Catalyst poisoning


Catalyst poisoning refers to the partial or total deactivation of a catalyst by a chemical compound. An important historic example was the poisoning of catalytic converters by leaded fuel. Poisoning refers specifically to chemical deactivation, rather than other mechanism of catalyst degradation such as thermal decomposition or physical damage. Although usually undesirable, poisoning may be helpful when it results in improved catalyst selectivity.

Poisoning of Pd catalysts

Organic functional groups and inorganic anions often have the ability to strongly adsorb to metal surfaces, i.e. they are poisons. Common catalyst poisons include the following: carbon monoxide, halide, cyanide, sulfide, sulfite, and phosphite and organic molecules such as nitriles, nitros, oximes and nitrogen-containing heterocycles. Agents vary their catalytic properties because of the nature of the transition metal. Lindlar catalyst is prepared by the reduction of palladium chloride in a slurry of calcium carbonate followed by poisoning with lead acetate. In a related case, the "Rosenmund reduction" of an acyl chloride to the corresponding aldehyde, the palladium catalyst is intentionally poisoned by the addition of sulfur or quinoline in order to lower the catalyst activity and thereby prevent reduction of the aldehyde product to the primary alcohol.

Other examples

The susceptibility of a noble metal-based catalyst to poisoning by elemental mercury is a common proof that the catalyst is heterogeneous. Homogeneous catalysts are typically unreactive toward Hg, whereas heterogeneous catalysts form inactive amalgams.