Catalyst used in Rosenmund reaction is:

A catalyst used in Rosenmund reaction can be prepared by reduction of $palladium(II)chloride$ solution in the presence of $BaS{O}_4$

The Palladium Catalyst used in Rosenmund’s reduction must be poisoned with $BaS{O}_4$ because the untreated catalyst $Palladium(Pd)$ is too reactive and will undergo over reduction forming other products.