Calorimetric and IR-Spectroscopic Study of Methanol Adsorption on Zeolites

Izmailova, S. G.; Karetina, I. V.; Khvoshchev, S. S.; Shubaeva, M. A.

doi:10.1006/jcis.1994.1235

Cited by 39 publications

(42 citation statements)

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“…The methanol crosses either the 4-ring or the window in structures 1 and 2, respectively. Even though structure 1 is less stable than structure 2, the adsorption enthalpy ∆H ad 0 calculated for both structures (Table 3) falls into the interval of measured adsorption heats 11,46,47 that were found for HZSM-5 and HM between 75 and 120 kJ/mol for θ(OH) < 100%. Compared to other structures published in the literature, 9,11,14 the ∆H ad 0 of structure 2 (95 kJ/mol, Table 3) approaches best the maximum value of calorimetric heats 11,46,47 (115-120 kJ/mol).…”

Section: Discussionmentioning

confidence: 88%

Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies

Kotrla¹,

Nachtigallová²,

Kubelková³

et al. 1998

J. Phys. Chem. B

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FTIR spectroscopy at ambient temperature, broad-line 1 H NMR spectroscopy at 4 K, and magic angle spinning (MAS) spectroscopy at ambient temperature, together with ab initio calculations at the Hartree-Fock and the second-order perturbation theory levels on the skeleton fragment HO-SiH 2 -O-SiH 2 -OH-AlH 2 -O-SiH 2 -OH are used to study interaction complexes of methanol-d 3 with bridging hydroxyls of zeolites (represented by H-mordenite and HZSM-5). The two-site neutral hydrogen-bonded methanol complex with bridging hydroxyl Si-OH-Al and the zeolite skeletal oxygen, which is predicted by the theory, is confirmed by the experimental observations provided that the number of adsorbed molecules is less than the number of bridging OH groups (Θ(OH) < 100%). Simulation of 1 H broad-line NMR indicates an average distance 193-200 pm between the zeolite and methanol hydrogens in magnetic interaction, which is in a reasonable agreement with ab initio calculations value 198.5-195 pm. The MAS NMR signal assigned to the exchange between methanol and bridging hydroxyls at very low OH coverage is found at 8.6 ppm, which is below the value reported for methoxonium ion. Using the Fermi resonance theory, the seven bands of OH groups observed in the infrared spectra allows us to determine the fundamental stretching and bending vibrations of bridging hydroxyls (1810-1790, 1375-1370, 880-866 cm -1 ) and OH groups of the methanol (3560-3555, 1375 cm -1 ) in the surface complex. The ab initio calculations on a large zeolite fragment show new possibilities of the localization of methanol on the zeolite surface. Nevertheless, compared to the theoretical calculations, the experiment still proves that the zeolitic hydrogen is much closer to the center between methanol and zeolite oxygens, and the methanol OH group is only little affected by the skeletal oxygen. The clusters of methanol adsorbed on bridging hydroxyls and affected by skeletal oxygens appear in methanol excess ((Θ(OH) ) 100-280%). The zeolite increases the charge of the cluster and the hydrogen bonding, which is higher than that for the liquid methanol.

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Section: Discussionmentioning

confidence: 88%

Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies

Kotrla¹,

Nachtigallová²,

Kubelková³

et al. 1998

J. Phys. Chem. B

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“…This indicates that also in the zeolite clustering of the methanol occurs, presumably around the favored adsorption sites, the Na + atoms; it has been established that the heat of adsorption of methanol to these sites is much higher than to the bare zeolite pore walls or silanol groups. 1 Indeed, upon increasing the pressure, both peaks increase in intensity, but at some point the ∼3530 cm -1 peak stops growing, suggesting that no more clusters can be formed. The 3350 cm -1 peak grows continuously with methanol pressure, indicating that the size of the clusters increases.…”

Section: Resultsmentioning

confidence: 99%

Dynamics of Infrared Photodissociation of Methanol Clusters in Zeolites and in Solution

et al. 1996

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We have investigated the dynamics of the O-H stretch vibration of clustered (hydrogen-bonded) methanol molecules in solution and in Na-zeolites with time-resolved (picosecond) pump-probe infrared spectroscopy. It is shown that in both cases, after resonant IR excitation, vibrational relaxation occurs by breaking the hydrogen bond between the methanol molecules. This process occurs much faster in solution (T 1 e 3 ps) than inside the zeolite (T 1 ) 10 ( 3 ps). A second remarkable difference is that whereas in solution a rapid hydrogen-bond reassociation occurs (τ r ) 25 ( 3 ps), in the zeolite this process takes considerably longer (τ r . 2 ns).

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“…The exact nature of adsorbed alcohol complexes has received a lot of attention in literature [60,61,62,63,64,65,66,67,68,69,70]. Mainly the issue whether the adsorbed complex is a neutral hydrogen-bonded (physisorbed) or a positively charged protonated (chemisorbed) complex is heavily debated.…”

Section: Physisorption Of Methanol and Ethanol In H-sapo-34 From Firsmentioning

confidence: 99%

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Hemelsoet

Ghysels

et al. 2011

Catalysis Today

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Theoretical and experimental IR data are combined to gain insight into the methanol and ethanol conversion over an acidic H-SAPO-34 catalyst. The theoretical simulations use a large finite cluster and the initial physisorption energy of both alcohols is calculated.Dispersive contributions turn out to be vital and the final adsorption of ethanol is predicted to be stronger compared to methanol (difference of 14 kJ mol −1 ). Calculated IR spectra of the alcohols and of formed aromatic cations upon conversion are also analyzed and support the peak assignment of the experimental in situ DRIFT spectra, in particular for the C-H and C=C regions. Theoretical IR spectra of the gas phase compounds are compared with those of the molecules loaded in a SAPO cluster and the observed shifts of the peak positions are discussed. To get a better understanding of these framework-guest interactions, a new theoretical procedure is proposed based on a normal mode analysis.A cumulative overlap function is defined and enables the characterization of individual peaks as well as induced frequency shifts upon adsorption.

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Calorimetric and IR-Spectroscopic Study of Methanol Adsorption on Zeolites

Cited by 39 publications

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Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies

Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies

Dynamics of Infrared Photodissociation of Methanol Clusters in Zeolites and in Solution

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

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Calorimetric and IR-Spectroscopic Study of Methanol Adsorption on Zeolites

Cited by 39 publications

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Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, 1H NMR and FTIR Studies

Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, 1H NMR and FTIR Studies

Dynamics of Infrared Photodissociation of Methanol Clusters in Zeolites and in Solution

Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

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Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies

Hydrogen Bonding of Methanol with Bridged OH Groups of Zeolites: Ab Initio Calculation, ¹H NMR and FTIR Studies