Theoretical Study of Pyridine and 4,4‘-Bipyridine Adsorption on the Lewis Acid Sites of Alumina Surfaces Based on Ab Initio and Density Functional Cluster Calculations

Kassab, E.; Castellà-Ventura, Martine

doi:10.1021/jp040524b

Cited by 28 publications

(14 citation statements)

References 108 publications

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“…In order to understand structural transition in MOF‐508, we primarily recorded the Raman and IR spectrum of MOF‐508a. Figure shows the Raman spectrum of MOF‐508a, with the corresponding band assignments in Table . Experimental and calculated IR spectra are presented in Figs S7 and S8 followed by the band assignments in Table S2.…”

Section: Resultsmentioning

confidence: 99%

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Kumari

Patil

Bhadram

et al. 2015

J Raman Spectroscopy

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Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non-porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′-Bipy) 0.5 · DMF(H 2 O) 0.5 } was selected for study. We have investigated structural transformation in MOF-508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF-508 framework is driven by ligand conformation change and inter-linker interactions. The presence of Raman signatures of adsorbed CO 2 and its librational mode at 149 cm À1 suggests cooperative adsorption of CO 2 in the MOF-508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol.Additional supporting information may be found in the online version of this article at the publisher's web site.Understanding guest and pressure-induced porosity

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Section: Resultsmentioning

confidence: 99%

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Kumari

Patil

Bhadram

et al. 2015

J Raman Spectroscopy

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“…3). The most evident band distinguishing molecular pyridine on strong Lewis acid sites is at 1450 cm −1 similar to alumina and silica-alumina [31,32] while pyridinium ions give rise to the characteristic band at 1545 cm −1 with both forms of adsorption contributing to the intensity at 1490 cm −1 [33]. In addition to this qualitative assessment, coupling to a gravimetric balance permitted the total acidity to be assessed (Table 1) along with the individual contributions due to adsorption on the different acid sites when coupling balance and FTIR data.…”

Section: Characterizationmentioning

confidence: 98%

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

et al. 2017

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The desorption of methanol and dimethyl ether has been studied over fresh and hydrocarbon-occluded ZSM-5 catalysts with Si/Al ratios of 25, 36 and 135 using a temporal analysis of products reactor. The catalysts were characterized by XRD, SEM, N 2 physisorption and pyridine FT-IR. The crystal size increases with Si/Al ratio from 0.10 to 0.78 µm. The kinetic parameters were obtained using the Redhead method and a plug flow reactor model with coupled convection, adsorption and desorption steps. ZSM-5 catalysts with Si/Al ratios of 25 and 36 exhibit three adsorption sites (low, medium, and high temperature sites), while there is no difference between medium and high temperature sites at a Si/Al ratio of 135. Molecular adsorption on the low temperature site and dissociative adsorption on the medium and high temperature sites give a good match between experiment and the plug flow reactor model. The DME desorption activation energy was systematically higher than that of methanol. Adsorption stoichiometry shows that methanol and DME form clusters onto the binding sites. When non-activated re-adsorption is accounted for, a local equilibrium is reached only on the low and medium temperature binding sites. No differences were observed, other than in site densities, when extracting the kinetic parameters for fresh and activated ZSM-5 catalysts at full coverage. Graphical AbstractElectronic supplementary material The online version of this article (https://doi

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“…More specifically, in solution, the ν 1 mode is shifted at increasingly higher frequencies upon hydrogen-bonding with water (1002 cm −1 ), protonation by a Brønsted acid (1010 cm −1 ), and formation of a complex with a Lewis acid (1019 cm −1 ). These measurable shifts, originating from changes in geometry and the direct effect of the ligand on the force constant, can thus be exploited to distinguish the different interactions of pyridine with its environment [45,46].…”

Section: Resultsmentioning

confidence: 99%

Resolving the Acid Site Distribution in Zn-Exchanged ZSM-5 with Stimulated Raman Scattering Microscopy

Fleury

Roeffaers

2020

Catalysts

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Zeolites are widely used acid catalysts in research and in industrial processes. The catalytic performance of these materials is affected by the nature and concentration of Brønsted and Lewis acid sites. The balance between these types of active sites—and thus the activity and selectivity of the zeolite—can be altered by the introduction of metal species, e.g., by ion exchange. Although the acidic properties of zeolites are routinely characterized by bulk-scale techniques, this ensemble-averaged approach neglects the local variations in the material. Insights into the distribution of active sites at the single-particle level are thus critical to better understand the impact of post-synthetic modifications on the zeolite acidity. In this contribution, we spatially resolve Brønsted and Lewis acid sites in protonated and Zn-exchanged ZSM-5 crystals. To this end, the vibrational modes of pyridine chemisorbed on active sites are mapped with stimulated Raman scattering (SRS) microscopy. The SRS images reveal sharp inter- and intra-particle heterogeneities in the distribution of Lewis acid sites introduced upon ion exchange, ascribed to local variations in the Al content. Besides assessing the impact of Zn exchange on the active site distribution in ZSM-5 crystals, this approach enables uniquely to map the distribution of Lewis acid sites in catalysts at the single-particle level.

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Theoretical Study of Pyridine and 4,4‘-Bipyridine Adsorption on the Lewis Acid Sites of Alumina Surfaces Based on Ab Initio and Density Functional Cluster Calculations

Cited by 28 publications

References 108 publications

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Mechanistic Insights into the Desorption of Methanol and Dimethyl Ether Over ZSM-5 Catalysts

Resolving the Acid Site Distribution in Zn-Exchanged ZSM-5 with Stimulated Raman Scattering Microscopy

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