Theoretical Study of Pyrrole Interaction with Alkali Metal Exchanged Zeolites: Investigation of the Reliability of Cluster and Periodic Models

2003 ◽  
Vol 68 (10) ◽  
pp. 1848-1860 ◽  
Author(s):  
Jan Kučera ◽  
Petr Nachtigall
Keyword(s):  
Alkali Metal ◽  
Theoretical Study ◽  
Interatomic Potential ◽  
Alkali Metal Cation ◽  
Cluster Models ◽  
Zeolite Framework ◽  
Stretching Vibration ◽  
Periodic Models ◽  
Experimental Shift ◽  
Good Agreement

The interaction of pyrrole with the alkali metal exchanged zeolites was investigated using cluster models of various sizes and with a hybrid quantum mechanics/interatomic potential function model (QM-pot). The interaction of pyrrole with the M+/zeolite is dominantly driven by the interaction of pyrrole π-system with the alkali metal cation. Further stabilization is due to the formation of the hydrogen bonds between NH and framework oxygen atoms. A good agreement between calculated and experimental shift of the N-H stretching vibration upon the adsorption of pyrrole in M+/zeolite was found with the periodic QM-pot model. The performance of the cluster models for the description of pyrrole interaction with M+/zeolite is discussed. Reliable results can be obtained only when large cluster models are used for description of the zeolite framework.

Theoretical Study of the Physisorption of CO on Metal Oxide Surfaces Using the KSCED-DFT Approach

1998 ◽  
Vol 63 (9) ◽  
pp. 1447-1459 ◽  
Author(s):  
Nathalie Vulliermet ◽  
Tomasz A. Wesolowski ◽  
Jacques Weber
Keyword(s):  
Metal Oxide ◽  
Frequency Shift ◽  
Electron Density ◽  
Effective Potential ◽  
Theoretical Study ◽  
Adsorbed Molecule ◽  
Theoretical Studies ◽  
Metal Oxide Surfaces ◽  
Stretching Vibration ◽  
Good Agreement

Theoretical studies on structure and stretching frequency of the CO molecule physisorbed on the MgO(100) or ZnO(1010) surfaces are reported. The properties of the adsorbed molecule were investigated by means of the recently developed formalism of Kohn-Sham equations with constrained electron density (KSCED). The KSCED method makes it possible to divide a large system into two subsystems and to study one of them using Kohn-Sham-like equations with an effective potential which takes into account the interactions between subsystems. This method (KSCED) was shown to be adequate to study the properties of the CO molecule adsorbed on the MgO(100) surface as reported in a previous paper (Wesolowski et. al.: J. Mol. Struct., THEOCHEM, in press). The effect of the interactions with the surface on the CO stretching frequency and geometry was analyzed for vertically bound (C-down) CO at the Zn-site of the ZnO(1010) surface. The ZnO(1010) surface was represented using several cluster models: Zn2+, (ZnO3)4-, or Zn9O9 embedded in a matrix of point charges. The KSCED frequency shift of the CO stretching vibration is blue-shifted and in good agreement with experiment.

Influence of alkali metal cations on the photoheterolysis of 9-cyclopropyl-9-fluorenol and the reactivity of the 9-cyclopropyl-9-fluorenyl cation in non-acidic zeolites

2003 ◽  
Vol 81 (6) ◽  
pp. 647-659 ◽  
Author(s):  
Melanie A O'Neill ◽  
Frances L Cozens
Keyword(s):  
Alkali Metal ◽  
Metal Cation ◽  
Diffuse Reflectance ◽  
Bond Cleavage ◽  
Alkali Metal Cation ◽  
Zeolite Framework ◽  
Time Resolved ◽  
Highly Sensitive ◽  
Cation Size ◽  
Acidic Zeolites

Alkali metal cation regulation of carbocation formation and reactivity in non-acidic zeolites is probed using the photoheterolysis reaction of 9-cyclopropyl-9-fluorenol. Nanosecond time-resolved diffuse reflectance is employed to directly observe the 9-cyclopropyl-9-fluorenyl cation as a transient species within the non-acidic zeolites. The efficiency of carbocation formation via photoheterolysis and the dynamics of other reaction pathways available to photoexcited 9-cyclopropyl-9-fluorenol are found to be strongly dependent on the zeolite alkali metal counterion. In particular, the yield of carbocation decreases with increasing counterion size in a manner consistent with the zeolite assisting the excited state C—O bond cleavage via Lewis acid catalysis involving the metal cation. Zeolite encapsulation is also found to modulate the ability of water and methanol to assist photoheterolysis. For instance, the influence of coadsorbed water on the photoheterolysis reaction within zeolites is found to be highly sensitive to the alkali metal cation. The rate constant for intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation increases significantly as the alkali metal cation size increases and as the Si–Al ratio decreases. These reactivity trends suggest that the intrazeolite decay of the 9-cyclopropyl-9-fluorenyl cation involves nucleophilic addition at the active site [Si-O-Al]– bridges of the zeolite framework. In addition, the reactivity of the 9-cyclopropyl-9-fluorenyl cation within alkali metal zeolites can be regulated by the co-inclusion of reagents such as methanol, water, and 1,1,1,3,3,3-hexafluoro-2-propanol.Key words: cation-exchanged zeolites, 9-cyclopropyl-9-fluorenyl cation, laser photolysis, reactivity.

scholarly journals Cation–π interactions in competition with cation microhydration: a theoretical study of alkali metal cation–pyrene complexes

2017 ◽  
Vol 23 (4) ◽  
Author(s):  
Hasan Pašalić ◽  
Adelia J. A. Aquino ◽  
Daniel Tunega ◽  
Georg Haberhauer ◽  
Martin H. Gerzabek ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Metal Cation ◽  
Theoretical Study ◽  
Alkali Metal Cation ◽  
Π Interactions

An Experimental and Theoretical Study of Alkali Metal Cation Interactions with Cysteine

2010 ◽  
Vol 114 (11) ◽  
pp. 3927-3937 ◽  
Author(s):  
P. B. Armentrout ◽  
Erin I. Armentrout ◽  
Amy A. Clark ◽  
Theresa E. Cooper ◽  
Elana M. S. Stennett ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Metal Cation ◽  
Theoretical Study ◽  
Alkali Metal Cation
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