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Catalyst Poisons

Catalyst poison is one of the major causes of catalyst performance deactivation.

Catalyst PoisonMechanismDegree of PoisonCountermeasure
Rust, Dust, Carbon, Solid Material Temporary Poison Less Poison Air Blow, Filtration
Oil Mist, Tar Temporary Poison Strong Poison Demister, Decoking
Organic Silicone Permanent Poison Very Strong Poison Guard Bed, Chemical Rejuvenation
Organic Phosphorous, Phosphorous Compounds Permanent Poison Strong Poison Guard Bed, Chemical Rejuvenation
Organic Metals, Metals Vapor Permanent Poison Strong Poison Guard Bed, Catalyst Reload
Halogens and Sulfur Compounds Temporary or Permanent Poison Depends on concentration Increase Temperature, Catalyst Reload

Rust, Foreign Particle, Dust, Other Solid Material

Generally physical dust is less effective to catalyst deactivation, however a large amount of poisons would have a chance to cover surface of catalyst and may cause to increase pressure drop. As one of the countermeasures, install a filter upstream of a catalyst reactor to reduce accumulation of the dust. In case that the catalyst is covered by the dust, water wash or air blow can be applied to remove them. Please keep the dust amount in exhaust gas less than 5mg/Nm3.

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Mist (Tar, Resin), Other Liquid Material

Usually tarry material is generated in the process of paint, dryer, etc. It is typically cooled and formed mist or solid and may be carried over to catalyst bed. In case catalyst inlet temperature is low, some of tar may not be combusted and deposit on the catalyst surface. It should cause catalyst deactivation. In such case, decoking by controlling temperature up to 500℃ is applicable to burn off tar and recovers catalyst performance.

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Organic Silicone, Organic Phosphorus, Organic Metal compound

When vaporized organic silicon, organic phosphorus, or organic metallic compounds attack to catalyst, they react with active metals (platinum, palladium, etc.) over the catalyst surface. Nonvolatile oxides are formed with the active metals on the catalyst and decline its catalyst performance. Even very low concentrations (ppb order) of these poisons may affect its catalyst performance.

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N-U has the following catalyst poison measures against organic silicone, organic phosphorus, and an organic metallic compounds.

  • Guard Bed Catalyst
    It is required to install upstream of catalyst bed in order to capture and decompose catalyst poisons (Organic Silicone, etc.).
  • Poison Durable Catalyst
    Poison durable catalyst is our own technology and is expected to extend its catalyst life.
  • Chemical Rejuvenation
    Chemical rejuvenation is our own technology and can recover catalyst performance.


Organic/inorganic halogen compounds deactivate catalyst even at a very low concentration (of the order of ppm). However, it does not behave as permanent catalyst poisons and the deactivation tendency is appeared as temporary adsorption of halogens over the catalyst. In general, if there are no halogen compounds in the gas stream, most of the catalyst performance is recovered. N-U has a series of halogen durable catalysts to improve hydrocarbon destruction efficiency in the presence of halogens.

Sulfur, Sulfuric Compounds

It is known that conventional oxidation catalysts (such as Pt/Al2O3) oxide sulfur compounds and generate SOx. Relatively a large amount of SOx may cause serious damage to the catalyst substrate (Al2O3) in a short period of time. In case of low concentration of sulfur, such as a few ppm or less, it is workable for conventional oxidation catalysts by increasing operation temperature or quantity of catalysts. In case of high concentration of sulfur, such as hundreds ppm or more, however, it is difficult to tolerate sulfur and it may cause permanent poison for the catalyst. N-U has a series of sulfur durable catalyst to improve the sulfur durability.

Catalyst Poison Measure

N-U has solutions for catalyst poisons ahead of the other companies, and developed a guard bed catalyst as a countermeasure against catalyst poisons. In case guard bed catalyst is not suitable for catalyst poisons such as halogens, sulfur/sulfur compounds, or guard bed catalyst cannot be used with some reasons, we can offer various types of durable catalysts as shown below.

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