Molybdenum Trioxide
Properties
| State | Solid |
| Color | Pale yellow to greenish-yellow |
| Solubility | Slightly soluble in water (0.1 g/100 mL); soluble in ammonia and alkali (as molybdate) |
| Melting Point | 795 °C |
| Boiling Point | 1155 °C |
About Molybdenum Trioxide
MoO3 is the pale-yellow oxide that sits at the center of molybdenum metallurgy, refinery catalysis, and — more recently — the OLED panel in your phone. The crystal is unusual: orthorhombic with distorted MoO6 octahedra sharing edges within layers and corners between layers, giving a 2D van-der-Waals lattice that can be exfoliated to single sheets the same way MoS2 can. The d0 Mo(VI) center is the thermodynamically stable form of molybdenum in air, and the compound sublimes cleanly at 700 °C, which is why it's so easy to evaporate as a thin film. Industrially the volume is enormous. MoO3 is the intermediate from which all primary molybdenum metal is reduced (H2 reduction at 1100 °C gives the powder used to make Mo wire, electrodes, and the Mo additions in superalloys). It is the active phase in the selective oxidation of propene to acrolein and methanol to formaldehyde — both multi-million-tonne processes. It is the precursor to the Co-Mo/Al2O3 catalysts that get sulfided into MoS2 inside hydrotreaters at every refinery. And in the last decade, vacuum-evaporated MoO3 thin films have replaced PEDOT:PSS as the hole-injection layer in commercial AMOLED displays.
Where you'll encounter it
If you've ever held a Samsung or LG OLED phone, you're looking at light coming through a MoO3 layer about 10 to 30 nm thick. The deposition runs in a thermal evaporator at around 600 °C in vacuum, and the resulting film has a work function near 6.7 eV — deep enough to inject holes efficiently from ITO into the organic transport layers below. In a catalysis lab, anyone who has ever calcined ammonium heptamolybdate has watched a white powder turn pale yellow as it converts to MoO3 around 350 °C. Glassblowers occasionally encounter it as the yellow-green deposit that forms when a Mo electrode runs hot in air. And in the refinery, every shipment of fresh hydrotreater catalyst arrives as oxide-form CoMo/Al2O3 extrudates that the operator sulfides in situ before bringing the unit on stream.
Common Uses
- Feedstock for Mo metal production via H2 reduction at 1100 °C
- Selective-oxidation catalyst for propene to acrolein and methanol to formaldehyde
- Precursor for Co-Mo and Ni-Mo hydrodesulfurization catalysts in oil refineries
- Hole-injection layer in commercial AMOLED panels from Samsung and LG Display
- Corrosion inhibitor in closed-loop industrial cooling water systems
- Trace-element source in agricultural micronutrient fertilizer blends
- Electrochromic layer in research-grade smart-window prototypes
Safety Information
GHS classifications: STOT Single Exposure Category 3 (respiratory tract), Eye Irritation Category 2A. Chronic inhalation causes mild lung irritation and can interfere with copper metabolism in livestock at sustained exposure — the same ruminant disease that motivated the original 1950s tox studies. OSHA PEL is 5 mg/m3 for soluble Mo compounds and 15 mg/m3 for total Mo dust; ACGIH TLV is 0.5 mg/m3 respirable and 10 mg/m3 inhalable. Use a P100 respirator for bulk handling. In aqueous ammonia or NaOH it dissolves to molybdate — wash spills with dilute alkali rather than acid. Standard PPE plus dust control. Not flammable, not water-reactive, no special storage required.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.