Adsorption of Unsaturated and Multifunctional Molecules: Bonding and Reactivity

Haubrich, Jan; Wandelt, K.

doi:10.1002/9783527680573.ch40

Cited by 4 publications

(5 citation statements)

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“…In terms of industrial interest, the production of high-purity butene streams for polymerization or copolymerization processes requires the hydrogenation of the butadiene impurities contained in the butene cuts from naphtha steam crackers, as with the acetylene impurities in the ethylene cuts. Palladium is also considered the best catalyst for this type of partial hydrogenation, ,− again either because of differences in relative adsorption strengths, , with the strongly adsorbing 1,3-butadiene displacing the more weakly adsorbing butenes, or thanks to its unique kinetics, by which the intermediate mono-olefin desorbs before more extensive hydrogenation can take place. , Yet, the performance of palladium-only catalysts is not always satisfactory; efforts are under way to improve that, either by modifying the structure of the supported Pd nanoparticles or, more commonly, via alloying with a second metal.…”

Section: Selectivitymentioning

confidence: 99%

“…From a mechanistic point of view, a number of surface intermediates have been proposed on the basis of results from both experimental and theoretical studies, including the half-hydrogenated species expected from the Horiuti–Polanyi mechanism as well as the more strongly bonded carbonaceous layers expected in hydrogenation reactions, as discussed in Section . − Much has been made of the difference in selectivity in processes with Pd versus Pt catalysts, , which different quantum-mechanic studies have explained in terms of relative differences in adsorption energies for different intermediates. The Sautet group, for instance, established that radical species are more clearly stabilized on Pt than on Pd, and proposed that while 1,3-butadiene may adsorb in a di-σ bonding mode and with minimal distortion on Pd, it may adopt a 1,2,3,4-tetra-σ structure on Pt .…”

Section: Selectivitymentioning

confidence: 99%

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The Surface Chemistry of Metal-Based Hydrogenation Catalysis

2017

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The promotion of hydrogenation reactions by transitionmetal-based heterogeneous catalysts was established many decades ago but is still quite common in the chemical industry. Because of their importance, these processes have been studied in great detail from both fundamental and practical points of view, and much has been learned about them. However, some key questions remain unanswered, and solutions to specific industrial needs are still pending. In this Perspective, we discuss the state-of-the-art of our understanding of some of the fundamental issues associated with hydrogenation catalysis. From the mechanistic point of view, we use the example of olefin hydrogenation to assess the status of our knowledge on the adsorption of the organic reactants, the role that the strongly adsorbed carbonaceous deposits that form during reaction play in defining the catalytic kinetics, the mechanistic details of the hydrogen dissociative uptake and surface mobility during reaction, and the dynamic changes of the structure of the surface induced by the catalytic conditions. We then introduce the issue of selectivity in connection with the hydrogenation of alkynes, dienes, trienes, and aromatics; unsaturated aldehydes and imines; and cases where hydrogenation competes with other types of reactions such as dehydrogenations, skeletal rearrangements, cyclizations, and hydrogenolysis. Two general approaches to the control of selectivity are discussed: via the tuning of the structure of the catalytic surface, which can now be addressed by using nanoparticles with specific sizes and shapes, and by modifying the electronic properties of the metal, via the addition of a second element. Finally, we make reference to the interest in designing enantioselective hydrogenation processes using heterogeneous metal catalysts, and we briefly summarize the ideas that have developed from surface-science studies toward this goal and the advances made in understanding the most promising approach to date, which involves the addition of molecular chiral modifiers to the reaction mixtures.

