X-RAY-ABSORPTION SPECTROSCOPIC STUDY OF PLATINUM SUPPORTED ON SULFATEION-TREATED ZIRCONIUM-OXIDE

Platinum particles supported on a sulfate ion-treated zirconium oxide (SO42- ZrO2) were characterized by means of X-ray absorption near edge structure (XANES) /extended X-ray absorption fine structure (EXAFS) a nd temperature-programmed reduction (TPR) in order to elucidate the na ture of the sulfur-aided metal-support interactions. X-ray edge shift and area calculation, which give the number of unoccupied d states of the platinum particles, are suggestive of electron transfer from the p latinum particle to the support and/or existence of the platinum unred uced cations. Fourier transforms (FTs) of k3-weighted EXAFS reveal tha t the Pt particles on the SO42-ZrO2 support after hydrogen treatment a t 623 K are a mixture of Pt metal (Pt-Pt bond length = 2.77 angstrom) and Pt oxides, whereas the Pt particles on ZrO2 exist as metal (Pt-Pt bond length = 2.73 angstrom). TEM reveals that the presence of sulfate ion causes an increase of the Pt particle size (30 angstrom --> 50 an gstrom). The low reducibility of the Pt particles on the SO42--ZrO2 su pport is evidenced by TPR results. The nature of the platinum-support interaction in the Pt/SO42--ZrO2 catalyst is understood in terms of a Redox (reduction-oxidation) metal-support interaction.