Visualizing pore architecture and molecular transport boundaries in catalyst bodies with fluorescent nanoprobes

Whiting, Gareth T.; Nikolopoulos, Nikolaos; Nikolopoulos, Ioannis; Chowdhury, Abhishek Dutta; Weckhuysen, Bert M.

doi:10.1038/s41557-018-0163-z

Cited by 83 publications

(111 citation statements)

References 60 publications

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“…This result was further corroborated by using confocal fluorescence microscopy (CFM, excitation laser = 560 nm, Figure S9), showing much stronger fluorescence emission at the wavelength > 580 nm in the a-oriented zeolite thin films. [17] Additionally, similar UV/ Vis DRS results in regards to internal and external coke species were also observed in zeolite thin films grown from a secondary growth media (SGM) solution with Si/Al = 125 ( Figure S10). Thus, the UV/Vis DRS results suggest that internal coke species can be readily formed in the straight channels, and the external coke species are more rapidly formed at the surface of the sinusoidal channels.…”

supporting

confidence: 56%

“…Previous studies on zeolite ZSM-5 in the MTH reaction have concentrated on either designing materials/reactors for kinetic studies [11,16,20,22,[24][25] or gaining spatial insights by using advanced characterization techniques. [17,18,[26][27][28][29][30][31] However, none of these studies have been capable of disentangling the structure-reactivity relationships for specific zeolite-channel orientations under operando conditions.…”

mentioning

confidence: 99%

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Disentangling Reaction Processes of Zeolites within Single‐Oriented Channels

Heijden

Stančiaková

et al. 2020

Angewandte Chemie

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Establishing structure–reactivity relationships for specific channel orientations of zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, a well‐defined model system was developed to build structure–reactivity relationships for specific zeolite‐channel orientations during various catalytic reaction processes, for example, the methanol‐ and ethanol‐to‐hydrocarbons (MTH and ETH) process as well as oligomerization reactions. The entrapped and effluent hydrocarbons from single‐oriented zeolite ZSM‐5 channels during the MTH process were monitored by using operando UV/Vis diffuse reflectance spectroscopy (DRS) and on‐line mass spectrometry (MS), respectively. The results reveal that the straight channels favor the formation of internal coke, promoting the aromatic cycle. Furthermore, the sinusoidal channels produce aromatics, (e.g., toluene) that further grow into larger polyaromatics (e.g., graphitic coke) leading to deactivation of the zeolites. This underscores the importance of careful engineering of materials to suppress coke formation and tune product distribution by rational control of the location of zeolite acid sites and crystallographic orientations.

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confidence: 56%

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confidence: 99%

Disentangling Reaction Processes of Zeolites within Single‐Oriented Channels

Heijden

Stančiaková

et al. 2020

Angewandte Chemie

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“…However, studies based on the visualization methods such as interference microscopy (IFM) and infrared microscopy (IRM) discovered that, in addition to intracrystalline diffusion, surface barriers can also dominate the mass transfer of guest molecules in some nanoporous materials 3,12,16 . Recently, Weckhuysen et al 17,18 developed a fluorescence microscopy approach to directly observe the diffusion behavior in porous materials. It is shown that the diffusivity derived from the commonly used uptake/release rate measurement is in fact the apparent diffusivity reflecting the combined influence of intracrystalline diffusion and surface barriers in the nanoporous crystalline materials 6,15,19,20 .…”

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confidence: 99%

Direct quantification of surface barriers for mass transfer in nanoporous crystalline materials

Gao

Yang

et al. 2019

Commun Chem

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Mass transfer of guest molecules in nanoporous crystalline materials has gained attention in catalysis, separation, electrochemistry, and other fields. Two mechanisms, surface barriers and intracrystalline diffusion, dominate the mass transport process. Lack of methods to separately quantify these two mechanisms restricts further understanding and thus rational design and efficient application of nanoporous materials. Here we derive an approximate expression of uptake rate relying solely on surface permeability, offering an approach to directly quantify surface barriers and intracrystalline diffusion. By use of this approach, we study the diffusion in zeolitic materials, and find that the intracrystalline diffusivity is intrinsic to the topological structure of host materials at low molecular loading for the given guest molecules, while the surface permeability is sensitive to the non-ideality of a crystalline surface owing to the physical and chemical properties of the crystalline surface, host-guest interaction at the surface, and change of the environment.

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“…Recently, Whiting et al [45] . showed that for the methanol‐to‐hydrocarbon (MTH) reaction a ring of large poly‐aromatic molecules is formed due to a boundary inside the catalyst extrudate.…”

Section: Resultsmentioning

confidence: 99%

High‐Pressure Operando UV‐Vis Micro‐Spectroscopy of Coke Formation in Zeolite‐based Catalyst Extrudates during the Transalkylation of Aromatics

Verkleij

Whiting

Esclapez³

et al. 2020

ChemCatChem

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The performance of zeolite‐based catalyst extrudates can be largely influenced by the choice of binder material. To investigate these binder effects in zeolite‐based catalyst extrudates in more detail, high spatiotemporal resolution techniques need to be further developed and employed. In this work, we present a new methodology to investigate binder effects in catalyst extrudates at different reaction pressures using operando UV‐vis diffuse reflectance (DR) micro‐spectroscopy coupled with on‐line gas chromatography. We have studied mm‐sized zeolite H‐ZSM‐5‐containing extrudates with either Al2O3 or SiO2 binder material, during the transalkylation of toluene with 1,2,4‐trimethylbenzene at 450 °C and at a pressure of either 1 or 5 bar. Using this technique, it was revealed that the binder material significantly influenced catalyst deactivation at different reaction pressures. By subsequent mapping of the cross sections of the cylindrical catalyst extrudates using UV‐vis micro‐spectroscopy, it was shown that the SiO2‐bound extrudate formed poly‐aromatic coke molecules homogeneously throughout the entire extrudate, whereas for the Al2O3‐bound extrudate a coke ring formed that moved inwards with increasing reaction time. Notably, the developed methodology is not limited to the transalkylation reaction, and can also be used to gain more insight into binder effects during a variety of important catalytic reactions.

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Visualizing pore architecture and molecular transport boundaries in catalyst bodies with fluorescent nanoprobes

Cited by 83 publications

References 60 publications

Disentangling Reaction Processes of Zeolites within Single‐Oriented Channels

Disentangling Reaction Processes of Zeolites within Single‐Oriented Channels

Direct quantification of surface barriers for mass transfer in nanoporous crystalline materials

High‐Pressure Operando UV‐Vis Micro‐Spectroscopy of Coke Formation in Zeolite‐based Catalyst Extrudates during the Transalkylation of Aromatics

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