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Section: Selectivitymentioning

confidence: 99%

Section: Selectivitymentioning

confidence: 99%

The Surface Chemistry of Metal-Based Hydrogenation Catalysis

2017

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“…The unsaturated aldehyde hydrogenation reactions are likely to be initiated by the molecular adsorption of the reactant (crotonaldehyde) on the hydrogen-covered platinum surface. Density functional theory (DFT) calculations have indicated that di-σ-bonded adsorbates resulting from rehybridization and bonding of either the CC or the CO bond (or both) to Pt surface atoms are quite stable; − therefore, those could be proposed as the starting point of these reactions. However, it is also well-known from both experimental data ,,,− and DFT calculations ,, that, at least with olefins, π bonding becomes dominant as the surface is modified with adsorbed hydrogen atoms, and that it is the π intermediate that becomes hydrogenated during catalysis. , In fact, the di-σ bonding that has been seen for crotonaldehyde on clean Pt(111) using sum-frequency generation (SFG) spectroscopy has been shown to disappear upon the addition of hydrogen to the reaction mixture .…”

mentioning

confidence: 99%

Selectivity in Hydrogenation Catalysis with Unsaturated Aldehydes: Parallel versus Sequential Steps

Dong

Zaera

2018

J. Phys. Chem. Lett.

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A high-flux molecular beam setup has been used to characterize the kinetics of the steady-state catalytic hydrogenation of unsaturated aldehydes, specifically of crotonaldehyde, promoted by platinum surfaces under single-collision conditions. Surprisingly, in addition to the hydrogenation of the individual single bonds, to yield the saturated aldehyde and the unsaturated alcohol, the formation of the saturated alcohol, the product of the hydrogenation of both C═C and C═O bonds, was detected as well. This indicates that the dual hydrogenation reaction is a primary pathway and not the result of secondary hydrogenation of the other products as commonly assumed. Moreover, an increase in the partial pressure of the reactant was found to shift the reaction selectivity from the saturated alcohol to the saturated aldehyde without significantly affecting the selectivity toward the production of the unsaturated alcohol. We explain these observations by proposing a mechanism involving the parallel formation of several monohydrogenated intermediates on the surface.

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“…Much research has been directed at trying to understand this correlation with particular emphasis on the details of adsorption on Pt surfaces. For instance, a combination of quantum mechanics calculations and experiments has indicated that the adsorption of acrolein on Pt(111) is strongly dependent on its coverage on the surface, with the most stable coordination being in a flat arrangement at low coverages and a more tilted geometry at high coverages. − Similar results have in general been obtained with other unsaturated aldehydes, but crucial differences have also been seen due to the additional substitutions, a methyl group in crotonaldehyde − or a phenyl aromatic ring in cinnamaldehyde. − Most trends identified with pure Pt catalysts seem to hold when using Pt-containing alloys. , …”

Section: Introductionmentioning

confidence: 74%

Adsorption of Acrolein, Crotonaldehyde, and Cinnamaldehyde on Pt(111) Surfaces: A Comparative DFT Study

Ponce Perez,

Guerrero-Sánchez,

Takeuchi

et al. 2024

J. Phys. Chem. C

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Using ab initio calculations, we have investigated the adsorption of both S-cis and S-trans isomers of acrolein, crotonaldehyde, and cinnamaldehyde on the Pt(111) surface at low and high surface coverages and for five types of coordinations. Emphasis was placed on identifying trends by highlighting the similarities and differences in the adsorption of all three molecules. Adsorption was found to depend on coverage: the most stable adsorption geometry at low coverages is flat, in either η 3 or η 4 coordinations with most atoms bonded to the surface, whereas a more tilted arrangement involving fewer atoms, in a η 2 -C 2 C 3 coordination mode, prevails at high coverages. The extra methyl group in crotonaldehyde was determined to lead to a destabilization of the multiply coordinated adsorbates at high coverages, whereas the aromatic ring in cinnamaldehyde was found to be able to bind itself to the Pt surface, at least at low coverages, and thus increase the absolute value of the adsorption energy by about 0.5 eV. Additional calculations using a noncovalent interaction index provided further insights into the variations in bonding to the surface across the three molecules versus coverage in terms of both covalent and noncovalent attractive and repulsive interactions.

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Adsorption of Unsaturated and Multifunctional Molecules: Bonding and Reactivity

Cited by 4 publications

References 214 publications

The Surface Chemistry of Metal-Based Hydrogenation Catalysis

The Surface Chemistry of Metal-Based Hydrogenation Catalysis

Selectivity in Hydrogenation Catalysis with Unsaturated Aldehydes: Parallel versus Sequential Steps

Adsorption of Acrolein, Crotonaldehyde, and Cinnamaldehyde on Pt(111) Surfaces: A Comparative DFT Study

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