XAS-INVESTIGATIONS OF COLLOIDAL PRECURSORS FOR PT RH BIMETALLIC CATALYSTS/

Innovative transition metal catalysts prepared on the basis of preform ed colloidal nano-particles and stabilized by surfactants are of speci al interest with regard to industrial applications. The physical chara cterization of the metal colloid precursors, i. e. the determination o f their geometric and electronic structure prior to supporting, has be en shown to be crucial for the optimization of new catalysts. Improved activity, selectivity and resistence against deactivation in case of bimetallic systems have been ascribed to 'synergetic effects' of the t wo metals present in the catalytically active components. The improved catalytic performance at a certain range of Pt:Rh atomic ratio in the precursor can be interpreted on the basis of a geometric lattice stru cture effect - rather than an electronic band structure effect. This h as been shown by an investigation of both the near edge structure and the EXAFS-region of Pt L-III X-ray absorption measurements, performed on a series of ammonium salt stabilized bimetallic Pt/Rh resp. monomet allic Pt colloids.