Thermal, texture and reconstruction properties of hydrotalcites substituted with Na⁺ or K⁺ ions

Abstract

In this work, the research has been conducted on the direct preparation and characterization of as-synthesized and calcined Mg–Al hydrotalcites substituted with Na⁺ or K⁺ ions, but only in a narrow 225–525 °C temperature range, the thermal, texture and reconstruction properties of products were explored. Mg–Al hydrotalcites substituted with Na⁺ or K⁺ ions having Mg/Al molar ratio of 2.0 were prepared by simple synthesis techniques, namely (1) hydrothermal synthesis (200 °C; 1 h) and (2) calcination at 225, 325, 425, 475 and 525 °C temperatures for 4 h and at 475 °C temperature for 4–72 h. It was determined that alkaline additives had a positive effect on both the formation and the memory effect of hydrotalcite. However, they strongly affected the specific surface area parameters, because the obtained S _BET and ∑ΔV _p values were much lower than in a pure sample. It should be noted that hydrothermally treated and then calcined hydrotalcite samples only partially reconstructed the layered structure of hydrotalcite. Additionally, the thermal decomposition of modified hydrotalcites and the reconstruction of the decomposed products in the presence of water have been investigated with respect to the structure (XRD), texture and surface area (BET) and thermal properties (DSC).