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Catalyst Activity Evaluation: From K Value to Field Verification

Part of the Testing & Analysis: The Complete Guide — this article is one of the detailed pages in the guide.

Direct answer: Catalyst activity is quantified as the activity constant K (m/h), derived from measured conversion at known gas flow, temperature and composition. The K value is the universal currency of catalyst performance — used for sizing, acceptance testing and lifecycle tracking — and it is only meaningful when the test conditions are stated alongside the number.

The K equation in practice

For a catalyst at area velocity AV and conversion η:

K = −AV × ln(1 − η)

A higher K means more activity per unit catalyst surface. Two catalysts with equal K values are equivalent for sizing purposes; comparing K values measured under different gas conditions is meaningless.

The three levels of evaluation

Level What happens What it answers
Laboratory rig Sample core tested with simulated gas Fresh-activity baseline, screening
Pilot / side-stream Catalyst exposed to the real plant gas Real-gas activity, poisoning rates
Field verification Full-scale conversion + slip measurement The guarantee: does it perform?

Standard test conditions

Activity tests fix the independent variables so results compare:

  • Gas composition — NOx, NH₃, SO₂, O₂, H₂O, and the NO₂/NOx ratio.
  • Temperature — activity is temperature-dependent; standard reference points are used.
  • Space/area velocity — flow per catalyst unit.
  • Sample condition — fresh, aged, regenerated; tested as cores or full modules.

Reading activity data honestly

  • A K value without gas composition is advertising, not data.
  • Fresh-activity K overstates in-service performance; the design uses end-of-life K.
  • Field conversion below the lab prediction usually means distribution problems or unexpected poisons — both are diagnosable by further testing.

Why periodic testing pays for itself

Tracking K over time turns replacement decisions from guesswork into planning: the trend line predicts when the catalyst crosses the end-of-life threshold, letting the plant order the replacement layer before compliance slips.

Manufacturer perspective

We publish K values with test conditions in writing and support customers with core sampling and third-party laboratory verification. An activity number is a promise — it should come with the evidence to be checked.

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