Industrial Catalysis

Carbon formation

Carbon is formed on the surface of the catalyst during steam reforming as the result of a number of side reactions.

a)

Cracking:

 

CH2

C + 2H2

 

 

 

 

 

 

 

b)

The Boudouard reaction:

 

2CO

C + CO2

 

 

 

 

 

 

 

c)

CO reduction:

 

CO + H2

C + H2O

 

 

 

Why do we want to avoid carbon formation?

Chemists try to prevent this happening because carbon deposits:

  • deactivate the catalyst
  • cause the catalyst to break up
  • cause the catalyst to overheat

Avoiding carbon formation

Since the reactions that cause the build up of carbon deposits on the catalyst surface are reversible, chemists chose operating conditions in which the overall rate of removal of carbon is greater than the rate at which carbon is deposited.
Conditions that will tend to minimise the problem of carbon deposition are:

  • making sure that the steam/methane ratio is above 2.5
  • choosing a catalyst that has a high activity
  • trying to ensure that the catalyst temperature does not rise excessively
Electron micrograph of carbon deposit on catalyst surface.