Heterogeneous Catalysis: The Horiuti–Polanyi Mechanism and Alkene Hydrogenation

Mattson, Bruce; Foster, W. H.; Greimann, Jaclyn; Hoette, Trisha M.; Le, Nhu Thi So; Mirich, Anne; Wankum, Shanna; Cabri, Ann; Reichenbacher, Claire; Schwanke, Erika

doi:10.1021/ed300437k

Cited by 84 publications

(80 citation statements)

References 25 publications

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“…In our previous work with ethene and 1-butene, 5 we also reported extensive D/H exchange, but under very mild conditions (ice bath). The chemisorption of H 2 and D 2 with Pd occurs at extremely low temperatures, despite the enormous H−H covalent bond energy, and is in fact exothermic.…”

Section: ■ Summarymentioning

confidence: 67%

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Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

et al. 2015

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Two gas phase deuterium/hydrogen exchange reactions are described utilizing a simple inexpensive glass catalyst tube containing 0.5% Pd on alumina through which gas mixtures can be passed and products collected for analysis. The first of these exchange reactions involves H 2 + D 2 , which proceeds at temperatures as low as 77 K yielding a mixture that includes HD. Products are analyzed by 1 H NMR spectrometry. At low temperatures, this reaction requires a catalyst, but it proceeds without a catalyst at high temperature of a gentle flame. The second deuterium/hydrogen exchange reaction involves CH 4 + D 2 producing a series of isotopologues, methane-d x , x = 0−4, with product analysis by GC−MS and 1 H NMR spectrometry. This reaction only takes place in the presence of a catalyst at elevated temperatures due to the large energy of activation of the sp 3 -carbon-to-hydrogen bond. Two outcomes have been observed in the literature regarding D/H exchange and methane. Some catalysts and temperature conditions yield a single-exchange result, methane-d 1 . Others yield multiple exchange results, such as we observe with our catalyst. The single exchange outcome is associated with lower temperatures. Two mechanisms, one by Kemball (1959) and one by Frennet (1974), have been put forth to explain single and multiple exchange outcomes. We discuss our results in the context of these mechanisms. Interested readers could develop a research experience for undergraduate chemistry students based on the openended experiments presented here.

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Section: ■ Summarymentioning

confidence: 67%

“…Over the past decade, we have used catalyst tubes to provide research experiences for undergraduate students. 4,5 In this paper, we present the basic experimental design for carrying out the reaction between methane and D 2 . We also present the proposed mechanisms described in the literature.…”

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confidence: 99%

Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

et al. 2015

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“…Since the mechanism was first proposed in 1934 it has received a sound confirmation from other experimental works on hydrogenation of different kinds of alkenes and other double bond containing molecules [49]. The two-step hydrogen insertion, with one step being rate-limiting and the other being equilibrated has been thoroughly confirmed by experiments of deuterium exchange with different reacting systems.…”

Section: Kinetic Modelingmentioning

confidence: 77%

Kinetic study of the selective hydrogenation of styrene over a Pd egg-shell composite catalyst

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Badano

Lederhos

et al. 2015

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This is a study on the kinetics of the liquid-phase hydrogenation of styrene to ethylbenzene over a catalyst of palladium supported on an inorganic-organic composite. This support has a better mechanical resistance than other commercial supports, e.g. alumina, and yields catalysts with egg-shell structure and a very thin active Pd layer. Catalytic tests were carried out in a batch reactor by varying temperature, total pressure and styrene initial concentration between 353-393 K, 10-30 bar, and 0.26-0.60 mol L -1 , respectively. Kinetic models were developed on the assumptions of dissociative hydrogen chemisorption and non-negligible adsorption of hydrogen and styrene. Final chemical reaction expressions useful for reactor design were obtained. The models that best fitted the experimental data were those ones that considered the surface reaction as the limiting step. In this sense a two-step Horiuti-Polanyi working mechanism with half hydrogenation intermediates gave the best fit of the experimental data. The heats of adsorption of styrene and ethylbenzene were also estimated.

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“…30 According to the Horiuti-Polanyi mechanism, the hydrogenation sequence of alkenes consists of three steps: (i) alkene adsorption on the surface of the hydrogenated metal catalyst, (ii) hydrogen migration to the β-carbon of the alkene with formation of a σ-bond between the metal and α-C, and finally (iii) reductive elimination of the free alkane. 71 This mechanism was adapted for the hydrogenation of dienes (i.e., 1,3-cyclooctadienes (6)), and thus, an additional step is included (step (iv): decoordination of the monoene (i.e., cyclooctene (7), see Scheme 4). The reaction rate of the hydrogenation of the 1,3-cyclooctadiene (6) was observed to be dependent on the fraction of catalyst surface covered by the substrate and zero-order with respect to hydrogen (Tables S6-S9 and Figures S10-S15).…”

Section: Mechanistic and Kinetic Evidence Of Palladium Surface Modifimentioning

confidence: 99%

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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Heterogeneous Catalysis: The Horiuti–Polanyi Mechanism and Alkene Hydrogenation

Cited by 84 publications

References 25 publications

Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

Kinetic study of the selective hydrogenation of styrene over a Pd egg-shell composite catalyst

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

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