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Title: Structure and Reactivity of Pt-Ru/SiO2 Catalysts for the Preferential Oxidation of CO Under Excess H2

Abstract

SiO{sub 2}-supported Pt-Ru bimetallic catalysts subjected to two different types of pretreatment protocols (i.e., subsequent oxidation-reduction treatments at 300 C and direct reduction in H{sub 2} at 300 C) were characterized by extended X-ray absorption fine structure spectroscopy (EXAFS), scanning transmission electron microscopy (STEM), Fourier transform infrared spectroscopy (FTIR) of adsorbed CO, and catalytic activity measurements for the preferential oxidation of CO in the presence of excess H{sub 2} (PROX). The EXAFS data show that both treatments led to the formation of dispersed bimetallic structures, with an average Pt-Ru bond distance of 2.68 {angstrom}. The close proximity between Pt and Ru helped stabilize Ru in a highly dispersed form and prevented its sintering after oxidation treatments. The FTIR results indicate that the adsorption of CO was substantially weaker on bimetallic samples than on the corresponding monometallic ones. Interparticle segregation (i.e., segregation of the two metals into individual particles) was observed with the Pt-Ru/SiO{sub 2} sample exposed to direct H{sub 2} treatment; in contrast, intraparticle segregation (i.e., segregation of the two metals within the same particle), with Pt preferentially occupying more surface sites, was observed when consequent O{sub 2}/H{sub 2} treatments were used. As a result, the direct H{sub 2} treatmentmore » yielded samples with PROX activity almost identical to that of monometallic Ru catalysts, whereas the O{sub 2}/H{sub 2} treatment yielded samples with PROX activity intermediate to those of monometallic Pt and Ru catalysts.« less

Authors:
; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930102
Report Number(s):
BNL-80740-2008-JA
Journal ID: ISSN 0021-9517; JCTLA5; TRN: US200822%%1191
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Catalysis; Journal Volume: 243; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; CARBON MONOXIDE; OXIDATION; CATALYSTS; PLATINUM; RUTHENIUM; CATALYTIC EFFECTS; SILICON OXIDES; CATALYST SUPPORTS; HYDROGEN; national synchrotron light source

