Catalyst Poisoning

When a catalyst is completely or partially rendered inactive by a chemical component, the condition is referred to as catalyst poisoning. In contrast to other modes of catalyst deterioration like heat disintegration or physical damage, poisoning particularly refers to chemical deactivation. When poisoning leads in increased catalyst selectivity (such as with Lindlar's catalyst), it can be advantageous even though it is often unwanted. Leaded gasoline poisoning of catalytic converters serves as a significant historical example. Inorganic anions and organic functional groups can frequently be aggressively adsorbed to metal surfaces. Carbon monoxide, halides, cyanides, sulphides, sulfites, phosphates, phosphites, and organic molecules such nitriles, nitro compounds, oximes, and nitrogen-containing heterocycles are examples of common catalyst poisons. Because of the characteristics of the transition metal, different agents have different catalytic properties. Palladium chloride is reduced in a calcium carbonate (CaCO3) slurry to produce Lindlar catalysts, which are then poisoned with lead acetate. In a similar situation, the palladium catalyst (over barium sulphate or calcium carbonate) is purposefully poisoned by the addition of sulphur or quinoline in order to reduce the catalyst activity and hence prevent over-reduction of the aldehyde product to the main alcohol.