Vibrational Spectroscopy and Related<i>In situ</i>Studies of Catalytic Reactions within Molecular Sieves

Stavitski, I.; Weckhuysen, Bert M.

doi:10.1002/9783527630295.ch8

Cited by 3 publications

(5 citation statements)

References 97 publications

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“…ZrMe + @SZO 300 . The use of formulation with preadsorbed Py allows for more than 4-fold increase of solvent DNP enhancement, 25 indicating the preservation of TEKPol as further evidenced by EPR spectroscopy (Figure S5). The 15 N DNP-SENS spectra of adsorbed Py show broad intense signals at ca.…”

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confidence: 84%

“…9 However, these are not general solutions, and alternative DNP formulations still need to be developed. Pyridine (Py) is a classical surface probe that allows interrogating the presence of Lewis and Brønsted acid sites by using IR 24,25 or solid-state NMR spectroscopy; previous NMR studies have shown that 15 N MAS NMR, 26−28 in particular when combined with DNP-enhanced NMR techniques, 29 is particularly powerful to readily distinguish between Py bound to Lewis and Brønsted acid sites with different strength, 28 as well as H-bonded Py. 29 Pyridine is also a typical ligand in coordination chemistry and has been used to tame (passivate) the reactivity of metal sites.…”

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confidence: 99%

“…Pyridine (Py) is a classical surface probe that allows interrogating the presence of Lewis and Brønsted acid sites by using IR , or solid-state NMR spectroscopy; previous NMR studies have shown that 15 N MAS NMR, − in particular when combined with DNP-enhanced NMR techniques, is particularly powerful to readily distinguish between Py bound to Lewis and Brønsted acid sites with different strength, as well as H-bonded Py . Pyridine is also a typical ligand in coordination chemistry and has been used to tame (passivate) the reactivity of metal sites. − We thus reasoned that it would be worthwhile investigating the addition of Py in DNP formulation with the goal to both protect highly reactive sites enabling their characterization and to probe the Lewis/Brønsted acid property of the surface sites.…”

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confidence: 99%

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A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts

Yakimov

Mance

Searles

et al. 2020

J. Phys. Chem. Lett.

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Dynamic nuclear polarization surface-enhanced NMR spectroscopy (DNP-SENS) has emerged as a powerful characterization tool in material chemistry and heterogeneous catalysis by dramatically increasing, by up to 2 orders of magnitude, the NMR signals associated with surface sites. DNP-SENS mostly relies on using exogenous polarizing agents (PAs), typically dinitroxyl radicals, to boost the NMR signals. However, the PAs may interact with the surface or even react with surface sites, thus leading to loss or quenching of DNP enhancements. Herein, we describe the development of a DNP-SENS formulation that allows broadening the application of DNP-SENS to samples containing highly reactive surface sites, namely a Ziegler−Natta propylene polymerization catalyst, a sulfated zirconia-supported metallocene, and a silica-supported cationic Mo alkylidene. The protocol consists of adsorbing pyridine prior to the DNP formulation (TEKPol/TCE). The addition of pyridine not only preserves the PAs and thereby restores the DNP enhancement but also allows probing Lewis/Brønsted acid surface sites that are often present on these catalysts.

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confidence: 84%

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confidence: 99%

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confidence: 99%

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A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts

Yakimov

Mance

Searles

et al. 2020

J. Phys. Chem. Lett.

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“…Conventional methods to characterize the chemical nature of acid sites in zeolites include solid-state nuclear magnetic resonance (NMR), , infrared spectroscopy (IR) based on probe molecules, , and X-ray absorption spectroscopy (XAS). , These methods have been used to characterize the heterogeneous population of T-sites in the zeolite framework. Recent advances in atom probe tomography (APT) have opened up new horizons in the sensitive structural characterization of single zeolite particles.…”

Section: Introductionmentioning

confidence: 99%

“…6,7 In addition to the structural parameters of a zeolite catalyst, the chemical nature of adsorbed reactants, physisorbed intermediates, and solvent environment may significantly affect the proton transfer rates and carbocationic chemistry. 8 Conventional methods to characterize the chemical nature of acid sites in zeolites include solid-state nuclear magnetic resonance (NMR), 9,10 infrared spectroscopy (IR) based on probe molecules, 11,12 and X-ray absorption spectroscopy (XAS). 13,14 These methods have been used to characterize the heterogeneous population of T-sites in the zeolite framework.…”

Section: ■ Introductionmentioning

confidence: 99%

Reversible and Site-Dependent Proton-Transfer in Zeolites Uncovered at the Single-Molecule Level

et al. 2018

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Zeolite activity and selectivity is often determined by the underlying proton and hydrogen-transfer reaction pathways. For the first time, we use single-molecule fluorescence microscopy to directly follow the real-time behavior of individual styrene-derived carbocationic species formed within zeolite ZSM-5. We find that intermittent fluorescence and remarkable photostability of carbocationic intermediates strongly depend on the local chemical environment imposed by zeolite framework and guest solvent molecules. The carbocationic stability can be additionally altered by changing para-substituent on the styrene moiety, as suggested by DFT calculations. Thermodynamically unstable carbocations are more likely to switch between fluorescent (carbocationic) and dark (neutral) states. However, the rate constants of this reversible change can significantly differ among individual carbocations, depending on their exact location in the zeolite framework. The lifetimes of fluorescent states and reversibility of the process can be additionally altered by changing the interaction between dimeric carbocations and solvated Brønsted acid sites in the MFI framework. Advanced multidimensional magic angle spinning solid-state NMR spectroscopy has been employed for the accurate structural elucidation of the reaction products during the zeolite-catalyzed dimerization of styrene in order to corroborate the single-molecule fluorescence microscopy data. This complementary approach of single-molecule fluorescence microscopy, NMR, and DFT collectively indicates that the relative stability of the carbocationic and the neutral states largely depends on the substituent and the local position of the Brønsted acid site within the zeolite framework. As a consequence, new insights into the host–guest chemistry between the zeolite and aromatics, in terms of their surface mobility and reactivity, have been obtained.

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Infrared Spectroscopy on Powder Catalysts

Stavitski¹

2013

In‐situ Characterization of Heterogeneous Catalysts

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Vibrational Spectroscopy and RelatedIn situStudies of Catalytic Reactions within Molecular Sieves

Cited by 3 publications

References 97 publications

A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts

A Formulation Protocol with Pyridine to Enable Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy on Reactive Surface Sites: Case Study with Olefin Polymerization and Metathesis Catalysts

Reversible and Site-Dependent Proton-Transfer in Zeolites Uncovered at the Single-Molecule Level

Infrared Spectroscopy on Powder Catalysts

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