Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts:: II.: Synthesis of platinum hydroxo complexes on the alumina surface as precursors of the active component of Pt/Al2O3 catalysts

The thermal hydrolysis of chloroplatinate adsorbed on gamma-Al2O3 is a possible approach to the synthesis of surface platinum hydroxo complexes as precursors to the active component of supported platinum catalysts. It is demonstrated by EXAFS and diffuse reflectance spectroscopy that the surface chloro complexes undergo deep hydrolysis under hydrothermal conditions at various processing times and temperatures. The average oxygen coordination number of platinum in these complexes is as large as 4.5. According to gradient elution data obtained using both the competitive replacement of adsorbed complex anions and variation of the charged state of the oxide surface, the resulting hydrolyzed precursor differs from the conventional chloride precursor in the nature of binding to the surface and interacts with alumina via a coordination mechanism.