Citation Formats

Chin,S., Alexeev, O., and Amiridis, J.. Structure and Reactivity of Pt-Ru/SiO2 Catalysts for the Preferential Oxidation of CO Under Excess H2. United States: N. p., 2006. Web. doi:10.1016/j.jcat.2006.08.004.
Chin,S., Alexeev, O., & Amiridis, J.. Structure and Reactivity of Pt-Ru/SiO2 Catalysts for the Preferential Oxidation of CO Under Excess H2. United States. doi:10.1016/j.jcat.2006.08.004.
Chin,S., Alexeev, O., and Amiridis, J.. Sun . "Structure and Reactivity of Pt-Ru/SiO2 Catalysts for the Preferential Oxidation of CO Under Excess H2". United States. doi:10.1016/j.jcat.2006.08.004.
@article{osti_930102,
title = {Structure and Reactivity of Pt-Ru/SiO2 Catalysts for the Preferential Oxidation of CO Under Excess H2},
author = {Chin,S. and Alexeev, O. and Amiridis, J.},
abstractNote = {SiO{sub 2}-supported Pt-Ru bimetallic catalysts subjected to two different types of pretreatment protocols (i.e., subsequent oxidation-reduction treatments at 300 C and direct reduction in H{sub 2} at 300 C) were characterized by extended X-ray absorption fine structure spectroscopy (EXAFS), scanning transmission electron microscopy (STEM), Fourier transform infrared spectroscopy (FTIR) of adsorbed CO, and catalytic activity measurements for the preferential oxidation of CO in the presence of excess H{sub 2} (PROX). The EXAFS data show that both treatments led to the formation of dispersed bimetallic structures, with an average Pt-Ru bond distance of 2.68 {angstrom}. The close proximity between Pt and Ru helped stabilize Ru in a highly dispersed form and prevented its sintering after oxidation treatments. The FTIR results indicate that the adsorption of CO was substantially weaker on bimetallic samples than on the corresponding monometallic ones. Interparticle segregation (i.e., segregation of the two metals into individual particles) was observed with the Pt-Ru/SiO{sub 2} sample exposed to direct H{sub 2} treatment; in contrast, intraparticle segregation (i.e., segregation of the two metals within the same particle), with Pt preferentially occupying more surface sites, was observed when consequent O{sub 2}/H{sub 2} treatments were used. As a result, the direct H{sub 2} treatment yielded samples with PROX activity almost identical to that of monometallic Ru catalysts, whereas the O{sub 2}/H{sub 2} treatment yielded samples with PROX activity intermediate to those of monometallic Pt and Ru catalysts.},
doi = {10.1016/j.jcat.2006.08.004},
journal = {Journal of Catalysis},
number = 2,
volume = 243,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • The promotional effect of Nb on Pt supported on alumina or on niobia, was studied for the preferential oxidation of CO (PROX) in hydrogen. The results show a unique effect of Nb as a promoter to Pt. At low Nb loadings on Pt/alumina, the CO oxidation activity and selectivity are significantly increased. The CO selectivity is 100% at conversions up to about 60%. For Pt supported on Nb{sub 2}O{sub 5}, however, the CO oxidation activity is strongly suppressed with low CO conversion but high H{sub 2} oxidation activity. Pt on niobia, therefore, is poorly selective for the PROX reaction, butmore » is an active hydrogen oxidation catalyst, resistant to CO poisoning. For Pt supported on highly loaded Nb-alumina or Nb{sub 2}O{sub 5}, XPS indicate an increase in the Pt and Nb oxidation states. These surface changes also correlate with changes in the DRIFTS spectra suggesting that CO is more weakly adsorbed on Pt/Nb{sub 2}O{sub 5} compared to Pt/Al{sub 2}O{sub 3}, or Pt/Nb-Al{sub 2}O{sub 3}.« less
  • Two series of nanostructured oxidized copper-cerium catalysts with varying copper loadings, and prepared, respectively, by impregnation of ceria and by coprecipitation of the two components within reverse microemulsions, have been characterized in detail at structural and electronic levels by X-ray diffraction (XRD), Raman spectroscopy, high-resolution electron microscopy (HREM), X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS) (including Ar{sup +}-sputtering), and X-ray absorption fine structure (XAFS). These results have been correlated with analysis of their catalytic properties for preferential oxidation of CO in a H{sub 2}-rich stream (CO-PROX), complemented by Operando-DRIFTS. A relevant difference between the two series of catalystsmore » concerns the nature of the support for the surface-dispersed copper oxide entities, which is essentially ceria for the samples prepared by impregnation and a Ce-Cu mixed oxide for those prepared by microemulsion-coprecipitation. The existence of copper segregation in the form of copper oxide or copper-enriched Cu-Ce mixed oxides for the latter type of samples is uniquely revealed by nanoprobe XEDS and XPS Ar{sup +}-sputtering experiments. The CO oxidation activity under CO-PROX conditions is correlated to the degree of support-promoted reduction achieved by the dispersed copper oxide particles under reaction conditions. Nevertheless, catalysts which display higher CO oxidation activity are generally more efficient also for the undesired H{sub 2} oxidation reaction. The balance between both reactions results in differences in the CO-PROX activity between the two series of catalysts which are examined on the basis of the structural differences found.« less
  • The reaction of Ru[sub 4]Pt[sub 2](CO)[sub 18] with Ru[sub 4](CO)[sub 13]([mu]-H)[sub 2] at 97[degrees]C yielded the new decanuclear platinum-ruthenium carbonyl cluster complex Ru[sub 8]Pt[sub 2](CO)[sub 23]([mu][sub 3]-H)[sub 2] 1 (22%). In a similar manner the reaction of Ru[sub 4]Pt[sub 2](CO)[sub 18] with Ru[sub 3]Pt(CO)[sub 10](COD)([mu]-H)[sub 2], 2, in 25% yield. Both compounds were characterized by IR, [sup 1]H NMR, and single-crystal X-ray diffraction analyses, and both were bound to consist of similar edge-fused bioctahedral clusters with platinum atoms along the edge-sharing sites. There are strong metal-metal bonds between the apices of the adjacent octahedra. Both compounds are electron deficient, andmore » one of the apical-apical Ru-Ru bonds is unusually short, 2.580 (2) [Angstrom] in 1 and 2.593 (5) [Angstrom] in 2. The hydrides are triply bridging ligands, and these were located and refined crystallographically in 1. The reaction of 1 with 1,2-bis(diphenylphosphino)ethane, dppe, yielded the adduct Ru[sub 8]Pt[sub 2](CO)[sub 21]([mu][sub 3]-CO)[sub 2](dppe)([mu]-H)[sub 2], 3, in 12% yield, which was shown to consist of a face-shared bioctahedral cluster of seven ruthenium and two platinum atoms with a ruthenium spike containing the dppe ligand extending from one triruthenium face. Two novel dihapto-triply bridging carbonyl ligands were found to bridge to the ruthenium spike. 1 and 2 both react with CO at 25[degrees]C, but only the product obtained from the reaction of 2, Ru[sub 6]Pt[sub 3](CO)[sub 21]([mu]-CO)([mu][sub 3]-H)[sub 2], 4, (55% yields), could be fully characterized. It was shown to contain a cluster of nine metal atoms arranged into trinuclear layers of pure ruthenium and pure platinum. The two triply bridging hydride ligands were located and refined crystallographically. 23 refs., 4 figs., 13 tabs.« less