PREPARATION AND CHEMICAL-REDUCTION OF PT(IV) CHLORIDE-GICS - SUPPORTED PT VS PT INCLUSION GRAPHITE COMPOUNDS

Different preparation methods of Pt(IV) chloride-graphite intercalation compounds from micrometer sized graphite powder and their subsequent chemical reduction are described. The reaction products were investigated by XRD, SEM, EDX and neutron activation analysis. Pt(IV) chloride-GIC was obtained by the isothermal vapour transport method of PtCl4 between 350 and 500 degrees C under a pressure of chlorine gas. Reduction of Pt(IV) chloride-GIC in a tetrahydrofuran (THF)-naphthalene-K solution led to a compound containing both included potassium and potassium chloride particles and a large proportion of well distributed platinum clusters supported on the graphite flakes. The latter originate from the unremovable excess of platinum chloride systematically observed in all samples prepared by this method. The reaction of H2PtCl6 with graphite in SOCl2 under an inert atmosphere also yields a Pt(IV) chloride-GIC of formula C74PtCl3.84. The hexachloroplatinic acid lost two HCl molecules during the intercalation process in thionyl chloride. This Pt(IV) chIoride-GIC prepared in SOCl2 was reduced either by potassium in a naphthalene-THF solution, by potassium in liquid ammonia, or by NaBHEt(3) in toluene. Irrespective of the reduction method, only Pt and KCl included in the graphite matrix were detected. The average diameter of the platinum particles was evaluated from the X-ray diffraction patterns and ranged from 27 to 38 Angstrom. When heated at 400 degrees C for 1 hour under a flow of argon, cubic KCl crystals and minute platinum particles emerged on the edges of the graphite flakes. It is concluded that the reduction occurs in the graphite galleries, and the reaction mechanism is discussed for each method.