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HMRC internal manual

Customs Special Procedures Manual

Production accessories: catalyst residues

If catalysts are used up during processing and lose their catalytic properties but residues that cannot be used further in that processing operation are left over, they should be identified in the authorisation as a Secondary Processed Product (SPP) (see SPE13030). Where such residues are retained within the EU, the rate of yield should be used to establish the amount of catalyst deemed to be present in those goods.

Notice 3001/2015, Annex D Section 4.8