Thermal Chemistry of C<sub>4</sub>Hydrocarbons on Pt(111):  Mechanism for Double-Bond Isomerization

Lee, Ilkeun; Zaera, Francisco

doi:10.1021/jp045443u

Cited by 59 publications

(98 citation statements)

References 59 publications

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“…[1][2][3] This is a surprising result that runs counter to thermodynamic expectations, and not what is usually observed in alkene catalytic conversions. 4,5 It was hypothesized that the cis-trans isomerization reversal may be associated with structural details of the surface, which could therefore be used to tune selectivity in catalysis.…”

contrasting

confidence: 64%

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Delbecq

Zaera

2008

J. Am. Chem. Soc.

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DFT calculations were performed to explain the preference for the conversion of trans-2-butene to its less stable cis isomer on Pt(111) surfaces reported previously. The results indicate that the main factors controlling the direction of this reaction are the lesser degrees of molecular rearrangement and surface reconstruction required in the adsorption of the cis isomer on the hydrogen-covered Pt surface. This is a case where hydrogen coverage and atomic restructuring not only dominate the energetics of adsorption but also define reaction selectivity.

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contrasting

confidence: 64%

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Delbecq

Zaera

2008

J. Am. Chem. Soc.

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“…In another example, the dehydrogenation of cyclohexene was found to be faster on Pt (111) than on Pt (100) single-crystal surfaces (16). Our recent surface-science investigations on the isomerization of unsaturated olefins (17)(18)(19) strongly suggest that selectivity toward the formation of the cis isomer may be favored by Pt (111) facets. Additional surfacescience reports on the conversion of alkyl and alkene adsorbates under vacuum conditions (20)(21)(22)(23)(24)(25), as well as studies with more realistic model systems (26,27), point to a potential structure sensitivity in the conversion of other olefins and unsaturated hydrocarbons.…”

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confidence: 96%

“…Although the conversion of alkenes by transition metals is one of the oldest and most studied systems in catalysis (51)(52)(53), key issues such as the dependence of activity on structure remain unresolved (54). As mentioned in our Introduction, results from recent surface-science work in our laboratory have indicated that, at least on Pt (111) single-crystal surfaces, the isomerization of trans-2-butene to its cis isomer is easier than the opposite cis-totrans conversion (17)(18)(19). A kinetic study on the catalytic conversion of butenes on single-crystal surfaces (55) has also suggested different selectivities on Pt (111) vs. Pt (100) surfaces.…”

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confidence: 99%

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Lee

Morales

Albiter

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272: 1924 -1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon-carbon doublebond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes. On the basis of their kinetic behavior, catalytic reactions are often classified as either mild or demanding (1-3). Demanding reactions-such as the oxidation of CO, NO, or hydrocarbons; the synthesis of ammonia; and most oil processing conversionsusually require high temperatures and pressures, and involve small concentrations of intermediates similar to those identified under vacuum. The performance of these reactions often depends strongly on the structure of the catalyst used (4, 5). In contrast, mild reactions-in particular, hydrogenations and isomerizations of unsaturated hydrocarbons-take place under less-demanding temperature and pressure conditions. Mild reactions have historically been considered structure-insensitive (6-8), but that conclusion has been drawn from studies on reactivity vs. metal dispersion that used ill-defined supported catalysts (9, 10) and has been questioned by more recent studies using better catalytic models (11). For instance, both experimental (12-14) and theoretical (15) studies on the selective catalytic hydrogenation of CAO bonds in unsaturated aldehydes have suggested that such reactions may be promoted by close-packed (111) surfaces. In another example, the dehydrogenation of cyclohexene was found to be faster on Pt (111) than on Pt (100) single-crystal surfaces (16). Our recent surface-science investigations on the isomerization of unsaturated olefins (17-19) strongly suggest that selectivity toward the formation of the cis isomer may be favored by Pt (111) facets. Additional surfacescience reports on the conversion of alkyl and alkene adsorbates under vacuum conditions (20-25), as well as studies with more realistic model systems (26, 27), point to a potential structure sensitivity in the conversion of other olefins and unsaturated hydrocarbons.These results not only s...

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“…Similar arguments can be made for the conversion of alcohols and for the oxidation of hydrocarbons [20]. Figure 8 displays the energy diagram of a third example, that of the migration and cis-trans isomerization of double bonds in olefins [167]. It can be seen there that the relative yields for 1-, cis-2-, and trans-2-butenes in a given catalytic process may rely on the relative rates for b-hydride elimination from different positions within the common 2-butyl surface intermediate.…”

Section: Discussionmentioning

confidence: 73%

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

Zaera

2005

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Catalysis is central to most industrial processes for chemical manufacturing. As catalytic processes have become more complex and more demanding, selectivity has become the central issue in their design. Selectivity is defined by the relative rates of competing reaction pathways available to crucial intermediates, and can be controlled by subtle changes in the nature of the catalyst, the reactants, and/or the reaction conditions. In order to be able to do this in a systematic manner, a good understanding of the catalytic reaction mechanisms is needed. Here a connection is drawn between the key elementary steps comprising hydrocarbon conversion reactions on surfaces and those known to occur on discrete organometallic complexes. This way, the hydrogenation, dehydrogenation, hydrogenolysis, chain growth, and isomerization reactions typical in heterogeneous catalysis are redefined in terms of hydride elimination, oxidative addition, reductive elimination, migratory insertion, and . 1, 2-shift elementary steps, among others. It is suggested that the knowledge already available from organometallic chemistry can be used to further advance the understanding of the surface science involved in heterogeneous catalysis. Thanks to the commonality of the chemistry involved, a better synergy could also be established between homogeneous and heterogeneous catalytic development. These ideas are discussed in this article in a critical and personal way.

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Thermal Chemistry of C₄Hydrocarbons on Pt(111): Mechanism for Double-Bond Isomerization

Cited by 59 publications

References 59 publications

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

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Thermal Chemistry of C4Hydrocarbons on Pt(111): Mechanism for Double-Bond Isomerization

Cited by 59 publications

References 59 publications

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Origin of the Selectivity for Trans-to-Cis Isomerization in 2-Butene on Pt(111) Single Crystal Surfaces

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Mechanisms of hydrocarbon conversion reactions on heterogeneous catalysts: analogies with organometallic chemistry

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Product

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Thermal Chemistry of C₄Hydrocarbons on Pt(111): Mechanism for Double-Bond Isomerization