Poisoning refers specifically to chemical deactivation, rather than other mechanisms of catalyst degradation such as thermal decomposition or physical damage.
Common catalyst poisons include carbon monoxide, halides, cyanides, sulfides, sulfites, phosphates, phosphites and organic molecules such as nitriles, nitro compounds, oximes, and nitrogen-containing heterocycles.
Lindlar catalysts are prepared by the reduction of palladium chloride in a slurry of calcium carbonate (CaCO3) followed by poisoning with lead acetate.
Poisoning decreases the number of active sites, and the average distance that a reactant molecule must diffuse through the pore structure before undergoing reaction increases as a result.
Adding cobalt and nickel [8] to either edges or partially incorporating them into the crystal lattice structure can improve the catalyst's efficiency.