| Hydrotalcite-like compounds are a sort of anionic clays with double-layer structure. Because of their special structure, they have exhibited excellent properties as a new type of catalytic materials and received much attention. Recently, the research work about hydrotalcites is proceeding. Before our work, we looked up plenty of references and completed a review. The review mainly consists of four sections: 1. The introduction of hydrotalcites. 2.The main techniques of synthesis and characterization of hydrotalcites. 3. The brief introduction of the derived composite oxides. 4. The catalytic application of hydrotalcites and their derived composite oxides. In this review, the information about the hydrotalcites and their application in catalysis is reported detailedly. It also includes some typical or special research techniques and recent achievements in this area.Two series of carbonate pillared ZnCr and CoCr hydrotalcites with different adding Zn/Cr or Co/Cr molar ratios are synthesized by coprecipitation . XRD> IR> DTA-TG and spectrophotometric techniques are used in research of the composition and structure of the products.The results of the XRD measurement certify that the hadrotalcites have been formed. They also show that both the ZnCr and CoCr hydrotalcites have a kind of ideal structure in which the MVM1" molar ratios are required to be 2~3. In the synthesis, if the adding M"/Mni molar ratios conform to the requirement, we can get the hydrotalcites with nice crystal forms and high purity. Otherwise, the crystal forms of the hydrotalcites in the products will be poor, and some impurities generated by the surplus metal ions which can't enter the structure of hydrotalcites will remain in the products.The results of IR analysis tell us it is the C032" that has been intercalated between the double layers of hydrotalcite-structure. There are the peaks reflecting M-0 vibration in hydrotalcites in all of theIR spectra of the tested samples. Through the IR analysis, we are more assured that the synthesis of carbonate pillared hydrotalcites is successful.It can be seen from the DTA-TG curves that all of the samples have two endothermic decomposition stages. The hydrotalcites will lose weight in the two stages respectively. Different samples exhibit different rates of weight loss. Furthermore, from the analysis, we can know the thermostability of the hydrotalcites with good crystal forms and high purity is higher than that of others.We have used the spectrophotometric technique to analyze the content of two kinds of metal elements in the products. From our experiments, spectrophotometric analysis is proved to be a practicable method to research these hydrotalcites. The results of the elementary analysis show that the M"/M"' molar ratios in some of the products accord with the adding M'VM1" molar ratios in synthesis. But in other products, there are some discrepancies to different extent between them. In the dissertation, we have given the possible reasons causing these phenomena. At last, on the basis of the data acquired by both the TG measurement and the elementary analysis, we have speculated the composition of some of the products and the formulae of hydrotalcites in the products.After calcined at 450℃, the ZnCr hydrotalcites are converted into derived composite oxides. Besides the ZnO phase , the spinel phase ZnC^CU is detected by XRD measurement, and the content of the spinel is increasing with the increasing amounts of the Cr in the hydrotalcite precursors.The catalytic activities of the derived composite oxides for catalyzing the dehydrogenation and dehydration of ethanol are tested by applying microcatalytic-chromatographic technique. We find that the concentration of basic site is much denser than that of acid site on the surface of the catalysts. To this reaction, IZnCr(O) has the highest catalytic activities. The activities of these catalysts generally decreased with the decreasing amounts of Cr in them.
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