CO Catalyst Deactivation: Poisoning, Sintering and Fouling

Part of the CO Oxidation: The Complete Guide — this article is one of the detailed pages in the guide.

Direct answer: CO oxidation catalysts lose activity through four routes: sulfur poisoning, halogen and metal poisoning, thermal sintering, and surface fouling. The dominant route depends on the application — sintering and flue gas favor sulfur; process off-gas favors halogens and heavy metals. Diagnosis from field symptoms usually identifies the route without laboratory work.

Deactivation routes

Route	Typical cause	Field symptom
Sulfur poisoning	SO₂ in gas at low-to-moderate temperature	Progressive conversion loss, partial recovery on heating
Halogen poisoning	HCl/Cl₂ from plastics, incineration	Rapid, often irreversible activity loss
Heavy metal / alkali	Pb, As, K from fuel or dust	Slow permanent loss, localized at inlet face
Thermal sintering	Exotherm excursions, hot spots	Sudden loss after an upset, no recovery
Fouling	Dust, soot, mist, sticky condensates	Rising pressure drop before conversion falls

Sulfur poisoning in detail

SO₂ competes for active sites and forms stable surface sulfates, particularly below about 200°C. Precious metal catalysts are vulnerable; manganese-based and some base-metal formulations are more tolerant. Where sulfur is present, choose a sulfur-tolerant formulation and operate above the temperature where sulfate decomposition is favorable.

Halogens — the fastest killer

Chlorine from PVC incineration or process vents attacks both precious metals (volatile chlorides) and supports (acid attack). Protection requires upstream scrubbing, dilution, or a catalyst formulated with halogen-tolerant chemistry — and in severe cases a sacrificial pre-bed.

Sintering from thermal excursions

Exceeding the catalyst's rated temperature collapses the metal dispersion that provides activity. The damage is structural and irreversible; regeneration cannot restore it. Prevention is engineering: exotherm control, temperature interlocks and staged beds.

Monitoring and diagnosis

Track conversion at fixed conditions — a trend line reveals deactivation early.
Compare light-off temperature — a rising T50/T90 flags progressive poisoning before full-load failure.
Note pressure drop — separates fouling from chemical deactivation.
Log upsets — any over-temperature event predicts future activity loss.

Manufacturer perspective

The cheapest deactivation management is selecting the right catalyst for the actual gas composition on day one — sulfur, halogens and metals must be in the specification. Where the gas is aggressive, we prefer a small side-stream pilot before full-scale commitment.

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