Preparation of CuMgAl Hydrotalcite-Like Compounds at Low MII/MIII Molar Ratios
CuMgAl hydrotalcite-like compounds with MII/MIII=1 and Cu/Mg molar ratios 3:1, 1:1, 1:3 and 1:19 were synthesized by coprecipitation and characterized by elemental analyses, XRD, SEM, FT-IR, TG-DTA and BET surface area test. XRD of all samples showed that Cu/Mg/Al hydrotalcites without any detectable impurity phase could be obtained at Cu/Mg molar ratios 1:3 and 1:19, however, at high Cu/Mg molar ratios 3:1 and 1:1, Al(OH)3 and copper hydroxides or oxides were obtained in the products besides the hydrotalcites, owing to the strong Jahn-Teller effect of Cu2+. It was also found that the crystallinity of the solids increased with an increase in copper content. IR results showed that the symmetry of carbonate was reduced from D3h to lower symmetry at high copper content. The thermal stability of the compounds decreased with increasing copper content, as indicated by TG-DTA measurements. Further thermal decomposition analyses showed that the surface area reached the maximum at calcination temperature of 500 ° C and mixed metal oxides with crystalline MgO, amorphous Al2O3 and highly dispersed CuO were obtained.
Alan K.T. Lau, J. Lu, Vijay K. Varadan, F.K. Chang, J.P. Tu and P.M. Lam
Y. M. Shen et al., "Preparation of CuMgAl Hydrotalcite-Like Compounds at Low MII/MIII Molar Ratios", Advanced Materials Research, Vols. 47-50, pp. 898-902, 2008