A series of Zn–Al hydrotalcites with Zn/Al molar ratios of 1, 2, 3 and 6 were prepared by co-precipitation method. TG-DTG results showed that the hydrotalcites decompose in two stages, corresponding to the two endothermic peaks around 180 and 220°C. After calcination at 400°C, the samples were converted into Zn–Al mixed oxides with the only XRD pattern of ZnO, except for the sample with the ratio of 6. The Zn–Al mixed oxides possess similar surface acidity revealed by microcalorimetric adsorption of NH3. The basicity of the samples increases with the order: ZnO>6Zn/Al>1Zn/Al>Al2O3.
Authors:N. Voyer, A. Soisnard, Sara Palmer, W. Martens, and R. Frost
Zn-Al hydrotalcites and Cu-Al hydrotalcites were synthesised by coprecipitation method and analysed by X-ray diffraction (XRD)
and thermal analysis coupled with mass spectroscopy. These methods provide a measure of the thermal stability of the hydrotalcite.
The XRD patterns demonstrate similar patterns to that of the reference patterns but present impurities attributed to Zn(OH)2 and Cu(OH)2. The analysis shows that the d003 peak for the Zn-Al hydrotalcite gives a spacing in the interlayer of 7.59 Å and the estimation
of the particle size by using the Debye-Scherrer equation and the width of the d003 peak is 590 Å. In the case of the Cu-Al
hydrotalcite, the d003 spacing is 7.57 Å and the size of the diffracting particles was determined to be 225 Å.
The thermal decomposition steps can be broken down into 4 sections for both of these hydrotalcites. The first step decomposition
below 100°C is caused by the dehydration of some water absorbed. The second stage shows two major steps attributed to the
dehydroxylation of the hydrotalcite. In the next stage, the gas CO2 is liberated over a temperature range of 150°C. The last reactions occur over 400°C and involved CO2 evolution in the decomposition of the compounds produced during the dehydroxylation of the hydrotalcite.
Authors:Jelliarko Palgunadi, Indri Yati, and Kwang Jung
induces the creation of active species during heat treatments. It is worth mentioning that highly dispersed nano-size copper particles, the active species of the methanol synthesis catalyst are readily generated from thermal decompositions of the Cu–Zn–Al-hydrotalcites