Extended X-ray absorption fine structure (EXAFS) studies of highly dispersed platinum catalysts

Abstract

Two platinum catalysts (6.3% Pt on SiO₂, dispersion > 50%, designated EUROPT-1 and 0.47% Pt on Al₂O₃, designated PTAL) have been studied by extended X-ray absorption fine structure (EXAFS). Each Fourier transform is dominated by a single radial distance, assigned to Pt—O bonding. In EUROPT-1 the Pt—O distance is 1.94 ± 0.05 Å, slightly shorter than the Pt—O distance in βPtO₂, 2.00 ± 0.02 Å. For PTAL a broad peak is observed centred at 2.00 ± 0.05 Å, which may contain a contribution due to Pt—C1 bonding. No evidence is found of metallic platinum or the Pt—Pt bonds in βPtO₂. The platinum particles are thus largely amorphous, consisting of PtO_x units (x⩽ 6). The comparitive ease of oxidation of small highly disperse platinum particles is discussed.