Site dependent dissociation of CO on supported Pd particle surface: A TPD study

Matolín, Vladimı́r; Jungwirthová, I.; Tomková, E.

doi:10.1016/0079-6816(90)90037-k

Cited by 12 publications

(4 citation statements)

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“…Differential heats of CO chemisorption on carbon-supported palladium [60] are in the range of 70-90 kJ mol À1 , which is lower than the corresponding values of palladium supported on oxide catalysts (71-150 kJ mol À1 ). [63,64] In contrast to early literature, [65,66] the adsorption enthalpy of carbon monoxide decreases with decreasing particle size by about 20 kJ mol À1 from about 145 kJ mol À1 for single crystals to 120 kJ mol À1 for initial coverages and down to 80 kJ mol À1 for saturation coverage independent of particle size. [63,64] In contrast to early literature, [65,66] the adsorption enthalpy of carbon monoxide decreases with decreasing particle size by about 20 kJ mol À1 from about 145 kJ mol À1 for single crystals to 120 kJ mol À1 for initial coverages and down to 80 kJ mol À1 for saturation coverage independent of particle size.…”

Section: Microcalorimetry Of Co Chemisorptionmentioning

confidence: 56%

“…[61,62] Recently, the particle size dependence of the heat of CO adsorption on palladium nanoclusters from 1.8 to 8 nm was investigated by single-crystal adsorption microcalorimetry. [63,64] In contrast to early literature, [65,66] the adsorption enthalpy of carbon monoxide decreases with decreasing particle size by about 20 kJ mol À1 from about 145 kJ mol À1 for single crystals to 120 kJ mol À1 for initial coverages and down to 80 kJ mol À1 for saturation coverage independent of particle size. These reference observations indicate that the catalysts in this study exhibit typically lower heats of adsorption (see Table 5 and Figure 8 a) than pure palladium systems; both gold atoms and subsurface species are responsible for this trend.…”

Section: Microcalorimetry Of Co Chemisorptionmentioning

confidence: 56%

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Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

et al. 2013

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This work aims to clarify the nanostructural transformation accompanying the loss of activity and selectivity for the hydrogen peroxide synthesis of palladium and gold-palladium nanoparticles supported on N-functionalized carbon nanotubes. High-resolution X-ray photoemission spectroscopy (XPS) allows the discrimination of metallic palladium, electronically modified metallic palladium hosting impurities, and cationic palladium. This is paralleled by the morphological heterogeneity observed by high-resolution TEM, in which nanoparticles with an average size of 2 nm coexisted with very small palladium clusters. The morphological distribution of palladium is modified after reaction through sintering and dissolution/redeposition pathways. The loss of selectivity is correlated to the extent to which these processes occur as a result of the instability of the particle at the carbon surface. We assign beneficial activity in the selective hydrogenation of oxygen to palladium clusters with a modified electronic structure compared with palladium metal or palladium oxides. These beneficial species are formed and stabilized on carbons modified with nitrogen atoms in substitutional positions. The formation of larger metallic palladium particles not only reduces the number of active sites for the synthesis, but also enhances the activity for deep hydrogenation to water. The structural instability of the active species is thus detrimental in a dual way. Minimizing the chance of sintering of palladium clusters by all means is thus the key to better performing catalysts.

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Section: Microcalorimetry Of Co Chemisorptionmentioning

confidence: 56%

Section: Microcalorimetry Of Co Chemisorptionmentioning

confidence: 56%

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

et al. 2013

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“…This reaction has been studied extensively for both Pd single crystals 1,6,[13][14][15][16] and Pd nanoparticles supported on metal oxides. 2,[17][18][19][20][21][22][23][24][25][26][27] It was shown by Ertl and others that CO oxidation on noble metals occurs by a Langmuir-Hinshelwood mechanism, where both reactants must adsorb on the surface before combining to form CO 2 , and that kinetics are controlled by competition between CO and oxygen for binding sites. 1,6,13,14 The Freund and Matolin groups studied CO on alumina-supported Pd, and noted an increase in low temperature CO desorption with decreasing Pd particle size, attributed to CO weakly bound atop small Pd particles, as opposed to in high coordination binding sites on larger particles.…”

