Preparation of alumina supported palladium catalysts by sol-gel method

The chemical reactivity of the aluminium-sec-butoxide (ASB) and the palladi um acetylacetonate Pd(acac)(2), used as precursors for the preparation of t he alumina supported palladium catalysts by sol-gel method was investigated by the spectroscopic study of the precursor mixture during ageing, using F TIR, UV-VIS and Al-27 NMR. The obtaind results showed that acetylacetonate ligands were linked to aluminum when the mixture was aged at 40 degreesC. T his was proved by the bands observed at 1530 and 1600 cm(-1) in the FTIR sp ectra, the band obtained at 289 nm in the UV-VIS spectra and the Al-27 NMR sharp peak at 3 ppm. Furthermore, in order to avoid the Pd(acac)(2) reducti on to metallic palladium by the SB occurring when the mixture is aged for 3 h, an optimum ageing time should be selected. The precursors modification and the preservation of the palladium oxidation state during ageing could b e the required conditions to create a bond between palladium and aluminium during the gelation step. This should be the reason of the thermal stabilit y improvement of the alumina supported palladium catalyst prepared by the s ol-gel method.