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

Abstract

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.

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

“…14 – 16 . The adsorption isotherms for gas components in SAPO-34 zeolites at low temperature were reported in our previous work 42 , 57 . The quantitative relation between adsorption isotherm and carbonaceous species deposited in SAPO-34 zeolites was measured by Intelligent Gravimetric Analyzer 57 .…”

“…1 and 4 . The molecular diffusivities and adsorption isotherms were obtained either from MD or uptake experiments 42 . For all SAPO-34 zeolite samples, the maximum deviation of 15% was achieved for crystal size and 6% for silica content, as shown in Supplementary Table 1 .…”

“…The quantitative relation between adsorption isotherm and carbonaceous species deposited in SAPO-34 zeolites was measured by Intelligent Gravimetric Analyzer 57 . The intracrystalline diffusivities and diffusion activation energies were decoupled the effect of surface barriers 42 . The parameters at catalyst ensemble scale, e.g., catalyst lifetime, gas product distribution, relative quantity of retained acid sites and quantity of carbonaceous species, were used as feedback to determine the kinetic constants, the parameters are listed in Supplementary Table 3 .…”

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

“…The intracrystalline diffusivity and surface permeability were decoupled as described in our previous work. 63 The…”

“…To further verify the applicability and accuracy of the proposed methods, Equations 1and 2were also applied to predict the F I G U R E 5 (a) Comparisons of predicted and measured intracrystalline diffusivity at infinite dilution for diverse molecules in FAU, 2 ISV, 71 MFI, 67,71 ITE, 71,72 LTA, 25,73 IWH, 72 RHO, 74 CHA, 53,55,63,74 and DDR 2,73 zeolitic frameworks at 300 K. (b) Comparisons of predicted and simulated intracrystalline diffusivity at infinite dilution of methane in VFI, CFI, CAN, MTW, TSC, MER, RHO, CHA, DDR, DFT, LEV, and GOO zeolites 35 at 300 K. (c) Comparisons of predicted and measured intracrystalline diffusivity at infinite dilution for 13 molecules in ZIF-8 MOF at 273, 308, 373, 423 K. 26 (d) Comparisons of predicted and simulated activation energy of diffusion of methane in zeolites 35,74 and MOFs. 21 Intracrystalline diffusivities are predicted by Equation 1and activation energies are predicted by Equation 6[Color figure can be viewed at wileyonlinelibrary.com] diffusion of guest molecules in ZIF-8 MOF under different temperature.…”