Investigation of layered double hydroxides type ZnMgAl-carbonate and derivates.

Layered double hydroxides (LDHs) or hydrotalite-like compounds belong to a class of synthetic two-dimensional inorganic materials with lamellar structures, where the hydroxyl-hydrated compounds are formed by chemical substitution of divalent ion of the brucite-like octahedral layers by trivalent ions [1]. The LDH are represented by the general formula, Figure a , where M2+, M3+ are divalent and trivalent cation and Am- is interlayer anion responsible by charge balancing, the range of divalent and trivalent ions (x) varies normally between 0.17 a 0.33. According Montanari and co-works [2] compounds type ZnAl-hydrotalcites (ZnAl-HT) have relevant industrial interest; however the scientific literature concerning this material as catalysts or catalyst precursor is scarce. Based on this fact, in the present communication we will present a studied on how the variation in percentage of Zinc in a ZnMgAl-HT catalyst precursor can influence the formation of mixed oxides after calcination. The ZnMgAl-HTs, Figure b , y=5, 10,15,20,25,50,75 and 100% were prepared by co-precipitation and urea method. Mg-Zn/Al mixed oxides were prepared from calcinations of hydrotalcites precursors at 500⁰C for 4 hours. The material synthesized were characterized by X-ray powder diffraction, the measurements were carried out in Bruker D8 DaVinci diffractometer, equipped with CuKα radiation , LynxEye linear Position Sensitive Detector, Ni-filter. Data was collect between 8 and 80⁰ in 2θ with step size of 0.02⁰ and the count time of 0.05 per step. Soller slit 2.5⁰ of divergence and 0.2 mm primary slit were used. For the ZnMgAl-HT samples the measurements were performed at different temperatures, range 25-1200⁰C, heating rate 5⁰C/min. It was observed differences among XRD patterns for y greater than 25% of Zn in urea method at 500⁰C, and for co-precipitation method just for the substitution at 50 and 75% of Zn. These results suggested that the increase in Zn percentage change the structure of calcinated samples.