Mass transport limitations in zeolite catalysts pose major hurdles for their optimal performance in diverse chemical reactions. Most approaches to reduce these restrictions focus on the synthesis of either hierarchical or nanosized zeolites. Here we demonstrate that the existence of a siliceous, catalytically inactive exterior rim on ZSM-5 particles dramatically reduces the diffusion limitations, which leads to an enhanced catalyst lifetime for the methanol-to-hydrocarbon reaction. Our findings reveal that binary inorganic and organic structure-directing agents enable a one-pot synthesis of Si-zoned ZSM-5 catalysts with diffusion properties that are characteristic of particles with a much smaller size. Operando ultraviolet–visible light diffuse reflectance spectroscopy reveals a marked reduction in external coking among Si-zoned samples. Molecular dynamics simulations to assess the diffusion of methanol and benzene in siliceous pores and in those with Brønsted acids reveal substantially reduced transport limitations in zoned regions, consistent with the improved catalyst activity of Si-zoned zeolites relative to that of ZSM-5 with a homogeneous acid-site distribution.
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Source data are provided with this paper. Data of main and extended data figures are available in the Supplementary Information, an online repository and upon request. Data from the molecular simulation studies are available in the online repository, including figure data, data from the USMD simulations (example input scripts for LAMMPS 12 December 2018 and PLUMED 2.4.3, initial and final configurations from the trajectories and BayesWHAM analysis scripts), and scripts and input files for evaluating the transmission coefficients using the effective positive flux method. Correspondence and request for materials should be addressed to J.D.R. or B.M.W.
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J.D.R. acknowledges support primarily from the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award no. DE-SC0014468. Additional support was provided by the Welch Foundation (Award E-1794 to J.D.R. and Award E-1882 to J.C.P.). This work is supported by the NWO Gravitation program, Netherlands Center for Multiscale Catalytic Energy Conversion (MCEC) and a European Research Council (ERC) Advanced Grant (no. 321140). This research used resources of the National Synchrotron Light Source II, a US Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. We thank J. E. Schmidt (Utrecht University) for useful discussions. We also thank A. Bhan (University of Minnesota) and Z. Shi (University of Minnesota) for their help with diffusivity measurements and technical guidance. M.E. Davis (Caltech) is acknowledged for assistance with TGA measurements. Computational resources were generously provided by the Hewlett Packard Enterprise Data Science Institute at the University of Houston and the Texas Advanced Computing Center at the University of Texas at Austin.
The authors declare no competing interests.
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Extended Data Fig. 1 Surface permeability of zoned and homogeneous zeolite samples.
Surface permeability, α, from fitting early uptake data in Supplementary Fig. 9 with a spherical particle model, plotted against the Al surface-to-bulk ratio of the following samples: Si-zoned (red symbols), homogeneous (purple symbols), and Al-zoned (blue symbol) zeolites.
Extended Data Fig. 2 Conversion and selectivity of zoned and homogeneous zeolite catalysts.
a, Conversion of methanol and dimethyl ether as a function of time-on-stream for the Al-zoned sample A-4 (blue cross), homogeneous samples H1-3 (purple circles) and H2-6 (purple triangles), and Si-zoned samples S1-1 (red squares), S2-1 (red inverted triangles), and S3-2 (red diamonds). All reactions were performed at 350 °C using a space velocity of 0.18–0.30 mol MeOH mol−1 H+ s−1. b, Selectivity profile (left y-axis) at sub-100% conversion (initial data point after 20 min induction period) and the ratio of ethene to the sum of 2-methylbutane and 2-methylbutene (symbols, right y-axis).
Extended Data Fig. 3 Relationship between turnover number and coke accumulation in zoned and homogeneous zeolite catalysts.
Turnover number (TON) of each tested catalyst plotted against the coke content in dry zeolite samples (listed in Supplementary Table 7).
Extended Data Fig. 4 Molecular dynamics simulations of methanol and benzene diffusion in zeolite MFI.
a, Free energy profile at 350 °C (potential of mean force, in units of the thermal energy kBT ≈ 0.0537 eV at T = 350 °C) for internal diffusion of methanol in the high loading limit (that is, 16 methanol per unit cell) through the straight channel (b-direction) of MFI with: aluminium sites (Si/Al = 23) occupied by methoxy groups (purple, MFI-CH3) and a purely siliceous material (orange, MFI). b, Free energy profile for internal diffusion of benzene in the low loading limit through the straight channel of MFI with: aluminum sites occupied by methoxy groups (purple, MFI-CH3) and Brønsted acids (blue, MFI-H), and purely siliceous material (orange, MFI). c, d, Images of benzene from Supplementary Movie 3 diffusing through a straight channel populated with methoxy groups. e, Image of benzene from Supplementary Movie 4 diffusing through a straight channel with Brønsted acid sites. Atom coloring is as follows: Si (yellow), O (red), H on acidic groups (blue), Al (green), C (black), and H on guest species (white).
Supplementary Methods, Tables 1–9, Discussion, Figs. 1–17 and References.
A 7 ns SMD trajectory in which methanol is pulled along the straight channel of an MFI framework with a methoxy group attached to O17 (Supplementary Fig. 17). The view is along , and the horizontal direction aligned to . Atom coloring is as follows: Si (yellow), O (red), H on acidic groups (blue), Al (green), C (black), and H on guest species (white).
A 7 ns SMD trajectory in which methanol is pulled along the straight channel of an MFI framework with a Brønsted acid site attached to O17 (Supplementary Fig. 17). The view is along , and the horizontal direction aligned to . Atom coloring is as follows: Si (yellow), O (red), H on acidic groups (blue), Al (green), C (black), and H on guest species (white).
A 7 ns SMD trajectory in which benzene is pulled along the straight channel of an MFI framework with a methoxy group attached to O17 (Supplementary Fig. 17). The view is along , and the horizontal direction aligned to . Atom coloring is as follows: Si (yellow), O (red), H on acidic groups (blue), Al (green), C (black), and H on guest species (white).
A 7 ns SMD trajectory in which benzene is pulled along the straight channel of an MFI framework with a Brønsted acid site attached to O17 (Supplementary Fig. 17). The view is along , and the horizontal direction aligned to . Atom coloring is as follows: Si (yellow), O (red), H on acidic groups (blue), Al (green), C (black), and H on guest species (white).
Source Data Figs. 1, 3, 4, 5, 6 and 7.
Source Data for Figs. 1c-d, 3a-c, 4a-d, 5b-d, 6a-b and 7a,f.
Source Data Extended Data Figs. 1, 2, 3 and 4
Source Data for Extended Data Figs. 1, 2a, 3 and 4a,b.
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Le, T.T., Qin, W., Agarwal, A. et al. Elemental zoning enhances mass transport in zeolite catalysts for methanol to hydrocarbons. Nat Catal 6, 254–265 (2023). https://doi.org/10.1038/s41929-023-00927-2