Activated carbon is the trade name for a carbonaceous adsorbent which is defined as follows: Activated carbons are non-hazardous, processed, carbonaceous products, having a porous structure and a large internal surface area. These materials can adsorb a wide variety of substances, i.e. they are able to attract molecules to their internal surface, and are therefore called adsorbents. The volume of pores of the activated carbons is generally greater than 0.2 ml g -1. The internal surface area is generally greater than 400 m2 g-1. The width of the pores ranges from 0.3 to several thousand nm. Activated carbons have been used for many years quite successfully for adsorptive removal of impurities from exhaust gas and waste water streams. However, for cost-effective removal of certain impurities contained in gases (such as hydrogen sulfide, mercury and ammonia), the adsorption capacities and the feasible removal rates must be substantially boosted by impregnation of the activated carbon by suitable chemicals. When these chemicals are deposited on the internal surface of the activated carbon, the removal mechanism also changes. The impurities are no longer removed by adsorption but by chemisorption. Impregnated activated carbons are carbonaceous adsorbents which have chemicals finely distributed on their internal surface. The impregnation optimizes the existing properties of the activated carbon giving a synergism between the chemicals and the carbon. This facilitates the cost-effective removal of certain impurities from gas streams which would be impossible otherwise. For environmental protection, various qualities of impregnated activated carbon are available and have been used for many years in the fields of gas purification, civil and military gas protection and catalysis.