Catalyst : Catalyst is a substance which accelerates rate of reaction between two reactants without itself getting altered at the end of the reaction. A catalyst can therefore be used and reused again and again till it gets deactivated as a result of impurities present in the reactants which block the active sites of the Catalyst or react with the catalyst and change its chemical composition.
Hydrogenation Catalyst : When one of the two reactants happen to be Hydrogen gas, the catalyst used is termed as Hydrogenation Catalyst.
The word "accelerates" used in the terminology implies that the hydrogenation reaction is taking place even without the catalyst, may be at slow pace. The fact however is, that the reaction practically does not take place in the absence of the catalyst. Presence of Catalyst is essential for reaction to proceed at a noticeable rate.
Promoters : A promoter is a substance which enhances the activity of a catalyst. Promoters are specific for a specific type of hydrogenation. Molybdenum, Chromium, Copper, Iron are known promoters for certain specific reactions involving Raney Nickel. Promoters are not added separately to the reactants but are to be incorporated in the Catalyst metal during their preparation.
Inhibitor : Inhibitors are substances which retard activity of a catalyst. Sulphur and Lead are inhibitors for precious metal Catalysts. However, Sulphur is not a poison for Raney Nickel.
Catalyst Poisons or Deactivators :
Presence of oxidizing agents or small amounts of deactivators cause deactivation or poisoning of hydrogenation catalyst. Amines and Chlorides are also known to deactivate catalyst.
Sometimes the product of reaction, reaction intermediates or by products act as catalytic deactivators and do not allow completion of reaction. Under such situations user should opt for a different type of catalyst.
The user should make a careful study of deactivators and poisons before conducting large scale hydrogenation. Care should be taken to minimize presence of catalytic deactivators and poisons in the reaction mixture so as to prolong life of the catalyst.
Catalyst manufactured by Vineeth Precious Catalysts Pvt. Ltd. are normally resistant to catalytic poisons if present in small quantities.