Thermal transformations of Cu–Mg (Zn)–Al(Fe) hydrotalcite-like materials into metal oxide systems and their catalytic activity in selective oxidation of ammonia to dinitrogen

Layered double hydroxides (LDHs) containing $Mg^{2+}$, $Cu^{2+}$ or $Zn^{2+}$ cations in the $Me^{II}$ positions and $Al^{3+}$ and $Fe^{3+}$ in the $Me^{III}$ positions were synthesized by co- precipitation method. Detailed studies of thermal trans- formation of obtained LDHs into metal oxide systems were performed using high temperature X-ray diffraction in oxidising and reducing atmosphere, thermogravimetry coupled with mass spectrometry and temperature-pro- grammed reduction. The LDH samples calcined at 600 and 900 $^{o}\textrm{C}$ were tested in the role of catalysts for selective oxidation of ammonia into nitrogen and water vapour. It was shown that all copper congaing samples presented high catalytic activity and additionally, for the Cu–Mg–Al and Cu–Mg–Fe hydrotalcite samples calcined at 600 $^{o}\textrm{C}$ rela- tively high stability and selectivity to dinitrogen was obtained. An increase in calcination temperature to 900 $^{o}\textrm{C}$ resulted in a decrease of their catalytic activity, possibly due to formation of well-crystallised metal oxide phase which are less catalytically active in the process of selective oxidation of ammonia.