The Synthesis And Characterization Of Pillared Hydrotalcite And Their Mixed Oxides

Isopoly and Heteropoly anion-Pillared Hydrotalcites (HTLCs-POMs) are a new type of materials. They can be synthesized by ion-exchange method directly. Because both POMs and hydrotalcites have catalytic activities, their combination can improve each's catalytic activity and obtain multiple-founction catalysts. Several CuMgAlFe-POMs and CuMgAlFeM-POMs (M=La,Co) were synthysized by the ion-exchange method. The mixed oxides were derived from the calcination of HTLCs-POMs precursors. The synthesized compounds were characterized by XRD, FT-IR and TPR. The catalytic activity of the mixed oxides was evaluated by catalytic oxidation of carbon monoxide and catalytic reduction of nitrous oxide by carbon monoxide.The XRD results showed that all the HTLCs-POMs synthesized by ion-exchange method have good hydrotalcite structure. Near 2 θ =6.01 — 6.3 ° , there is a diffraction peak(d₀₀₃) of poly-anion with ion diameter of about 0.97⁰.99nm which is similar to that of Keggin ions reported in the literatures. The FT-IR analysis indicated that the NO₃^- of CuMgAlFe-NO₃ and CuMgAlFeM-NO₃ has disappeared and is taken place by POMs without changing their Keggin structures. On the same time, some stretching frequencies for the HTLCs-POMs have shifted to lower frequency, which attribute to the interaction of the brucite and POMs in the layer. TPR (Temperature Programmed Reduction) results showed that the reduction peaks of CuO, WO3 and MoO₃ have changed. Based on the results of catalytic avtivity test, it can be safely concluded that the existence state of active elements on the surface of catalysts has something to do with the temperature of reduction peaks. Those components that are highly distributed and have lower reduction temperature have higher catalytic activities.The activity evaluation results showed that with the intercalation of Isopoly and Heteropoly anions, the activity of the catalysts has been improved. The catalyst C-PW-500 exhibited high activity in the catalyticcombustion of CO. As far as N2O+CO is concerned, all of the catalysts exhibited lower activity because of most of the active component-CuO had lost during the ion-exchange process.