Synthesis and structural characterization of Pt/amorphous Al2O3 catalyst

The synthesis of Pt supported on nonhydrolytic derived amorphous alumina catalyst was studied. The Pt was introduced both by in situ gelation with the alumina precursor and by impregnation of the amorphous alumina matrix. The in situ precursors were PtBr4 and (C6H5CN)2PtCl2, while the impregnation precursors were H2PtCl6 solution in water and Pt(acac)2 solution in toluene. For comparison, samples of commercial γ-Al2O3 were impregnated by the same methods. Complete fixation of the Pt precursor from the solution to the amorphous alumina support was achieved for both impregnation methods. After 773 K calcination in air the Pt dispersion, determined by H2 pulse chemisorption, for the in situ gelation-based catalysts was 32%. The corresponding Pt dispersion of the impregnated catalysts, prepared with H2PtCl6 and Pt(acac)2, was 15 and 49%, respectively. The low dispersion obtained using H2PtCl6 solution in water is explained by the partial burial of the Pt by a dissolution reprecipitation of the amorphous alumina and by a condensation reaction which occurs upon contact with water. These processes also cause reduction in the surface area of the amorphous alumina upon subsequent calcination.