Elementary steps and reaction pathways in the aqueous phase alkylation of phenol with ethanol

Eckstein, Sebastian; Hintermeier, Peter H.; Olarte, Mariefel V.; Liu, Yue; Baráth, Eszter; Lercher, Johannes A.

doi:10.1016/j.jcat.2017.06.002

Cited by 39 publications

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“…In our previous work, we found that increasing hydronium ion concentrations ([H 3 O + hydr. ]) in zeolite H‐MFI limited the adsorption of phenol from the aqueous phase . To explore the reasons for this limitation in adsorption properties, the nature of the confined environment and its interaction with an adsorbate, we selected a molecule with a substantial hydrocarbon part, i.e., cyclohexanol (Cy).…”

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confidence: 99%

“…in zeolite H-MFI limited the adsorption of phenol from the aqueous phase. [6] To explore the reasons for this limitation in adsorption properties,t he nature of the confined environment and its interaction with an adsorbate,w es elected am olecule with as ubstantial hydrocarbon part, i.e., cyclohexanol (Cy). We chose zeolite H-MFI as the framework structure,because it allows comparison with aw ide range of hydronium ion concentrations in ah ighly crystalline environment.…”

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confidence: 99%

“…Solid lines in (A) represent regressions to the Langmuir isotherm while solid lines in (B) serve as guide to eyes. Data of phenol in (C) are from reference[6].…”

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Influence of Hydronium Ions in Zeolites on Sorption

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Influence of Hydronium Ions in Zeolites on Sorption

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“…[6] To explore the reasons for this limitation in adsorption properties,t he nature of the confined environment and its interaction with an adsorbate,w es elected am olecule with as ubstantial hydrocarbon part, i.e., cyclohexanol (Cy). in zeolite H-MFI limited the adsorption of phenol from the aqueous phase.…”

Section: Understandingandcontrollingtheinteractionsofmoleculesmentioning

confidence: 99%

“…Data of phenol in (C) are from reference[6]. C) Remaining volume in H-MFI micropores at saturated adsorption of cyclohexanol and phenol.…”

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Influence of Hydronium Ions in Zeolites on Sorption

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In the presence of sufficient concentrations of water, stable,hydrated hydronium ions are formed in the pores and at the surface of solid acids such as zeolites.F or am edium-pore zeolite,s uch as zeolite MFI, hydrated hydronium ions consist of eight water molecules and have an effective volume of 0.24 nm 3 .I ntheir presence,larger organic molecules can only adsorb in the portions of the pore that are not occupied by hydronium ions.Asaconsequence,the available pore volume decreases proportionally to the concentration of the hydronium ions.T he higher charge density (the increasing ionic strength) that accompanies an increasing concentration of hydronium ions leads to an increase in the activity coefficients of the adsorbed substrates,t hus,w eakening the interactions between the organic part of the molecules and the zeolite and favoring the interactions with polar groups.T he quantitative understanding of these interactions makes it possible to link ac ollective property such as hydrophilicity and hydrophobicity of zeolites to specific interactions on molecular level. Understandingandcontrollingtheinteractionsofmoleculesin confined space of varying polarity is central to the action of enzymes and to properties that link zeolite catalysis with synthetic mimics of enzyme functions. [1] Thee nvironment interacts with the sorbed molecules,either via directed bonds that include hydrogen bonding and electron pair donoracceptor interactions or via nondirected dispersion forces. [2] Therelative dominance of the two types of interactions in an aqueous environment makes specific regions of the materials hydrophilic or hydrophobic, which is,i nt urn, manifested in colligative properties such as the specific surface tension, wetting, and the enrichment of polar or nonpolar components in complex mixtures.T his classification of interactions is widely used conceptually,but the classifications are empirical ("hydrophobicity scale") [3] and are difficult to extend and transfer between systems.Thes imultaneous presence of polar and nonpolar domains in proximity in catalyst/enzyme environments and its importance for catalytic properties make it imperative to explore the heterogeneity and its impact on interactions with substrates at an atomistic and molecular level. Zeolites,which have aw ell-defined three-dimensional pore structure with nonpolar channel walls and polar Brønsted acidic OH groups (Brønsted acid sites,B AS), are ideal systems to explore this complexity.The combination of active sites and pore structure offers au nique way to influence both ground and transition states in catalyzed reaction pathways.Understanding the influence of such an environment on reacting molecules becomes even more complex, when zeolites are used in the presence of water. Then, the Brønsted acid sites transform into charged hydrated hydronium ions (H 3 O + hydr. ). [4] It has been observed that the hydronium ions strongly affect adsorption properties in the micropore confines. [5] On am acroscopic level, zeolites with very low concentration...

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