Hydrogenation & Hydrogenation Catalysts
HYDROGENATION :
Reaction of Hydrogen with another reactant molecule is known as Hydrogenation of that molecule.
This reaction may be a simple addition of Hydrogen atom / atoms to the molecule or it may cause substitution / replacement of another atom or group of atoms present on or attached to the molecule.
Hydrogenation of a molecule is also known as Reduction of that molecule. Thus Hydrogenation of Alkenes, Alkynes, Nitro Compounds, Aromic Compounds is also termed as reduction of Alkenes, Alkynes, Nitro Compounds, Aromic Compounds respectively.
HYDROGENOLYSIS : When hydrogenation causes knocking out of another atom or group attached directly to a molecule it is known as hydrogenolysis of that atom or group. Dehalogenation, debenzylation etc., denote specific type hydrogenolysis.
DEHYDROGENATION : Removal of Hydrogen from a molecule is termed as dehydrogenation.
CATALYST : A Catalyst is a substance which causes two reactants to react with each other for producing a new molecule without itself getting consumed, theoretically.
HYDROGENATION CATALYST : Catalyst which is used in a reaction where one of the reactants happen to be Hydrogen is known as Hydrogenation Catalyst.
Theoretically thus a small quantity of hydrogenation catalyst should be capable of producing infinitely large amount of hydrogenated product. In actual practice it is not so. Though small quantity of catalyst does cause proportionately large quantity of a reactant to react with Hydrogen but it is not an infinitely large quantity. Factors like deactivation or poisoning or catalyst do not allow endless / unlimited use of the catalyst.
Note : A good hydrogenation catalyst in the absence of external supply of hydrogen can also act as a catalyst for dehydrogenation. However much higher quantity of catalyst is required to be used for dehydrogenation.
WHY HYDROGENATION / HYDROGENOLYSIS / REDUCTION : When interaction of a molecule with Hydrogen produces another molecule with higher utility or having a different type of application, hydrogenation becomes not only a technical need but a commercial need as well. It is thus a techno-commercial requirement.
Types of Hydrogenation Catalyst :
Numerous types of hydrogenation catalyst have been mentioned in the technical literature on the subject. Vineeth Precious Catalysts Pvt. Ltd., however, deal only in two main and versatile types of hydrogenation catalyst, namely, Raney Nickel Catalyst and Noble Metal Catalyst. Noble Metal ( Palladium and Platinum )
catalysts are supported on carbon or other inert materials as well as unsupported like Adam's Catalyst, PtO2.
Besides, Vineeth Chemicals also manufactures special catalyst viz Lindlar Catalyst ( Palladium on Calcium Carbonate partially deactivated by Lead )
Whereas Raney Nickel Catalyst can be used for virtually any types of hydrogenation but has a limitation that it cannot be used in acidic media, i.e. below pH of 5.5, supported noble metal catalyst can be used in acidic media as well. Supported noble metal catalysts are generally used for selective hydrogenation at relatively lower temperature and pressure. Noble metal catalysts are thus very useful for heat sensitive compounds ex. perfumery compounds synthesis and can be used in acidic conditions as well.
Promoters :
A Promoter is a substance which enhances the activity of a catalyst. Promoters are specific for a specific type of a catalyst. Promoters are specific for a specific type of hydrogenation. What is a promoter for one type of hydrogenation need not act as promoter for other type of hydrogenation.
