Abstract
Platinum particles supported on a sulfate ion-treated zirconium oxide (SO 4 2− -ZrO 2) were characterized by means of X-ray absorption near edge structure (XANES )/extended X-ray absorption fine structure (EXAFS) and temperature-programmed reduction (TPR) in order to elucidate the nature of the sulfar-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 platinum particle to the support and/or existence of the platinum unreduced cations. Fourier transforms (FTs) of k 3-weighted EXAFS reveal that the Pt particles on the (SO 4 2− -ZrO 2 support after hydrogen treatment at 623 K are a mixture of Pt metal ( Pt-Pt bond length = 2.77A˚) and Pt oxides, whereas the Pt particles on ZrO 2 exist as metal (Pt-Pt bond length = 2.73A˚). TEM reveals that the presence of sulfate ion causes an increase of the Pt particle size (30A˚→50A˚). The low reducibility of the Pt particles on the (SO 2- 4-ZrO 2 support is evidenced by TPR results. The nature of the platinum-support interaction in the Pt/(SO 4 2− -ZrO 2 catalyst is understood in terms of a Redox (reduction-oxidation) metal-support interaction.
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