ADSORPTION BEHAVIOR OF PLATINUM AMMINE CO MPLEX-IONS ONTO SILICA-GEL

Adsorption behavior of platinum (II) ammine complex ions onto silica g el was investigated at 30 degrees C in basic ammoniacal solution with varying concentrations of ammonium chloride. Two reactions were sugest ed for the platinum adsorption as follows: GNH(4) + Pt(NH3)(4)(++) + C l- reversible arrow GPt(NH3)(4)Cl + NH4+ K-1 GNH(4) + GH + Pt(NH3)(4)( ++) + NH3 reversible arrow G(2)Pt(NH3)(4) + 2 NH4+ K-2 where GH denote s silanol groups on silica gel. The composite process of these reactio ns gives the following equation, and it agreed with experimental data. =K-1[GNH(4)][Cl-]/[NH4+]+K-2'[GNH(4)](2)/[NH4+](2) The bidentate adso rption of platinum ammine complex ion onto silica gel retains a site o f ammonia and an adjacent site of free silanol group. In the reduction process of platinum ammine complex ions adsorbed on silica gel into p latinum metal, calcination in the air at 350 degrees C prior to reduct ion in H-2 causes an exothermic reaction due to the combustion of ammo nia adsorbed. The exothermic reactin induces sintering of platinum par ticles. The direct reduction in H-2 at 350 degrees C led to highly dis persed platinum on silica gel.