Methanol-to-hydrocarbon initiation reactions over a zeolite catalyst: reactive molecular dynamics simulations
Corpus note
Maintainer catalog (SI/galley/proof PDF roles): https://github.com/asepehri93/vanDuinWiki/blob/main/docs/corpus/NON_PRIMARY_ARTICLE_PAPER_SLUGS.md
The ingested file is an RSC Accepted Manuscript PDF (Gonzalez_zeolite_HCO_PCCP_2025_galley.pdf); formatting and pagination may differ from the final issue.
Summary¶
The authors develop a ReaxFF parameterization—starting from the Pitman–van Duin C/Si/O/Al/Ca zeolite–clay line and adding C/O training relevant to methanol-to-hydrocarbons (MTH) initiation—and apply LAMMPS NPT dynamics on an H-ZSM-5 model spanning 600–1200 K to capture dynamic acidity, water-assisted chemistry, and cation mobility during early methanol conversion, beyond static DFT pictures.
Methods¶
- Force-field basis: Pitman–van Duin C/Si/O/Al/Ca ReaxFF with documented H/O/Si, H/O/Al, Ca/O, Ca/H sub-blocks; additional C/O bond/angle/torsion training against DFT profiles of first methanol conversion steps (full specification in Section 2 of the paper).
- MD protocol (LAMMPS): All stages in LAMMPS; simulations begin with energy minimization, 100 ps NPT at 1 atm, then heating at 10 K s\(^{-1}\) under NPT; production NPT segments at target temperatures; time step 0.1 fs; Nosé–Hoover thermostats/barostats for NVT/NPT stages as listed in the manuscript. Zeolite flexibility handled via variable cell NPT (see Computational Methodology §2.2 in the paper). PBC / periodic supercell for the H-ZSM-5 model (full cell vectors and atom counts in the article).
- System chemistry: Methanol conversion to water, DME, and surface methoxy (SMS) species monitored in the H-ZSM-5 framework; optional humidity cases at 800 K described in the Results/Abstract.
Zeolite model and mobility checks. The H-ZSM-5 framework is treated as flexible under NPT so Al sites, Brønsted protons, and extra-framework species can redistribute during high-temperature MTH chemistry—contrasting with static DFT cells that freeze lattice atoms. Production segments record framework Al–O stretch-like proxies and cation/proton hopping statistics discussed in the article as entropy-relevant degrees of freedom. N/A — no external electric field; N/A — umbrella sampling / metadynamics / replica exchange (not used in the workflow summarized here).
Findings¶
- Methanol conversion rises from 800 K to 1000 K, producing water and SMS; SMS yields fall by 1200 K as methane becomes more prevalent.
- Humidity at 800 K shifts Brønsted acidity toward dynamic H\(_3\)O\(^+\)-like behavior, enhancing hydrogen-transfer pathways and framework activation relative to the drier case described.
- Cation diffusion is common in the reactive MD trajectories; authors argue this alleviates entropic bottlenecks relative to static DFT studies that fix framework Al/H positions.
Quantitative rates and mechanism details should be checked against the version-of-record (or the sibling VOR at paper:2025grajales-gonz-xe1-physical-che-methanol-to-hydrocarbon-initiation) if pagination matters; this page uses the galley PDF in pdf_path as catalogued.
Limitations¶
High-temperature ReaxFF sampling can favor entropically dominated channels; the authors flag >1200 K regimes as potentially unreliable for chemistry. Full limitations are discussed in the PCCP text.
Relevance to group¶
Grajales-González, van Duin, and Sarathy: ReaxFF MTH initiation on H-ZSM-5 with temperature-dependent framework dynamics—complements zeolite/catalysis threads in the corpus.