 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 (CaCO3) followed by poisoning with lead acetate.In a related case, the "Rosenmund reduction" of an acyl chloride to the corresponding aldehyde, the palladium catalyst (over barium sulfate or calcium carbonate) 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.