduction (H2-TPR). Samples were characterized before and after calcination at 550 °C. The characterization of reference materials (pure zeolites) and their comparison with the obtained hybrid compounds confirmed the structural and thermal stability of the zeolites under both synthesis and calcination conditions. The hydrotalcite phase formed via co-precipitation in the presence of ZSM-5 zeolites exhibited the typical layered structure, indicating that the zeolite support does not influence the formation of hydrotalcite. In the case of zeolite Y, confirmation of hydrotalcite formation required indirect evidence obtained through TGA analysis. Post-calcination characterization confirmed the formation of copper oxides; however, a more detailed description of their distribution and availability requires further investigation.