Name one case in which catalyst poisoning is useful?
alkynes can react with hydrogen in the presence of a catalyst such as palladium to form alkanes, if they catalyst is poisoned you can produce alkenes instead
Usually, catalyst poisoning is undesirable as it leads to a loss of usefulness of expensive noble metals or their complexes. However, poisoning of catalysts can be used to improve selectivities of reactions. In the classical Rosenmund reduction of acyl chlorides to aldehydes, the palladium catalyst (over barium sulfate or calcium carbonate) is poisoned by the addition of sulfur or quinoline. This system reduces triple bonds faster than double bonds allowing for an especially selective reduction. Lindlar's catalyst is another example — palladium poisoned with lead salts. As described by its inventor,[1][2] the catalyst is prepared by reduction of palladium chloride in a slurry of calcium carbonate followed by adding lead acetate. By this approach, one obtains a catalyst with a large surface area. Further deactivation of the catalyst with quinoline enhances its selectivity, preventing formation of alkanes. An example of alkyne reduction is the reduction of phenylacetylene to styrene.[1] en.wikipedia.org/wiki/Lindlar%27s...
