XANES study of the support effect on the state of platinum catalysts

Abstract

Pt I~u and Ln-edges XANES clarified the oxidation state of platinum catalysts supported on various metal oxides. The acidbase property seemed one of the most dominant factors to control the electron state of platinum. On the reduced samples, there was a tendency that acidic support reduced the 5d-electron density of platinum, while the oxidized samples on acidic support contained more metallic platinum. The latter tendency agreed well with high activity of platinum catalysts on acidic supports toward propane combustion in oxidizing condition, and it was explained by a hypothetical mechanism for prevention of oxidation of platinum by acidic supports.Keyword: Pt catalyst; Pt L-edge XANES; d-electron density; support effect; oxidation state of platinum.

XAFS study of the additive cation effect on the oxidation-resistance of platinum catalyst

“…In the previous paper, the authors reported that the white line intensity at Pt L III -edge XANES spectra of platinum catalysts supported on various oxides decreases with an increase in the acid strength of support materials (Yoshida et al, 1999;Yazawa et al, 2000). The present study revealed that the additives have the same effect.…”

“…In this atmosphere, noble metal is oxidized to some extent under the reaction condition, and the oxidation state of noble metal is one of key factors to control its performance. Recently, in propane combustion over noble metal catalysts, the authors showed that the catalytic activity can be improved by the selection of support materials through the controlling the oxidation state of noble metal (Yazawa et al, 1999;Yoshida et al, 1999;Yazawa et al, 2000). In the case of platinum catalysts, the stronger acidic support gives the higher oxidationresistance to platinum catalyst, leading to the higher catalytic activity for propane combustion, since combustion activity of platinum decreases as platinum is oxidized (Voelter et al, 1987;Nunan et al, 1992).…”

Sulfur stabilizing metal nanoclusters on carbon at high temperatures

“…2 a, e ). The white line intensity directly reflects the unoccupied density of states of Pt 5d orbitals 37 . The lower intensity of white line peak for Pt/S–C suggests that the S–C support can donate electrons to Pt nanoclusters, which leads to an electron-enriched state of Pt nanoclusters on S–C.…”

Catalytic oxidation of NO over TiO2 supported platinum clusters I. Preparation, characterization and catalytic properties

“…The catalytic deactivation of platinum catalysts by O 2 and NO 2 due to oxides formation in the reaction has been proved and investigated in details [9][10][11][12]. In the research of support effect on the state of platinum catalysts, Yoshida et al [15] suggested that electrophilic acidic support suppress the formation of platinum oxides through electrons donation from support to platinum. The electron-interaction between platinum and support may be considered as promising tool to suppress the formation of platinum oxides.…”