Selective Hydrogenation and H-D Exchange of Unsaturated Hydrocarbons on Pd(100)-P(1×1)-H(D)

Guo, Xuan; Madix, R. J.

doi:10.1006/jcat.1995.1215

Cited by 70 publications

(57 citation statements)

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“…64 Pd-NPs embedded in ILs also achieved similar selectivities than those reported herein. Moreover, the selectivity for monoenes, during the hydrogenation of 1,3-butadiene (13) by the classical heterogeneous catalyst Pd/C (5% Degussa) in the presence of IL, is very low even at low substrate concentrations.…”

Section: 61supporting

confidence: 74%

“…It is noteworthy that the high selectivity obtained for the monoenes (usually ≥99%) suggests that the selectivity is intrinsic to the Pd-metallic surfaces in this IL-hybrid organosilica environment, and probably, it is due to its highly electron deficient nature ( Table 1) that displays higher adsorption affinity for the diene than to the monoene. [63][64][65] This suggests that SILP/PdNPs under multiphase conditions (dynamic asymmetric mixture) 66 operates akin to catalytically active membranes 67 , i.e., far from thermodynamic equilibrium. 68 In this case, the dienes, which are at least four times more soluble in the hybrid catalytic materials than the monoenes 69,70 , displace the formed monoenes from the Pd-NP surface, which are then extracted by the organic phase (before reaching thermodynamic equilibrium).…”

Section: 61mentioning

confidence: 99%

See 1 more Smart Citation

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

et al. 2016

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Ionic liquid (IL)-hybrid organosilicas based on 1-n-butyl-3-(3-trimethoxysilylpropyl)-imidazolium cations associated with hydrophilic and hydrophobic anions decorated with well dispersed and similar sized (1.8-2.1 nm) Pd nanoparticles (PdNPs) are amongst the most active and selective catalysts for the partial hydrogenation of conjugated dienes to monoenes. The location of the sputter-imprinted Pd-NPs on different supports, as determined by RBS and HS-LEIS analysis, is modulated by the strength of the contact ion pair formed between the imidazolium cation and the anion, rather than the IL-hybrid organosilica pore size and surface area. In contrast, the pore diameter and surface area of the hybrid supports display a direct correlation with the anion hydrophobicity. XPS analysis showed that the Pd(0) surface component decreases with increasing ionic bond strength between the imidazolium cation and the anions (contact ion pair). The finding is corroborated by changes in the coordination number associated with the Pd-Pd scattering in EXAFS measurements. Hence, the interaction of the IL with the metal surface is found to occur via IL contact pairs (or aggregates). The observed selectivities of ≥99% to monoenes at full diene conversion indicate that the selectivity is intrinsic to the electron deficient Pd-metallic surfaces in this "restricted" ionic environment. This suggests that ILhybrid organosilica/Pd-NPs under multiphase conditions ("dynamic asymmetric mixture") operate akin to catalytically active membranes, i.e. far from the thermodynamic equilibrium. Detailed kinetic investigations show that the reaction rate is zero-order with respect to hydrogen and dependent on the fraction of catalyst surfaces covered by either the substrate and/or the product. The reaction proceeds via rapid inclusion and sorption of the diene to the IL/Pd metal surface saturated with H species. This is followed by reversible hydride migration to generate a π-allyl intermediate. The reductive elimination of this intermediate, the formal ratedetermining step (RDS), generates the alkene that is rapidly expelled from the IL phase to the organic phase.

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Section: 61supporting

confidence: 74%

Section: 61mentioning

confidence: 99%

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

et al. 2016

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“…Therefore, our data clearly demonstrate that alkene hydrogenation to alkane is observed on the Pd nanoparticles only and not on the Pd(111) (and Pd(100) [11] ) single crystals.…”

Section: Angewandte Chemiementioning

confidence: 59%

“…[9,10] There is considerably less data on the interaction of higher hydrocarbons. [11][12][13][14] Madix and co-workers studied the adsorption of various alkenes and dienes on the clean and hydrogen (deuterium) precovered Pd(111) and Pd(100) surfaces by TPD. [11,12] They observed an H-D exchange reaction, which was assumed to proceed via a half-hydrogenated intermediate species.…”

mentioning

confidence: 99%

Hydrogenation on Metal Surfaces: Why are Nanoparticles More Active than Single Crystals?

Doyle¹,

Shaikhutdinov²,

Jackson³

et al. 2003

Angew Chem Int Ed

300

243

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Hydrogenation of unsaturated hydrocarbons occurs efficiently on noble-metal catalysts, such as platinum, rhodium, and palladium.[1] The reaction mechanism first proposed by Horiuti and Polanyi [2] in 1934 proceeds by a) hydrogen dissociation on the metal surface, b) alkene adsorption, c) subsequent hydrogen addition to alkene and, finally, d) desorption of the product (alkane). Real hydrogenation catalysts represent very complex systems for studying reaction mechanisms at the molecular level. Therefore, model systems with a reduced complexity have been invoked ranging from single crystals to metal particles deposited on oxide films. [3][4][5][6][7][8] The conclusions regarding reaction mechanism and structural sensitivity are often based upon experiments on single metal crystals.[3] In particular, hydrogenation of alkenes has been shown to be structure insensitive.Herein, we report results showing that alkene hydrogenation reaction under low-pressure conditions, which does not occur on Pd(111) single crystal, proceeds efficiently on palladium nanoparticles. We show that the formation of weakly bound "subsurface" hydrogen is a key factor for hydrogenation to occur efficiently. The subsurface hydrogen exists in both Pd systems. However, the nanoparticle dimensions are such that this hydrogen is accessible to the adsorbed alkene, and hydrogenation occurs. In contrast, for crystals, the hydrogen atoms diffuse so deep into the bulk that they are not accessible to an adsorbed alkene, and therefore hydrogenation does not occur.We have studied the surface chemistry of ethene and different pentene isomers on both Pd(111) single crystal and Pd particles deposited on a thin alumina film (Figure 1). The particles studied are approximately 5 nm in diameter and consist primarily (% 90 %) of (111) facets [8] (% 10 % are (100) facets). The experiments were performed in ultrahigh vacuum on clean and well-defined systems. Using the temperatureprogrammed desorption (TPD) technique, we have observed that a number of hydrocarbon transformations, such as dehydrogenation and H-D exchange, occur on both palla-

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“…Pd(111) is known to bind the unsaturated substrate stronger as compared to Pd(110) (125) which reduces the surface hydrogen concentration leading to the suppressed alkane formation (20). In addition, Pd(100) does not hydrogenate alkenes but isomerizes them while showing absolute selectivity to alkene in an alkyne hydrogenation due to the strong metal-hydrogen bonding on Pd(100) (126).…”

Section: Nanocatalysis With Controlled Shape and Sizementioning

confidence: 99%

Recent Advances in the Liquid‐Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

2009

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Selective Hydrogenation and H-D Exchange of Unsaturated Hydrocarbons on Pd(100)-P(1×1)-H(D)

Cited by 70 publications

References 0 publications

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

Catalytically Active Membranelike Devices: Ionic Liquid Hybrid Organosilicas Decorated with Palladium Nanoparticles

Hydrogenation on Metal Surfaces: Why are Nanoparticles More Active than Single Crystals?

Recent Advances in the Liquid‐Phase Synthesis of Metal Nanostructures with Controlled Shape and Size for Catalysis

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