CO Oxidation: The Complete Guide
Direct answer: CO oxidation catalysts convert carbon monoxide to CO₂ at 150–350°C — far below the temperature where thermal oxidation works — using precious-metal (Pt, Pd) or base-metal active systems on honeycomb or pellet substrates. They serve sintering, incineration, furnace exhaust and safety duties wherever CO must be removed from oxygen-containing gas. This guide is the hub for the whole CO oxidation topic; detailed articles are linked throughout.
1. Why CO oxidation matters
Carbon monoxide forms wherever combustion is incomplete: sintering machines, furnaces, kilns, dryers and incineration units. It is toxic and tightly regulated in stack gas. Catalytic oxidation is the standard answer when:
- CO concentration is in the hundreds to thousands of ppm,
- the gas already contains oxygen (typically 3–20%),
- and the stream temperature is 150–350°C — above light-off but below the ~600°C+ where thermal oxidation becomes self-sustaining.
The reaction is simple: 2CO + O₂ → 2CO₂, exothermic (~283 kJ/mol), self-accelerating once light-off is reached.
2. Catalyst families
| Property | Precious metal (Pt / Pd) | Base metal (Mn-Cu, hopcalite type) |
|---|---|---|
| Light-off (T50) | From ~150°C | Typically 200°C+ |
| Activity density | High | Moderate |
| Cost | Higher | Lower |
| Thermal stability | Good | More limited |
| SO₂ tolerance | Sensitive | Formulation-dependent |
Full comparison and the four selection questions (temperature, SO₂, moisture, duty pattern) are in CO Catalyst Selection.
3. Light-off: T50 and T90
Catalyst effectiveness is quoted as T50 and T90 — the temperatures for 50% and 90% conversion under defined conditions. These numbers shift with space velocity, moisture, SO₂ and CO concentration, so the operating temperature must sit 20–40°C above the expected T90 in the real gas. Cold-start dynamics and pre-heating options are covered in Light-Off Temperature.
4. Key design parameters
| Parameter | Typical range | Notes |
|---|---|---|
| Operating temperature | 150–350°C | Lower with precious metals + pre-heating |
| Space velocity | 5,000–20,000 h⁻¹ | Duty-dependent |
| Face velocity | 1–4 m/s (honeycomb) | Pressure drop budget |
| O₂ requirement | Lean (≥3%) | Stoichiometric air added if needed |
| CO range | Hundreds–thousands ppm | Concentration drives exotherm |
5. The four application scenarios
Different industries impose different constraints — detailed in Application Scenarios - Reactor Bed Design — space velocity, pressure drop, module sealing. - Exotherm Management — adiabatic rise, staging, heat recovery. - Catalyst Deactivation - Sintering Machine CO Control — the hardest CO duty, field results. - Waste Incineration CO Control — polishing after gas cleaning. — sulfur, halogens, sintering, fouling.:
- Sintering exhaust: huge flow, moderate temperature, SO₂ + moisture + dust.
- Waste incineration: dynamic CO spikes, HCl and heavy metals upstream.
- Furnaces & kilns: intermittent duty, cold starts, fuel switching.
- Enclosed-space safety: continuous low-temperature CO abatement with heating tube systems.
6. Deactivation and life
- SO₂ poisoning progressively raises light-off temperature.
- Moisture competes for sites at low temperature.
- Thermal sintering limits high-temperature duty.
- Dust blinding on poorly filtered streams.
Trend light-off temperature over time — a rising T50 is the earliest deactivation signal, visible before conversion falls at the operating point. See Light-Off Temperature for the monitoring practice.
7. Quick reference: symptom → cause
| Symptom | Most likely cause | Go to |
|---|---|---|
| Won't light off in service | Below T90 in real gas (moisture/SO₂) | Light-Off |
| Light-off rises month by month | SO₂ poisoning | Selection |
| Fails after cold start | Thermal shock / condensation | Scenarios |
| Face blinded with dust | Missing upstream filtration | Selection |
8. The complete CO oxidation series
- CO Catalyst Selection — precious vs base metal, the four questions.
- Light-Off Temperature — T50/T90, test conditions, cold start.
- Application Scenarios — sintering, incineration, furnaces, safety duty.
9. Manufacturer perspective
The most common sizing error is selecting on CO concentration alone. The full stream — moisture, SO₂, temperature range, flow and duty pattern — decides whether a catalyst lights off at all in service. We ask for the complete gas analysis and recommend simulation testing on non-standard streams.