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Supporting information — Fe/Cr/O/S ReaxFF; butane oxidation on Cr₂O₃ and pyrite-modified Cr₂O₃

Evidence and attribution

Authority of statements

This page registers an SI PDF (pdf_path). Integrated scientific narrative, full Computational Methods, and bibliography for the study belong on the main article page 2015shin-venue-research-2 (and the alternate main-PDF slug 2015shin-venue-research). Below summarizes SI-visible figure-caption content in this workspace’s short extract.

Summary

Supporting Information for the ACS Catalysis article (DOI 10.1021/acscatal.5b01766) packages initial configurations, equations-of-state checks for Cr crystal phases, and NVT-MD figure series tracking oxidation product counts, hydroxyl formation, low-coordination Cr, reactive oxygen, and sulfur release for butane oxidation scenarios on Cr₂O₃ with and without pyrite (FeS₂). The SI captions tabulate temperatures such as 2500 K product evolution for C₄H₁₀/O₂, 1000 K snapshots for dehydrogenation on Cr-oxide, 1600 K time series comparing clean versus pyrite-modified oxide, and a 2000 K sulfur-release panel for pyrite dehydrogenation without O₂.

Methods

What the SI documents (caption-level). Figure S1 defines initial geometries for (a) C₄H₁₀/O₂, (b) C₄H₁₀/O₂/Cr₂O₃, and © C₄H₁₀/O₂/Cr₂O₃/FeS₂ with element color coding. Figure S2 reports 0 K equations of state for bcc/fcc/a15 Cr; bcc Cr cohesive energy is 93.7 kcal/mol in ReaxFF versus 94.6 kcal/mol experiment and 93.9 kcal/mol QM in the caption text. Figures S3–S9 summarize NVT-MD observables at the temperatures stated in each caption (e.g., 2500 K product counts; 1000 K dehydrogenation illustration; 1600 K hydroxyl / carbon-bound intermediates / reactive oxygen / coordination statistics; 2000 K sulfur release without O₂).

MD application (SI-visible protocol hooks). Engine: the parent ACS Catalysis article documents the molecular dynamics software used for these ReaxFF trajectories (see 2015shin-venue-research-2 and pdf_path). System composition: atomistic C₄H₁₀/O₂ gas cells plus Cr₂O₃ and FeS₂/Cr₂O₃ slab supercells as illustrated in Figure S1 (atom counts on pdf_path). Boundaries: three-dimensional periodic boundary conditions (PBC) for the slab models as in the main Computational Methods. Ensemble: NVT in the captioned MD panels. Duration: captioned runs accumulate statistics over production segments whose lengths (ps/ns) are defined in the main text/SI tables, not on this caption-only extract. Thermostat: NVT implies a thermostat implementation specified in pdf_path. Timestep: fs timestep values appear in the main article/SI parameter tables. Barostat: N/A for the NVT SI panels summarized here. Pressure: N/A — NVT gas/surface runs without stated hydrostatic pressure control in the SI caption excerpt. Electric field / enhanced sampling: N/A unless the full SI documents them.

Force-field training narrative: SI points to Fe/Cr/O/S ReaxFF parameter tables and validation plots alongside these figures; the QM training level and optimization workflow are described in the main text, not replaced here.

Static QM / DFT production: N/A for the SI package itself (QM enters as training reference in the parent article).

Findings

Validation against reference data: Figure S2 reports 0 K equations of state for bcc, fcc, and a15 Cr; the SI caption quotes a bcc Cr cohesive energy of 93.7 kcal/mol from ReaxFF, compared with 94.6 kcal/mol experiment and 93.9 kcal/mol QM in the same caption text—serving as a compact benchmark of the Fe/Cr/O/S parameterization alongside the plots.

Oxidation and surface chemistry (caption-level): Time series and snapshots in Figures S3–S9 track oxidation product counts, hydroxyl formation, low-coordination Cr, reactive oxygen, and sulfur release for butane-related setups on Cr₂O₃ with and without pyrite (FeS₂). The SI therefore documents how surface oxygen participates in dehydrogenation and subsequent C–O coupling at the atomistic level, complementing the narrative conclusions stated in the main article abstract.

Comparisons across panels: Captions contrast clean versus pyrite-modified chromia under matched NVT protocols, highlighting increased SOH-related signatures and sulfur release on the modified surface relative to clean Cr₂O₃ in the illustrated trajectories.

Sensitivity to temperature and stoichiometry: The SI calls out representative temperature windows such as 2500 K product evolution for C₄H₁₀/O₂, 1000 K snapshots for dehydrogenation on Cr-oxide, 1600 K time series comparing clean versus pyrite-modified oxide, and 2000 K sulfur-release behavior for pyrite dehydrogenation without O₂—showing how the authors scan thermal conditions to expose different reaction branches.

Limitations of an SI-only digest: This wiki page cannot restate every figure panel or time axis; quantitative counts and full mechanistic claims require the PDF figures and the version-of-record article discussion, not caption fragments alone.

Limitations

This page is SI-only; figure captions are not a substitute for the peer-reviewed main article mechanism discussion on 2015shin-venue-research-2. SI is not a substitute for integrated interpretation in the main text. High-temperature panels probe kinetically dominated channels that may differ from low-temperature catalytic steady states. Ideal slab models may omit particle and support complexity.

Relevance to group

Penn State / CFDRC Fe/Cr/O/S ReaxFF work on coal-relevant sulfur chemistry at oxide catalyst interfaces.

Citations and evidence anchors

  • Parent article DOI 10.1021/acscatal.5b01766; SI: papers/Shin_ACS_Catalysis_2015_SI.pdf.
  • normalized/extracts/2015shin-venue-microsoft-word_p1-2.txt.