An inhibitory substance characterized by its propensity to attach very strongly, by a true chemical bond (e.g. covalent) to the surface atoms or ions constituting the catalytically active sites. Poisons act in minute quantities. Typical poisons are S
, etc. In most cases, activity and/or selectivity cannot be recovered without a drastic change in operating conditions (most often a regeneration). recovery, if at all, takes place very slowly and/or only partially.
PAC, 1991, 63, 1227. 'Manual on catalyst characterization (Recommendations 1991)' on page 1244 (https://doi.org/10.1351/pac199163091227)