It's the volume of the catalyst

It is better to refer to the mass of the catalyst, unless you know the porosity of the catalyst bed - so volume of catalyst in the bed .

Regards

it's the catalyst volume -practice

*required contact time () determined by laboratory performance testing and experience

* kinetic theory con provide interpolation  for alternative condition

*rate are normally transformed for nominal condition

SI=1atm ,0 oc= Nm3/hr per m3 of catalyst