EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Layered double hydroxides (LDHs) are widely applied in commercial products as catalysts, catalyst support precursors, absorbents and so on. Usually, after calcination at moderate temperature (such as 300-500 °C, highly depending on composition), the layered double oxides (LDOs) obtained are able to reform LDH when in contact with solutions containing anions. Investigation of the reformed LDHs and their properties is very important for the recyclability of reactions catalyzed by LDOs.

The differences in the rehydration of metal oxides derived from Mg-Al layered double hydroxides (LDHs) at high calcination temperatures (600-900 °C) were studied in vapor and liquid (both pure water) condition at room temperature for 6-48 h. XRD patterns showed that the metal oxides obtained from thermally treating LDHs can rehydrate into LDHs under the above conditions. However, the rehydration process in vapor condition is slower than that in liquid condition. When the calcination temperature was increased to 900 °C a spinel phase appeared, which remained in the particles under both vapor and liquid rehydration conditions. Other characterizations including IR, SEM and N2 adsorption were applied to elucidate further differences between the rehydrated samples, produced under different conditions. Differences between as synthesized LDH and rehydrated LDHs were observed, illustrating that the process of the rehydration of the LDO into the LDH forms a new LDH rather than reconstructing it into the former LDH. Moreover, research also suggested that even high temperature calcined samples need to be stored carefully in case the rehydration reaction happens at room temperature and ambient, moist containing atmosphere.