Characterization of CO- and H-2-adsorbed Au6Pt-phosphine clusters supported on SiO2 by EXAFS, TPD, and FTIR

Abstract

The adsorption of CO and H-2 on a SiO2-supported Au6Pt cluster [(AuPPh3)(6)Pt(PPh3)](NO3)(2) (1) has been studied by means of FTIR, TPD, and EXAFS. CO adsorbed on 1/SiO2 to form a CO-adduct complex, which exhibited an IR band at ca. 1972 cm(-1). The adsorbed CO was desorbed below 403 K, showing a peak maximum at 363 K in TPD. There was little change in the coordination number of Pt-Au in Pr L-3-edge EXAFS upon CO adsorption, but the coordination number of Au-Au in Au L-3-edge EXAFS slightly increased and the peak ascribed to Pt-(Au)-P in the Pr L-3-edge EXAFS Fourier transform remarkably increased. The increase in the intensity of the Pt-(Au)-P peak was interpreted by the multiple scattering effect owing to the change of Pt-Au-P bond angle. The original EXAFS oscillations at both Pt and Au L-3-edges were regenerated after evacuation of the CO-adsorbed sample for 2 h at 353 K, indicating the recovery of the original cluster structure. This is entirely different from the case of the cluster 1 in solution, where the cluster framework is fragmented by the CO adsorption-desorption process. The adsorption of H-2 on 1/SiO2 was totally reversible at room temperature: it provided no contribution to the EXAFS oscillation