Regeneration Methods for Poisoned Carbon Monoxide Catalysts: Industrial Practices and Technical Insights

1. Types of Catalyst Poisoning and Deactivation Mechanisms

Catalyst poisoning refers to the phenomenon in which impurities in the feed gas chemically or physically interact with the active sites of the catalyst, resulting in a loss of activity. The deactivation of carbon monoxide catalysts can be divided into the following main categories.

Chemical poisoning. Impurities such as sulfides (e.g., H₂S, COS) and chlorides in the feed gas react irreversibly with the active metal components to form stable compounds, permanently destroying the active sites. This is the most difficult type of deactivation to remedy by conventional regeneration methods.

Coking (carbon deposition). During the catalytic reaction, CO may undergo a disproportionation reaction (2CO → C + CO₂), generating carbonaceous deposits that cover active sites and block catalyst pores. Coking is a reversible form of deactivation and is one of the most common failure modes in industrial practice.

Water vapor inhibition. For copper‑manganese Hopcalite catalysts, water vapor molecules compete with CO for adsorption on active sites, causing a sharp decline in activity when humidity exceeds a certain threshold. This type of deactivation can usually be reversed by thermal desorption.

Thermal sintering. When the operating temperature exceeds the catalyst's thermal tolerance, the active component crystallites migrate and agglomerate, leading to a loss of specific surface area. Sintering is essentially irreversible, and regeneration offers limited recovery.

Accurately diagnosing the dominant deactivation mechanism is a prerequisite for selecting an appropriate regeneration method.

2. Thermal Regeneration: The Most Versatile Physical Restoration Route

Thermal regeneration removes adsorbed poisons from active sites by heating, making it the most generally applicable method, especially for water‑vapor inhibition and mild coking.

(1) Conventional Thermal Regeneration

For copper‑manganese hopcalite catalysts, conventional thermal regeneration is typically carried out at 150–200 °C. If the catalyst has been deactivated by high‑humidity conditions, preheating at 80–150 °C for 2–20 minutes is recommended, with the optimum conditions being 100–130 °C for 4–10 minutes. Under these conditions, the catalyst activity can be restored to more than 90% of its initial level.

(2) In‑Situ CO Treatment

For noble‑metal Pt‑CeO₂ catalysts, an in‑situ treatment using the reactant CO itself at 200 °C has been shown to provide the best durability enhancement. The mechanism involves the generation of surface oxygen vacancies (Oᵥ) during CO treatment, which strengthens the adsorption and activation of O₂ at the interface. This finding indicates that, in some systems, the reactant itself can serve as a regeneration medium without the need for additional regeneration gases.

(3) Extended Mechanistic Insights

For cobalt‑doped manganese oxide (Co₀.₄Mn) catalysts, treatment at 200 °C for 1 hour achieves a significant degree of activity recovery while preserving the integrity of the crystal structure. This provides a reference temperature window for the regeneration of manganese‑based catalysts.

3. Oxidative Regeneration: The Core Process for Coke Removal

For carbon monoxide catalysts deactivated by coking, oxidative regeneration is the most direct and effective solution. The underlying principle is to combust the carbonaceous deposits to CO₂ via controlled oxidation.

For palladium‑based CO catalysts, regeneration can be accomplished by air oxidation at low temperatures as low as 16.5–65 °C, with complete recovery of activity and the ability to repeat the process multiple times. This method consumes very little energy and is especially suitable for catalysts supported on heat‑sensitive carriers.

For supported cobalt oxide catalysts (Co₃O₄), regeneration in an atmosphere of 10% O₂/Ar is significantly more efficient than in pure argon. Temperature‑programmed oxidation (TPO) experiments confirm the presence of carbonate and surface carbon species on the deactivated catalyst, and oxidative regeneration effectively removes these deposits.

Oxidative regeneration requires careful control of temperature and oxygen concentration. Excessively high oxygen levels or rapid heating rates can cause violent exothermic reactions, leading to localized overheating and subsequent sintering of the active phase. In industrial practice, low oxygen concentrations (1–5% O₂/N₂) are typically used in combination with programmed temperature ramping to ensure both safety and effectiveness.

