The controlled partial conversion of propyne (${\text{CH}}_3\text{C}\equiv \text{CH}$) to propene (${\text{CH}}_3\text{CH}={\text{CH}}_2$) requires which of the following reagents?

The selective partial reduction of an alkyne to an alkene without further reduction into an alkane requires a partially deactivated or "poisoned" palladium catalyst supported on calcium carbonate or barium sulfate, commonly known as Lindlar's catalyst. A normal unpoisoned metal catalyst like ${\text{H}}_2/\text{Pd}$ would reduce it completely to propane (${\text{CH}}_3{\text{CH}}_2{\text{CH}}_3$).