Section: Introductionmentioning

confidence: 99%

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

2013

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A series of model catalysts were prepared by depositing different size Pd(n) clusters on alumina films grown to variable thickness on a Ta(110) support. Samples were characterized by a combination of X-ray photoelectron spectroscopy, low energy He+ scattering, and temperature-programmed reaction and desorption (TPR/ TPD). For the activity studies, the samples were first exposed to 18O2 at Tox, and then to 13CO at 180 K, where CO sticks to Pd, but not to the alumina support. CO oxidation activity increased with increasing thickness of the alumina support up to approximately 4.5 nm, but was constant for greater thicknesses. Activity increased, with Tox up to 400 K, but then declined for Tox = 500 K. Activity was also found to be non-monotonically dependent on deposited cluster size, with Pd(n) (n < or = 6) being generally more reactive than the larger clusters studied. Activity was only weakly correlated with exposed Pd binding sites, which decreased with increasing cluster size, however, there does appear to be a correlation between activity and electronic structure, as probed via the Pd 3d binding energy. Unlike previous systems we have studied, the activity of small Pd(n) on these alumina films was quite stable, with essentially no changes observed in up to eight successive TPR experiments.

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“…1, 5, and 10-13) and supported Pd model catalysts. [2][3][4][5][6][7][14][15][16][17][18][19][20] This reaction therefore, is a good test system for probing changes in the physical and chemical properties of metal particles as their size is reduced into the range (<50 atoms) where a number of size-selected deposition studies have shown behavior quite different from what could be predicted by scaling bulk properties. 4,6,7,14,15,[21][22][23][24][25][26][27][28][29] Recently, we reported a study of CO oxidation over Pd n / TiO 2 (110) (n ≤ 25) where both CO adsorption and CO 2 production varied non-monotonically with size, and where activity was shown to correlate strongly with shifts in the electronic properties of the Pd clusters, as probed by X-ray photoelectron spectroscopy (XPS) of the Pd 3d core level.…”

Section: Introductionmentioning

confidence: 99%

CO adsorption and desorption on size-selected Pdn/TiO2(110) model catalysts: Size dependence of binding sites and energies, and support-mediated adsorption

Kaden

Kunkel

Roberts

et al. 2012

The Journal of Chemical Physics

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The nature of CO adsorption on Pd(n)/TiO(2)(110) (n = 1, 2, 7, 20) has been examined using temperature-programmed desorption (TPD), temperature-dependent helium ion scattering (TD-ISS), and X-ray photoelectron spectroscopy (XPS). All samples contain the same number of Pd atoms (0.10 ML-equivalent) deposited as different size clusters. The TPD and TD-ISS show that CO binds in two types of sites associated with the Pd clusters. The most stable sites are on top of the Pd clusters ("on-top" sites), however, there are also less stable sites, in which CO is bound in association with, but not on top of the Pd ("peripheral" sites). For saturation CO coverage over a fixed atomic concentration of Pd (present in the form of Pd(n) clusters of varying size), the population of CO in peripheral sites decreases with increasing cluster size, while the on-top site population is size-independent. This is consistent with what geometric considerations would predict for the density of the two types of sites, provided the clusters adsorb predominantly as 2D islands, which ISS results suggest to be the case. The XPS analysis indicates that CO-Pd binding is dominated by π-backbonding to the Pd(n) clusters. The results also show evidence for efficient support-mediated adsorption (reverse-spillover) of CO initially impinging on TiO(2) to binding sites associated with the Pd clusters.

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Site dependent dissociation of CO on supported Pd particle surface: A TPD study

Cited by 12 publications

References 7 publications

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

CO adsorption and desorption on size-selected Pdn/TiO2(110) model catalysts: Size dependence of binding sites and energies, and support-mediated adsorption

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Site dependent dissociation of CO on supported Pd particle surface: A TPD study

Cited by 12 publications

References 7 publications

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H2O2

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H2O2

Alumina support and Pdn cluster size effects on activity of Pdn for catalytic oxidation of CO

CO adsorption and desorption on size-selected Pdn/TiO2(110) model catalysts: Size dependence of binding sites and energies, and support-mediated adsorption

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Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂

Dynamics of Palladium on Nanocarbon in the Direct Synthesis of H₂O₂