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In this mini-review, we describe the currently available literature concerning synthesis and applications of layered double hydroxides (LDHs) containing rare earth cations (RE-LDHs), focusing on the catalytic activity of those compounds. The lack of studies of some rare earth elements (REE) and the insufficient knowledge of their catalytic activity in the structure of LDHs indicate the need for further research.

Cerium-containing cobalt-aluminum layered double hydroxide was successfully synthesized via coprecipitation followed by hydrothermal treatment. Molar ratios of metal cations were predetermined as following: Co 2+ /(Al 3+ + Ce 3+ ) = 3 and Ce 3+ /(Al 3+ + Ce 3+ ) = 0.05. According to X-ray diffraction data, the obtained sample was well crystallized single-phase product with a hydrotalcite-like structure. The presence of cerium was confirmed by elemental analysis. The synthesized material consisted of hexagonal plate-like particles with an average size of 277 nm. The study of thermal behavior showed that the compound decomposed with the formation of oxides mixture, which is typical for layered double hydroxides. Its rehydration ability was expressed very weakly and the "memory effect" was observed only after heat treatment at a temperature not higher than 200 • C.

For the first time, nickel-aluminum layered double hydroxides containing holmium, thulium or lutetium cations were successfully synthesized via the coprecipitation method followed by hydrothermal treatment. X-ray diffraction data show the formation of hydrotalcite-like structures with the absence of impurity phases. The presence of lanthanides is confirmed by energy-dispersive X-ray spectrometry. Assumed empirical formulae for these compounds are [Ni0.796Al0.193Ho0.011] [(NO3)0.204·yH2O], [Ni0.808Al0.178Tm0.015] [(NO3)0.193·yH2O] and [Ni0.765Al0.219Lu0.016] [(NO3)0.235·yH2O]. These novel layered compounds demonstrate the fundamental ability of doping hydrotalcite-like compounds with any lanthanide cation, which gives rise to the synthesis of new materials with specific properties.

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