Synthesis and characterization of Pt/Mg(Al)O catalysts obtained from layered double hydroxydes by different roiutes

Pt-containing Mg/Al Layered Double Hydroxides (LDHs) at different Pt loadings in the range 0-3.2 wt-% were prepared by coprecipitation, impregnation and sol-gel methods. After activation and reduction treatments, Pt nanoclusters interacting with Mg(Al)O supports are obtained.. The nature of the Pt phase and the acid-base properties were investigated by FT-IR spectroscopy upon adsorption of CO and CH3CN, respectively. In particular, the ratio between the number of basic and acid sites, Ib/Ia, was found to be in good agreement with the Mg/Al ratio in the solid, the basic character of the mixed oxides increasing with the Mg content. Moreover, for each Pt loading, the Ib/Ia ratio found after oxidizing treatment was markedly lower than after reduction. This feature was ascribed to the formation of a well dispersed surface Ptd+Ox phase. CO adsorption reveals, in the coprecipitated and impregnated samples, the presence of Pt sites, isolated or belonging to very small clusters, strongly interacting with the basic oxygen anions of the support. Finally, the behaviour of Pt/Mg(Al)O systems as multifunctional catalysts were checked in the cascade reaction between benzaldehyde (BAL) and propanal (PAL).