Poisoning of Hydrogen Reactions

Poisoning of metal-gas reactions at ambient temperature is a wide-spread phenomenon but the word poisoning is used for the characterization of quite different processes which retard the rate of a reaction. In catalytic processes, for example, molecules from the adjacent liquid or gas phase are adsorbed on a solid surface. There, with other species new molecules are formed as reaction products which are then released back to the liquid or gas phase. The reactivity of a surface acting as a catalyzer depends on active sites where the intermediate adsorption products are formed. These sites can be specific sites such as steps or adatoms or all sites on a clean surface. If they are blocked by immobile chemisorption compounds, the reaction is poisoned.