Abstract
To investigate bimetallic interactions, Pt-Ru/C catalysts were prepared by coimpregnation (Pt-Ruco/C) and successive impregnation (Ru-Ptse/C), while Pt/C, Ru/C, and reduced Pt-Rublackwere used as reference. Those samples were characterized by XAS and TPR. When Pt(absorber)-Ru(backscatter)phase-and-amplitude correction is applied to Fourier transformed (FT) EXAFS of Pt-Rublackat Pt edge, the characteristic peak of Pt-Ru interactions appears at 2.70 Å´, whereas, when Pt-Pt correction is applied, the peak appears at about 2.5 Å´. Detailed EXAFS analysis for Pt-Ruco/C and Pt-Ruse/C confirms the nature of the characteristic peak and further indicates that the interactions can semiquantitatively be determined by the relative intensity between Pt-Ru and Pt-Pt characteristic peaks. This simple method in determining bimetallic interaction can be extended to characterize Pt-Pd/γ-Al2O3. However, for Pt-Re/γ-Al2O3, Pt-Re interactions cannot be determined by the method because of the overlap of Pt-Pt and Pt-Re characteristic peaks due to similar phase functions.
Highlights
Several explanations have been offered for the role of M2nd in improving the catalytic performance: (1) it may change the morphology of Pt clusters and help anchor Pt and maintain it in a state of high dispersion [14, 20,21,22,23,24,25,26]; (2) it may convert the poisonous species into harmless compound in the reaction [2, 27]; (3) in bonding with Pt, it may change the electronic properties and geometric features of Pt thereby decreasing the adsorption of poisonous species on Pt [18, 24, 28,29,30,31,32,33]; and (4) in association with Pt, it may modify the catalytic properties of Pt [34,35,36,37,38]
Inferred from the mechanism for the platinum-catalyzed rhenium reduction in Pt-Re/γ-Al2O3 [39, 63], the temperature-programmed reduction (TPR) spectra characterized by a single peak of the Pt-Ruco/C suggest (a)
Pt-Ru bimetallic interaction can be detected by Pt-Pt phase-and-amplitude corrected Fourier transformed extended X-ray absorption fine structure (EXAFS) function and the Pt-Ru contributions were characterized by the peak appearing at 2.5 A
Summary
It has been reported that the catalytic properties of supported Pt catalysts can be markedly changed by the addition of the second metal (M2nd); for example, Ru are known to substantially improve the catalytic performance in the electrochemical oxidation of hydrogen fuels contaminated by carbon monoxide [1,2,3,4,5,6,7,8,9,10]; Re and Ir stabilize the Pt catalyst in naphtha reforming reaction; and Pd improves sulfur tolerance level of Pt for catalytic saturation of aromatics in diesel fuel [11,12,13,14,15,16,17,18,19].Several explanations have been offered for the role of M2nd in improving the catalytic performance: (1) it may change the morphology of Pt clusters and help anchor Pt and maintain it in a state of high dispersion [14, 20,21,22,23,24,25,26]; (2) it may convert the poisonous species into harmless compound in the reaction [2, 27]; (3) in bonding with Pt, it may change the electronic properties and geometric features of Pt thereby decreasing the adsorption of poisonous species on Pt [18, 24, 28,29,30,31,32,33]; and (4) in association with Pt, it may modify the catalytic properties of Pt [34,35,36,37,38]. It has been reported that the catalytic properties of supported Pt catalysts can be markedly changed by the addition of the second metal (M2nd); for example, Ru are known to substantially improve the catalytic performance in the electrochemical oxidation of hydrogen fuels contaminated by carbon monoxide [1,2,3,4,5,6,7,8,9,10]; Re and Ir stabilize the Pt catalyst in naphtha reforming reaction; and Pd improves sulfur tolerance level of Pt for catalytic saturation of aromatics in diesel fuel [11,12,13,14,15,16,17,18,19]. M2nd in improving the catalytic performances, it is crucial to determine the structure of the catalysts, the extent of bimetallic interaction. TPR (temperature programmed reduction) has been widely used to characterize the bimetallic interactions. Decomposition of surface functional groups in hydrogen reduction may change diffusion rate
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