Since heterogeneous catalysts work by adsorbing reactants on to the surface, they are often easily poisoned by impurities which can bind strongly to the active sites on the surface.

Poisoning also occurs with homogeneous catalysts as well. Substances which are poisonous to humans often operate by blocking an enzyme-catalysed reaction. Many pesticides are designed to do just that in pests.

In applications of catalysis ways are devised for regenerating catalyst surfaces, or else careful purification is carried out beforehand to remove potential poisons.

For example leaded petrol cannot be used in vehicles with catalytic converters because lead is strongly adsorbed to the catalyst surface. In residential fuel cell systems CO must be removed from the fuel because it is strongly adsorbed on the catalyst surface. Removal of CO from the feedstock is built into ammonia manufacturing.

Plant construction materials may have to be chosen to reduce the risk of catalyst poisoning.

Sometimes regeneration of spent catalyst is built in to an industrial process, providing heating for endothermic processes.