Use of Infrared Spectroscopy in Catalytic Characterization

The IR-Spectroscopy is very useful for characterization of catalyst. It is already known that IR measurement can be used to study the nature of bonding of small molecules such as CO (Carbon monoxide) to the surface of transition metal catalyst.

Some of the important uses of IR Spectroscopy in catalyst characterization are —

  1. IR-Spectroscopy, for the first time showed that benzene loses its aromatic character when it is absorbed on certain catalyst.
  2. When Hydrogen gas is adsorbed on ZnO catalyst, dissociation leads to formation of ZnH and OH linkage on the surface. This could be detected with IR-Spectroscopy.
  3. IR-Spectroscopy conclusively proved that when HCHO is adsorbed on butyl surface, only C-H linkage are formed and no CH2 linkage.
  4. When amines are interacted into clay catalyst, IR-Spectroscopy showed that protonated species are formed on the surface.
  5. When HCOOH comes into contact with a large number of metal surfaces, IR-Spectroscopy showed that the metal gets covered with a monomolecular layer.
  6. IR-Spectroscopy can also identify various Bronsted and Lewis acid site on the catalyst when bases like pyridine is adsorbed.

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Characterisation of Industrial Catalyst

All industrial catalysts must have the following properties :

  • It should adsorb one or more reactants sufficiently strongly.
  • The adsorption must not be strong to prevent desorption of products.

For example :

Silver (Ag) — Doesn’t have strong adsorption properties.

Tungsten (W) — Adsorbs very strongly so desorption will not occur. So, Ag and W are not considered as good catalyst but Pt and Ni fulfills both the conditions to become good catalyst.

The two most important considerations for a solid to become good catalyst are–

  • High activity.
  • Long term stability or durability.

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