4. Reductive Regeneration: Restoring Metallic Active Sites

For some poisoned CO catalysts, the active metals may be in an oxidized state or complexed with poisons, and a reducing atmosphere is required to restore the metallic active sites.

For platinum catalysts poisoned by CO, a periodic alternating treatment with oxidizing gas (oxygen or oxygen‑containing gas) and reducing gas (hydrogen or hydrogen‑containing gas) at low heating temperatures can be applied. The rationale is that the oxidation step oxidizes adsorbed CO to CO₂ and desorbs it, while the reduction step reduces the formed Pt‑O species back to metallic Pt and removes residual surface species. At 80 °C, an activity recovery of more than 90% can be achieved.

Nickel‑based catalysts can also recover activity after treatment in a H₂ atmosphere for a certain period. The mechanism involves the reduction of oxidized NiO to metallic Ni by H₂, while some sulfides are converted to H₂S and desorbed.

5. Chemical Regeneration: Targeted Remediation for Specific Poisons

For certain types of chemical poisoning, more targeted chemical regeneration methods are required.

Steam treatment (desulfurization). For medium‑temperature CO shift catalysts poisoned by H₂S, steam treatment is a viable regeneration approach. Water vapor reacts with sulfides to form H₂S, which is carried away with the gas stream. Thermodynamic analysis indicates that in an O₂ atmosphere, the catalyst can be oxidized and regenerated to Fe₃O₄ or Fe₂O₃, and XRD characterization confirms the feasibility of this pathway.

Upcycling and repurposing. For spent platinum‑based CO oxidation catalysts, a simple Ni impregnation treatment can convert the deactivated catalyst modules into active catalysts for the dry reforming of methane (DRM). Under DRM reaction conditions at 750 °C, the converted catalyst can sustain stable operation for more than 7 hours. This approach goes beyond simple activity recovery, achieving a transformation of the catalyst's function and resource valorization.

6. Post‑Regeneration Evaluation and Operational Precautions

Regenerated catalysts must undergo systematic evaluation before being returned to service, focusing on the following aspects.

(1) Activity Testing

The CO conversion efficiency should be measured under standard operating conditions. For hopcalite catalysts, a CO conversion of at least 85% is generally required for qualification. The specific surface area (BET) should be restored to more than 80% of its original value. In addition, the bed pressure drop should be checked to ensure that the catalyst has not suffered from pulverization or compaction during regeneration.

(2) Operating Condition Adaptation

Regenerated catalysts may exhibit slightly reduced resistance to poisons and moisture compared to fresh catalysts, so operating parameters should be adjusted accordingly. For copper‑manganese catalysts, it is advisable to use a desiccant in combination and to keep the ambient humidity within a suitable range. In low‑temperature applications, a preheater can be employed to prevent condensation of water vapor that could cause secondary inhibition.

(3) Storage Guidelines

If the regenerated catalyst is not used immediately, it should be stored in a sealed, dry environment, away from sources of sulfides, chlorides, and other poisons, to prevent secondary deactivation.

7. Concluding Remarks

The regeneration of poisoned carbon monoxide catalysts is a systematic engineering task that encompasses deactivation diagnosis, method selection, process execution, and performance evaluation. From thermal regeneration to oxidative, reductive, and chemical regeneration, each technical route has its specific applicability boundaries and process parameters. The choice of method depends on three dimensions: the catalyst system, the dominant deactivation factor, and the industrial operating conditions.

Industrial users are encouraged to establish a full life‑cycle management system for catalysts: strictly purify the feed gas to keep sulfur, chlorine, and other poisons below the catalyst tolerance limits; precisely control reaction temperatures to avoid overheating and sintering; implement a regular monitoring schedule to detect activity loss early and schedule regeneration in a timely manner; and select the appropriate regeneration process for each catalyst system. minstrong’s oxygen‑free CO catalyst can directly oxidize CO to CO₂ under anoxic conditions and supports cyclic regeneration. Its active component content exceeds 80%, and its specific surface area is in the range of 180–240 m²/g. Transforming catalysts from “single‑use consumables” into “recyclable assets” is not only a practical way to reduce operating costs but also an inevitable direction for efficient resource utilization.

author: Gloria
date:2026/07/08