Difference between Lindlar and Rosenmund catalysts?

Question

Is there any difference between the Lindlar and Rosenmund catalysts? I've checked around, and it seems the same compounds are used to make both. Is there a difference in their reactivities or are they essentially the same?

Answer 1

There is a usage difference and basic configuration difference between these.

A Lindlar catalyst is a heterogeneous catalyst that consists of palladium deposited on calcium carbonate which is then poisoned with various forms of lead or sulphur. 

Poisoning with lead or sulfur prevents reduction of the alkene to an alkane,

catalysed by palladium on barium sulfate, which is sometimes called the Rosenmund catalyst. Barium sulfate has a low surface area which reduces the activity of the palladium, preventing over-reduction. However, for certain reactive acyl chlorides the activity must be reduced further, by the addition of a poison. Originally this was thioquinanthrene although thiourea^[2] has also been used.^[3][4] Deactivation is required because the system must reduce the acyl chloride but not the subsequent aldehyde. If further reduction does take place it will create a primary alcohol which would then react with the remaining acyl chloride to form an ester.

Palladium deposited on Calcium Carbonate enables the same side addition of a H2 molecule to the alkyne plane of a hydrocarbon.

Palladium on Barium Sulfate allows the removal of the halogen from the acyl chloride and replacement with a Hydrogen atom. This catalyst needs to be poisoned to prevent production of an alcohol in the synthesis and finally an ester.

The difference in makeup is Barium Carbonate and Calcium Carbonate