X-ray absorption fine structure investigation of MCM-41 materials containing Pt and PtSn nanoparticles prepared via direct hydrothermal synthesis

摘要

Pt- and PtSn- containing MCM-41 materials were prepared by direct introduction of metal precursors with fumed silica and cetyltrimethylammonium surfactant. The precursor of Pt, with or without Sn precursor, was introduced in the initial synthesis mixture by dissolving both Pt(NH_3)_4(NO_3) and K_2SnO_3. The highly ordered MCM-41 mesoporous structure of two samples was revealed by a four-peaked XRD patterns, sharp capillary condensation in nitrogen isotherms, and a high surface area. After reduction, the coordination number of Pt particles in the MCM-41 samples decreased from 8.7 to 6.4 with simultaneous incorporation of Sn. The nearest Pt-Pt distance is almost the same, 0.276 nm, in both samples. The whiteline intensity of X-ray absorption at the Pt L_Ⅲ edge was decreased to that of metal foil during the reduction. It is suggested from the coordination number of the first shell that Pt particles are generated in the MCM-41 mesoporous molecular sieves by direct introduction and that simultaneous addition of Sn leads to a decrease of particle size.