Catalyst Poisons

Catalyst Poisons

 

substances that induce the “poisoning” of catalysts (usually heterogeneous catalysts), that is, reduce their catalytic activity or completely stop the catalytic effect. The poisoning of heterogeneous catalysts occurs as a result of the adsorption of the poison or the product of its chemical transformation on the surface of the catalyst. The poisoning may be temporary or permanent. For example, during the synthesis of ammonia on an iron catalyst, oxygen and its derivatives temporarily poison Fe. In this case, the surface of the catalyst is freed of oxygen under the action of a pure N2 + H 2 mixture and the degree of poisoning is reduced. Sulfur compounds permanently poison Fe, since the activity of the catalyst is not successfully reduced by the action of the pure mixture. Thorough purification is required to prevent poisoning of the reacting mixture that passes onto the catalyst.

The most widespread catalyst poisons for metal catalysts include substances containing oxygen (H20, CO, C02), sulfur (H2S, CS2, C2H5SH), selenium, tellurium, nitrogen, phosphorus, arsenic, and antimony, as well as unsaturated hydrocarbons (C2H4, C2H2) and metal ions (Cu2+, Sn2+, Hg2+, Fe2+, Co2+, Ni2+). Acidic catalysts are usually poisoned by basic admixtures and basic catalysts, by acidic admixtures.

References in periodicals archive ?
Protection of three-way catalyst poisons by reducing the volatility of the phosphorus in the lubricant
Consideration should be given to the selection of fillers and pigments potentially used in the compound due to the well-known possibility for interaction between the platinum catalyst and such materials as sulfur, amines and other catalyst poisons.
In these studies the catalysts are exposed to relatively high amounts of catalyst poisons. The common conclusion is that the decreased ammonia storage capacity observed upon catalyst poisoning is due to physical or chemical blockage of the adsorption sites.
The encapsulation of metal particles in nano-sized pores of the catalytic material limits the access of hydrogen to the particles and excludes bulky sulfur and nitrogen compounds (catalyst poisons).
As such, the system is very tolerant to catalyst poisons such as phosphor, sulphur, calcium and zinc.
The potential for catalyst poisons exist if the VOC stream contains silicon, phosphorous, arsenic or other heavy metals that may be used in the manufacture of wood products.
Monomer and solvent must have a very low level of catalyst poisons in them for the polymerization process to work.