XAFS Study of Dried and Reduced PtSn/C Catalysts: Nature and Structure of the Catalytically Active Phase

Abstract

Bimetallic PtSn/C catalysts, prepared on two activated carbon supports of different surface chemistry by two different preparation procedures, have been analyzed by XAFS spectroscopy. The main goal is to identify the effect of the support surface oxidation and the preparation procedure (coimpregnation or successive impregnations) in the interaction of platinum with the support and/or with tin atoms. XAFS results reveal the effect of the mentioned variables in the structure of the supported phase. It has been found in dried samples that the interaction of the platinum species with the support is stronger if the carbon surface is oxidized. The two-step impregnation, compared with the coimpregnation method, renders samples with a stronger platinum-support interaction. Such an interaction determines the distribution of the active phase on the support particles. The structure of the metallic phase after reduction is quite different for samples prepared with the oxidized and nonoxidized carbon support and is also dependent on the preparation procedure. From the XAFS data, the presence of the following platinum containing structures is suggested: PtSn alloy, Pt-O-Sn 2+ species and pure Pt clusters. The relative proportion of these structures in the catalysts and their distribution on the support determine the catalytic activity for cyclohexane dehydrogenation.

Carbon-supported PtSn Catalysts: Characterization and Catalytic Properties

“…On the other hand, comparing the results obtained with catalysts prepared on carbons C and C-HP, the effect of the support surface chemistry on the state of platinum can be deduced. In catalysts prepared with the oxidized support (C-HP), the intensity of the main peak is lower than in catalysts prepared with carbon C. This effect was also observed with the monometallic Pt/carbon samples 11) . These results can be explained by a higher coordination of Pt with O and/or C atoms in the oxidized support.…”

“…The Pt _ Sn distance in an alloy is about 2.7 Å 21),49) and about 2.5 Å in the [Pt(SnCl3)5] 3− complex 50) . The absence of a Pt _ Sn interaction can also be deduced because of the great similarity with the FT-EXAFS profiles obtained for the monometallic Pt/C and Pt/C-HP catalysts 11) . On the other hand, comparing the results obtained with catalysts prepared on carbons C and C-HP, the effect of the support surface chemistry on the state of platinum can be deduced.…”

Effect of W on PtSn/C catalysts for ethanol electrooxidation

“…To further improve ethanol reactivity, we have introduced ruthenium as a third metal in the PtSn catalyst composition, which enhanced the power density from ca. 30 [8,10,19,26,[28][29][30][31][32][33][34] to 50 mW cm -2 [30]. A power density of 32 mW cm -2 when PtSnIr is used as anode has been reported [28].…”

Anode Catalysts for Low‐Temperature Direct Alcohol Fuel Cells

“…Impregnation method involves soaking up of a dissolved metal precursor into the pores of carbon support, and subsequently reducing the precursor into metal nanoparticles using reducing agent such as HCHO, HCOONa, NaBH 4 , NH 2 NH 2 , H 2 , and so on at optimized conditions [143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158]. Since the nucleation formation and particle growth are mainly confined within the carbon-support pores, the morphology of the porous substrate and the pore size distribution play a key role in terms of penetration and wetting of the precursor and also providing confinement for nanoparticle growth.…”