SO3
Sulfur trioxide · Sulfuric anhydride
Sulfur trioxide is a stable, insulating oxide of sulfur that functions as the primary industrial precursor for the manufacturing of sulfuric acid.
About Sulfur trioxide
Sulfur trioxide is a highly reactive inorganic compound that exists as a wide-gap insulating oxide. As a thermodynamically stable phase, it occupies a significant position in chemical synthesis, particularly due to its role as the primary precursor for large-scale industrial acid production. Its structural versatility is evidenced by the numerous reported configurations across major materials databases. This compound is essential for manufacturing processes that require strong dehydrating agents and chemical intermediates. Its ability to act as a potent Lewis acid makes it indispensable in the synthesis of various sulfonated organic compounds and industrial detergents.
Key Properties
Cross-validated computational properties for Sulfur trioxide, aggregated across 3 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of SO3. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for SO3, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| — | — | 5.42 | 0.0000 | -1.406 | — |
| P21/c (No. 14) | monoclinic | 5.35 | 0.0000 | -1.048 | — |
| P21/c (No. 14) | monoclinic | 5.16 | 0.0000 | -6.326 | 2.49 |
| Pna21 (No. 33) | orthorhombic | 5.14 | 0.0036 | -6.323 | 2.34 |
| — | — | 4.43 | 0.0507 | -1.355 | — |
| — | — | 5.44 | 0.0516 | -1.355 | — |
| — | — | 3.20 | 0.2123 | -1.194 | — |
| — | — | 1.82 | 0.8552 | -0.551 | — |
| — | — | 0.00 | 1.0074 | -0.399 | — |
| — | — | 0.61 | 1.2934 | -0.113 | — |
| — | — | 0.00 | 2.3354 | 0.929 | — |
| — | — | 0.00 | 2.4982 | 1.092 | — |
Applications
Where Sulfur trioxide is used.
Patent Landscape
21 patents reference SO3 or close compositional variants.
| Patent | Title | Assignee | Granted |
|---|---|---|---|
| 6500402 | Catalyst for oxidizing SO2 to SO3 and utilization of the catalyst in a method for producing sulfuric acid | — | — |
| 10307741 | Shaped catalyst body for the catalytic oxidation of SO2 into SO3 | — | — |
| 5538707 | Acid concentration control in SO.sub.3 absorption | — | — |
| 3950493 | Process for absorbing SO.sub.3 | — | — |
| 4548789 | Mono-stage device to generate gaseous SO.sub.3 from melted sulphur | — | — |
| 4419423 | Nonaqueous cells employing heat-treated MnO.sub.2 cathodes and a PC-DME-LiCF.sub.3 SO.sub.3 electrolyte | — | — |
| 4766104 | Process for producing a V.sub.2 O.sub.5 -and-alkali-metal-sulfate-containing catalyst for oxidizing SO.sub.2 t | — | — |
| 4304759 | Process for obtaining metal oxide and SO.sub.2 -containing gases essentially free of SO.sub.3 and H.sub.2 SO.s | — | — |
| 9487401 | Process for the oxidation of SO2 to SO3 | — | — |
| 5387402 | Contact reactor for a quasi-isothermal catalytic oxidation of SO.sub.2 to SO.sub.3 and method of operating sam | — | — |
Frequently Asked Questions
Common questions about Sulfur trioxide, answered from cross-validated data.
What is SO3?
Sulfur trioxide is a stable, insulating oxide of sulfur that functions as the primary industrial precursor for the manufacturing of sulfuric acid.
What is SO3 used for?
What is the band gap of SO3?
Is SO3 a metal, semiconductor, or insulator?
Is SO3 thermodynamically stable?
What is the crystal structure of SO3?
What is the density of SO3?
How many polymorphs of SO3 are known?
What elements does SO3 contain?
Where does the data for SO3 come from?
How It Compares
As a fundamental inorganic oxide, sulfur trioxide stands as a critical reference point for sulfur-based chemistry. Unlike many transient or metastable oxides, its position on the thermodynamic convex hull ensures its reliability as a chemical building block in industrial applications.
Data sources & attribution
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- mpaloe — Data from MP-ALOE. Cite: Kuner et al., npj Comput. Mater. (2025), doi:10.1038/s41524-025-01834-9.
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