Synthesis and characterization of Zn/Al and Pt/Zn/Al layered double hydroxides obtained by the sol-gel method

The influence of the nature of the Zn, Al and Pt precursors, and of the temperature of precipitation and aging have been studied in connection with the preparation of Zn/Al and Pt/Zn/Al layered double hydroxides (LDH) by the sol-gel method. Whatever the precursors the XRD analysis shows that LDH is formed at the expense of ZnO when the precipitation and aging temperatures decrease from 353 K to 273 K. Moreover, chemical composition and TG analysis suggest the presence of weak amounts of hydrozincite, hydrozincite-like and Al(OH)3 phases. When the precursors are Zn acetate-2-hydrate or Al acetylacetonate the amount of LDH reaches a maximum of 50 mol% at 273 K. At variance, about 90 mol% of LDH is obtained when using Zn acetylacetonate and Al isopropoxide as precursors, which are precipitated at 273 K. This proportion is slightly improved for the Pt-containing sample prepared under the same conditions. The specific surface areas of the different samples obtained after calcination at 723 K increase with their LDH content, reaching values of 110-120 m2 g−1. They make them particularly attractive for catalytic applications.