The Synthesis And Characterization Of Hydrotalcites And Studies On Catalytic Activities Of The Derived Composite Oxide

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 paper on hydrotalcites is increasing.Before our work, we looked up plenty of references and completed a review. In this review, We summarized the HTs' application in a broad spectrum of organic reactions, such as base catalyst, redox catalyst and catalyst support material and all kinds of synthesis methods with 60 references.A series of MgFe hydrotalcite-like compounds were synthesized by coprecipitation. XRD,DTA,TG and Chelatometry were used to research the composition and structure of the products. The results of the XRD showed that the hydrotalcites with Mg/Fe molar ratios of 2 to 4 have the nice crystal form and high purity. TG-DTA results revealed that the decomposition of the hydrotalcite samples proceeded in two stages, corresponding to the two endothermic peaks around 175℃ and 353℃, respectively.The results of the elementary analysis exhibited that Mg/Fe molar ratios in MgFe hydrotalcite-like compounds and Mg/Fe molar ratios in reagent are the same. According to the results of TG-DTA and elementary analysis ,we presumed the molecular formula of MgFe hydrotalcite-like compounds.NiFe and MgFe hydrotalcites were synthesized by coprecipitation. The decomposition of the hydrotalcite samples was investigated by using TG-DTA .The changes of the physico-chemical property of the hydrotalcite following increasing the calcination temperature were investigated.The results revealed that after calcination at 500℃, the hydrotalcites were transformed into NiFeO mixed oxides and MgFeO mixed oxides, respectively. The mixed oxides exhibited the same XRD patterns as that of NiO and MgO, respectively.Two series of Mg-Fe-M and Ni-Fe-N hydrotalcites were synthesized by coprecipitation. After calcination at 500°C, two series of hydrotalcites were transformed into mixed oxides. The catalytic activities of the mixed oxides for catalyzing the dehydrogenation and dehydration of ethanol are tested by applyingmicrocatalytic-chromatographic technique. We find that the concentration of basic site is much denser than that of acid site on the surface of all catalysts except Mg-Fe-Zn and Ni-Fe-Zn.