A modeling study on reaction and diffusion in MTO process over SAPO-34 zeolites

Liu

et al. 2020

Nat Commun

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Direct visualization of spatiotemporal evolution of molecules and active sites during chemical transformation in individual catalyst crystal will accelerate the intuitive understanding of heterogeneous catalysis. So far, widespread imaging techniques can only provide limited information either with large probe molecules or in model catalyst of large size, which are beyond the interests of industrial catalysis. Herein, we demonstrate a feasible deep data approach via synergy of multiscale reaction-diffusion simulation and super-resolution structured illumination microscopy to illustrate the dynamical evolution of spatiotemporal distributions of gas molecules, carbonaceous species and acid sites in SAPO-34 zeolite crystals of several micrometers that are typically used in industrial methanol-to-olefins process. The profound insights into the inadequate utilization of activated acid sites and rapid deactivation are unveiled. The notable elucidation of molecular reaction-diffusion process at the scale of single catalyst crystal via this approach opens an interesting method for mechanism study in materials synthesis and catalysis.

Section: Methodsmentioning

confidence: 73%

Section: Methodsmentioning

confidence: 99%

Imaging spatiotemporal evolution of molecules and active sites in zeolite catalyst during methanol-to-olefins reaction

Liu

et al. 2020

Nat Commun

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“…he past decades saw the rapid development and utilization of nanoporous crystalline materials in a wide variety of scientific researches and industrial processes [1][2][3][4][5][6][7][8][9][10][11] . Typical applications are, but not limited to, catalysis [1][2][3][4] , separation [5][6][7] , and electrochemistry 8 .…”

mentioning

confidence: 99%

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

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.

“…31 The potential application of proposed correlations is expected to provide fundamental parameters of mass transport and adsorption for heterogeneous catalysis. 1,14,15,18,81 Another application for current correlation is to estimate the ideal separation selectivity for system with low molecular loading or pressure. 21,35 In this case, as shown by Keskin and Sholl,82 the ideal separation selectivity can be obtained by intracrystalline diffusivity and adsorption entropy suppose the F I G U R E 6 Comparisons of predicted and measured adsorption entropies for different molecules in KFI, TON, MFI, FER, MOR, and LTL zeolitic frameworks.…”

Section: Applicable Scope Of Correlationsmentioning

confidence: 99%

“…For instance, the engineered nanoscale pores have been frequently applied in sorbents to control the behaviors of guest molecules and thus discriminate these molecules. 10 In addition, various experimental [11][12][13] and computational [14][15][16][17][18] studies have discovered that the shape selectivity of zeolite catalysts 18,19 is closely related to the diffusion of guest molecules in the nanoscale pores and cavities, which constraints the motion of large molecules and alter the selectivity of targeted products.…”

mentioning

confidence: 99%

An approach for predicting intracrystalline diffusivities and adsorption entropies in nanoporous crystalline materials

et al. 2020

AIChE Journal

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Confinement of molecules in nanoporous crystalline materials results in the unique and diverse characteristics of intracrystalline diffusion and adsorption, which can significantly affect the efficiency of gas separation and/or catalysis. However, understanding the interplay between confinement and intracrystalline diffusion and adsorption remains elusive at the quantitative level. In this work, it is found that the intracrystalline diffusion could be related to the hopping rate, which might be further connected to the translational and rotational motion of molecules and quantified by corresponding partition functions. Based on this analysis, the correlations capable of predicting the intracrystalline diffusivity and the adsorption entropy are developed. It is shown that the correlations can well capture the experimental and simulation results of more than 20 frameworks, including zeolites and MOFs, for a wide range of guest molecules. This approach can potentially serve as rapid screening tool for nanoporous crystalline materials in gas separation and catalysis.