Units for Reaction Rates in Porous Zones

What is the unit of reaction rates in the porous zone when determined via define_vr_rate?

It is kmol/sec/m^3 where the m3 express the gas volume only. Ansys Fluent takes this value for the UDF and multiplies it by the porosity which is (gas volume/total) volume so it ends up in the transport equation as kmol/sec/m3(total volume).

In other words, if you are using it in UDF then in your UDF you need to supply it as per gas volume only.