Skip to content

Methanol-to-hydrocarbon initiation reactions over a zeolite catalyst: reactive molecular dynamics simulations

Summary

The work reports a ReaxFF reactive force field tailored to the equilibration stage of methanol-to-hydrocarbons (MTH) chemistry in H-ZSM-5, studied with reactive MD to capture dynamic acidity, cations, and water inside the zeolite—phenomena that static DFT studies often omit. The repository includes the PCCP article PDF at pdf_path; the summary is aligned with the journal abstract, introduction context, and normalized/extracts/2025grajales-gonz-xe1-physical-che-methanol-to-hydrocarbon-initiation_p1-2.txt. The PCCP framing distinguishes pre-steady-state dehydration chemistry from later olefin/hydrocarbon-pool stages that dominate long-time MTH kinetics in many mechanistic discussions. A galley-labelled PDF is registered separately as 2025gonzalez-x-paper for the same DOI.

Methods

  • Reactive FF (training): Extends the Pitman–van Duin C/Si/O/Al/Ca ReaxFF line with C/O bond/angle/torsion terms fit to DFT energies and reaction profiles for first methanol conversion steps; parameter optimization by least-squares (or equivalent) objective on those QM reference data (full training set and weighting in PCCP Section 2; mirror 2025gonzalez-x-paper for parallel prose).
  • MD application (LAMMPS): LAMMPS reactive molecular dynamics; minimization, then NPT equilibration and heating ramps as in the manuscript; production NPT at target temperatures; 0.1 fs time step; Nosé–Hoover thermostat and NPT barostat in the NVT/NPT stages described in PCCP (≈1000 ps per 600–1200 K isothermal window as in the abstract).
  • PBC and system: H-ZSM-5 in 3D PBC supercells; lattice and atom counts in the article.
  • Focus (chemistry): Equilibration-stage dehydration toward DME, water, and surface methoxy species (SMS) (before olefin / hydrocarbon-pool kinetics).

Zeolite unit cell setup, Brønsted site representation, Al distribution assumptions, and analysis of acid speciation are in the PCCP Computational sections of pdf_path (and force-field training in Section 2 of the paper as referenced on 2025gonzalez-x-paper). N/A — external electric field; N/A — umbrella sampling / metadynamics / replica exchange (not stated for this study in the abstract-level summary).

Findings

  • Temperature trends (abstract): Methanol conversion rises between 800 K and 1000 K, producing water and SMS; SMS formation drops at 1200 K as undesired methane becomes prevalent. The authors caution that T > 1200 K can make reactions unreliable in the model owing to entropy effects.
  • Humidity at 800 K (abstract): Water shifts zeolite acidity from static to dynamic, with hydronium-like species; hydrogen transfer and framework activation (water protonation leaving a negatively charged framework) are said to favor protonated methanol conversion to water and SMS.
  • Cations (abstract): Cation diffusion is widespread; the authors hypothesize it lowers entropic barriers for key steps, highlighting dynamic effects beyond static DFT pictures.

The abstract cautions readers that very high temperature MD may become unreliable when entropy-sensitive steps dominate, motivating careful interpretation of absolute rates from classical reactive runs. Corpus: the VOR PDF at pdf_path is the main evidence anchor; p1–2 extracts are not a substitute for section-level tables.

Limitations

Wiki prose here is a navigation aid; definitive numbers and full force-field training tables are in the PCCP article and SI at pdf_path (and any Supporting Information referenced there), not on this page alone.

Relevance to group

Van Duin-group ReaxFF development and zeolite / MTH chemistry aligned with reactive catalysis simulation lines.

Citations and evidence anchors

https://doi.org/10.1039/D5CP02704G — Phys. Chem. Chem. Phys. 27, 22776–22798 (2025).

Reader notes (navigation)