Chelating agents or chelanting agents for hydroteating catalysts are chemicals with which hydrotreating catalyst are impregnated and dried. Upon sulfiding of the catalyst this agent helps in dispersion of active catalyst metals and thus increases the activity of the catalyst. These are normally, used for Type-II fresh or regenerated hydroteating catalysts.
Typical chelating agents used in the market are Oxalic acid, citric acid, tartaric acid, malonic acid, butanediol, glycol aldehyde etc.
More about type-II catalysts can be found at “Hydrotreating Catalysts”