Methanol loading dependent methoxylation in zeolite H-ZSM-5

Matam, Santhosh Kumar; Nastase, Stefan A. F.; Logsdail, Andrew J.; Catlow, C. Richard A.

doi:10.1039/d0sc01924k

Cited by 28 publications

(35 citation statements)

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“…Using computational modelling Catlow, Logsdail and co-workers have shown that the initial interaction between methanol and the protonated ZSM-5 leads to a surface methoxyl. 35 This confirms that with an acidic zeolite methanol acts as a methylating agent. However, as noted above the energetic barrier to the formation of an isolated gas phase carbene remains high.…”

Section: Computer Modelling and Advanced Spectroscopy Studies Of The supporting

confidence: 65%

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Hutchings

2021

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Section: Computer Modelling and Advanced Spectroscopy Studies Of The supporting

confidence: 65%

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Hutchings

2021

Faraday Discuss.

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“…Prior to the quasi-elastic neutron scattering (QENS) experiments, the zeolite was dehydrated under vacuum (10 -3 to 10 -4 mbar) at 350 °C for 12 h and thereafter handled in an argon-filled glovebox. For the methanol loaded samples, methanol (Sigma-Aldrich, ≥ 99.9%) loading was conducted at room temperature by flowing dry N 2 (100 mL min −1 ) through a methanol saturator that consisted of a Dreschel bottle at the same temperature [18]. The loading was continued until there was no further uptake by the zeolite (gravimetrically determined) and resulted in a methanol loading of around 30 molecules per unit cell (i.e., ≈ 7.5 molecules per acidic site) [18].…”

Section: Zeolite H-zsm-5mentioning

confidence: 99%

Methanol dynamics in H-ZSM-5 with Si/Al ratio of 25: a quasi-elastic neutron scattering (QENS) study

et al. 2021

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Methanol dynamics in zeolite H-ZSM-5 (Si/Al of 25) with a methanol loading of ~ 30 molecules per unit cell has been studied at 298, 323, 348 and 373 K by incoherent quasi-elastic neutron scattering (QENS). The elastic incoherent structure factor (EISF) reveals that the majority of methanol is immobile, in the range between 70 and 80%, depending on the measurement temperature. At 298 K, ≈ 20% methanol is mobile on the instrumental timescale, exhibiting isotropic rotational dynamics with a rotational diffusion coefficient (DR) of 4.75 × 1010 s−1. Upon increasing the measurement temperature from 298 to 323 K, the nature of the methanol dynamics changes from rotational to translational diffusion dynamics. Similar translational diffusion rates are measured at 348 and 373 K, though with a larger mobile fraction as temperature increases. The translational diffusion is characterised as jump diffusion confined to a sphere with a radius close to that of a ZSM-5 channel. The diffusion coefficients may be calculated using either the Volino–Dianoux (VD) model of diffusion confined to a sphere, or the Chudley–Elliot (CE) jump diffusion model. The VD model gives rise to a self-diffusion co-efficient (Ds) of methanol in the range of 7.8–8.4 × 10–10 m2 s−1. The CE model gives a Ds of around 1.2 (± 0.1) × 10–9 m2 s−1 with a jump distance of 2.8 (either + 0.15 or − 0.1) Å and a residence time (τ) of ~ 10.8 (either + 0.1 or − 0.2) ps. A correlation between the present and earlier studies that report methanol dynamics in H-ZSM-5 with Si/Al of 36 is made, suggesting that with increasing Si/Al ratio, the mobile fraction of methanol increases while DR decreases.

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“…The low-temperature framework methylation was recently validated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), quasielastic neutron scattering (QENS), and inelastic neutron scattering (INS) experiments. 30 − 32 These studies highlighted that, when employing specific conditions, namely, a high methanol loading (at least three methanol molecules per acid site) and a Si/Al ratio of 30, the framework methylation takes place in H-ZSM-5 but not in H-Y. 31 Both experimental and theoretical 33 investigations showed that this reaction may occur faster when increasing the methanol loading because of the formation of methanol clusters that facilitate a spontaneous proton transfer.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic Insight into the Framework Methylation of H-ZSM-5 for Varying Methanol Loadings and Si/Al Ratios Using First-Principles Molecular Dynamics Simulations

et al. 2020

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The methanol-to-hydrocarbon process is known to proceed autocatalytically in H-ZSM-5 after an induction period where framework methoxy species are formed. In this work, we provide mechanistic insight into the framework methylation within H-ZSM-5 at high methanol loadings and varying acid site densities by means of first-principles molecular dynamics simulations. The molecular dynamics simulations show that stable methanol clusters form in the zeolite pores, and these clusters commonly deprotonate the active site; however, the cluster size is dependent on the temperature and acid site density. Enhanced sampling molecular dynamics simulations give evidence that the barrier for methanol conversion is significantly affected by the neighborhood of an additional acid site, suggesting that cooperative effects influence methanol clustering and reactivity. The insights obtained are important steps in optimizing the catalyst and engineering the induction period of the methanol-to-hydrocarbon process.

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Methanol loading dependent methoxylation in zeolite H-ZSM-5

Abstract:
Room temperature methoxylation is methanol loading dependent: the higher the methanol loading, the faster the methoxylation. Methanol load of ≥2 leads to methoxylation while no methoxylation is observed with ≤1 molecule per Brønsted acidic site.

Cited by 28 publications

References 73 publications

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Methanol dynamics in H-ZSM-5 with Si/Al ratio of 25: a quasi-elastic neutron scattering (QENS) study

Mechanistic Insight into the Framework Methylation of H-ZSM-5 for Varying Methanol Loadings and Si/Al Ratios Using First-Principles Molecular Dynamics Simulations

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Methanol loading dependent methoxylation in zeolite H-ZSM-5

Abstract: Room temperature methoxylation is methanol loading dependent: the higher the methanol loading, the faster the methoxylation. Methanol load of ≥2 leads to methoxylation while no methoxylation is observed with ≤1 molecule per Brønsted acidic site.

Cited by 28 publications

References 73 publications

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Spiers Memorial Lecture: Understanding reaction mechanisms in heterogeneously catalysed reactions

Methanol dynamics in H-ZSM-5 with Si/Al ratio of 25: a quasi-elastic neutron scattering (QENS) study

Mechanistic Insight into the Framework Methylation of H-ZSM-5 for Varying Methanol Loadings and Si/Al Ratios Using First-Principles Molecular Dynamics Simulations

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Abstract:
Room temperature methoxylation is methanol loading dependent: the higher the methanol loading, the faster the methoxylation. Methanol load of ≥2 leads to methoxylation while no methoxylation is observed with ≤1 molecule per Brønsted acidic site.