Kinetic effects of molecular clustering and solvation by extended networks in zeolite acid catalysis

Bates, Jason S.; Gounder, Rajamani

doi:10.1039/d1sc00151e

Cited by 27 publications

(27 citation statements)

References 96 publications

(78 reference statements)

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“…Substrate clustering effects were also reported for small-pore zeolites by di Iorio et al [36] who tried to explain observed high-pressure inhibition of methanol dehydration turnover rates by clustering of molecules of adsorbed substrate which can increase the apparent barriers to form kinetically relevant transition states. Recently, similar substrate clustering effects on the kinetics of methanol and ethanol dehydration over chabazite zeolites were reported also by Bates et al [37][38][39] who claimed that such solventmediated charge interactions which influence the free energy landscape have broader implications for kinetics of heterogeneous catalyzed reactions.…”

Section: Introductionsupporting

confidence: 64%

“…For chabazite samples, the TPSR method showed that the value of activation energy depends on the number of ethanol molecules in the unit cell of zeolite and decreases from values similar to those determined from the H/D methodology to values of about 102-105 kJ•mol −1 . This effect is most likely due to the formation of the interparticle clusters mentioned in other studies [37][38][39], which promote the deprotonation of chabazite zeolitic acid sites.…”

mentioning

confidence: 77%

“…Protonating the alcohol molecule weakens the C-O bond, making the protonated monomer more susceptible to elimination and substitution reactions. Increased number of ethanol molecules in CHA zeolite can most likely even pronounce the ethanol protonation effect due to the substrate clustering effect mentioned in the introduction [35,37]. Such effects can explain observed shifts of values of the ethanol dehydration apparent activation energy in CHA samples with the increasing amount of ethanol pre-adsorbed prior of the TPSR experiments.…”

Section: Temperature Programmed Surface Reaction (Tpsr)mentioning

confidence: 97%

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Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

et al. 2022

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The catalytic activity of zeolites is often related to their acid–base properties. In this work, the relationship between the value of apparent activation energy of ethanol dehydration, measured in a fixed bed reactor and by means of a temperature-programmed surface reaction (TPSR) depending on the amount of ethanol in the zeolite lattice and the value of activation energy of H/D exchange as a measure of acid–base properties of MFI and CHA zeolites, was studied. Tests in a fixed bed reactor were unable to provide reliable reaction kinetics data due to internal diffusion limitations and rapid catalyst deactivation. Only the TPSR method was able to provide activation energy values comparable to the activation energy values obtained from the H/D exchange rate measurements. In addition, for CHA zeolite, it has been shown that the values of ethanol dehydration activation energies depend on the amount of ethanol in the CHA framework, and this effect can be attributed to the substrate clustering effects supporting the deprotonation of zeolite Brønsted centers.

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Section: Introductionsupporting

confidence: 64%

mentioning

confidence: 77%

Section: Temperature Programmed Surface Reaction (Tpsr)mentioning

confidence: 97%

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Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

et al. 2022

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“…The catalytic consequences of distinct reaction environments manifest as differences in the activation and adsorption enthalpies and entropies that comprise free energy landscapes. Precise molecular-level descriptions of adsorbate and transition state solvation require that catalytic turnover rates be measured as functions of reactant thermodynamic activities and rigorously normalized by the number of active sites that facilitate such chemical transformations. , This allows for kinetic data to be interpreted in terms of equilibrium adsorption constants and apparent (or intrinsic) rate constants in order to extract free energy differences between final and initial states for a sequence of elementary catalytic steps and establish structure–function relationships that describe catalysis at solid–liquid interfaces …”

Section: Catalytic Turnover Rates Depend On Lewis Acidic Active Site ...mentioning

confidence: 99%

“…Solid catalytic surfaces often interact strongly with solvent molecules via interfacial adsorption or unwanted side reactions and, as a result, can undergo profound and sometimes irreversible changes in their structure and catalytic performance . Thus, the design of catalysts capable of performing selective chemical transformations in the liquid phase requires a deep understanding of the interactions that occur between solvent molecules, active sites, and reactive moieties during catalysis. , Biological catalysts navigate such complex free energy landscapes by manipulating solvent molecules to facilitate catalytic transformations via specific arrangements of hydrophobic and hydrophilic amino acid residues that comprise microporous reaction environments (<2 nm in diameter). These precise architectures regulate the structure of occluded solvent and substrate molecules along the reaction coordinate, granting enthalpy–entropy compromises that alter reaction free energy landscapes and enhance turnover rates .…”

