Adsorption of Carbon Monoxide on Pd(111) and Palladium Model Catalysts

Voogt, E.H.; Coulier, L; Gijzeman, O.L.J.; Geus, J.W.

doi:10.1006/jcat.1997.1708

Cited by 29 publications

(9 citation statements)

References 31 publications

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“…Recent papers , definitely show that for Pd supported on oxides bridge-bonded CO is the most abundant species, even if for very small particles an increasing strength of the Pd−CO linear bond was found . As it was very recently demonstrated that bridge-bonded CO species increase when the support acidity decreases, on carbon-supported Pd practically the whole chemisorbed CO should be bridge-bonded, thus fully supporting our experimental data.…”

Section: Resultssupporting

confidence: 91%

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

et al. 2000

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In this work we have determined, on a series of 0.5% Pd/C catalysts, the palladium particle sizes by the following physical techniques: (i) X-ray diffraction (XRD) line broadening (LB) method, associated with the Rietveld method, (ii) small-angle X-ray scattering, and (iii) transmission electron microscopy. The catalysts, suitably aged at different temperatures (673, 773, 873, and 973 K), had significantly different metal dispersions. Since the XRD-LB technique is not able to measure directly very small metal particles or clusters (roughly e25 Å in size), because they give diffuse X-ray scattering spreading out into the background, we have tackled this problem by means of a suitably tailored Rietveld quantitative analysis. This analysis allowed determination of the Pd fraction "visible" in the Voigtian XRD peaks and its average crystallite size using the LB method. As to the nanoparticle size of the undetectable fraction, an average value of 20 Å was assumed, corresponding to the size of a cubooctahedral perfect cluster of the fourth order. Combining all these data, real effective Pd average particle sizes could be calculated and compared with the corresponding values found by CO chemisorption. It was found that a surface Pd/CO stoichiometry of 2 must be assumed, irrespective of Pd dispersion, to get correct values of the average Pd particle size.

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Section: Resultssupporting

confidence: 91%

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

et al. 2000

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“…The fraction of linearly bonded Pd atoms could also increase as particle size decreases, as proposed by some researchers. −, In particular, in the paper by Sheu, Karpinski, and Sachtler, a plot is reported in which, for very high dispersions corresponding to particle sizes of about 15 Å, the average Pd/CO stoichiometry decreases to about 1.65, starting from values of about 1.9 for sizes of about 50 Å. On the other hand, some researchers claim that there is no particle effect with the adsorption of CO on SiO 2 /Si(100)-supported Pd particles . In any case, many researchers have recently shown, using such diverse techniques as microcalorimetry and TPD, ellipsometry, IR, and other spectroscopic investigations in function of the support alkalinity, that bridge-bonded CO is always the dominant CO(ads) species.…”

Section: Resultsmentioning

confidence: 91%

Pd/CO Average Chemisorption Stoichiometry in Highly Dispersed Supported Pd/γ-Al₂O₃Catalysts

et al. 2002

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Following our previous papers regarding Pd/C and Pd/SiO2 catalysts, the determination of the Pd/CO average chemisorption stoichiometry from experimental data has been extended to the Pd/alumina system. To this purpose, the Pd crystallite size determined by the well-established line-broadening (LB) method, using X-ray powder diffraction (XRPD) associated with the Fourier analysis of suitable best-fitted peak profiles, and the chemisorbed CO volume, determined by the pulse flow method, were employed. HRTEM was also used to check the structural features of the Pd particles, which proved to be monodomains of cubooctahedral shape. A high-dispersion 5 wt % Pd/alumina catalyst was prepared by impregnation and thermally treated at different temperatures up to 1073 K. Even at this high temperature a good Pd dispersion was retained. A suitable subtraction of the X-ray scattering, due to the support, was done to obtain the real profile of the supported metal, from which the surface-weighted average particle diameters were calculated. Using these values and the corresponding CO chemisorbed volumes, a Pd/CO average chemisorption stoichiometry close to 2 was obtained. On the basis also of our previous work regarding Pd/C and Pd/SiO2 catalysts, it can be concluded that for all supported Pd catalysts such stoichiometry is close to 2, independent of support nature and Pd dispersion, when chemisorbed volumes are measured by the routinely used pulse flow method.

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“…For CO/Pd(111) no microcalorimetry has been reported, but TPD data − lead to 30−35 kcal/mol. A very recent slab calculation at two different coverages on Pd(111) gives 33 kcal/mol for the c(2 × 2) structure [higher coverage] and 46 kcal/mol for the ( × ) structure [lower coverage].…”

Section: Results For Ptmentioning

confidence: 99%

Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to Direct Methanol Fuel Cells

1999

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Using first principles quantum mechanics [nonlocal density functional theory (B3LYP)], we calculated the 13 most likely intermediate species for methanol oxidation on clusters of all 2nd and 3rd row Group VIII transition metals for all three likely binding sites (top, bridge, and cap). This comprehensive set of binding energies and structures allows a detailed analysis of possible reaction mechanisms and how they change for different metals. This illustrates the role in which modern quantum chemical methods can be used to provide data for combinatorial strategies for discovering and designing new catalysts. We find that methanol dehydrogenation is most facile on Pt, with the hydrogens preferentially stripped off the carbon end. However, water dehydrogenation is most facile on Ru. These results support the bifunctional mechanism for methanol oxidation on Pt−Ru alloys in direct methanol fuel cells (DMFCs). We find that pure Os is capable of performing both functionalities without cocatalyst. We suggest that pure Os be examined as a potential catalyst for low overpotential, highly dispersed catalyst DMFCs. Pathways to form the second C−O bond differ between the pure metals (Pt and Os) in which (CO)ads is probably activated by (OH)ads and the Pt−Ru binary system in which (COH)ads is probably activated by Oads. For all cases we find that formation of (COOH)ads is an important precursor to the final dehydrogenation to desorb CO2 from the surface.

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Adsorption of Carbon Monoxide on Pd(111) and Palladium Model Catalysts

Cited by 29 publications

References 31 publications

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

Pd/CO Average Chemisorption Stoichiometry in Highly Dispersed Supported Pd/γ-Al₂O₃Catalysts

Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to Direct Methanol Fuel Cells

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Adsorption of Carbon Monoxide on Pd(111) and Palladium Model Catalysts

Cited by 29 publications

References 31 publications

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

Nanostructural Features of Pd/C Catalysts Investigated by Physical Methods: A Reference for Chemisorption Analysis

Pd/CO Average Chemisorption Stoichiometry in Highly Dispersed Supported Pd/γ-Al2O3Catalysts

Oxidation of Methanol on 2nd and 3rd Row Group VIII Transition Metals (Pt, Ir, Os, Pd, Rh, and Ru): Application to Direct Methanol Fuel Cells

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Pd/CO Average Chemisorption Stoichiometry in Highly Dispersed Supported Pd/γ-Al₂O₃Catalysts