Proline-Derived Structural Phases on Cu{311}

Madden, David C.; Temprano, Israel; Jenkins, Stephen J.; Driver, S.M.

doi:10.1007/s11244-015-0400-2

Cited by 6 publications

(5 citation statements)

References 41 publications

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“…Alternatively, adsorbed chiral molecules may bestow chirality on metal surfaces. With relatively inert metals such as copper, it has been shown that the adsorption of chiral molecules can lead to the formation of many ordered homochiral structures. − Perhaps more interestingly, on the surface of more active metals such as Pt or Pd, chiral sites can be generated via the adsorption of submonolayer coverages of “templating” chiral molecules. − In that case, it is presumed that the adsorbates form supramolecular structures on the surface containing chiral pockets that can act as enantioselective adsorption sites for other adsorbates. Unfortunately, as mentioned before, these ideas generated from experiments using model systems are yet to translate into the design of realistic enantioselective catalysts.…”

Section: Selectivitymentioning

confidence: 99%

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%

The Surface Chemistry of Metal-Based Hydrogenation Catalysis

2017

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“…After adsorption and subsequent annealing to 350 -420 K, the pyrrolidine ring dehydrogenates and hydrogen is evolved, as indicated by reflection absorption infrared spectroscopy (RAIRS) and confirmed by TPRS. 38 At temperatures of 460 -480 K, the carboxylate group dissociates from the dehydrogenated ring and desorbs from the surface as CO2 with the dehydrogenated ring desorbing as pyrolle at slightly higher temperatures.…”

Section: Figurementioning

confidence: 99%

“…These m/z ratios were selected based on TPRS performed by other research groups. 36,38,40,50,51 Figure 3 shows the TPRS signals versus temperature for the m/z ratios monitored during D-Pro decomposition. The peak at 475 K in the m/z = 2 signal is consistent with hydrogen desorption due to the dehydrogenation of the pyrrolidine ring.…”

Section: Pro Decomposition Mechanismmentioning

confidence: 99%

“…Given these interesting observations, Pro adsorption and surface chemistry has been studied extensively by a number of researchers. [35][36][37][38][39] Tysoe et al studied the adsorption and decomposition of L-Pro on Pd(111) using temperature programmed reaction spectroscopy (TPRS) and x-ray photoemission spectroscopy (XPS). They found that Pro on Pd(111) is adsorbed as a zwitterion in the monolayer and decomposes via a complex pathway, starting with the dissociation of the Cα-COO bond to form CO2 and pyrrolidine, (CH2)4NH, which in turn dehydrogenates to pyrrole (C4H4NH), HCN and other nitrile compounds, detected by mass spectrometry as a complex mixture.…”

Section: Introductionmentioning

confidence: 99%

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Enantiospecific equilibrium adsorption and chemistry of d‐/l‐proline mixtures on chiral and achiral Cu surfaces

Dutta

Gellman

2019

Chirality

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A fundamental understanding of the enantiospecific interactions between chiral adsorbates and understanding of their interactions with chiral surfaces is key to unlocking the origins of enantiospecific surface chemistry. Herein, the adsorption and decomposition of the amino acid proline (Pro) has been studied on the achiral Cu(110), Cu(111) surfaces and on the chiral Cu(643) R&S surfaces. Isotopically labelled 1-13 C-L-Pro has been used to probe the Pro decomposition mechanism and to allow mass spectrometric discrimination of D-Pro and 1-13 C-L-Pro when adsorbed as mixtures. On the Cu(111) surface, Xray photoelectron spectroscopy reveals that Pro adsorbs as an anionic species in the monolayer. On the chiral Cu(643) R&S surface, adsorbed Pro enantiomers decompose with non-enantiospecific kinetics. However, the decomposition kinetics were found to be different on the terraces versus the kinked steps. Exposure of the chiral Cu(643) R&S surfaces to a racemic gas phase mixture of D-Pro and 1-13 C-L-Pro resulted in the adsorption of a racemic mixture; i.e. adsorption is not enantiospecific. However, exposure to non-racemic mixtures of D-Pro and 1-13 C-L-Pro resulted in amplification of enantiomeric excess on the surface, indicative of homochiral aggregation of adsorbed Pro. During coadsorption, this amplification is observed even at very low coverages, quite distinct from the behaviour of other amino acids, which begin to exhibit homochiral aggregation only after reaching monolayer coverages. The equilibrium adsorption of D-Pro and 1-13 C-L-Pro mixtures on achiral Cu(110) did not display any aggregation, consistent with prior STM observations of DL-Pro/Cu(110). This demonstrates convergence between findings from equilibrium adsorption methods and STM experiments and corroborates formation of a 2D random solid solution.

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“…The UHV system used in this work has been fully described in our previous work, [35][36][37] so here we describe the relevant sections only briefly. The system is divided into three different levels, each accommodating different components.…”

Section: Rairs Experimentsmentioning

confidence: 99%