Section: Introductionmentioning

confidence: 99%

Tailoring Distinct Reactive Environments in Lewis Acid Zeolites for Liquid Phase Catalysis

2021

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Metrics & MoreArticle Recommendations CONSPECTUS: Lewis acidic zeolites are microporous crystalline materials that offer promise as catalysts for the activation and conversion of biomassderived precursors in the liquid phase due to their unique water tolerance and synthetic versatility. The active site environment in zeolite catalysts is multifaceted in nature and is composed of a primary catalytic binding site, the secondary pore structure that confines such binding sites, and occluded solvent and reactant molecules that interact with adsorbed species. Moreover, Lewis acidic heteroatoms can adopt structurally diverse coordination that selectively catalyze different classes of chemical transformations and can be difficult to control synthetically or characterize spectroscopically. Thus, precise mechanistic interpretation of liquid-phase zeolite catalysis necessitates the development of synthetic, spectroscopic, and kinetic methods that can decouple such complex active site structures and probe the interactions that occur between confined active sites, solvent and reactant molecules, and adsorbed intermediates and transition states.In this Account, we describe the development and application of synthetic, spectroscopic, and kinetic methods to investigate chemically distinct Lewis acid zeolite environments in siliceous zeolites for liquid-phase catalysis. Identification of unique Lewis acidic active site structures relied on the development of direct and indirect solid-state nuclear magnetic resonance (NMR) methods that probe the number and connectivity of framework Lewis acid sites for a diverse range of metal heteroatoms. Such methods enabled the quantitative comparison of catalytic turnover rates, on a per active site basis, measured on different catalysts in order to establish structure−function relationships between active site structure and reactivity. Rigorous normalization of turnover rate further permits comparison of catalytic turnover rates across materials of varying topology, metal heteroatom identity, solvent, and framework polarity to extract salient thermodynamic descriptors of catalysis through kinetic probes. Ex situ interrogation of alcohols adsorbed within hydrophobic and hydrophilic Sn-containing zeolites revealed that hydrophobic voids induce structural order on confined alcohol hydrogen-bonding networks, which give rise to enhanced turnover rates of liquid-phase transfer hydrogenation catalysis. This acceleration of turnover rates arises because ordered alcohol networks occluded within the pores of hydrophobic zeolites stabilize adsorbed transfer hydrogenation intermediates and transition states to a greater extent than liquidlike solvent networks observed in hydrophilic zeolites. The effects of confined solvent molecules can also influence catalysis, independent of framework polarity, due to differences in solvent polarity and substituent effects, which alter turnover rates via changes in how different solvent molecules interact with adsorbed intermediates and transition states. These observ...

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Maximum Impact of Ionic Strength on Acid‐Catalyzed Reaction Rates Induced by a Zeolite Microporous Environment

et al. 2022

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The intracrystalline ionic environment in microporous zeolite can remarkably modify the excess chemical potential of adsorbed reactants and transition states, thereby influencing the catalytic turnover rates. However, a limit of the rate enhancement for aqueousphase dehydration of alcohols appears to exist for zeolites with high ionic strength. The origin of such limitation has been hypothesized to be caused by the spatial constraints in the pores via, e.g., size exclusion effects. It is demonstrated here that the increase in turnover rate as well as the formation of a maximum and the rate drop are intrinsic consequences of the increasingly dense ionic environment in zeolite. The molecularly sized confines of zeolite create a unique ionic environment that monotonically favors the formation of alcohol-hydronium ion complexes in the micropores. The zeolite microporous environment determines the kinetics of catalytic steps and tailors the impact of ionic strength on catalytic rates.

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Kinetic effects of molecular clustering and solvation by extended networks in zeolite acid catalysis

Abstract: “Solvent effects” at interfaces in heterogeneous catalysts are described by transition state theory treatments that identify kinetic regimes associated with molecular clustering and the solvation of such clusters by extended molecular networks.

Cited by 27 publications

References 96 publications

Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

Influence of Substrate Concentration on Kinetic Parameters of Ethanol Dehydration in MFI and CHA Zeolites and Relation of These Kinetic Parameters to Acid–Base Properties

Tailoring Distinct Reactive Environments in Lewis Acid Zeolites for Liquid Phase Catalysis

Maximum Impact of Ionic Strength on Acid‐Catalyzed Reaction Rates Induced by a Zeolite Microporous Environment

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